Yeah as has been said, I don't think all of these are reaction wood. Maples are naturally twisty among different specimen. It's not really a reaction to anything I don't think. Reaction wood is something like a denser xylem layer on one side of the trunk due to wind erosion hitting the tree throughout its life on the same side. It's basically a tree's attempt to remain strong against some physical force.
Reaction Wood
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Yup I reckon all here are right this is somthin else not reaction wood by definition. Oddly I have few in my area so a genetic malfunction the likely suspect so call it twistytwirlywoodii .
Ah but today I found this. Not great pic,s as the morning lite was to bright and no I will not be soxin this to cross section for your pleasure.
I do have another good twisty in Allocasuarina thats going to go bye soon so I get more pics.
The Count
Addicted to ArboristSite
unfortunately, I am not able to give you an reliable scientific answer on this one.
however, some trees have been selected for some features. selection, trait based, differ than natural selection by the fact that the selected gene, that is of most interest, often express itself in the detriment of the resistance genes. this way, a plant "forgets" the need for survival and manifests other traits that appeal to us, mainly because of their beauty or weirdness. mutations, occur very often but are usually corrected by the cell mechanism. those uncorrected are lethal most of the times.
what causes the fiber to grow that way could be either a mutation, a deficiency in the geo/ photo tropism area. also might be an adaptation to the environment. don`t know but this might help a little:
Kubler found that spiral growth conferred two main survival advantages for trees on harsh sites. First, spiral growth allowed water from each individual root to reach around to nearly every branch on the tree. And second, branches with spiral growth bent more easily, which allowed them to be more effective at dumping heavy snowfalls, and tended to prevent breakage in high winds. Both of these traits would be important for trees growing in harsh mountaintop conditions.
No cause for the direction of spiralling was given, but Kubler did note that almost all conifers start life with a left spiral, that is, the grain spirals upwards and to the left as you look at the tree. Then, after they become 10-15 years of age, almost all conifers switch to a right spiral for the remainder of their lives. As yet, this trait remains unexplained. And some trees switch back and forth throughout their lives.
As for survival advantage, Kubler found that spiral grain was definitely adaptive for dry, rocky sites. This has proved true in my experience; the rockier the site, the more twisted the trees are likely to be. And very seldom have I ever seen a tree with a noticeable spiral grain growing in good bottom land. In theory, the branches on a perfectly straight grained tree are fed only by the roots that are directly below them. Water from the root system follows the grain of the stem wood up the tree with minimal lateral movement. So, in a straight grained tree, if all the roots on the south side of the tree were cut, or did not receive moisture, the branches on that side of the tree would eventually die.
On a tree with spiral grain however, each root feeds nearly the whole tree, so if all the roots on one side of the tree die the foliage should survive unharmed. The reason for this is because the xylem, the stem wood that carries moisture from the roots to the crown, will spiral less far around the stem as the tree grows and stem diameter increases. Each new year of growth will be slightly offset from previous years growth, with the end result that the flow from one root will be distributed nearly completely around the tree bole, rather than just in a narrow band spiralling around the stem. This has been proven by injecting conifers with dye at the base. As conditions get harsher, the grain will tend to spiral at a more extreme angle around the stem.
And the system works in reverse too. Tree nutrients descend from the foliage in a spiral path to feed the whole root system, rather than just a single root. This return system is not quite as efficient as the root-to-foliage system is, since nutrients are transported only in a very thin layer of living cells called the phloem. Since the phloem is never more than one or two years growth thick, it lacks the depth to distribute its flow as widely as the xylem does. However, this is not a serious problem since tree roots can live for months or longer without food, while the foliage can generally only live a few days without water.
Old trees with spiral grain frequently have a beautiful corkscrew pattern of dead wood running up the stem. In extreme cases the majority of the stem is dead weathered wood, and only a thin strip of bark spiralling around the trunk is keeping the tree alive. I am not sure what causes this, but I would tend to believe that it probably originates from some stress in the foliage, with the resultant death of a narrow band of phloem cells down the stem, rather than from some stress in the roots.
Kubler also found that spiral grain actually made trees structurally weaker, but at the same time allowed them to bend more under wind and snow, and thus avoid breakage. So while a tree with a pronounced spiral grain will not make nearly as good a grade of lumber as its straight grained counterpart, it will have a definite survival advantage when it comes to shedding heavy loads of snow, or surviving a mountain windstorm.
Kubler found that genetics, age, and exposure to wind and dry conditions were the main determinants of spiral grain. Some trees seem genetically predetermined to show spiral grain no matter where they grow. In most however, spiral grain is a sign of harsh conditions; of fierce winds, unpredictable precipitation and great age.
So now, when you see that twisted old pine or juniper in a pot, you will know that this tree is a long term survivor of all nature has to offer. I have found that since spiral grain generally indicates decades or even centuries of poor growing conditions and very slow growth, it is one of the most accurate indicators of very old age in a tree, at least in the species I am familiar with. As such, it lends all the charm and charisma of bona fide antiquity to the trees it graces.
however, some trees have been selected for some features. selection, trait based, differ than natural selection by the fact that the selected gene, that is of most interest, often express itself in the detriment of the resistance genes. this way, a plant "forgets" the need for survival and manifests other traits that appeal to us, mainly because of their beauty or weirdness. mutations, occur very often but are usually corrected by the cell mechanism. those uncorrected are lethal most of the times.
what causes the fiber to grow that way could be either a mutation, a deficiency in the geo/ photo tropism area. also might be an adaptation to the environment. don`t know but this might help a little:
Kubler found that spiral growth conferred two main survival advantages for trees on harsh sites. First, spiral growth allowed water from each individual root to reach around to nearly every branch on the tree. And second, branches with spiral growth bent more easily, which allowed them to be more effective at dumping heavy snowfalls, and tended to prevent breakage in high winds. Both of these traits would be important for trees growing in harsh mountaintop conditions.
No cause for the direction of spiralling was given, but Kubler did note that almost all conifers start life with a left spiral, that is, the grain spirals upwards and to the left as you look at the tree. Then, after they become 10-15 years of age, almost all conifers switch to a right spiral for the remainder of their lives. As yet, this trait remains unexplained. And some trees switch back and forth throughout their lives.
As for survival advantage, Kubler found that spiral grain was definitely adaptive for dry, rocky sites. This has proved true in my experience; the rockier the site, the more twisted the trees are likely to be. And very seldom have I ever seen a tree with a noticeable spiral grain growing in good bottom land. In theory, the branches on a perfectly straight grained tree are fed only by the roots that are directly below them. Water from the root system follows the grain of the stem wood up the tree with minimal lateral movement. So, in a straight grained tree, if all the roots on the south side of the tree were cut, or did not receive moisture, the branches on that side of the tree would eventually die.
On a tree with spiral grain however, each root feeds nearly the whole tree, so if all the roots on one side of the tree die the foliage should survive unharmed. The reason for this is because the xylem, the stem wood that carries moisture from the roots to the crown, will spiral less far around the stem as the tree grows and stem diameter increases. Each new year of growth will be slightly offset from previous years growth, with the end result that the flow from one root will be distributed nearly completely around the tree bole, rather than just in a narrow band spiralling around the stem. This has been proven by injecting conifers with dye at the base. As conditions get harsher, the grain will tend to spiral at a more extreme angle around the stem.
And the system works in reverse too. Tree nutrients descend from the foliage in a spiral path to feed the whole root system, rather than just a single root. This return system is not quite as efficient as the root-to-foliage system is, since nutrients are transported only in a very thin layer of living cells called the phloem. Since the phloem is never more than one or two years growth thick, it lacks the depth to distribute its flow as widely as the xylem does. However, this is not a serious problem since tree roots can live for months or longer without food, while the foliage can generally only live a few days without water.
Old trees with spiral grain frequently have a beautiful corkscrew pattern of dead wood running up the stem. In extreme cases the majority of the stem is dead weathered wood, and only a thin strip of bark spiralling around the trunk is keeping the tree alive. I am not sure what causes this, but I would tend to believe that it probably originates from some stress in the foliage, with the resultant death of a narrow band of phloem cells down the stem, rather than from some stress in the roots.
Kubler also found that spiral grain actually made trees structurally weaker, but at the same time allowed them to bend more under wind and snow, and thus avoid breakage. So while a tree with a pronounced spiral grain will not make nearly as good a grade of lumber as its straight grained counterpart, it will have a definite survival advantage when it comes to shedding heavy loads of snow, or surviving a mountain windstorm.
Kubler found that genetics, age, and exposure to wind and dry conditions were the main determinants of spiral grain. Some trees seem genetically predetermined to show spiral grain no matter where they grow. In most however, spiral grain is a sign of harsh conditions; of fierce winds, unpredictable precipitation and great age.
So now, when you see that twisted old pine or juniper in a pot, you will know that this tree is a long term survivor of all nature has to offer. I have found that since spiral grain generally indicates decades or even centuries of poor growing conditions and very slow growth, it is one of the most accurate indicators of very old age in a tree, at least in the species I am familiar with. As such, it lends all the charm and charisma of bona fide antiquity to the trees it graces.
sgreanbeans
Treeaculterologist
good stuff, answered questions you have!
I have a Silver Maple in the empty lot next to my house, gonna post a pic later of it, when its light out! it was a volunteer, not planted, grew as a clump, on one side, three of the branches have begun to twist around themselves, incorporating all three together, it does not have competition for sun, so I don't think it is a photo-tropic deal. low wind, as it is protected by my forest. If I where too describe it, I would say it looks like 3 bread twistys weaving around them selves? I counted 13 different twist, all going to the right. What would cause this? Ill get a pic up later
I have a Silver Maple in the empty lot next to my house, gonna post a pic later of it, when its light out! it was a volunteer, not planted, grew as a clump, on one side, three of the branches have begun to twist around themselves, incorporating all three together, it does not have competition for sun, so I don't think it is a photo-tropic deal. low wind, as it is protected by my forest. If I where too describe it, I would say it looks like 3 bread twistys weaving around them selves? I counted 13 different twist, all going to the right. What would cause this? Ill get a pic up later
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The Count
Addicted to ArboristSite
I agree; one must study the case in order to be right.
Two apparently symillar phenotypes can occur due to different factors.
If I were to jump to a guess, think it is genetic. just the way shar pei skin desease is so appreciated in dog lovers world, we embrace those trees as nature`s wonder and beauty
I just want to point out that over the ages, peoples have came up with lots of theories for why things are the way they are.
I am an geneticist. but I am not like medieval doctors, good at anything; I study genetic modiffied organisms, corn especially and how the gene flow affects neighboring crops.
I know verry little of trees.
and what it takes to know? remember A.C.Kinsey and his gall wasp ? he collected over a million wasps to study.
there was a great lady, Barbara McClintock that postulated the theory of jumping genes. She was called "the mad scientist" until they all came to know she was right; she was awarded with the Nobel Prize and in protest she didn`t appeared at the ceremony;
what I am saying is one shouldn`t be quick to tell others wrong or right.
only an idiot has certitudes (are you sure professor? -I am certain of it.
) )
Even nowadays literature sais one thing, it doesn`t mean that one day someone will come and shead a bigger light on the matter;
Two apparently symillar phenotypes can occur due to different factors.
If I were to jump to a guess, think it is genetic. just the way shar pei skin desease is so appreciated in dog lovers world, we embrace those trees as nature`s wonder and beauty
I just want to point out that over the ages, peoples have came up with lots of theories for why things are the way they are.
I am an geneticist. but I am not like medieval doctors, good at anything; I study genetic modiffied organisms, corn especially and how the gene flow affects neighboring crops.
I know verry little of trees.
and what it takes to know? remember A.C.Kinsey and his gall wasp ? he collected over a million wasps to study.
there was a great lady, Barbara McClintock that postulated the theory of jumping genes. She was called "the mad scientist" until they all came to know she was right; she was awarded with the Nobel Prize and in protest she didn`t appeared at the ceremony;
what I am saying is one shouldn`t be quick to tell others wrong or right.
only an idiot has certitudes (are you sure professor? -I am certain of it.
) )Even nowadays literature sais one thing, it doesn`t mean that one day someone will come and shead a bigger light on the matter;
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Opsy just got back to here n find my last pics did not load, ah well they were not too good anyhoo I will find a better time of day for the subject n get em up soon. Will be ah,hem for want of better description reaction/braiding trunk on a Cor mac. Nice work Count n ekka adding some good clear thought to the mix.
sgreanbeans
Treeaculterologist
Ok, so, as a novice trying to pick up what you guys are laying down, based on everything I have read on this. Basically, there is no definite answer on the "why" these trees do this, as everyone is different and all are based on situation's at the sites. In other words, its all conditional. That it is up to the individual to investigate each situation, independent of the others. No different than a tree that has a disease, while the same species next to it, in the same yard, does not. Some trees are genetically pre-dispositioned to this, while others are not but still do?
To sum it up, nature has its way?
Deep stuff, genuinely trying to learn/understand! Had to get out the books to understand some of this! But they were not much help, the books I have anyways!
To sum it up, nature has its way?
Deep stuff, genuinely trying to learn/understand! Had to get out the books to understand some of this! But they were not much help, the books I have anyways!
"Not so long ago Cassian Humphries also printed in the Australian Arbor Age a piece on Braided Reaction-wood of Corymbia maculata, edited by more experts."
Really? How many experts, and how do you know--by your own publications there?
"The concept or idea that wood is "braided" is absurd to begin with (unless topiaried like shown), as braiding involves intertwining two or more parts of rope/hair, fibres etc. In none of the pictures seen in this thread could one believe that entire fibres and sections are being interwoven like rope and plaited hair.
Nor could one expect to see with the naked eye the cellular pattern and even if they did it would not support any hypothesis on external factors or gentical factors unless many species with and without the trait were genetically mapped .... way beyond arboriculture now but how the issue should be approached in this day and age."
His use of the term was qualified, and not as represented above..
"To find fact amongst such personalities and ego's can be a task,"
If there are any larger egos than yours, they would be gargantuan.
"there are ways to think logically in the scientific realm to ensure one doesn't fall into traps of making incorrect assumptions"
Even if it was an assumption, which it was not, you have not proven it incorrect.
" like calling regular growth braided wood or reaction wood."
All wood is reaction wood.
Really? How many experts, and how do you know--by your own publications there?
"The concept or idea that wood is "braided" is absurd to begin with (unless topiaried like shown), as braiding involves intertwining two or more parts of rope/hair, fibres etc. In none of the pictures seen in this thread could one believe that entire fibres and sections are being interwoven like rope and plaited hair.
Nor could one expect to see with the naked eye the cellular pattern and even if they did it would not support any hypothesis on external factors or gentical factors unless many species with and without the trait were genetically mapped .... way beyond arboriculture now but how the issue should be approached in this day and age."
His use of the term was qualified, and not as represented above..
"To find fact amongst such personalities and ego's can be a task,"
If there are any larger egos than yours, they would be gargantuan.
"there are ways to think logically in the scientific realm to ensure one doesn't fall into traps of making incorrect assumptions"
Even if it was an assumption, which it was not, you have not proven it incorrect.
" like calling regular growth braided wood or reaction wood."
All wood is reaction wood.
treevet
Addicted to ArboristSite
"Not so long ago Cassian Humphries also printed in the Australian Arbor Age a piece on Braided Reaction-wood of Corymbia maculata, edited by more experts."
Really? How many experts, and how do you know--by your own publications there?
"The concept or idea that wood is "braided" is absurd to begin with (unless topiaried like shown), as braiding involves intertwining two or more parts of rope/hair, fibres etc. In none of the pictures seen in this thread could one believe that entire fibres and sections are being interwoven like rope and plaited hair.
Nor could one expect to see with the naked eye the cellular pattern and even if they did it would not support any hypothesis on external factors or gentical factors unless many species with and without the trait were genetically mapped .... way beyond arboriculture now but how the issue should be approached in this day and age."
His use of the term was qualified, and not as represented above..
"To find fact amongst such personalities and ego's can be a task,"
If there are any larger egos than yours, they would be gargantuan.
"there are ways to think logically in the scientific realm to ensure one doesn't fall into traps of making incorrect assumptions"
Even if it was an assumption, which it was not, you have not proven it incorrect.
" like calling regular growth braided wood or reaction wood."
All wood is reaction wood.
:agree2:
treevet
Addicted to ArboristSite
and what it takes to know? remember A.C.Kinsey and his gall wasp ? he collected over a million wasps to study.
what I am saying is one shouldn`t be quick to tell others wrong or right.
only an idiot has certitudes (are you sure professor? -I am certain of it.
;
"Sad to see so many so called experts getting it so wrong"
Only thing worse than opinions based on theory and conjecture based on conjecture based on scientific research is
opinions based on theory and conjecture based on no scientific research.
Alex Shigo "dissected over 15,000 trees (longitudenally) for his research data". That is the man I want to talk to about this subject but sadly he is no longer with us. But were he alive he may even say "I do not know, there is so much that is still unknown". I heard him say that personally many times.
The Count
Addicted to ArboristSite
If there is someone in here that knows first hand about this, by all means, let him/her step up. we`ll listen. I think this thread is not about how smart we appear but how much we can learn.
Hey JPS I thought it was pronounced par-EN-ke-ma...wuddoo I know...:help:
"However if Dr Shigo were still alive he would have been the first to want to know more of the facts backed by research. He also would have wanted people to pick up the ball where he left off, not accepting that his work was the end of arboriculture but a stable platform to take it to the next level!"
Truer words were never spoken.
Truer words were never spoken. I do not know first hand but I know someone who does. google for the complete paper:
A unified hypothesis of mechanoperception in plants1
Frank W. Telewski2
W. J. Beal Botanical Garden, Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824 USA
Received for publication March 31, 2006. Accepted for publication August 16, 2006.
ABSTRACT
The perception of mechanical stimuli in the environment is crucial to the survival of all living organisms. Recent advances have led to the proposal of a plant-specific mechanosensory network within plant cells that is similar to the previously described network in animal systems. This sensory network is the basis for a unifying hypothesis, which may account for the perception of numerous mechanical signals including gravitropic, thigmomorphic, thigmotropic, self-loading, growth strains, turgor pressure, xylem pressure potential, and sound. The current state of our knowledge of a mechanosensory network in plants is reviewed, and two mechanoreceptor models are considered: a plasmodesmata-based cytoskeleton–plasma membrane–cell wall (CPMCW) network vs. stretch-activated ion channels. Post-mechanosensory physiological responses to mechanical stresses are also reviewed, and future research directions in the area of mechanoperception and response are recommended.
Key Words: gravitropism • gravity • mechanoperception • sound • thigmomorphogenesis • thigmotropism • turgor pressure • wind
The ability to sense and respond to physical stimuli is of key importance to all living things. Among the common environmental stimuli detected by living organisms are light, temperature, and a variety of chemical signals. A number of these stimuli appear to be closely related and can be considered as physical–mechanical stimuli, that is differences in a mechanical force or pressure perceived by the living cell. A cell may perceive gravity; strains caused by self-loading and internal growth; mechanical loading by snow, ice, and fruit, wind, rainfall, touch, sound; and the state of hydration within a cell (turgor pressure). All organisms appear to perceive these mechanical signals, regardless of their taxonomic classification or life habit (sessile vs. motile). The significant differences between taxonomic groups, specifically plants and animals, are found in the individual molecular components of the microstructure of the internal cellular sensing network (Jaffe et al., 2002 and in the response of an individual organism to each mechanical stimulus.
Internal mechanical forces
The sensing of gravitropic signals by plants has been studied for 200 years (Knight, 1806 ). Since the first study, the elucidation of the mechanism of gravitropic perception has been researched in a broad array of plants from algae to trees and in a variety of plant organs. To date, two compelling hypotheses exist regarding graviperception in plants: the starch–statolith hypothesis and the hydrostatic model of gravisensing (for reviews, see Sack, 1991 Both hypotheses ultimately rely on the sensing of a mechanical signal at the cytoskeleton–plasma membrane–cell wall interface (CPMCW) interface. In the case of statoliths, falling starch grains or other organelles impact the plasma membrane thus inducing an internal mechanical signal (Sack, 1991).
Similarly, the reorientation of a plant organ within a gravitational field is proposed to induce internal pressure differences at the CPMCW interface, which can be considered an external mechanical signal (Staves et al., 1997). Therefore, a more broadly unifying mechanism may underlie graviperception in plants than that evoked by a hypothesis that relies on how the mechanical signal is initiated; an actual sensory structure within the cell may allow for mechanoperception as the plant is reoriented with respect to gravity. Supporting the concept of a unified hypothesis for mechanical sensing in the gravitropic response is the work of Massa and Gilroy (2003) who reported when a root cap came in contact with a horizontal glass plate (inducing thigmotropic stimulus), the root cells behind the growing tip began to grow horizontally. This allowed the root cap to maintain contact with the plate, while the rest of the root grew over and parallel to the obstacle with a step-like growth form. The authors suggested that the gravisensitive cells of the root cap also sense the touch and signal the columella cells to alter their gravitropic response, so that they act together to redirect root growth to avoid obstacles while continuing a general downward pattern of growth.
In plants, gravitropism can occur in either primary or secondary tissues. In primary growth, the gravitropic curvature results from differential cell elongation on opposite sides of the displaced organ. In the case of secondary growth, the gravitropic response includes the formation of reaction wood; tension wood in porous angiosperms and compression wood in nonporous angiosperms and gymnosperms (Timell, 1986a ). Tension wood forms on the upper side of a displaced stem and is characterized by the formation of gelatinous fibers with lower lignin content, smaller diameter, and fewer vessels and by a realignment of cellulose microfibrils into a vertical orientation within the gelatinous layer, which forms inside a partially developed and lignified S2 layer of secondary cell walls of gelatinous fibers. Compression wood forms in response to gravity on the lower side of displaced stems and is characterized by tracheids with a thickened secondary cell wall with higher lignin content, a round cross section, intracellular spaces at cell corners, and a realignment of cellulose microfibrils in the S2 layer to a 45° to 60° orientation with respect to the axis of the stem.
The formation of reaction wood in stems, branches, and roots is not an exclusive response to gravity in woody plants. The formation of reaction wood has also been observed to develop in branches and stems as a means of reshaping crowns and as a possible phototropic response (Engler, 1924 ). Tension wood has been reported to form in the vertical stems of rapidly growing poplar (Populus) trees (for a review, see Telewski et al., 1996 suggested that the reaction wood may form to keep woody plants in balance with their physical environment (e.g., gravity, wind, and light), subsequently generating internal growth strains that result in the physical reorientation of woody plant organs.
The maturation of xylem cells in the cambial zone involves the alteration of individual cell lengths. In many instances, there is intrusive growth in which the cells elongate within the relatively rigid structure of the stem, inducing internal compressive forces (Boyd, 1985; Fournier et al., 1991a D In other cases, the cells shrink upon maturation inducing a tensile force within the stem. The generation of these internal growth strains is responsible for the realignment of stems in the gravitropic response, with compression wood developing a compressive growth strain and tension wood forming a tensile growth strain (Wilson, 1981 ). Growth strains also develop in stems aligned vertically with respect to gravity and may function to maintain mechanical balance within woody plants as part of a phototropic response, self-loading, or from differential loading caused by crown asymmetry (Archer, 1987
Within a vertically aligned stem, there are two potential sources of compressive force loading. The most obvious is due to self-loading along the vertical axis of the stem as a result of the accelerating force of gravity. A second compressive force has been suggested to be induced by the constrictive nature of bark tissues (referred to as bark pressure), resulting in a radial compressive force that affects xylogenesis in the cambial zone (DeVries, 1875 ). In earlier studies, the radial compressive force of a constricting outer bark was hypothesized to increase during the growing season from the radial growth of the cambium and to be responsible for the formation of smaller, denser latewood cells and the ultimate formation of annual growth rings (for a review, see Larson, 1960 ). In subsequent studies, this hypothesis was refuted, and annual growth rings were found to form in response to external environmental stimuli including day length and changes in plant growth regulator content (for review, see Little and Savidge, 1987 ). Although the bark pressure hypothesis appears to bear little on the formation of annual growth rings, the application of a compressive force to cambial explants (tissue culture) appears to function in maintaining the structure and organization of the vascular cambium in vitro, ensuring the continued production of apparently normal xylem (Brown and Sax, 1962 ).
"However if Dr Shigo were still alive he would have been the first to want to know more of the facts backed by research. He also would have wanted people to pick up the ball where he left off, not accepting that his work was the end of arboriculture but a stable platform to take it to the next level!"
Truer words were never spoken.
Truer words were never spoken.
I do not know first hand but I know someone who does. google for the complete paper:A unified hypothesis of mechanoperception in plants1
Frank W. Telewski2
W. J. Beal Botanical Garden, Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824 USA
Received for publication March 31, 2006. Accepted for publication August 16, 2006.
ABSTRACT
The perception of mechanical stimuli in the environment is crucial to the survival of all living organisms. Recent advances have led to the proposal of a plant-specific mechanosensory network within plant cells that is similar to the previously described network in animal systems. This sensory network is the basis for a unifying hypothesis, which may account for the perception of numerous mechanical signals including gravitropic, thigmomorphic, thigmotropic, self-loading, growth strains, turgor pressure, xylem pressure potential, and sound. The current state of our knowledge of a mechanosensory network in plants is reviewed, and two mechanoreceptor models are considered: a plasmodesmata-based cytoskeleton–plasma membrane–cell wall (CPMCW) network vs. stretch-activated ion channels. Post-mechanosensory physiological responses to mechanical stresses are also reviewed, and future research directions in the area of mechanoperception and response are recommended.
Key Words: gravitropism • gravity • mechanoperception • sound • thigmomorphogenesis • thigmotropism • turgor pressure • wind
The ability to sense and respond to physical stimuli is of key importance to all living things. Among the common environmental stimuli detected by living organisms are light, temperature, and a variety of chemical signals. A number of these stimuli appear to be closely related and can be considered as physical–mechanical stimuli, that is differences in a mechanical force or pressure perceived by the living cell. A cell may perceive gravity; strains caused by self-loading and internal growth; mechanical loading by snow, ice, and fruit, wind, rainfall, touch, sound; and the state of hydration within a cell (turgor pressure). All organisms appear to perceive these mechanical signals, regardless of their taxonomic classification or life habit (sessile vs. motile). The significant differences between taxonomic groups, specifically plants and animals, are found in the individual molecular components of the microstructure of the internal cellular sensing network (Jaffe et al., 2002 and in the response of an individual organism to each mechanical stimulus.
Internal mechanical forces
The sensing of gravitropic signals by plants has been studied for 200 years (Knight, 1806 ). Since the first study, the elucidation of the mechanism of gravitropic perception has been researched in a broad array of plants from algae to trees and in a variety of plant organs. To date, two compelling hypotheses exist regarding graviperception in plants: the starch–statolith hypothesis and the hydrostatic model of gravisensing (for reviews, see Sack, 1991 Both hypotheses ultimately rely on the sensing of a mechanical signal at the cytoskeleton–plasma membrane–cell wall interface (CPMCW) interface. In the case of statoliths, falling starch grains or other organelles impact the plasma membrane thus inducing an internal mechanical signal (Sack, 1991).
Similarly, the reorientation of a plant organ within a gravitational field is proposed to induce internal pressure differences at the CPMCW interface, which can be considered an external mechanical signal (Staves et al., 1997). Therefore, a more broadly unifying mechanism may underlie graviperception in plants than that evoked by a hypothesis that relies on how the mechanical signal is initiated; an actual sensory structure within the cell may allow for mechanoperception as the plant is reoriented with respect to gravity. Supporting the concept of a unified hypothesis for mechanical sensing in the gravitropic response is the work of Massa and Gilroy (2003) who reported when a root cap came in contact with a horizontal glass plate (inducing thigmotropic stimulus), the root cells behind the growing tip began to grow horizontally. This allowed the root cap to maintain contact with the plate, while the rest of the root grew over and parallel to the obstacle with a step-like growth form. The authors suggested that the gravisensitive cells of the root cap also sense the touch and signal the columella cells to alter their gravitropic response, so that they act together to redirect root growth to avoid obstacles while continuing a general downward pattern of growth.
In plants, gravitropism can occur in either primary or secondary tissues. In primary growth, the gravitropic curvature results from differential cell elongation on opposite sides of the displaced organ. In the case of secondary growth, the gravitropic response includes the formation of reaction wood; tension wood in porous angiosperms and compression wood in nonporous angiosperms and gymnosperms (Timell, 1986a ). Tension wood forms on the upper side of a displaced stem and is characterized by the formation of gelatinous fibers with lower lignin content, smaller diameter, and fewer vessels and by a realignment of cellulose microfibrils into a vertical orientation within the gelatinous layer, which forms inside a partially developed and lignified S2 layer of secondary cell walls of gelatinous fibers. Compression wood forms in response to gravity on the lower side of displaced stems and is characterized by tracheids with a thickened secondary cell wall with higher lignin content, a round cross section, intracellular spaces at cell corners, and a realignment of cellulose microfibrils in the S2 layer to a 45° to 60° orientation with respect to the axis of the stem.
The formation of reaction wood in stems, branches, and roots is not an exclusive response to gravity in woody plants. The formation of reaction wood has also been observed to develop in branches and stems as a means of reshaping crowns and as a possible phototropic response (Engler, 1924 ). Tension wood has been reported to form in the vertical stems of rapidly growing poplar (Populus) trees (for a review, see Telewski et al., 1996 suggested that the reaction wood may form to keep woody plants in balance with their physical environment (e.g., gravity, wind, and light), subsequently generating internal growth strains that result in the physical reorientation of woody plant organs.
The maturation of xylem cells in the cambial zone involves the alteration of individual cell lengths. In many instances, there is intrusive growth in which the cells elongate within the relatively rigid structure of the stem, inducing internal compressive forces (Boyd, 1985; Fournier et al., 1991a D In other cases, the cells shrink upon maturation inducing a tensile force within the stem. The generation of these internal growth strains is responsible for the realignment of stems in the gravitropic response, with compression wood developing a compressive growth strain and tension wood forming a tensile growth strain (Wilson, 1981 ). Growth strains also develop in stems aligned vertically with respect to gravity and may function to maintain mechanical balance within woody plants as part of a phototropic response, self-loading, or from differential loading caused by crown asymmetry (Archer, 1987
Within a vertically aligned stem, there are two potential sources of compressive force loading. The most obvious is due to self-loading along the vertical axis of the stem as a result of the accelerating force of gravity. A second compressive force has been suggested to be induced by the constrictive nature of bark tissues (referred to as bark pressure), resulting in a radial compressive force that affects xylogenesis in the cambial zone (DeVries, 1875 ). In earlier studies, the radial compressive force of a constricting outer bark was hypothesized to increase during the growing season from the radial growth of the cambium and to be responsible for the formation of smaller, denser latewood cells and the ultimate formation of annual growth rings (for a review, see Larson, 1960 ). In subsequent studies, this hypothesis was refuted, and annual growth rings were found to form in response to external environmental stimuli including day length and changes in plant growth regulator content (for review, see Little and Savidge, 1987 ). Although the bark pressure hypothesis appears to bear little on the formation of annual growth rings, the application of a compressive force to cambial explants (tissue culture) appears to function in maintaining the structure and organization of the vascular cambium in vitro, ensuring the continued production of apparently normal xylem (Brown and Sax, 1962 ).
John Paul Sanborn
Above average climber
http://www.encyclo.co.uk/search.php
This is a good meta-encyclopedia, I've used for a number of technical terms. It helped with a few I was shaky with in the above paper.
This is a good meta-encyclopedia, I've used for a number of technical terms. It helped with a few I was shaky with in the above paper.
John Paul Sanborn
Above average climber
I is more correct to say pH effecting the uptake of metals. I am trying to wrap my tinny brain around it right now with a book on Fe uptake and chlorosis. The talk about how Zn, Cu and Cd can be replaced in the chelate as pH rises. There are a number of papers on phytoremediation that talk about how to.
With Iron there are two strategies for uptake, gramaceous grasses can actually exude a reductase that "fixes" Fe(III) componds to more available Fe(II)
ScienceDirect - Trends in Plant Science : Iron solutions: acquisition strategies and signaling pathways in plants
this is one.
http://www.sciencedirect.com/scienc...27273ee873b6e3178551e77bbfc11730&searchtype=a
this one I just found looking for Ca uptake Al
http://www.sciencedirect.com/scienc...4b596dc20cd974c82ca66491c705e31f&searchtype=a
disrupted calmodulin function
treemandan
Tree Freak
I don't believe the photos being posted are of reaction wood in the sense of the term used in arboriculture..... but instead may be a phenomenon called fasciation......and in the cases posted it is likely a gentic mutation that is inheritable.
Sycamore (Acer pseudoplatanus) Fasciation, teratology, Cecidology
Fasciation
Fasciation Colorado State University Extension
Fasciated plants
Photos taken a few minutes ago.
Here's where normal and fasciated tissue diverge on a Dr. Martin heirloom pole lima bean stem. I've been saving seed for a few years now and this is the first fasciation I've seen on these beans. I will save seed from this plant separately this year in the hope of preserving the mutation.
Here's the whole mutated stem showing where it attaches to the normal stem:
Here's a dry stem on a brugmansia that that was alive last year. This brug has had fasciated stems for five years now...with only a few on the plant each year. Brugs in this climate die back to the root system and grow back each year. This one gets eight feet tall. This stem is wide or narrow depending on the view.
I agree its not 'reaction wood' due the weighting of the tree but reaction due to some other kind of force like disease or mutuation.
Toddppm
Addicted to ArboristSite
Is this reaction wood, a mutation or just a form I haven't seen before? Looks like bulging muscles but rippled too. These are Ailanthus trees roadside out in the country we drove by yesterday, had to turn around and get a few shots. On both sides of the road. Not great cause I was on a blind hill trying not to get hit.
Corymbia
ArboristSite Operative
Defining our terms
I think we need to define our terms.
Reaction wood is wood that contains cells with altered chemical makeup in the cell wall (S1-S3) that arises from some external stimuli - wind gravity etc. This alteration occurs after the cell is formed after mitosis as the cell heads towards maturity.
Fasciation occurs at mitosis (so it is about too much or too little cell division) and then may still result in the development of reaction wood to compensate for the often poor geometry.
The spiraling grain formation that our learned friend talked about relates to the orientation of the cells (a function of mitosis) and not the make up of the cell walls. This again is not reaction wood
I think we need to define our terms.
Reaction wood is wood that contains cells with altered chemical makeup in the cell wall (S1-S3) that arises from some external stimuli - wind gravity etc. This alteration occurs after the cell is formed after mitosis as the cell heads towards maturity.
Fasciation occurs at mitosis (so it is about too much or too little cell division) and then may still result in the development of reaction wood to compensate for the often poor geometry.
The spiraling grain formation that our learned friend talked about relates to the orientation of the cells (a function of mitosis) and not the make up of the cell walls. This again is not reaction wood
boo
ArboristSite Operative
agreed on "all wood is reaction wood"
just as standing back and looking at the big picture... using our ability to reason.(most valuable tool)
cells slightly changed by soil, water, sun, species, even wind(as beating a sapling with a newspaper) it's all reaction wood... just like he kinda pissed you off because he didn't agree with you, and by your dna, lunch, brain chemicals, neurons, etc.... you reacted.
I haven't done the math... but even plastic changes to temperature and chemicals.
You don't have to be Dr. Alex Shigo to see the big picture.
I think he was more up for finding out "why".
just as standing back and looking at the big picture... using our ability to reason.(most valuable tool)
cells slightly changed by soil, water, sun, species, even wind(as beating a sapling with a newspaper) it's all reaction wood... just like he kinda pissed you off because he didn't agree with you, and by your dna, lunch, brain chemicals, neurons, etc.... you reacted.
I haven't done the math... but even plastic changes to temperature and chemicals.
You don't have to be Dr. Alex Shigo to see the big picture.
I think he was more up for finding out "why".
Corymbia
ArboristSite Operative
I am not sure that it has anything to do with the grain. In fact reaction wood has nothing to do with the grain and everything to do with the secondary cell walls of those cells that are in the reaction wood zone. You can have, and in fact often do have, reaction wood forming in a completely different orientation to the grain.
The fact that cells alter the composition of the cell walls in response to forces allows them to respond appropriately to physical stimuli. (Thin about the axiom of uniform stress). When a tree has gravity pushing don on a limb how does the tree deal with that. In short a gymnosperm uses compression wood to push against gravity whilst an angiosperm uses tension wood to pull against gravity,
Perhaps the best example of compression wood is when the top breaks or is removed out of a young gymnosperm. You will often see compression wood "push" a horizontal branch to vertical and have it take over as the new stem. This does not happen to any great extent with angiosperms.
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it's the pseudotransverse divisions that give us the spiral tree.
Is that like a Panzer Division?
opcorn:
