One proposed mechanism for plant memory storage in the bud is the relative rise in Ca2+ concentration within the cytosol of plant cells via calcium waves (4) . The cytoplasm of plant cells has a relatively low concentration of Ca2+, but the cell has stores of Ca2+ throughout. These stores of Ca2+ are usually membrane bound organelles that have inositol-3-phosphate (IP3) dependent Ca2+ channels within their membranes. These channels only open when they are bound to IP3, a molecule that is produced through intracellular processes governed by the enzyme phospholipase C. Some of the Ca2+ channels are not IP3 dependent and open in response to other stimuli like electrical gradients or the stretching of a membrane. Once a CA2+ channel (IP3 gated or not) opens, it can briefly stimulate the opening of adjacent channels. This allows for a wave of calcium to be released from these Ca2+ stores into the cytoplasm of the plant cell. Calcium will flow down its concentration gradient, from an area of high Ca2+ concentration to an area of low Ca2+ concentration, through the now open Ca2+ channels. Because (1) there are many forms of Ca2+ channels on these storage organelles (2) these channels respond to different stimuli and (3) depend on the relative concentration gradients of these stimuli, the kinetics and magnitude of calcium waves are specific to the stimuli that triggered them. The respective elevation in the concentration of Ca2+ in the cytoplasm “stores” the memory of the stimuli. This proposed mechanism is a form of plant memory storage. Another potential mechanism involves electrical signals and calcium. When Ca2+ floods the cytoplasm it allows the plant to store a memory, the duration and amplitude of this Ca2+ wave is determined by the type of stimulus that was perceived and how the plant will store the memory. (4) Electric signals are induced by variation potentials which are stimulated by an injury such as heat or a cut. There are also action potentials but these are stimulated by non-damaging stimuli such as temperature. The variation potential travels through the xylem and is regulated by both hydraulic pressure and system potentials, such as the Ca2+ flux. Two methods by which a signal may travel over a short distance is by propagating over the cell membrane through the plasmodesmata, or secondly the current of one cell membrane may depolarize a neighboring cell membrane without having to be in direct contact. But for memory purposes the electric signal needs to travel over a longer distance, sieve tubes are used since they have pores and a continuous plasma membrane which makes sieve tubes low resistance. With a trauma the xylem can have a change in hydrostatic pressure which leads to turgor changes in the neighboring parenchyma cells and then via mechano-sensors membrane potential changes. Sheath cells protect the signal when traveling from the mesophyll to the phloem which contains the sieve tubes. Although there are many suggested methods by which long distance electric signals may travel, the exact ion channels that are used are still unknown, but recently GLR genes have been proposed to mediate wound stimulus through cation channels. (10) Another possible method on storage memory and recall is the hormone auxin and how it reacts to a trauma. While there are many hormones that dictate major plant processes and eventual changes in physiology, auxin remains the most prevalent hormone. Auxin serves to increase cell length, stimulated by light or gravity in processes known as phototropism and gravitropism, respectively. In terms of plant memory, Auxin may act as the mechanism as to which plants respond to stimuli previously encountered. Auxin moves to different sides of the cell, depending on the particular cell type and process initiated. (11). In phototropism, auxin is transported to the side of the plant shaded. This is accomplished through the PIN transport proteins. PIN proteins act as a conduit for auxin, allowing auxin to flow between cells. As auxin accumulates on the shaded side of the plant, the hormone promotes cell elongation in the cells. Auxin does this by stimulating the expansibility of cell walls. This allows cells to expand and elongate, making the plant bend in one direction. This also occurs in the roots, under a different stimulus. Auxin also plays a role in regulating gene expression. The genes that are regulated are correlated with cell expansion biochemistry and physiology. In What a Plant Knows, David Chamovitz describes an experiment in which they test a plants long term memory regarding past trauma (12) . While the experiment (stated above) concluded that plants can store trauma memory, the exact mechanism is unknown. Chamovitz, along with the original perpetrators of the experiment Rudolf Dostal and Michel Tellier, postulate that Auxin may play a pivotal role in trauma memory because of the hormone's role in regulation of growth through multiple mechanisms including long term gene expression.
One proposed mechanism for plant memory storage in the bud is the relative rise in Ca2+ concentration within the cytosol of plant cells via calcium waves . The cytoplasm of plant cells has a relatively low concentration of Ca2+, but the cell has stores of Ca2+ throughout. These stores of Ca2+ are usually membrane bound organelles that have inositol-3-phosphate (IP3) dependent Ca2+ channels within their membranes. These channels only open when they are bound to IP3, a molecule that is produced through intracellular processes governed by the enzyme phospholipase C. Some of the Ca2+ channels are not IP3 dependent and open in response to other stimuli like electrical gradients or the stretching of a membrane. Once a CA2+ channel (IP3 gated or not) opens, it can briefly stimulate the opening of adjacent channels. This allows for a wave of calcium to be released from these Ca2+ stores into the cytoplasm of the plant cell. Calcium will flow down its concentration gradient, from an area of high Ca2+ concentration to an area of low Ca2+ concentration, through the now open Ca2+ channels. Because (1) there are many forms of Ca2+ channels on these storage organelles (2) these channels respond to different stimuli and (3) depend on the relative concentration gradients of these stimuli, the kinetics and magnitude of calcium waves are specific to the stimuli that triggered them. The respective elevation in the concentration of Ca2+ in the cytoplasm “stores” the memory of the stimuli. This proposed mechanism is a form of plant memory storage. Another potential mechanism involves electrical signals and calcium. When Ca2+ floods the cytoplasm it allows the plant to store a memory, the duration and amplitude of this Ca2+ wave is determined by the type of stimulus that was perceived and how the plant will store the memory. Electric signals are induced by variation potentials which are stimulated by an injury such as heat or a cut. There are also action potentials but these are stimulated by non-damaging stimuli such as temperature. The variation potential travels through the xylem and is regulated by both hydraulic pressure and system potentials, such as the Ca2+ flux. Two methods by which a signal may travel over a short distance is by propagating over the cell membrane through the plasmodesmata, or secondly the current of one cell membrane may depolarize a neighboring cell membrane without having to be in direct contact. But for memory purposes the electric signal needs to travel over a longer distance, sieve tubes are used since they have pores and a continuous plasma membrane which makes sieve tubes low resistance. With a trauma the xylem can have a change in hydrostatic pressure which leads to turgor changes in the neighboring parenchyma cells and then via mechano-sensors membrane potential changes. Sheath cells protect the signal when traveling from the mesophyll to the phloem which contains the sieve tubes. Although there are many suggested methods by which long distance electric signals may travel, the exact ion channels that are used are still unknown, but recently GLR genes have been proposed to mediate wound stimulus through cation channels. (10) Another possible method on storage memory and recall is the hormone auxin and how it reacts to a trauma. While there are many hormones that dictate major plant processes and eventual changes in physiology, auxin remains the most prevalent hormone. Auxin serves to increase cell length, stimulated by light or gravity in processes known as phototropism and gravitropism, respectively. In terms of plant memory, Auxin may act as the mechanism as to which plants respond to stimuli previously encountered. Auxin moves to different sides of the cell, depending on the particular cell type and process initiated. (11). In phototropism, auxin is transported to the side of the plant shaded. This is accomplished through the PIN transport proteins. PIN proteins act as a conduit for auxin, allowing auxin to flow between cells. As auxin accumulates on the shaded side of the plant, the hormone promotes cell elongation in the cells. Auxin does this by stimulating the expansibility of cell walls. This allows cells to expand and elongate, making the plant bend in one direction. This also occurs in the roots, under a different stimulus. Auxin also plays a role in regulating gene expression. The genes that are regulated are correlated with cell expansion biochemistry and physiology. In What a Plant Knows, David Chamovitz describes an experiment in which they test a plants long term memory regarding past trauma . While the experiment (stated above) concluded that plants can store trauma memory, the exact mechanism is unknown. Chamovitz, along with the original perpetrators of the experiment Rudolf Dostal and Michel Tellier, postulate that Auxin may play a pivotal role in trauma memory because of the hormone's role in regulation of growth through multiple mechanisms including long term gene expression.
D
(4)
D
(4)
D
(12)