Storage and recall of environmental signals in a plant: modelling by use of a differential (continuous) formulation

The breaking of the symmetry of bud growth in Bidens seedlings involves a sort of plant 'memory'. An asymmetrical stimulus (e.g., the pricking of one of the seedling cotyledons) stores a 'symmetry-breaking' signal within the plants (function STO). Depending on other stimuli received by the seedlings, the stored signal may remain silent or be recalled (RCL function) and take effect in the seedling morphogenesis (asymmetry of the growth of the cotyledonary buds, with a statistical advantage to the bud at the axil of the non-stimulated cotyledon). We show that this memory mechanism can be interpreted by a model taking into account a genetic control exerted on a non-linear enzymatic system that is able to choose trajectories going to different attractors, depending on the stimulation intensity.     

Memory Processes in the Response of Plants to Environmental Signals

Plants are sensitive to stimuli from the environment (e.g., wind, rain, contact, pricking, wounding). They usually respond to such stimuli by metabolic or morphogenetic changes. Sometimes the information corresponding to a stimulus may be “stored” in the plant where it remains inactive until a second stimulus “recalls” this information and finally allows it to take effect. Two experimental systems have proved especially useful in unravelling the main features of these memory-like processes.In the system based on Bidens seedlings, an asymmetrical treatment (e.g., pricking, or gently rubbing one of the seedling cotyledons) causes the cotyledonary buds to grow asymmetrically after release of apical dominance by decapitation of the seedlings. This information may be stored within the seedlings, without taking effect, for at least two weeks; then the information may be recalled by subjecting the seedlings to a second, appropriate, treatment that permits transduction of the signal into the final response (differential growth of the buds). Whilst storage is an irreversible, all-or-nothing process, recall is sensitive to a number of factors, including the intensity of these factors, and can readily be enabled or disabled. In consequence, it is possible to recall the stored message several times successively.In the system based on flax seedlings, stimulation such as manipulation stimulus, drought, wind, cold shock and radiation from a GSM telephone or from a 105 GHz Gunn oscillator, has no apparent effect. If, however, the seedlings are subjected at the same time to transient calcium depletion, numerous epidermal meristems form in their hypocotyls. When the calcium depletion treatment is applied a few days after the mechanical treatment, the time taken for the meristems to appear is increased by a number of days exactly equal to that between the application of the mechanical treatment and the beginning of the calcium depletion treatment. This means that a meristem-production information corresponding to the stimulation treatment has been stored in the plants, without any apparent effect, until the calcium depletion treatment recalls this information to allow it to take effect. Gel electrophoresis has shown that a few protein spots are changed (pI shift, appearance or disappearance of a spot) as a consequence of the application of the treatments that store or recall a meristem-production signal in flax seedlings. A SIMS investigation has revealed that the pI shift of one of these spots is probably due to protein phosphorylation. Modifications of the proteome have also been observed in Arabidopsis seedlings subjected to stimuli such as cold shock or radiation from a GSM telephone.Key Words: memory, environmental signals, meristems, mobile telephone, bud growth, proteome, plants     

A mathematical model for storage and recall functions in plants

In plantlets of Bidens pilosa L., under severely limiting environmental conditions the growth of the buds at the axil of the cotyledons (cotyledonary buds) is asymmetric (i.e. one of the buds starts growing before the other one), this asymmetry being oriented by the pricking of one of the cotyledons (i.e. pricking one cotyledon increases the probability that the bud at the axil of the other cotyledon be the first to start to grow). As long as the plant apex (i.e. the terminal bud) is present, the growth of the cotyledonary buds is inhibited (apical dominance), but the souvenir of the asymmetric message caused by sub-optimal environmental conditions and the orientation given by the cotyledon pricking is always present in the plant and can be revealed by removing the apex. Depending on the conditions for removing the plant apex and/or on the application of a variety of symmetrical treatments (e.g. thermal treatment, symmetrical pricking treatments, etc.) the stored asymmetry will either take effect (the bud at the axil of the non-pricked cotyledon will be the first to start to grow more often than the other one) or not (both buds will have equal chance to be the first to start to grow). This has been termed 'recalling' the stored asymmetry. By combining several successive symmetrical treatments, it is possible to reversibly switch on and off the recall function several times. This recall of the stored plant-asymmetry is analogous to the evocation function of a memory system. In this paper, we will present first a discrete logical version of the observed interaction structure between the main components of the bud growth system, then a continuous differential version, taking into account the main features of the observed experimental reality and trying to explain this phenomenology. The interaction structure of both the discrete and the continuous models presents similar positive and negative feedback circuits, necessary condition for observing multistationarity and stability.     

Storage of environmental signals in flax. Their morphogenetic effect as enabled by a transient depletion of calcium

It is possible to induce the formation of epidermal meristems in the hypocotyl of non-injured and non-hormone-treated plantlets of flax, by combining various sorts of physical stimulations with a transient depletion of calcium. The characteristic times for the decrease of the tissue concentration of calcium during calcium depletion and for the recovery of the normal tissue concentration of calcium after resupplying the latter ion, are close to 1 day. The stimuli may correspond to wind or drought or even to the manipulation stress occurring when the plantlets are transferred from their germination to their growth vessel. Meristem production is increased by combining several physical stimulations. When calcium depletion is delayed relative to the application of the physical stimulation(s), the production of meristems is delayed accordingly. This means that the signal induced by the physical stimulation(s) may be stored within the plants, without apparent effect, until a calcium depletion finally allows the stored signal to take effect (formation of meristems). For storage periods of up to 8 days no loss of the potency of the stored signal was observed. A few other examples of storage of morphogenetic signals in plants have been described in the literature. The mechanism involved in signal storage is still not clearly understood. However, it seems that the sensing and/or storing of the signals require that the plant tissues are sufficiently rich in calcium, whereas the licensing of the plants for the translation of signals into the final response (meristem production) is done by a transient calcium depletion.     

Some factors affecting germination of Peronospora farinosa conidia in water

The germination of conidia of Peronospora farinosa f. sp. betae, collected from sugar beet and suspended in deionized water, was inhibited by dilution with 10% solutions of glycerol, glucose or sucrose and with sap from sugar-beet leaves. Germination was stimulated by diluting with deionized water but not with tap water or biological saline. Substances that diffused from excised buds of sugar-beet plants into deionized water also stimulated germination of conidia but diffusates from leaves did not. This may partly explain why buds are more susceptible to downy mildew than leaves in sugar beet. Germination of conidia was apparently stimulated more by diffusates from buds of seedlings than by those from buds of older plants; this may help to explain why sugar-beet seedlings are more susceptible to downy mildew than older plants. Diffusates from plants of four sugar-beet stocks, that differed from each other in susceptibility to downy mildew, had very similar effects on germination of P. farinosa conidia. Stimulation of spore germination on the surfaces of buds and leaves did not seem, therefore, to be an important factor in determining resistance or susceptibility to downy mildew in these stocks.     

Control of a symmetry-breaking process in the course of the morphogenesis of plantlets of Bidens pilosa L.

A mechanism involving transport, storage and retrieval of a symmetry-breaking message controls the relative growth rate of the cotyledonary buds of plantlets of Bidens pilosa L. The asymmetry was induced by administering a few needle pricks to one cotyledon of each plant. The storage of the symmetry-breaking message was independent of the number of pricks (all or nothing process) and irreversible. However, various treatments could render the plants either able to retrieve the stored symmetry-breaking message (in which case, the bud opposite to the pricked cotyledon began to elongate statistically sooner than the one associated with the stimulated cotyledon) or not (both buds then had an equal chance to be the first to start to grow). The retrieval process was also associated with a temporal oscillation. At the level of the whole plants, bud growth was observed only after the removal of apical dominance, and its degree of asymmetry was expressed by use of a parameter g ranging from zero (symmetrical case) to ± 1 (full asymmetry in favor of one of the cotyledonary buds). The highest g-values observed in the present contribution were of the order of 0.5. At the cellular level, the pricking of one cotyledon caused a number of cells, which were within the meristem of the bud associated with the pricked cotyledon and were in cell-cycle phases S or G2, to undergo cellular division and then be blocked in phase G1, whereas the cells of the opposite bud were practically unchanged.We thank Drs. Jean Guern (Laboratoire Hormones végétales, Gif-sur-Yvette, France) Grégoire Nicolis (Service de Chimie Physique II, Bruxelles, Belgique) and Erasmo Marrè (Dipartimento di Biologia, Università di Milano, Milano, Italy) for stimulating discussions, and Mrs. Chantal Eraud, Monique Loiseau and Monique d'Alleizette for their technical assistance.     

Variations nycthémérales de l'intensité des corrélations entre les cotylédons et leur bourgeon axillaire induites par des traumatismes faits unilatéralement sur l'un des deux cotylédons de Bidens pilosus

Different methods (physiological, electrophysiological and biochemical) were used in order to show, during a 24 h period, a change in sensitivity of Bidens pilosus seedlings to the pricking of one of the cotyledons. The sensitivity is maximum in the morning and in the evening; it decreases during the light period (day) and the dark period (night). The minimum of the sensitivity occurs in the middle of the day and 3 to 4 h after the beginning of the night.     

The induction of soluble peroxidase activity in bean leaves by wind-induced mechanical perturbation

The induction of defense-related peroxidase (POD) activity in plants occurs in response to many biotic and abiotic stimuli. This controlled greenhouse study was an attempt to provide insight into the nature of the induction of soluble POD activity by noninjurious wind-induced mechanical perturbation (MP). In a time course study, exposure of common bean (Phaseolus vulgaris) seedlings to daily periods of fan-produced wind induced a significant and sustained increase in soluble POD activity in primary leaves of 7-9-d-old seedlings. In a wind-gradient study, wind-induced MP led to increases in soluble POD activity in leaves that were proportionally related to the wind speed experienced by individual seedlings. Wind-induced MP enhanced soluble POD activity to a degree similar to treatment with 5 mmol/L HgCl(2), a potent oxidizing elicitor of POD activity in plants. However, no further increases in POD activity were induced by HgCl(2) on plants that were preconditioned with wind-induced MP. Finally, short periods of brushing-induced MP enhanced soluble POD activity to the same degree as longer periods of wind-induced MS, suggesting a greater sensitivity to thigmic stimuli than to seismic stimuli in leaves of bean seedlings. This study illustrates the potential importance of wind and other mechanical stimuli as inducers of POD activity and interacting factors in the elicitation of POD activity by other environmental stimuli.     

Hypocotyl Growth and Peroxidases of Bidens pilosus: EFFECT OF COTYLEDONARY PRICKINGS AND LITHIUM PRETREATMENT

Pricking one cotyledon of young Bidens pilosus plants induces rapid inhibition of hypocotyl growth, essentially in its middle portion. Analysis of soluble peroxidases indicates rapid changes (increase of activity) in basic isoenzymes followed by more progressive enhancement of the acidic ones. Pretreatment of the plants with lithium prevents the inhibition of elongation due to pricking as well as the peroxidase changes. The phenomenon is similar to the previously described thigmomorphogenetic process in Bryonia dioica.     

The role of mineral ions in controlling morphogenesis in plants: a case of the inhibition of growth of the hypocotyle of Bidens pilosa L

Mineral ions are implicated in various events occurring in the transduction of messages in plants, from the reception of the initial signal to the final morphogenetic expression. Ions may be involved also in the possible migration, storage and retrieval of the message. In a number of cases, cellular exchange of Ca2+ have been shown to occur at the reception of a signal. This is the reason why Ca2+ has often been considered as a "second messenger". For the possible message migration, cellular exchanger of Cl-, K+, H+ and Ca2+ are involved in the propagation of a wave of electric depolarization. The mechanisms underlying the possible storage of the message in a plant are still not clearly understood. However, ions such as K+, Na+ and Ca2+ interfere with the retrieval of the stored information. There are some indications that protons are involved in the metabolic reactions responsible for the final morphogenetic expression of the original signal. Moreover, the addition of Li+ ions inhibits, or shifts the latter effects, while the action of Li+ is counterbalanced by increasing the concentration of K+. The particular case of the inhibition of the growth of Bidens hypocotyles following delivering a few needle pricks to the cotyledons has been examined in more details.     

Pharmacological Evidence for Calcium Involvement in the Long-Term Processing of Abiotic Stimuli in Plants

Information about abiotic conditions is stored for long periods in plants and, in flax seedlings, can lead to the production of meristems. To investigate the underlying mechanism, flax seedlings were given abiotic stimuli that included a mechanical stimulus (by manipulation), one or two cold shocks, a slow cold treatment and a drought stress and, if these seedlings were then subjected to a temporary (1 to 3 days) depletion of calcium, epidermal meristems were produced in the seedling hypocotyls. This production was inhibited by the addition to the nutrient media of EGTA, ruthenium red, lanthanum or gadolinium that affect calcium availability or calcium transport. Use of these agents revealed a period of vulnerability in information processing that was less than two min for mechanical stimuli and over five min for other abiotic stimuli, consistent with information about mechanical stimuli being stored particularly fast. We propose that external calcium is needed for the transduction/storage of the information for meristem production whilst a temporary depletion of external calcium is needed for the actual production of meristems. Such roles for calcium would be consistent with a mechanism based on ion condensation on charged polymers.Key Words: memory, environmental signals, calcium, pharmacological agents, meristems, bud growth, plants     

Localization of Stem Elongation Control in Cucumis sativus L

Reciprocal grafts, and applications of gibberellin (GA) and indoleacetic acid (IAA) were used to localize the site of control for stem elongation in cucumber (Cucumis sativus L.). Dwarf and tall plants were reciprocally grafted to determine influence of stems and roots on stem elongation. At 21 days there were no significant differences in length between stems grafted to their own roots and those grafted to roots of the other type. GA₃, GA₄₊₇, and IAA were applied to seedlings with and without live apical buds. Seedlings with live apical buds responded to level of added GA, but not to added IAA. GA₄₊₇ was more effective than GA₃. Hypocotyls of tall plants responded more to both GA treatments than did those of the dwarves when both types had live apical buds. When either GA₄₊₇ or IAA was applied to seedlings with dead apical buds, elongation of the hypocotyl responded to level of the growth regulator, but there was no difference in response between the dwarf and tall plants.     

Release of lateral buds from apical dominance by glyphosate in soybean and pea seedlings

Application of a sublethal dose of glyphosate (N-[phosphonomethyl]glycine) to the seedlings of soybean (Glycine max L. Merr. cv. Evans) and pea (Pisum sativum L. cv. Alaska) promoted growth of the cotyledonary and other lateral buds. The pattern of the glyphosate-induced lateral bud growth was different from that induced by decapitation. Under the experimental condition, glyphosate did not kill the apical buds. Feeding stem sections of the seedlings with radiolabeled indole-3-acetic acid ([2¹⁴C]IAA) and subsequent analysis of free [2-¹⁴C]IAA and metabolite fractions revealed that the glyphosate-treated plants had higher rates of IAA metabolism than the control plants. The treated pea plants metabolized 75% of [2-¹⁴C]IAA taken up in the 4-h incubation period compared to 46.5% for the control, an increase of 61%. The increase was small but consistent in soybean seedlings. As a result, the glyphosate-treated plants had less free IAA and ethylene than the control plants. The increase of IAA metabolism induced by glyphosate is likely to change the auxin-cytokinin balance and contribute to the release of lateral buds from apical dominance in these plants.     

Kallistatin结构功能与信号通路

Kallistatin是一种丝氨酸蛋白酶抑制剂.早期研究发现,它能与组织激肽释放酶结合并抑制其活性,随后kallistatin的抗血管生成、抗炎、抗肿瘤、抗氧化等功能也逐步被发现.Kallistatin有2个主要功能结构域:反应中心环和肝素结合结构域,各自发挥不同的作用.Kallistatin通过肝素结合结构域竞争性抑制血管内皮生长因子(VEGF)和肿瘤坏死因子与它们的受体结合,进而起到抗血管生成和抗炎作用.近年研究发现,kallistatin的多种功能由不同信号通路介导,主要为PI3K-Akt信号通路和TNF-α-NF-κB信号通路.此外,kallistatin还通过丝裂原活化激酶(mitogen-activated protein kinase,MAPK)等信号通路发挥作用.本文就目前研究的kallistatin的结构功能及其在PI3K-Akt、TNF-α等多种信号通路中的调节功能和作用机制进行阐述.     

Release of lateral buds from apical dominance by glyphosate in soybean and pea seedlings

Application of a sublethal dose of glyphosate (N-[phosphonomethyl]glycine) to the seedlings of soybean (Glycine max L. Merr. cv. Evans) and pea (Pisum sativum L. cv. Alaska) promoted growth of the cotyledonary and other lateral buds. The pattern of the glyphosate-induced lateral bud growth was different from that induced by decapitation. Under the experimental condition, glyphosate did not kill the apical buds. Feeding stem sections of the seedlings with radiolabeled indole-3-acetic acid ([2¹⁴C]IAA) and subsequent analysis of free [2-¹⁴C]IAA and metabolite fractions revealed that the glyphosate-treated plants had higher rates of IAA metabolism than the control plants. The treated pea plants metabolized 75% of [2-¹⁴C]IAA taken up in the 4-h incubation period compared to 46.5% for the control, an increase of 61%. The increase was small but consistent in soybean seedlings. As a result, the glyphosate-treated plants had less free IAA and ethylene than the control plants. The increase of IAA metabolism induced by glyphosate is likely to change the auxin-cytokinin balance and contribute to the release of lateral buds from apical dominance in these plants.     

Stress resistance levels at the time of lifting affect post-planting performance of Quercus robur seedlings

The objective of this study was to describe the physiological condition of bare-root pedunculate oak (Quercus robur L.) seedlings at the time of lifting for cold storage or planting in 1996/1997 and 1997/1998. Dormancy intensity and other physiological measurements and field performance were assessed. Heat treatments were used to assess the taproot resistance to stress using root electrolyte leakage, but the results indicated that the plants were least resistant when mostdormant. Root electrolyte leakage and root growth potential were lowest during the deep dormancy stage and increased again as shoot dormancy was released, coinciding with the period that the plants were most resistant to storage stresses. Dry weight fraction of the shoots was a good indicator of storability, but the other measures were less useful. Despite good survival rates, shoot quality was poor for seedlings lifted early (October) or late (April, May) in the lifting season.     

3种入侵植物叶片挥发物对旱稻幼苗根的影响

入侵植物通过化感作用对入侵地的生态系统构成了严重的威胁,影响了入侵域农作物的生产。采用石蜡切片技术,利用光学显微镜进行观察,研究了不同质量浓度的黄顶菊、三叶鬼针草、胜红蓟3种入侵植物的叶片挥发物对旱稻幼苗初生根的结构以及根系发育的影响,结果表明:低质量浓度(5g)的三叶鬼针草和胜红蓟叶片挥发物对根皮层起抑制作用,低质量浓度(5g)的三叶鬼针草挥发物对维管柱有促进作用,而黄顶菊挥发物对髓腔影响比较大,表现为低浓度抑制,高浓度促进;20g质量浓度的三种入侵植物叶片挥发物对旱稻幼苗初生根结构影响最大,均出现结构上的变异;对侧根的发育随浓度的增加而呈现明显的抑制作用,20g质量浓度时没有侧根的发生。表明入侵植物对受体植物根结构的影响随植物种类和挥发物浓度的不同而有不同的特点。     

Comparative analysis of plant and animal calcium signal transduction element using plant full-length cDNA data

We obtained 32K full-length cDNA sequence data from the rice full-length cDNA project and performed a homology search against NCBI GenBank data. We have also searched homologs of Arabidopsis and other plants' genes with the databases. Comparative analysis of calcium ion transport proteins revealed that the genes specific for muscle and nerve calcium signal transduction systems (VDCC, IP3 receptor, ryanodine receptor) are very different in animals and plants. In contrast, Ca elements with basic functions in cell responses (CNGC, iGlu receptor, Ca(2+)ATPase, Ca2+/Na(+)-K+ ion exchanger) are basically conserved between plants and animals. We also performed comparative analyses of calcium ion binding and/or controlling signal transduction proteins. Many genes specific for muscle and nerve tissue do not exist in plants. However, calcium ion signal transduction genes of basic functions of cell homeostasis and responses were well conserved; plants have developed a calcium ion interacting system that is more direct than in animals. Many species of plants have specifically modified calcium ion binding proteins (CPK, CRK), Ca2+/phospholipid-binding domains, and calcium storage proteins.