Effect of Lithium on Thigmomorphogenesis in Bryonia dioica Ethylene Production and Sensitivity

Transgenic tomatoes showing higher glutathione peroxydase antioxidant activity are more resistant to an abiotic stress but more susceptible to biotic stresses

The function of selenium independent glutathione peroxidase (GPx) in response to biotic and abiotic stresses was investigated in transgenic tomato plants overexpressing an exogenous GPx and exhibiting a 50% increase in total GPx activity. GPx-overexpressing and control plants were challenged either by a mechanical stress or by infection with the biotrophic parasite Oidium neolycopersici or the necrotrophic parasite Botrytis cinerea. In mechanically stressed plants, internode growth was significantly less modified in GPx-overexpressing plants compared to controls. This stress resistant phenotype was not accompanied with any change in the global antioxidant response of the plants other than their increased GPx activity. Following infection by O. neolycopersici or by B. cinerea, lesion extension was increased in GPx-overexpressing plants compared with controls. These results showed that GPx overexpression provoked opposite effects in situations of biotic and abiotic challenges, suggesting a key role for this scavenger enzyme in controlling biotic and abiotic stress responses.

Thigmomorphogenesis in Solanum lycopersicum: morphological and biochemical responses in stem after mechanical stimulation

The activation of the phenylpropanoid pathway in plants by environmental stimuli is one of the most universal biochemical stress responses known. In tomato plant, rubbing applied to a young internode inhibit elongation of the rubbed internode and his neighboring one. These morphological changes were correlated with an increase in lignification enzyme activities, phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD) and peroxidases (POD), 24 hours after rubbing of the forth internode. Furthermore, a decrease in indole-3-acetic acid (IAA) content was detected in the rubbed internode and the upper one. Taken together, our results suggest that decrease in rubbed internode length is a consequence of IAA oxidation, increases in enzyme activities (PAL, CAD and POD), and cell wall rigidification associated with induction of lignification process.

Characterization and expression analysis under bending and other abiotic factors of PtaZFP2, a poplar gene encoding a Cys2/His2 zinc finger protein

In plants, mechanoperception and transduction of mechanical signals have been studied essentially in Arabidopsis thaliana L. and Lycopersicon esculentum L. plants, i.e., in nonwoody plants. Here, we have described the isolation of both the full-length cDNA and the regulatory region of PtaZFP2, encoding a member of Cys2/His2 zinc finger protein (ZFP) family in Populus tremula L. x Populus alba L. Time course analysis of expression demonstrated that PtaZFP2 mRNA accumulated as early as 5 min in response to a controlled stem bending and is restricted to the organ where the mechanical stimulus is applied. The real-time quantitative Reverse Transcriptase Polymerase Chain Reaction experiments showed that PtaZFP2 was also rapidly up-regulated in poplar stems in response to gravitropism suggesting that PtaZFP2 is induced by different mechanical signals. Abundance of PtaZFP2 transcripts also increased highly in response to wounding and to a weaker extent to salt treatment and cold, which is consistent with the numerous putative cis-elements found in its regulatory region. As in other species, these data suggest that Cys2/His2 ZFPs could function in poplar as key transcriptional regulators in the acclimation response to different environmental factors.

Thigmomorphogenesis: a complex plant response to mechano-stimulation

In nature, plants are challenged with hurricane winds, monsoon rains, and herbivory attacks, in addition to many other harsh mechanical perturbations that can threaten plant survival. As a result, over many years of evolution, plants have developed very sensitive mechanisms through which they can perceive and respond to even subtle stimuli, like touch. Some plants respond behaviourally to the touch stimulus within seconds, while others show morphogenetic alterations over long periods of time, ranging from days to weeks. Various signalling molecules and phytohormones, including intracellular calcium, jasmonates, ethylene, abscisic acid, auxin, brassinosteroids, nitric oxide, and reactive oxygen species, have been implicated in touch responses. Many genes are induced following touch. These genes encode proteins involved in various cellular processes including calcium sensing, cell wall modifications, and defence. Twenty-three per cent of these up-regulated genes contain a recently identified promoter element involved in the rapid induction in transcript levels following mechanical perturbations. The employment of various genetic, biochemical, and molecular tools may enable elucidation of the mechanisms through which plants perceive mechano-stimuli and transduce the signals intracellularly to induce appropriate responses.

Unique ethylene-regulated touch responses of Arabidopsis thaliana roots to physical hardness

Although touch responses of plant roots are an important adaptive behavior, the molecular mechanism remains unclear. We have developed a bioassay for measuring root-bending responses to physical hardness in Arabidopsis thaliana seedlings. Our test requires a two-layer solid medium. Primary roots growing downward through an upper layer of 0.3% phytagel either penetrate the lower layer or bend along an interface between the upper and lower layers with different concentrations (0.2-0.5%, corresponding to 1.57-6.79 gw mm(-2) in hardness). In proportion to increasing hardness of the lower layer, we found that the percentage of bending roots increased and ethylene production decreased, suggesting an inverse relationship between the root-bending response and ethylene production. Studies with ethylene biosynthesis modulators and mutants also suggested that bending and non-bending responses of roots to medium hardness depend, respectively, on decreased and increased ethylene biosynthesis. In addition, the degrees of root-tip softening and differential root-cell growth, both possible factors determining root-bending response, were enhanced and attenuated by decreased and increased amounts of ethylene, respectively--also in bending roots and non-bending roots. Our findings indicate that ethylene regulates root touch responses, probably through a combination of root-tip softening (or hardening) and differential root-cell growth.

Use of differential display for the identification of touch-induced genes from an ethylene-insensitive Arabidopsis mutant and partial characterization of these genes

Touch has been shown to affect plant growth and development and ethylene has been shown to have similar effects. However, the mechanisms responsible for touch-induced responses remain unclear. Differential display PCR was used to identify touch-regulated genes from 3-week-light-grown ethylene-insensitive etr1-3 Arabidopsis (Columbia ecotype) mutant plants. The differential display PCR screening process yielded 32 cDNA fragments. Subsequent screening of the 32 fragments using northern analysis yielded three touch-inducible clones (A8A, G5A and G7F). These three cDNA were then used to screen a cDNA library. A 1.2kb fragment for OPR3 was obtained from A8A screenings. This cDNA fragment encodes 12-oxophytodienoate-10, 11-reductase (OPR), an enzyme in the jasmonic acid biosynthetic pathway. OPR3 was found to be induced by touch, wounding, methyl jasmonate (MeJA), NaCl and CaCl(2) while ethylene and darkness had no effect. A 2kb cDNA encoding a calcium-dependent protein kinase (CDPK32) was obtained with G5A screenings. CDPK32 was shown to be induced by touch, wounding, NaCl and darkness while ethylene and MeJA had little or no effect. A 1.4kb cDNA encoding a novel protein was recovered from the cDNA library screenings with a G7F fragment. This cDNA had some sequence similarity to GDA1 and was designated GDL for GDA1-like cDNA. GDL was activated by touch, wounding, MeJA, NaCl and CaCl(2) while there was no induction with ethylene and darkness. Using differential display PCR we have successfully been able to identify three clones that are inducible by touch and not by ethylene.

In touch: plant responses to mechanical stimuli

Perception and response to mechanical stimuli are likely essential at the cellular and organismal levels. Elaborate and impressive touch responses of plants capture the imagination as such behaviors are unexpected in otherwise often quiescent creatures. Touch responses can turn plants into aggressors against animals, trapping and devouring them, and enable flowers to be active in ensuring crosspollination and shoots to climb to sunlit heights. Morphogenesis is also influenced by mechanical perturbations, including both dynamic environmental stimuli, such as wind, and constant forces, such as gravity. Even individual cells must sense turgor and wall integrity, and subcellular organelles can translocate in response to mechanical perturbations. Signaling molecules and hormones, including intracellular calcium, reactive oxygen species, octadecanoids and ethylene, have been implicated in touch responses. Remarkably, touch-induced gene expression is widespread; more than 2.5% of Arabidopsis genes are rapidly up-regulated in touch-stimulated plants. Many of these genes encode calcium-binding, cell wall modifying, defense, transcription factor and kinase proteins. With these genes as tools, molecular genetic methods may enable elucidation of mechanisms of touch perception, signal transduction and response regulation.

Long-distance transport, storage and recall of morphogenetic information in plants. The existence of a sort of primitive plant 'memory'

An asymmetrical treatment of Bidens seedlings (pricking one of the seedling cotyledons) causes the cotyledonary buds to grow asymmetrically after release of apical dominance by decapitation of the seedlings. The symmetry-breaking signal propagates within the seedlings at a rate of at least a fraction of a millimetre per second. This information may be 'stored' (STO function) within the seedlings, without taking effect, for at least 2 weeks; then the information may be 'recalled' (RCL function), thus permitting transduction of the signal into the final response (differential growth of the buds), as a consequence of subjecting the seedlings to various symmetrical or asymmetrical treatments. A similar behaviour was observed with stimuli other than pricking (including non-traumatic stimuli), with plants other than Bidens (flax, tomato), and with responses other than cotyledonary-bud growth (hypocotyl elongation, induction of meristems, thigmomorphogenesis). There are indications that storage may involve the activation of elements implicated in cell cycle control, and that the last steps of the final response involve genes such as tch1 and hsp70. The adaptive advantage for plants in possessing STO/RCL functions is discussed. Manipulating the STO/RCL functions may have interesting practical applications, e.g. in the resistance of plants to natural stresses. The existence of the STO/RCL functions in plants constitutes an elementary form of 'memory' which may provide an experimental system simpler than the animal brain to test the validity of the theoretical models of interpretation of important features such as memory storage and evocation.

Arabidopsis thaliana responses to mechanical stimulation do not require ETR1 or EIN2

Plants exposed to repetitive touch or wind are generally shorter and stockier than sheltered plants. These mechanostimulus-induced developmental changes are termed thigmomorphogenesis and may confer resistance to subsequent stresses. An early response of Arabidopsis thaliana to touch or wind is the up-regulation of TCH (touch) gene expression. The signal transduction pathway that leads to mechanostimulus responses is not well defined. A role for ethylene has been proposed based on the observation that mechanostimulation of plants leads to ethylene evolution and exogenous ethylene leads to thigmomorphogenetic-like changes. To determine whether ethylene has a role in plant responses to mechanostimulation, we assessed the ability of two ethylene-insensitive mutants, etr1-3 and ein2-1, to undergo thigmomorphogenesis and TCH gene up-regulation of expression. The ethylene-insensitive mutants responded to wind similarly to the wild type, with a delay in flowering, decrease in inflorescence elongation rate, shorter mature primary inflorescences, more rosette paraclades, and appropriate TCH gene expression changes. Also, wild-type and mutant Arabidopsis responded to vibrational stimulation, with an increase in hypocotyl elongation and up-regulation of TCH gene expression. We conclude that the ETR1 and EIN2 protein functions are not required for the developmental and molecular responses to mechanical stimulation.

Effects of a mechanical stimulation of localization of annexin-like proteins in Bryonia dioica internodes

Mechanical stimulation exerted by rubbing a young internode of Bryonia dioica plants inhibits its growth. Previous cellular and biochemical studies showed that this growth inhibition is associated with Ca(2+) redistribution and profound modifications of plasma membrane characteristics. We extracted and purified Ca(2+)-dependent phospholipid-binding proteins from B. dioica internodes. Two main proteins, p33 and p35, and other minor bands were isolated and identified as annexin-like proteins because of their biochemical properties and their cross-reactions with antibodies against maize (Zea mays L.) annexins. Rabbit antiserum was obtained by injection of B. dioica p35. This antiserum was used for the immunocytolocalization of annexin-like proteins in internode parenchyma cells. It appeared that the distribution of annexin-like proteins was different before and 30 min after the mechanical stimulation. Western analysis of proteins in membrane fractions after separation by free-flow electrophoresis showed that p35 was present in most fractions, whereas p33 appeared mainly in plasmalemma-enriched fractions after the mechanical stimulation. It is hypothesized that a subcellular redistribution of these proteins might be involved in growth inhibition by mechanical stress.

Changes in plasma membrane fluidity of Bryonia dioica internodes during thigmomorphogenesis

Fluidity changes in plasma membrane (PM) lipid extracts or native membranes isolated from Bryonia dioica internodes after a mechanical stimulation were monitored by steady-state fluorescence polarization with 1,6-diphenyl-1,3,5-hexatriene as a probe. The signal was shown to rapidly induce an increase in the bulk lipid fluidity. This event was closely related to a relative enrichment in some phospholipid species (PC, PG and PS) as well as a significant increase in the unsaturation index of total fatty acyl chains. Free sterols and protein content did not appear to be involved into this process. After 48 h, lipids from rubbed internodes became less fluid than PM lipids from control internodes.

Thigmomorphogenesis: the effect of mechanical perturbation on plants

Thigmomorphogenetic responses occur in many environmental settings. The most pronounced effects are found under conditions of extremely high rates of turbulent wind or water flow. However, it is an ubiquitous phenomenon, since mechanical perturbations are to be encountered under all but the most stringent laboratory conditions. Our present understanding of these phenomena is the result of studies at the ecological, anatomical, physiological, biochemical, biophysical and molecular biological levels.

Cytological indication of the involvement of calcium and calcium-related proteins in the early responses of Bryonia dioica to mechanical stimulus

The distribution of membrane-bound calcium, activated calmodulin, and callose synthesis was visualized in Bryonia dioica internodes before and after mechanical stimulus, using fluorescent probes, respectively, chlorotetracycline, fluphenazine, and aniline blue. Bright chlorotetracycline fluorescence remains localized in the plasma membrane of control cells, 30 s after stimulation calcium left the plasmalemma. A delocalization of activated calmodulin was observed after wounding and deposition of callose, which could not be detected before, appeared in the same times in most cells. The callose formation and the decrease in membrane-associated calcium suggest a rapid influx of calcium in the cytosol and an intervention of this ion in the cascade of the early events underlying Bryonia dioica thigmomorphogenesis.

Changes in peroxidases associated with radiation-induced sprout inhibition in garlic (Allium satiyum L.)

The effects of an acute dose of gamma-rays (10 Gy) to post-dormant garlic cloves on inner sprout growth and changes in peroxidases and soluble proteins were evaluated up to 100 days of storage in darkness at 19 +/- 1 degree C and 42 +/- 2% relative humidity. Radiation-induced inhibition of sprout growth became evident after 25 days of treatment and was synchronous with a marked increase in peroxidase activity. Thin-layer isoelectric focusing revealed that radiation induced an increase in the number of anodic peroxidase isoenzymes at 100 days, suggesting modifications in the vascularization process. Neither the soluble protein content nor the protein pattern were affected by irradiation. These results are discussed in terms of a possible mediating effect of peroxidase on radiation-induced sprout inhibition in garlic.

Characterization of peroxidase in plant cells

Two peroxidases, one anionic and one cationic, have been purified from the proteins secreted by peanut (Arachis hypogaea L. var Virginia 56R) cells in suspension culture. These two peroxidases apparently have identical catalytic properties.