The role of calcium in the recall of stored morphogenetic information by plants

Flax seedlings grown in the absence of environmental stimuli, stresses and injuries do not form epidermal meristems in their hypocotyls. Such meristems do form when the stimuli are combined with a transient depletion of calcium. These stimuli include the "manipulation stimulus" resulting from transferring the seedlings from germination to growth conditions. If, after a stimulus, calcium depletion is delayed, meristem production is also delayed; in other words, the meristem-production instruction can be memorised. Memorisation includes both storage and recall of information. Here, we focus on information recall. We show that if the first transient calcium depletion is followed by a second transient depletion there is a new round of meristem production. We also show that if an excess of calcium follows calcium depletion, meristem production is blocked; but if the excess of calcium is in turn followed by another calcium depletion, again there is a new round of meristem production. The same stored information can thus be recalled repeatedly (at least twice). We describe a conceptual model that takes into account these findings.     

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     

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     

Isolated plant nuclei as mechanical and thermal sensors involved in calcium signalling

Calcium signals in the nucleus elicit downstream effects that are distinct from those of cytosolic calcium signals. In the present work, we have evaluated the ability of plant nuclei to sense stimuli directly and to convert them into calcium changes. We show that individual mechanical stimulation of isolated nuclei elicits a single calcium transient at acidic pHs, whereas a series of stimulations leads to oscillations whose frequency reflects that of the stimuli. Conversely, at alkaline pHs, nuclei respond to temperature but not to stretch. The stretch- and the temperature-activated processes differ by their sensitivity to pharmacological drugs known to affect ion channel activities in animal cells. Our data demonstrate that isolated nuclei are able to gauge physical parameters of their environment. This might have a profound influence on the functioning of calcium-dependent processes known to control a large array of molecular events in the nucleus.     

Transpiration inhibition by stored xylem sap from well-watered maize plants

There is increasing evidence that a chemical signal exists in xylem sap of plants subjected to water deficits which influences physiological responses in plant shoots. An important method of studying this signal is the transpiration response of excised leaves exposed to xylem sap collected from plants. However, Munns et al [Plant, Cell & Environment 16, 867–877] cautioned that transpiration inhibition is observed when xylem sap collected from wheat and barley is stored before determining physiological activity. The objective of the study reported here was to determine if transpiration inhibition develops in maize sap collected from well-watered plants when the sap is stored under various conditions. It was found that storage of maize sap collected from well-watered plants for only 1 d at -20°C resulted in the development of substantial transpiration inhibition in bioassay leaves. Storage of sap at 4°C resulted in the development of the effect after 2 weeks, while storage at ?86°C showed only small transpiration inhibition after 3 weeks. The major source of the transpiration inhibition was the development of a substance in the stored sap that resulted in physical blockage of the transpiration stream in bioassay leaves. However, a small signal component may also have developed in the stored sap. Because of the possibility of ionic activity under freezing conditions at ?20°C, calcium was studied for its potential involvement in the transpiration inhibition. However, the calcium concentrations found to inhibit transpiration were nearly an order of magnitude larger than the calcium concentrations observed in xylem sap.     

Extracellular calcium transients at single excitations in rabbit atrium measured with tetramethylmurexide

Extracellular calcium transients were resolved within the time course of single contraction cycles in rabbit left atrium using tetramethylmurexide (2 mM) as the calcium-sensitive dye (150-250 microM total calcium, 80-150 microM free calcium). Net extracellular calcium depletion began within 2-4 ms upon excitation; over the following 5-20 ms, depletion continued steeply and amounted to 0.2 mumol/kg wet weight X 10 ms (135 microM free extracellular calcium). In regularly excited muscles (0.5-2 Hz), net depletion slowed rapidly and stopped early during the rise of contractile motion monitored by transmitted light. Maximum depletions amounted to 0.2-0.5% of total extracellular calcium (0.2-0.5 mumol/kg wet weight with 135 microM free calcium). Replenishment of extracellular calcium began at the latest midway to the peak of the motion signal. Calcium replenishment could be complete for the most part by an early phase of relaxation or could take place continuously through relaxation. The maximal net depletion per beat decreased manyfold with a decrease of frequency from 1 to 0.05 Hz. During paired pulse stimulation (200-300-ms twin pulse separation at basal rates of 0.3-1 Hz), extracellular calcium accumulation was enhanced at the initial potentiated contraction; extracellular calcium depletion was prolonged at the low-level premature contraction. With quadruple stimulation (three premature excitations), the apparent rate of net extracellular calcium accumulation at potentiated contractions approached or exceeded the apparent rate of early net calcium depletion. Under the special circumstance of a strongly potentiated post-stimulatory contraction after greater than 5 s rest, repolarization beyond -40 mV occurred within 10 ms, net extracellular calcium accumulation began with the onset of muscle motion, and net extracellular calcium accumulation (1-3 microM/kg wet weight) coincided with a more positive late action potential in comparison with subsequent action potentials. Consistent changes of the apparent rate of early net calcium depletion were not found with any of the simulation patterns examined. In ryanodine-pretreated atria, the duration of depletion was clearly limited by action potential duration at post-rest stimulations; in the presence of 4-aminopyridine (2 mM), depletion continued essentially undiminished for up to 200 ms. The resulting net depletion magnitudes were greater than 10 times larger than the transient depletions found during steady stimulation.     

Fibronectin promotes calcium signaling by interferon-gamma in human neutrophils via G-protein and sphingosine kinase-dependent mechanisms

A common intracellular signal activating polymorphonuclear leukocytes (PMN) in inflammation is a change in cytosolic calcium concentration. Previously, we have shown that interferon-γ (IFN-γ) induces transient calcium signals in PMN, but only after intracellular calcium store depletion. Using a digital imaging system, we show that adhesion of PMN is critical for IFN-γ-induced calcium signals, and with PMN attached to the optimal coating, the calcium signals are evoked even in presence of extracellular calcium, that is, non-depleted calcium stores. Adhesion to fibronectin, pure or extracted from plasma by gelatin, improved the IFN-γ responses compared with serum, plasma, or vitronectin coats. In accordance with previous observations, IFN-γ-induced calcium signals in fibronectin adherent cells were totally abolished by the G-protein inhibitor pertussis toxin and were also inhibited by the sphingosine kinase inhibitors dimethylsphingosine (DMS) and N-acetylsphingosine (N-Ac-Sp). PMN contact with fibronectin alone, measured in cells sedimenting onto a fibronectin-coated surface or by addition of fibronectin to glass-adherent cells, evoked transient calcium signals. However, PMN in suspension did not respond to the addition of fibronectin or arginine-glycine-aspartate (RGD). The fibronectin-induced calcium signals were also clearly depressed by pertussis toxin and by the sphingosine kinase inhibitors DMS, dihydrosphingosine (DHS), and N-Ac-Sp. When the product of sphingosine kinase activity, sphingosine I-phosphate (S1-P), was added to the cells, similar calcium signals were induced, which were dependent on a pertussis toxin-sensitive G-protein activity. Finally, addition of S1-P to the cells prior to stimulation with IFN-γ partly mimicked the priming effect of fibronectin. In conclusion, fibronectin contact evokes by itself a calcium signal in PMN and further promotes calcium signaling by IFN-γ. We suggest that fibronectin might activate sphingosine kinase, and that the sphingosine 1-phosphate thereby generated induces a calcium signal via a G-protein-dependent mechanism. Apparently, sphingosine kinase activity is also involved in IFN-γ induced calcium signals.     

Pronectin Promotes Calcium Signaling by Interferon-γ Human Neutrophils via G-Protein and Sphingosine Kinase-Dependent Mechanisms

A common intracellular signal activating polymorphonuclear leukocytes (PMN) in inflammation is a change in cytosolic calcium concentration. Previously, we have shown that interferon-γ (IFN-γ) induces transient calcium signals in PMN, but only after intracellular calcium store depletion. Using a digital imaging system, we show that adhesion of PMN is critical for IFN-γ-induced calcium signals, and with PMN attached to the optimal coating, the calcium signals are evoked even in presence of extracellular calcium, that is, non-depleted calcium stores. Adhesion to fibronectin, pure or extracted from plasma by gelatin, improved the IFN-γ responses compared with serum, plasma, or vitronectin coats. In accordance with previous observations, IFN-γ-induced calcium signals in fibronectin adherent cells were totally abolished by the G-protein inhibitor pertussis toxin and were also inhibited by the sphingosine kinase inhibitors dimethylsphingosine (DMS) and N-acetylsphingosine (N-Ac-Sp). PMN contact with fibronectin alone, measured in cells sedimenting onto a fibronectin-coated surface or by addition of fibronectin to glass-adherent cells, evoked transient calcium signals. However, PMN in suspension did not respond to the addition of fibronectin or arginine-glycine-aspartate (RGD). The fibronectin-induced calcium signals were also clearly depressed by pertussis toxin and by the sphingosine kinase inhibitors DMS, dihydrosphingosine (DHS), and N-Ac-Sp. When the product of sphingosine kinase activity, sphingosine I-phosphate (S1-P), was added to the cells, similar calcium signals were induced, which were dependent on a pertussis toxin-sensitive G-protein activity. Finally, addition of S1-P to the cells prior to stimulation with IFN-γ partly mimicked the priming effect of fibronectin. In conclusion, fibronectin contact evokes by itself a calcium signal in PMN and further promotes calcium signaling by IFN-γ. We suggest that fibronectin might activate sphingosine kinase, and that the sphingosine 1-phosphate thereby generated induces a calcium signal via a G-protein-dependent mechanism. Apparently, sphingosine kinase activity is also involved in IFN-γ induced calcium signals.     

植物感受盐胁迫及相关钙信号的研究进展

盐胁迫对植物的生长和发育造成严重影响,其危害包括渗透胁迫、离子毒害等,严重损害了农业生产和粮食安全。在盐胁迫下,植物相关感受器接受刺激,使得Ca²⁺通过细胞膜以及细胞内钙库膜上打开的Ca²⁺通道进入细胞质基质,导致细胞质内Ca²⁺浓度升高,产生钙信号。钙离子作为重要的第二信使,在植物细胞内和细胞间传递信号,信号往下游传递,在不同生长和发育阶段引起植物一系列的生理响应来应对盐胁迫影响。钙信号主要通过钙调蛋白（CaM）、钙调素样蛋白（CML）、钙依赖性蛋白激酶（CDPK）、钙调磷酸酶B样蛋白（CBL）和CBL互作蛋白激酶（CIPK）感知并将特异的钙信号信息传递到下游;从而激活植物盐胁迫生理响应。本文主要综述植物如何感知盐胁迫刺激,以及钙信号产生与传导机制,并对该研究领域需解决的问题进行了展望。     

Immunohistochemical localisation of ubiquitin and the proteasome in sunflower (Helianthus annuus cv. Giganteus)

This study provides an immunohistochemical demonstration of the involvement of the ubiquitin- and proteasome-dependent pathway during differentiation and organogenesis in plants. The localisation of ubiquitin and the proteasome was studied in meristems, leaves, stems and roots of sunflower (Helianthus annuus L. cv. Giganteus). By using a new technique that enhances very low antigen signals, we obtained information on the structural distribution of the ubiquitin- and proteasome-dependent pathway, and of the importance of this pathway during organogenesis and plant development. Ubiquitin and the proteasome showed overall similarities in their cellular localisation. The highest antigenic signal was observed in the root and shoot apical meristems, in leaf primordia and vascular tissue. The cambium showed less expression than the apical meristems. During adventitious root formation in cuttings, no sign of increased expression was observed within dedifferentiating tissue, but as organogenesis progressed, the antigenic signal of ubiquitin and the proteasome gradually increased in the developing roots. Comparison of immunochemical results and Western blots demonstrated that important changes in the cellular antigen signal could only be detected by immunochemistry.     

Possible link of different slow calcium signals generated by membrane potential and hormones to differential gene expression in cultured muscle cells

The study of fluorescent calcium signals from cultured rat myotubes has provided interesting results in the past few years. Both K+ depolarization and tetanic electrical stimulation were shown to produce slow Ca2+ signals, unrelated to contraction and associated to regulation of gene expression in cultured rat myotubes. We studied the effect of IGF-I, insulin and testosterone on intracellular Ca2+ in cultured muscle cells. Insulin produced a fast (< 1 s) and transient [Ca2+] increase lasting less than 10 s. IGF-I induced a transient [Ca2+] increase, reaching a fluorescence peak 6 s after stimulus, to return to basal values after 60 s. Testosterone induced delayed (35 s) and long lasting (100-200 s) signals, frequently associated with oscillations. IGF-I, testosterone and electrical stimulation-induced Ca2+ signals were shown to be dependent on IP3 production. All of these Ca2+ signals were blocked by inhibitors of the IP3 pathway. On the other hand, insulin-induced Ca2+ increase was dependent on ryanodine receptors and blocked by either nifedipine or ryanodine. The different intracellular Ca2+ patterns produced by electrical stimulation, testosterone, IGF-I and insulin, may help to understand the role of intracellular calcium kinetics in the regulation of gene expression by various stimuli in skeletal muscle cells.     

PPF1 inhibits programmed cell death in apical meristems of both G2 pea and transgenic Arabidopsis plants possibly by delaying cytosolic Ca2+ elevation

PPF1 encodes a putative calcium ion carrier that affects the flowering time of transgenic Arabidopsis by modulating Ca(2+) storage capacities in chloroplasts of a plant cell. In the current work, we found that differential expression of PPF1 might affect processes of programmed cell death (PCD) since DNA fragmentation was detected in senescencing apical buds of long day-grown G2 pea (Pisum sativum L.) plants, but was not in non-senescencing short day-grown counterparts at all growth stages. An animal inhibitor of caspase-activated DNase (ICAD) homologue was detected in short day-grown plant continuously throughout the whole experiment and only in early stages of long day-grown pre-floral G2 pea apical buds. DNA fragmentation was significantly inhibited in apical meristems of transgenic Arabidopsis that over-expressed the PPF1 gene when compared to that of either wild-type control or to PPF1 (-) plants. The expression of ICAD-like protein decreased to undetectable level at 45 dpg in apical tissues of PPF1 (-) Arabidopsis, which was much earlier than that found in PPF1 (+) or wild-type controls. In epidermal cells of PPF1 (-) plants, we recorded significantly earlier calcium transient prior to PCD. We suggest that the expression of PPF1, a chloroplast localized Ca(2+) ion channel may inhibit programmed cell death in apical meristems of flowering plants by keeping a low cytoplasmic calcium content that might inhibit DNA fragmentation in plant cells.     

Establishment of multiple shoot clumps from maize (Zea mays L.) and regeneration of herbicide-resistant transgenic plantlets

A kind of quick, efficient and season-free inducing embryoid and multiple shoot clumps system from shoot tip meristems that derived from elite inbreds of maize was established. The herbicide-resistant gene als (coding Acetolactate synthase) isolated from a mutant of Arabidopsis thaliana was transferred to tissue pieces of maize multiple shoot clumps by microprojectile bombardment. Herbicide-resistant tissue and regenerants were obtained through selections with herbicide chlorsulfuron. PCR analysis and Southern blot hybridization indicated that gene als has been transferred to some regenerants. The test of spraying chlorsulfuron displayed that the transgenic plantlets and R1 plants had favorable herbicide-resistant trait. We have established a new genotype-free system of maize which could rapidly and efficiently produce large quantities of transgenic plantlets.     

Long-term Partitioning, Storage and Remobilization of 14C Assimilated by Trifolium repens (cv. Blanca)

The fourth fully expanded leaf on the main stolon of white cloverplants was exposed to ¹⁴CO₂. Thereafter, quantitative and fractionalanalysis of the partitioning, storage and remobilization afterdefoliation of the ¹⁴C labelled assimilate was sequentiallyconducted over a 2- to 3-week period. In undefoliated plants, most ¹⁴C reached its final destinationwithin 24 h of feeding. Forty percent of assimilated ¹⁴C waslost through respiration, while the rest was exported, predominantlyto meristems, but also to roots, stolons and leaves. The ¹⁴Cinitially translocated to meristems was subsequently recoveredin stolon and leaf tissue as the plants matured. Approximately 10% of assimilated ¹⁴C was invested into long-termstorage in roots and stolons. These reserves were remobilizedafter both partial and total defoliation, and a portion of theremobilized ¹⁴C was incorporated into new growth, Partly defoliatedplants regrew more rapidly than totally defoliated plants, butmore ¹⁴C reserve depletion took place in the totally defoliatedtreatment. Reserve depletion took place from both stolons androots, but stolon reserves were preferentially utilized. Bothhigh and low molecular weight storage compounds were involved. Trifolium repens, white clover, assimilate partitioning, storage, remobilization, defoliation     

One-way calcium spill-over during signal transduction in Paramecium cells: from the cell cortex into cilia, but not in the reverse direction

We asked to what extent Ca(2+) signals in two different domains of Paramecium cells remain separated during different stimulations. Wild-type (7S) and pawn cells (strain d4-500r, without ciliary voltage-dependent Ca(2+)-channels) were stimulated for trichocyst exocytosis within 80 ms by quenched-flow preparation and analysed by energy-dispersive X-ray microanalysis (EDX), paralleled by fast confocal fluorochrome analysis. We also analysed depolarisation-dependent calcium signalling during ciliary beat rerversal, also by EDX, after 80-ms stimulation in the quenched-flow mode. EDX and fluorochrome analysis enable to register total and free intracellular calcium concentrations, [Ca] and [Ca(2+)], respectively. After exocytosis stimulation we find by both methods that the calcium signal sweeps into the basis of cilia, not only in 7S but also in pawn cells which then also perform ciliary reversal. After depolarisation we see an increase of [Ca] along cilia selectively in 7S, but not in pawn cells. Opposite to exocytosis stimulation, during depolarisation no calcium spill-over into the nearby cytosol and no exocytosis occurs. In sum, we conclude that cilia must contain a very potent Ca(2+) buffering system and that ciliary reversal induction, much more than exocytosis stimulation, involves strict microdomain regulation of Ca(2+) signals.     

Mechanical signalling,calcium and plant form

Calcium is a dynamic signalling molecule which acts to transduce numerous signals in plant tissues. The basis of calcium signalling is outlined and the necessity for measuring and imaging of calcium indicated. Using plants genetically transformed with a cDNA for the calcium-sensitive luminescent protein, aequorin, we have shown touch and wind signals to immediately increase cytosol calcium. Touch and wind signal plant cells mechanically, through tension and compression of appropiate cells. Many plant tissues and cells are very sensitive to mechanical stimulation and the obvious examples of climbing plants, insectivorous species as well as other less well-known examples are described. Touch sensing in these plants may be a simple evolutionary modification of sensitive mechanosensing system present in every plant. The possibility that gravitropism may be a specific adaptation of touch sensing is discussed. There is a growing appreciation that plant form may have a mechanical basis. A simple mechanical mechanism specifying spherical, cylindrical and flat-bladed structures is suggested. The limited morphological variety of plant tissues may also reflect mechanical specification. The article concludes with a discussion of the mechanisms of mechanical sensing, identifying integrin-like molecules as one important component, and considers the specific role of calcium.     

Meristem culture and virus eradication in Alstroemeria

Stem apical meristems, rhizome apical meristems and rhizome axillary meristems excised from Alstroemeria plants were grown in vitro on modified Murashige and Skoog (MS) media containing different concentrations of gibberellic acid and 6-benzylaminopurine (BA). Plantlets developed from stem apical meristems never regenerated a rhizome and eventually died. The highest regeneration rate (74.1%) of plantlets with a rhizome was observed when rhizome axillary meristems were grown on modified MS medium containing M 8.9 of BA. Alstroemeria mosaic potyvirus (AlMV) could be eradicated from infected Alstroemeria plants through meristem culture. The rate of virus eradication was 73.7 and 14.7% for plantlets developing from explants measuring 0.7 mm and 2.0 mm, respectively. Greenhouse evaluation of virus-negative and AlMV-infected Alstroemeria plants showed that healthy plants produced more floral stems, more vegetative stems, longer floral stems and gave a higher fresh weight than infected plants.     

Distinguishing splanchnic nerve and chromaffin cell stimulation in mouse adrenal slices with fast-scan cyclic voltammetry

Electrical stimulation is an indispensible tool in studying electrically excitable tissues in neurobiology and neuroendocrinology. In this work, the consequences of high-intensity electrical stimulation on the release of catecholamines from adrenal gland slices were examined with fast-scan cyclic voltammetry at carbon fiber microelectrodes. A biphasic signal, consisting of a fast and slow phase, was observed when electrical stimulations typically used in tissue slices (10 Hz, 350 μA biphasic, 2.0 ms/phase pulse width) were applied to bipolar tungsten-stimulating electrodes. This signal was found to be stimulation dependent, and the slow phase of the signal was abolished when smaller (≤250 μA) and shorter (1 ms/phase) stimulations were used. The slow phase of the biphasic signal was found to be tetrodotoxin and hexamethonium independent, while the fast phase was greatly reduced using these pharmacological agents. Two different types of calcium responses were observed, where the fast phase was abolished by perfusion with a low-calcium buffer while both the fast and slow phases could be modulated when Ca2(+) was completely excluded from the solution using EGTA. Perfusion with nifedipine resulted in the reduction of the slow catecholamine release to 29% of the original signal, while the fast phase was only decreased to 74% of predrug values. From these results, it was determined that high-intensity stimulations of the adrenal medulla result in depolarizing not only the splanchnic nerves, but also the chromaffin cells themselves resulting in a biphasic catecholamine release.     

Plant sensitivity to low intensity 105 GHz electromagnetic radiation

Exposing seedlings of the flax, Linum usitatissimum L., to a variety of weak environmental stresses followed by a 2 day calcium deprivation, triggers the common response of production of epidermal meristems (actively dividing groups of cells) in the hypocotyl, which is the part of the stem between the root and the cotyledons (the pre-existing leaves in the embryo). This production reaches a plateau of 10-20 meristems after a month in the case of mechanical stimulation and cold shock. Recently, we have shown that radiation from a global system for mobile communication (GSM) telephone also triggers production of meristems with a plateau of around six meristems. Here, we show that a single 2 h exposure to radiation emitted at 105 GHz at non-thermal levels by a Gunn oscillator induces meristem production with kinetics similar to that induced by weak environmental stimuli and radiation from GSM telephone.