Calcium: just another regulator in the machinery of life?

Intrinsic Mechanism of CaCl2 Alleviation of H2O2 Inhibition of Pea Primary Root Gravitropism

Normal root growth is essential for the plant uptake of soil nutrients and water. However, exogenous H2O2 inhibits the gravitropic growth of pea primary roots. It has been shown that CaCl2 application can alleviate H2O2 inhibition, but the exact alleviation mechanism is not clear. Therefore, the present study was carried out by combining the transcriptome and metabolome with a view to investigate in depth the mechanism of action of exogenous CaCl2 to alleviate the inhibition of pea primordial root gravitropism by H2O2. The results showed that the addition of CaCl2 (10 mmol·L-1) under H2O2 stress (150 mmol·L-1) significantly increased the H2O2 and starch content, decreased peroxidase (POD) activity, and reduced the accumulation of sugar metabolites and lignin in pea primary roots. Down-regulated genes regulating peroxidase, respiratory burst oxidase, and lignin synthesis up-regulated PGM1, a key gene for starch synthesis, and activated the calcium and phytohormone signaling pathways. In summary, 10 mmol·L-1 CaCl2 could alleviate H2O2 stress by modulating the oxidative stress response, signal transduction, and starch and lignin accumulation within pea primary roots, thereby promoting root gravitropism. This provides new insights into the mechanism by which CaCl2 promotes the gravitropism of pea primary roots under H2O2 treatment.

Thriving under Salinity: Growth, Ecophysiology and Proteomic Insights into the Tolerance Mechanisms of Obligate Halophyte Suaeda fruticosa

Studies on obligate halophytes combining eco-physiological techniques and proteomic analysis are crucial for understanding salinity tolerance mechanisms but are limited. We thus examined growth, water relations, ion homeostasis, photosynthesis, oxidative stress mitigation and proteomic responses of an obligate halophyte Suaeda fruticosa to increasing salinity under semi-hydroponic culture. Most biomass parameters increased under moderate (300 mmol L-1 of NaCl) salinity, while high (900 mmol L-1 of NaCl) salinity caused some reduction in biomass parameters. Under moderate salinity, plants showed effective osmotic adjustment with concomitant accumulation of Na+ in both roots and leaves. Accumulation of Na+ did not accompany nutrient deficiency, damage to photosynthetic machinery and oxidative damage in plants treated with 300 mmol L-1 of NaCl. Under high salinity, plants showed further decline in sap osmotic potential with higher Na+ accumulation that did not coincide with a decline in relative water content, Fv/Fm, and oxidative damage markers (H2O2 and MDA). There were 22, 54 and 7 proteins in optimal salinity and 29, 46 and 8 proteins in high salinity treatment that were up-regulated, down-regulated or exhibited no change, respectively, as compared to control plants. These data indicate that biomass reduction in S. fruticosa at high salinity might result primarily from increased energetic cost rather than ionic toxicity.

Ubiquitylome analysis reveals the involvement of ubiquitination in the cold responses of banana seedling leaves

Low temperature is a crucial environmental factor limiting the productivity and distribution of banana. Ubiquitination (Kub) is one of the main posttranslational modifications (PTMs) involved in plant responses to abiotic stresses. However, little information is available on the effects of Kub on banana under cold stress. In this study, we used label-free quantification (LFQ) to identify changes in the protein expression and Kub levels in banana seedling leaves after chilling treatment. In total, 4156 proteins, 1089 ubiquitinated proteins and 2636 Kub sites were quantified. Western blot assays showed that Kub was abundant in leaves after low-temperature treatment. Our results show that the proteome and ubiquitylome were negatively correlated, indicating that Kub could be involved in the degradation of proteins in banana after chilling treatment. Based on bioinformatics analysis, low-temperature stress-related signals and metabolic pathways such as cold acclimation, glutathione metabolism, calcium signaling, and photosynthesis signaling were identified. In addition, we found that transcription factors and chromatin remodeling factors related to low-temperature stress were ubiquitinated. Overall, our work presents the first systematic analysis of the Kub proteome in banana under cold stress and provides support for future studies on the regulatory mechanisms of Kub during the cold stress response in plants. SIGNIFICANCE: Banana is a typical tropical fruit tree with poor low-temperature tolerance,however, the role of PTMs such as Kub in the cold response of banana remains unclear. This study highlights the fact that the effects of low-temperature on proteome and ubiquitylome in the banana seedling leaves, we discussed the correlation between transcriptome and proteome, ubiquitylome and proteome, and we analyzed the expression and the changes of ubiquitination levels of low-temperature related proteins and pathway after chilling treatment, and we found that transcription factors and chromatin remodeling factors related to low-temperature stress were ubiquitinated. This study provides new insights into the ubiquitination pathway of banana under cold stress.

Antioxidants in Shell and Nut Yield Components after Ca, Mg and K Preharvest Spraying on Hazelnut Plantations in Southern Chile

To determine the effects of pre-harvest calcium (Ca), magnesium (Mg) and potassium (K) spraying on the antioxidant activity and capacity of hazelnut (Corylus avellana L.) shells, as an approach to sustain the utilization of the main residue derived from this industry, four commercial hazelnut (Tonda di Giffoni) orchards located in Southern Chile (Cunco, Gorbea, Perquenco and Radal), during the 2018/19 season were sprayed three times with five combinations of Ca (300 and 600 mg L^-1), Mg (300 and 600 mg L^-1) and K (300 and 600 mg L^-1). Yield components were determined in harvested whole nuts, whereas Ca, Mg and K concentrations, as well as total phenolic compounds, free radical scavenging antioxidant activity, and oxygen radical absorbance capacity, were determined in shells. All spray treatments with both Ca, Mg and K combinations showed a significant interaction between locality and treatment (L × T) on increased stabilized nut yield (kg ha^-1) in comparison with the control treatments, whereas nut quality was differentially affected by treatment and orchard locality, thus confirming a significant L × T relationship regarding nut length and kernel yield. However, locality showed a major effect on kernels and shells. A significant relationship was determined between locality and the Ca, Mg and K spraying (L × T) concerning antioxidant compounds such as phenolics, whose amounts exceeded those of the control treatments by three times. Antioxidant capacity and activity in shells showed a significant L × T relationship, and nutshells collected from Cunco showed remarkably (3-4 times) higher levels of these factors than the other evaluated localities. Interactions between spray treatment and orchard location were responsible for the different values obtained in the experiments, confirming the influence of the environment on the efficacy of the treatments. Finally, these shells are worth further study as an interesting residue of the hazelnut industry due to their nutritional and antioxidant properties.

Review: Microtubules monitor calcium and reactive oxygen species signatures in signal transduction

Signal transductions require calcium (Ca²⁺) or reactive oxygen species (ROS) signatures, which act as chemical and electrical signals in response to various biotic and abiotic stresses. Calcium as an ion or second messenger affects the membrane potential and microtubules (MTs) dynamicity, while MTs can modulate auto-propagating waves of calcium and ROS signatures in collaboration with ion channels depending on the stimulus type. Thus, in the current review, we highlight advances in research focused on the relationship between dynamic MTs and calcium and ROS signatures in short-distance transmission. The challenges of Ca²⁺-MTs-ROS crosstalk in cold sensing are addressed, which could suggest the prioritization of ROS or Ca²⁺ in signalling.

A calcium sensor calcineurin B-like 9 negatively regulates cold tolerance via calcium signaling in Arabidopsis thaliana

Calcineurin B-like protein 9 (CBL9) plays important roles in response to ABA, K⁺ deprivation in plants. However, whether CBL9 modulates plant adaptation to low-temperature stress is elusive. In this study, we demonstrated that the cbl9 mutants increased freezing tolerance under both cold-acclimating and nonacclimating conditions in Arabidopsis. Cold-induced changes of cytosolic free calcium concentration ([Ca²⁺]_cyt) were then monitored by aequorin-expressed Arabidopsis plants. The results showed that the cold-triggered increases in [Ca²⁺]_cyt levels in cbl9 mutants were clearly higher than those in wild type (WT) plants, while cold-affected changes in free calcium concentration within cytosolic microdomains adjacent to the vacuolar membrane ([Ca²⁺]_md) in cbl9 mutants were similar to those in WT plants. In addition, treatments of seedlings with Ca²⁺ chelator ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) and Ca²⁺ channel blocker lanthanum chloride markedly inhibit changes of [Ca²⁺]_cyt in cbl9 mutants, while the inhibition of calcium release by lithium chloride from intracellular pools demonstrated consistent suppression of [Ca²⁺]_cyt in cbl9 mutants and WT plants. Together, these results indicate that CBL9 negatively modulates cold tolerance through decreasing [Ca²⁺]_cyt in Arabidopsis.

Salinity in Autumn-Winter Season and Fruit Quality of Tomato Landraces

Tomato landraces, originated by adaptive responses to local habitats, are considered a valuable resource for many traits of agronomic interest, including fruit nutritional quality. Primary and secondary metabolites are essential determinants of fruit organoleptic quality, and some of them, such as carotenoids and phenolics, have been associated with beneficial proprieties for human health. Landraces' fruit taste and flavour are often preferred by consumers compared to the commercial varieties' ones. In an autumn-winter greenhouse hydroponic experiment, the response of three Southern-Italy tomato landraces (Ciettaicale, Linosa and Corleone) and one commercial cultivar (UC-82B) to different concentrations of sodium chloride (0 mM, 60 mM or 120 mM NaCl) were evaluated. At harvest, no losses in marketable yield were noticed in any of the tested genotypes. However, under salt stress, fresh fruit yield as well as fruit calcium concentration were higher affected in the commercial cultivar than in the landraces. Furthermore, UC-82B showed a trend of decreasing lycopene and total antioxidant capacity with increasing salt concentration, whereas no changes in these parameters were observed in the landraces under 60 mM NaCl. Landraces under 120 mM NaCl accumulated more fructose and glucose in the fruits, while salt did not affect hexoses levels in UC-82B. Ultra-performance liquid chromatography-tandem mass spectrometry analysis revealed differential accumulation of glycoalkaloids, phenolic acids, flavonoids and their derivatives in the fruits of all genotypes under stress. Overall, the investigated Italian landraces showed a different behaviour compared to the commercial variety UC-82B under moderate salinity stress, showing a tolerable compromise between yield and quality attributes. Our results point to the feasible use of tomato landraces as a target to select interesting genetic traits to improve fruit quality under stress conditions.

Calcium Signaling-Mediated Plant Response to Cold Stress

Low temperatures have adverse impacts on plant growth, developmental processes, crop productivity and food quality. It is becoming clear that Ca²⁺ signaling plays a crucial role in conferring cold tolerance in plants. However, the role of Ca²⁺ involved in cold stress response needs to be further elucidated. Recent studies have shown how the perception of cold signals regulate Ca²⁺ channels to induce Ca²⁺ transients. In addition, studies have shown how Ca²⁺ signaling and its cross-talk with nitric oxide (NO), reactive oxygen species (ROS) and mitogen-activated protein kinases (MAPKs) signaling pathways ultimately lead to establishing cold tolerance in plants. Ca²⁺ signaling also plays a key role through Ca²⁺/calmodulin-mediated Arabidopsis signal responsive 1 (AtSR1/CAMTA3) when temperatures drop rapidly. This review highlights the current status in Ca²⁺ signaling-mediated cold tolerance in plants.

Electrophysiological experiments in microgravity: lessons learned and future challenges

Advances in electrophysiological experiments have led to the discovery of mechanosensitive ion channels (MSCs) and the identification of the physiological function of specific MSCs. They are believed to play important roles in mechanosensitive pathways by allowing for cells to sense their mechanical environment. However, the physiological function of many MSCs has not been conclusively identified. Therefore, experiments have been developed that expose cells to various mechanical loads, such as shear flow, membrane indentation, osmotic challenges and hydrostatic pressure. In line with these experiments, mechanical unloading, as experienced in microgravity, represents an interesting alternative condition, since exposure to microgravity leads to a series of physiological adaption processes. As outlined in this review, electrophysiological experiments performed in microgravity have shown an influence of gravity on biological functions depending on ion channels at all hierarchical levels, from the cellular level to organs. In this context, calcium signaling represents an interesting cellular pathway, as it involves the direct action of calcium-permeable ion channels, and specific gravitatic cells have linked graviperception to this pathway. Multiple key proteins in the graviperception pathways have been identified. However, measurements on vertebrae cells have revealed controversial results. In conclusion, electrophysiological experiments in microgravity have shown that ion-channel-dependent physiological processes are altered in mechanically unloaded conditions. Future experiments may provide a better understanding of the underlying mechanisms.

The calmodulin-like protein, CML39, is involved in regulating seed development, germination, and fruit development in Arabidopsis

We show that the calcium sensor, CML39, is important in various developmental processes from seeds to mature plants. This study bridges previous work on CML39 as a stress-induced gene and highlights the importance of calcium signalling in plant development. In addition to the evolutionarily-conserved Ca²⁺ sensor, calmodulin (CaM), plants possess a large family of CaM-related proteins (CMLs). Using a cml39 loss-of-function mutant, we investigated the roles of CML39 in Arabidopsis and discovered a range of phenotypes across developmental stages and in different tissues. In mature plants, loss of CML39 results in shorter siliques, reduced seed number per silique, and reduced number of ovules per pistil. We also observed changes in seed development, germination, and seed coat properties in cml39 mutants in comparison to wild-type plants. Using radicle emergence as a measure of germination, cml39 mutants showed more rapid germination than wild-type plants. In marked contrast to wild-type seeds, the germination of developing, immature cml39 seeds was not sensitive to cold-stratification. In addition, germination of cml39 seeds was less sensitive than wild-type to inhibition by ABA or by treatments that impaired gibberellic acid biosynthesis. Tetrazolium red staining indicated that the seed-coat permeability of cml39 seeds is greater than that of wild-type seeds. RNA sequencing analysis of cml39 seedlings suggests that changes in chromatin modification may underlie some of the phenotypes associated with cml39 mutants, consistent with previous reports that orthologs of CML39 participate in gene silencing. Aberrant ectopic expression of transcripts for seed storage proteins in 7-day old cml39 seedlings was observed, suggesting mis-regulation of early developmental programs. Collectively, our data support a model where CML39 serves as an important Ca²⁺ sensor during ovule and seed development, as well as during germination and seedling establishment.

Cell Dynamics in the Correct Control of Bone Metabolism Using Natural Treatments

The present study was undertaken in order to assess the efficacy of a commercial product containing calcium and silicon (Osteosil-Calcium®) on cell metabolism. MG-63 osteblast-like cells were cultured in the presence of three different drug concentrations (10, 5 and 2.5 μg/mL). Either serum-free culture and standard culture with serum were investigated. Morpho-functional tests (MTT and ALP), scanning electron microscopy (SEM), microanalysis (EDAX) and time-lapse video microscopy were performed. Cell actin cytoskeletal modification with fluorescence phalloidin staining was also tested. Our data show the in vitro functional efficacy of Osteosil-Calcium® on MG63 cell viability and ALP production. This study demonstrates its positive effect on the metabolism of the single cell and suggests wider uses of this drug in health protection and or in Regenerative Medicine therapies which are currently applied to the elderly

Emerging evidence for potential role of Ca2+-ATPase-mediated calcium accumulation in symbiosomes of infected root nodule cells

Symbiosomes are organelle-like compartments responsible for nitrogen fixation in infected nodule cells of legumes, which are formed as a result of symbiotic association of soil bacteria rhizobia with certain plant root cells. They are virtually the only source of reduced nitrogen in the Earth's biosphere, and consequently, are of great importance. It has been proven that the functioning of symbiosomes depends to a large extent on the transport of various metabolites and ions - most likely including Ca2+ - across the symbiosome membrane (SM). Although it has been well established that this cation is involved in the regulation of a broad spectrum of processes in cells of living organisms, its role in the functioning of symbiosomes remains obscure. This is despite available data indicating both its transport through the SM and accumulation within these compartments. This review summarises the results obtained in the course of studies on the given aspects of calcium behaviour in symbiosomes, and on this basis gives a possible explanation of the proper functional role in them of Ca2+.

Phosphogypsum as a soil fertilizer: Ecotoxicity of amended soil and elutriates to bacteria, invertebrates, algae and plants

Phosphogypsum (PG) is a metal and radionuclide rich-waste produced by the phosphate ore industry, which has been used as soil fertilizer in many parts of the world for several decades. The positive effects of PG in ameliorating some soil properties and increasing crop yields are well documented. More recently concerns are emerging related with the increase of metal/radionuclide residues on soils and crops. However, few studies have focused on the impact of PG applications on soil biota, as well as the contribution to soils with elements in mobile fractions of PG which may affect freshwater species as well. In this context the main aim of this study was to assess the ecotoxicity of soils amended with different percentages of Tunisian phosphogypsum (0.0, 4.9, 7.4, 11.1, 16.6 and 25%) and of elutriates obtained from PG - amended soil (0.0, 6.25, 12.5 and 25% of PG) to a battery of terrestrial (Eisenia andrei, Enchytraeus crypticus, Folsomia candida, Hypoaspis aculeifer, Zea mays, Lactuca sativa) and aquatic species (Vibrio fischeri, Daphnia magna, Raphidocelis subcapitata, Lemna minor). Both for amended soils and elutriates, invertebrates (especially D. magna and E. andrei) were the most sensitive species, displaying acute (immobilization) and chronic (reproduction inhibition) effects, respectively. Despite the presence of some concerning metals in PG and elutriates (e.g., zinc and cadmium), the extremely high levels of calcium found in both test mediums, suggest that this element was the mainly responsible for the ecotoxicological effects observed. Terrestrial and aquatic plants were the most tolerant species, which is in line with studies supporting the application of PG to increase crop yields. Nevertheless, no stimulatory effects on growth were observed for any of the species tested despite the high levels of phosphorus added to soils by PG. Given the importance of soil invertebrates for several soil functions and services, this study gives rise to new serious concerns about the consequences of PG applications on agricultural soils.

Comparative proteomics of root plasma membrane proteins reveals the involvement of calcium signalling in NaCl-facilitated nitrate uptake in Salicornia europaea

Improving crop nitrogen (N) use efficiency under salinity is essential for the development of sustainable agriculture in marginal lands. Salicornia europaea is a succulent euhalophyte that can survive under high salinity and N-deficient habitat conditions, implying that a special N assimilation mechanism may exist in this plant. In this study, phenotypic and physiological changes of S. europaea were investigated under different nitrate and NaCl levels. The results showed that NaCl had a synergetic effect with nitrate on the growth of S. europaea. In addition, the shoot nitrate concentration and nitrate uptake rate of S. europaea were increased by NaCl treatment under both low N and high N conditions, suggesting that nitrate uptake in S. europaea was NaCl facilitated. Comparative proteomic analysis of root plasma membrane (PM) proteins revealed 81 proteins, whose abundance changed significantly in response to NaCl and nitrate. These proteins are involved in metabolism, cell signalling, transport, protein folding, membrane trafficking, and cell structure. Among them, eight proteins were calcium signalling components, and the accumulation of seven of the above-mentioned proteins was significantly elevated by NaCl treatment. Furthermore, cytosolic Ca(2+) concentration ([Ca(2+)]cyt) was significantly elevated in S. europaea under NaCl treatment. The application of the Ca(2+) channel blocker LaCl3 not only caused a decrease in nitrate uptake rate, but also attenuated the promoting effects of NaCl on nitrate uptake rates. Based on these results, a possible regulatory network of NaCl-facilitated nitrate uptake in S. europaea focusing on the involvement of Ca(2+) signalling was proposed.

Live-cell SERS endoscopy using plasmonic nanowire waveguides

Live-cell surface-enhanced Raman spectroscopy (SERS) endoscopy is developed by using plasmonic nanowire waveguides as endoscopic probes. It is demonstrated that the probe insertion does not stress the cell. Opposed to conventional SERS endoscopy, with excitation at the hotspot within the cell, the remote excitation method yields low-background SERS spectra from specific cell compartments with minimal associated photodamage.

Basis for a neuronal version of Grover's quantum algorithm

Grover's quantum (search) algorithm exploits principles of quantum information theory and computation to surpass the strong Church–Turing limit governing classical computers. The algorithm initializes a search field into superposed N (eigen)states to later execute nonclassical “subroutines” involving unitary phase shifts of measured states and to produce root-rate or quadratic gain in the algorithmic time (O(N^1/2)) needed to find some “target” solution m. Akin to this fast technological search algorithm, single eukaryotic cells, such as differentiated neurons, perform natural quadratic speed-up in the search for appropriate store-operated Ca²⁺ response regulation of, among other processes, protein and lipid biosynthesis, cell energetics, stress responses, cell fate and death, synaptic plasticity, and immunoprotection. Such speed-up in cellular decision making results from spatiotemporal dynamics of networked intracellular Ca²⁺-induced Ca²⁺ release and the search (or signaling) velocity of Ca²⁺ wave propagation. As chemical processes, such as the duration of Ca²⁺ mobilization, become rate-limiting over interstore distances, Ca²⁺ waves quadratically decrease interstore-travel time from slow saltatory to fast continuous gradients proportional to the square-root of the classical Ca²⁺ diffusion coefficient, D^1/2, matching the computing efficiency of Grover's quantum algorithm. In this Hypothesis and Theory article, I elaborate on these traits using a fire-diffuse-fire model of store-operated cytosolic Ca²⁺ signaling valid for glutamatergic neurons. Salient model features corresponding to Grover's quantum algorithm are parameterized to meet requirements for the Oracle Hadamard transform and Grover's iteration. A neuronal version of Grover's quantum algorithm figures to benefit signal coincidence detection and integration, bidirectional synaptic plasticity, and other vital cell functions by rapidly selecting, ordering, and/or counting optional response regulation choices.

Effect of salinity and calcium on tomato fruit proteome

Salinity is a major abiotic stress that adversely affects plant growth and productivity. The physiology of the tomato in salty and nonsalty conditions has been extensively studied, providing an invaluable base to understand the responses of the plants to cultural practices. However few data are yet available at the proteomic level looking for the physiological basis of fruit development, under salt stress. Here, we report the effects of salinity and calcium on fruit proteome variations of two tomato genotypes (Cervil and Levovil). Tomato plants were irrigated with a control solution (3 dSm(-1)) or with saline solutions (Na or Ca+Na at 7.6 dSm(-1)). Tomato fruits were harvested at two ripening stages: green (14 days post-anthesis) and red ripe. Total proteins were extracted from pericarp tissue and separated by two-dimensional gel electrophoresis. Among the 600 protein spots reproducibly detected, 53 spots exhibited significant abundance variations between samples and were submitted to mass spectrometry for identification. Most of the identified proteins were involved in carbon and energy metabolism, salt stress, oxidative stress, and proteins associated with ripening process. Overall, there was a large variation on proteins abundance between the two genotypes that can be correlated to salt treatment or/and fruit ripening stage. The results showed a protective effect of calcium that limited the impact of salinization on metabolism, ripening process, and induced plant salt tolerance. Collectively, this work has improved our knowledge about salt and calcium effect on tomato fruit proteome.

Towards the Physics of Calcium Signalling in Plants

Calcium is an abundant element with a wide variety of important roles within cells. Calcium ions are inter- and intra-cellular messengers that are involved in numerous signalling pathways. Fluctuating compartment-specific calcium ion concentrations can lead to localised and even plant-wide oscillations that can regulate downstream events. Understanding the mechanisms that give rise to these complex patterns that vary both in space and time can be challenging, even in cases for which individual components have been identified. Taking a systems biology approach, mathematical and computational techniques can be employed to produce models that recapitulate experimental observations and capture our current understanding of the system. Useful models make novel predictions that can be investigated and falsified experimentally. This review brings together recent work on the modelling of calcium signalling in plants, from the scale of ion channels through to plant-wide responses to external stimuli. Some in silico results that have informed later experiments are highlighted.

Ciliates learn to diagnose and correct classical error syndromes in mating strategies

Preconjugal ciliates learn classical repetition error-correction codes to safeguard mating messages and replies from corruption by “rivals” and local ambient noise. Because individual cells behave as memory channels with Szilárd engine attributes, these coding schemes also might be used to limit, diagnose, and correct mating-signal errors due to noisy intracellular information processing. The present study, therefore, assessed whether heterotrich ciliates effect fault-tolerant signal planning and execution by modifying engine performance, and consequently entropy content of codes, during mock cell–cell communication. Socially meaningful serial vibrations emitted from an ambiguous artificial source initiated ciliate behavioral signaling performances known to advertise mating fitness with varying courtship strategies. Microbes, employing calcium-dependent Hebbian-like decision making, learned to diagnose then correct error syndromes by recursively matching Boltzmann entropies between signal planning and execution stages via “power” or “refrigeration” cycles. All eight serial contraction and reversal strategies incurred errors in entropy magnitude by the execution stage of processing. Absolute errors, however, subtended expected threshold values for single bit-flip errors in three-bit replies, indicating coding schemes protected information content throughout signal production. Ciliate preparedness for vibrations selectively and significantly affected the magnitude and valence of Szilárd engine performance during modal and non-modal strategy corrective cycles. But entropy fidelity for all replies mainly improved across learning trials as refinements in engine efficiency. Fidelity neared maximum levels for only modal signals coded in resilient three-bit repetition error-correction sequences. Together, these findings demonstrate microbes can elevate survival/reproductive success by learning to implement classical fault-tolerant information processing in social contexts.

Apoplastic calcium executes a shut-down function on plant peroxidases: a hypothesis

Recently it was demonstrated that PO activity is switched by calcium within the typical range of apoplastic free calcium concentrations (Plieth and Vollbehr, Plant Signal Behav 2012;7: 650-660). The heat stability of POs is also dependent on calcium. Here, a scenario is put forward which assigns calcium a switch-off function under heat: Peroxidases are switched off by heat stress-triggered apoplastic calcium depletion. It is assumed that this initiates apoplastic accumulation of reactive oxygen species (ROS) and eventually triggers a self-amplifying cascade of cellular events involving plasma membrane ion transport. Calcium depletion-initiated ROS accumulation (CaDIRA) may also trigger signal percolation and the formation of systemic responses to many different stress factors in plants. This hypothesis can explain some as yet unexplained observations.

Calcium promotes activity and confers heat stability on plant peroxidases

In this paper we demonstrate how peroxidase (PO) activities and their heat stability correlate with the availability of free Ca(2+) ions. Calcium ions work as a molecular switch for PO activity and exert a protective function, rendering POs heat stable. The concentration ranges of these two activities differ markedly. POs are activated by µM Ca(2+) concentration ranges, whereas heat stabilization is observed in the nM range. This suggests the existence of different Ca(2+) binding sites. The heat stability of POs depends on the source plant species. Terrestrial plants have POs that exhibit higher temperature stability than those POs from limnic and marine plants. Different POs from a single species can differ in terms of heat stability. The abundance of different POs within a plant is dependent on age and developmental stage. The heat stability of a PO does not necessarily correlate with the maximum temperature the source species is usually exposed to in its natural habitat. This raises questions on the role of POs in the heat tolerance of plants. Consequently, detailed investigations are needed to identify and characterize individual POs, with regard to their genetic origin, subcellular expression, tissue abundance, developmental emergence and their functions in innate and acquired heat tolerance.

Calcium promotes activity and confers heat stability on plant peroxidases

In this paper we demonstrate how peroxidase (PO) activities and their heat stability correlate with the availability of free Ca(2+) ions. Calcium ions work as a molecular switch for PO activity and exert a protective function, rendering POs heat stable. The concentration ranges of these two activities differ markedly. POs are activated by µM Ca(2+) concentration ranges, whereas heat stabilization is observed in the nM range. This suggests the existence of different Ca(2+) binding sites. The heat stability of POs depends on the source plant species. Terrestrial plants have POs that exhibit higher temperature stability than those POs from limnic and marine plants. Different POs from a single species can differ in terms of heat stability. The abundance of different POs within a plant is dependent on age and developmental stage. The heat stability of a PO does not necessarily correlate with the maximum temperature the source species is usually exposed to in its natural habitat. This raises questions on the role of POs in the heat tolerance of plants. Consequently, detailed investigations are needed to identify and characterize individual POs, with regard to their genetic origin, subcellular expression, tissue abundance, developmental emergence and their functions in innate and acquired heat tolerance.

High-resolution imaging of Ca2+ , redox status, ROS and pH using GFP biosensors

Many plant response systems are linked to complex dynamics in signaling molecules such as Ca(2+) and reactive oxygen species (ROS) and to pH. Regulatory changes in these molecules can occur in the timeframe of seconds and are often limited to specific subcellular locales. Thus, to understand how Ca(2+) , ROS and pH form part of plants' regulatory networks, it is essential to capture their rapid dynamics with resolutions that span the whole plant to subcellular dimensions. Defining the spatio-temporal signaling 'signatures' of these regulators at high resolution has now been greatly facilitated by the generation of plants expressing a range of GFP-based bioprobes. For Ca(2+) and pH, probes such as the yellow cameleon Ca(2+) sensors (principally YC2.1 and 3.6) or the pHluorin and H148D pH sensors provide a robust suite of tools to image changes in these ions. For ROS, the tools are much more limited, with the GFP-based H(2) O(2) sensor Hyper representing a significant advance for the field. However, with this probe, its marked pH sensitivity provides a key challenge to interpretation without using appropriate controls to test for potentially coupled pH-dependent changes. Most of these Ca(2+) -, ROS- and pH-imaging biosensors are compatible with the standard configurations of confocal microscopes available to many researchers. These probes therefore represent a readily accessible toolkit to monitor cellular signaling. Their use does require appreciation of a minimal set of controls but these are largely related to ensuring that neither the probe itself nor the imaging conditions used perturb the biology of the plant under study.

Parabolic flight induces changes in gene expression patterns in Arabidopsis thaliana

Our primary objective was to evaluate gene expression changes in Arabidopsis thaliana in response to parabolic flight as part of a comprehensive approach to the molecular biology of spaceflight-related adaptations. In addition, we wished to establish parabolic flight as a tractable operations platform for molecular biology studies. In a succession of experiments on NASA's KC-135 and C-9 parabolic aircraft, Arabidopsis plants were presented with replicated exposure to parabolic flight. Transcriptome profiling revealed that parabolic flight caused changes in gene expression patterns that stood the statistical tests of replication on three different flight days. The earliest response, after 20 parabolas, was characterized by a prominence of genes associated with signal transduction. After 40 parabolas, this prominence was largely replaced by genes associated with biotic and abiotic stimuli and stress. Among these responses, three metabolic processes stand out in particular: the induction of auxin metabolism and signaling, the differential expression of genes associated with calcium-mediated signaling, and the repression of genes associated with disease resistance and cell wall biochemistry. Many, but not all, of these responses are known to be involved in gravity sensing in plants. Changes in auxin-related gene expression were also recorded by reporter genes tuned to auxin signal pathways. These data demonstrate that the parabolic flight environment is appropriate for molecular biology research involving the transition to microgravity, in that with replication, proper controls, and analyses, gene expression changes can be observed in the time frames of typical parabolic flight experiments.

Three endo-β-mannanase genes expressed in the micropylar endosperm and in the radicle influence germination of Arabidopsis thaliana seeds

Mannans are hemicellulosic polysaccharides in the plant primary cell wall (CW). Mature seeds, specially their endosperm cells, have CWs rich in mannan-based polymers that confer a strong mechanical resistance for the radicle protrusion upon germination. The rupture of the seed coat and endosperm are two sequential events during the germination of Arabidopsis thaliana. Endo-β-mannanases (MAN; EC. 3.2.1.78) are hydrolytic enzymes that catalyze cleavage of β1 → 4 bonds in the mannan-polymer. In the genome of Arabidopsis, the endo-β-mannanase (MAN) family is represented by eight members. The expression of these eight MAN genes has been systematically explored in different organs of this plant and only four of them (AtMAN7, AtMAN6, AtMAN2 and AtMAN5) are expressed in the germinating seeds. Moreover, in situ hybridization analysis shows that their transcript accumulation is restricted to the micropylar endosperm and to the radicle and this expression disappears soon after radicle emergence. T-DNA insertion mutants in these genes (K.O. MAN7, K.O. MAN6, K.O. MAN5), except that corresponding to AtMAN2 (K.O. MAN2), germinate later than the wild type (Wt). K.O. MAN6 is the most affected in the germination time course with a t (50) almost double than that of the Wt. These data suggest that AtMAN7, AtMAN5 and specially AtMAN6 are important for the germination of A. thaliana seeds by facilitating the hydrolysis of the mannan-rich endosperm cell walls.

Molecular analysis of endo-β-mannanase genes upon seed imbibition suggest a cross-talk between radicle and micropylar endosperm during germination of Arabidopsis thaliana

The endo-β-mannanase (MAN) family is represented in the Arabidopsis genome by eight members, all with canonical signal peptides and only half of them being expressed in germinating seeds. The transcripts of these genes were localized in the radicle and micropylar endosperm (ME) before radicle protrusion and this expression disappears as soon as the endosperm is broken by the emerging radicle tip. However, only three of these MAN genes, AtMAN5, AtMAN7 and especially AtMAN6 influence the germination time (t50) as assessed by the analysis of the corresponding knock-out lines. The data suggest a possible interaction between embryo and ME regarding the role of MAN during the Arabidopsis germination process.

Signal percolation through plants and the shape of the calcium signature

Plants respond to almost any kind of external stimulus with transients in their cytoplasmic free calcium concentration ([Ca(2+)](c)). A huge variety of kinetics recorded by optical techniques has been reported in the past. This variety has been credited the specificity needed to explain how information about incoming stimuli is evaluated by the organism and turned into the right physiological responses which provide advantages for survival and reproduction. A physiological response often takes place away from the site of stimulation. This requires cell-to-cell communication. Hence, responding cells are not necessarily directly stimulated but rather receive an indirect stimulus via cell-to-cell communication. It appears unlikely that the '[Ca(2+)](c) signature' in the primarily stimulated cell is conveyed over long distances via cell-to-cell communication from the 'receptor cells' to the 'effector cells'. Here, a novel aspect is highlighted to explain the variety of [Ca(2+)] kinetics seen by integrating methods of [Ca(2+)](c) recording. Plants can generally be seen as cellular automata with specific morphology and capable for cell-to-cell communication. Just a few rules are needed to demonstrate how waves of [Ca(2+)](c)-increases percolate through the organism and thereby deliver a broad variety of 'signatures'. Modelling intercellular signalling may be a possible way to find explanations for different kinds of signal transmission, signal amplification, wave formation, oscillations and stimulus-response coupling. The basic examples presented here show that care has to be taken when interpreting cellular '[Ca(2+)](c) signatures' recorded by optical techniques which integrate over a big number of cells or even whole plants.

Gibberellic acid and cGMP-dependent transcriptional regulation in Arabidopsis thaliana

An ever increasing amount of transcriptomic data and analysis tools provide novel insight into complex responses of biological systems. Given these resources we have undertaken to review aspects of transcriptional regulation in response to the plant hormone gibberellic acid (GA) and its second messenger guanosine 3',5'-cyclic monophosphate (cGMP) in Arabidopsis thaliana, both wild type and selected mutants. Evidence suggests enrichment of GA-responsive (GARE) elements in promoters of genes that are transcriptionally upregulated in response to cGMP but downregulated in a GA insensitive mutant (ga1-3). In contrast, in the genes upregulated in the mutant, no enrichment in the GARE is observed suggesting that GARE motifs are diagnostic for GA-induced and cGMP-dependent transcriptional upregulation. Further, we review how expression studies of GA-dependent transcription factors and transcriptional networks based on common promoter signatures derived from ab initio analyses can contribute to our understanding of plant responses at the systems level.

Calcium-dependent physiological processes in trees

Among the various plant nutrients, calcium appears to occupy a unique position, acting as an important regulator in many processes related to both growth and responses to environmental stresses. This applies to stomatal function, cell division, cell wall synthesis, signalling functions in plant defence, repair of damage from biotic and abiotic stress and to the structural chemistry and function of woody tissues. The calcium content in the cambium of poplar was shown to rise transiently by as much as 40% in spring, indicating the significant role that calcium plays in the onset of cambial reactivation. Moreover, during bud flush and the beginning of cell division, calcium was reported to increase significantly in the apical meristem. A reduction in calcium supplies also proved to strongly affect wood formation, as evidenced in the pronounced reduction in wood increment, vessel size and fibre length, as well as in reduced carbonyl and methoxy groups from S-lignin. Induced wounding revealed that calcium acts as an intracellular signal and, furthermore, proved its involvement in long-distance electrical signalling. Environmental stimuli such as cold shock or wounding showed that poplar grown under calcium-starved conditions was incapable of responding to this type of stress. The above evidence highlights the important role of calcium in tree functions, both as a signal in minute physiologically active pools within the cytoplasm, and in higher concentrations for its impact on the structural integrity of cell walls and woody tissues.

Cold-induced cytosolic free calcium ion concentration changes in wheat

Relatively little is known about changes in the cytosolic free calcium ion concentration ([Ca(2+)](c)) in monocotyledonous plants. Therefore, we produced transgenic winter wheat lines stably expressing the calcium-sensitive photoprotein aequorin constitutively in the cytosol. [Ca(2+)](c) was detected in vivo by luminometry, and [Ca(2+)](c) elevations were imaged at video rate. Experiments with the transgenic seedlings focused on potential changes in [Ca(2+)](c) during cold exposure. Temperature-induced changes in [Ca(2+)](c) were found to be more dependent on the change in temperature (dT dt(-1)) than on the absolute value of temperature. [Ca(2+)](c) increased only at cooling rates higher than 8 degrees Cmin(-1), indicating that an overall cellular [Ca(2+)](c) increase is of minor relevance as a signal for cold acclimation in wheat under ecological conditions. The results are discussed with regard to the so-called 'calcium signature hypothesis'.

Calcium fingerprints induced by calmodulin interactors in eukaryotic cells

Calcium (Ca2+) is a ubiquitous second messenger which promotes cell responses through transient changes in intracellular concentrations. The prominent role of Ca2+ in cell physiology is mediated by a whole set of proteins constituting a Ca2+-signalling toolkit involved in Ca2+-signal generation, deciphering and arrest. The different Ca2+-signalosomes deliver Ca2+-signals with spatial and temporal dynamics to control the function of specific cell types. Among the intracellular proteins involved in Ca2+-signal deciphering, calmodulin (CaM) plays a pivotal role in controlling Ca2+-homeostasis and downstream Ca2+-based signalling events. Due to its ubiquitous expression in eukaryotic cells and the variety of proteins it interacts with, CaM is central in Ca2+-signalling networks. For these reasons, it is expected that disrupting or modifying CaM interactions with its target proteins will affect Ca2+-homeostasis and cellular responses. The resulting calcium response will vary depending on which interactions between CaM and target proteins are altered by the molecules and on the specific Ca2+-toolkit expressed in a given cell, even in the resting state. In the present paper, the effect of six classical CaM interactors (W5, W7, W12, W13, bifonazole and calmidazolium) was studied on Ca2+-signalling in tumor initiating cells isolated from human glioblastoma (TG1) and tobacco cells (BY-2) using the fluorescent Ca2+-sensitive Indo-1 dye and aequorin, respectively. Various Ca2+-fingerprints were obtained depending both on the CaM interactor used and the cell type investigated. These data demonstrate that interaction between the antagonists and CaM results in a differential inhibition of CaM-dependent proteins involved in Ca2+-signal regulation. In addition, the distinct Ca2+-fingerprints in tobacco and human tumor initiating glioblastoma cells induced by a given CaM interactor highlight the specificity of the Ca2+-signalosome in eukaryotic cells.

Transient effect of weak electromagnetic fields on calcium ion concentration in Arabidopsis thaliana

BACKGROUND

Weak magnetic and electromagnetic fields can influence physiological processes in animals, plants and microorganisms, but the underlying way of perception is poorly understood. The ion cyclotron resonance is one of the discussed mechanisms, predicting biological effects for definite frequencies and intensities of electromagnetic fields possibly by affecting the physiological availability of small ions. Above all an influence on Calcium, which is crucial for many life processes, is in the focus of interest. We show that in Arabidopsis thaliana, changes in Ca2+-concentrations can be induced by combinations of magnetic and electromagnetic fields that match Ca2+-ion cyclotron resonance conditions.

RESULTS

An aequorin expressing Arabidopsis thaliana mutant (Col0-1 Aeq Cy+) was subjected to a magnetic field around 65 microtesla (0.65 Gauss) and an electromagnetic field with the corresponding Ca2+ cyclotron frequency of 50 Hz. The resulting changes in free Ca2+ were monitored by aequorin bioluminescence, using a high sensitive photomultiplier unit. The experiments were referenced by the additional use of wild type plants. Transient increases of cytosolic Ca2+ were observed both after switching the electromagnetic field on and off, with the latter effect decreasing with increasing duration of the electromagnetic impact. Compared with this the uninfluenced long-term loss of bioluminescence activity without any exogenic impact was negligible. The magnetic field effect rapidly decreased if ion cyclotron resonance conditions were mismatched by varying the magnetic fieldstrength, also a dependence on the amplitude of the electromagnetic component was seen.

CONCLUSION

Considering the various functions of Ca2+ as a second messenger in plants, this mechanism may be relevant for perception of these combined fields. The applicability of recently hypothesized mechanisms for the ion cyclotron resonance effect in biological systems is discussed considering it's operating at magnetic field strengths weak enough, to occur occasionally in our all day environment.

Statolith sedimentation kinetics and force transduction to the cortical endoplasmic reticulum in gravity-sensing Arabidopsis columella cells

The starch statolith hypothesis of gravity sensing in plants postulates that the sedimentation of statoliths in specialized statocytes (columella cells) provides the means for converting the gravitational potential energy into a biochemical signal. We have analyzed the sedimentation kinetics of statoliths in the central S2 columella cells of Arabidopsis thaliana. The statoliths can form compact aggregates with gap sizes between statoliths approaching <30 nm. Significant intra-aggregate sliding motions of individual statoliths suggest a contribution of hydrodynamic forces to the motion of statoliths. The reorientation of the columella cells accelerates the statoliths toward the central cytoplasm within <1 s of reorientation. During the subsequent sedimentation phase, the statoliths tend to move at a distance to the cortical endoplasmic reticulum (ER) boundary and interact only transiently with the ER. Statoliths moved by laser tweezers against the ER boundary experience an elastic lift force upon release from the optical trap. High-resolution electron tomography analysis of statolith-to-ER contact sites indicate that the weight of statoliths is sufficient to locally deform the ER membranes that can potentially activate mechanosensitive ion channels. We suggest that in root columella cells, the transduction of the kinetic energy of sedimenting statoliths into a biochemical signal involves a combination of statolith-driven motion of the cytosol, statolith-induced deformation of the ER membranes, and a rapid release of kinetic energy from the ER during reorientation to activate mechanosensitive sites within the central columella cells.

Transcriptome analysis approaches for the isolation of trichome-specific genes from the medicinal plant Cistus creticus subsp. creticus

Cistus creticus subsp. creticus is a plant of intrinsic scientific interest due to the distinctive pharmaceutical properties of its resin. Labdane-type diterpenes, the main constituents of the resin, exhibit considerable antibacterial and cytotoxic activities. In this study chemical analysis of isolated trichomes from different developmental stages revealed that young leaves of 1-2 cm length displayed the highest content of labdane-type diterpenes (80 mg/g fresh weight) whereas trichomes from older leaves (2-3 or 3-4 cm) exhibited gradual decreased concentrations. A cDNA library was constructed enriched in transcripts from trichomes isolated from young leaves, which are characterized by high levels of labdane-type diterpenes. Functional annotation of 2,022 expressed sequence tags (ESTs) from the trichome cDNA library based on homology to A. thaliana genes suggested that 8% of the putative identified sequences were secondary metabolism-related and involved primarily in flavonoid and terpenoid biosynthesis. A significant proportion of the ESTs (38%) displayed no significant similarity to any other DNA deposited in databases, indicating a yet unknown function. Custom DNA microarrays constructed with 1,248 individual clones from the cDNA library facilitated transcriptome comparisons between trichomes and trichome-free tissues. In addition, gene expression studies in various Cistus tissues and organs for one of the genes highlighted as the most differentially expressed by the microarray experiments revealed a putative sesquiterpene synthase with a trichome-specific expression pattern. Full length cDNA isolation and heterologous expression in E. coli followed by biochemical analysis, led to the characterization of the produced protein as germacrene B synthase.

Relationship between calcium decoding elements and plant abiotic-stress resistance

Serving as an important second messenger, calcium ion has unique properties and universal ability to transmit diverse signals that trigger primary physiological actions in cells in response to hormones, pathogens, light, gravity, and stress factors. Being a second messenger of paramount significance, calcium is required at almost all stages of plant growth and development, playing a fundamental role in regulating polar growth of cells and tissues and participating in plant adaptation to various stress factors. Many researches showed that calcium signals decoding elements are involved in ABA-induced stomatal closure and plant adaptation to drought, cold, salt and other abiotic stresses. Calcium channel proteins like AtTPC1 and TaTPC1 can regulate stomatal closure. Recently some new studies show that Ca(2+) is dissolved in water in the apoplast and transported primarily from root to shoot through the transpiration stream. The oscillating amplitudes of [Ca(2+)](o) and [Ca(2+)](i) are controlled by soil Ca(2+) concentrations and transpiration rates. Because leaf water use efficiency (WUE) is determined by stomatal closure and transpiration rate, so there may be a close relationship between Ca(2+) transporters and stomatal closure as well as WUE, which needs to be studied. The selection of varieties with better drought resistance and high WUE plays an increasing role in bio-watersaving in arid and semi-arid areas on the globe. The current paper reviews the relationship between calcium signals decoding elements and plant drought resistance as well as other abiotic stresses for further study.

Signal transduction during cold stress in plants

Cold stress signal transduction is a complex process. Many physiological changes like tissue break down and senescence occur due to cold stress. Low temperature is initially perceived by plasma membrane either due to change in membrane fluidity or with the help of sensors like Ca(2+) permeable channels, histidine kinases, receptor kinases and phospholipases. Subsequently, cytoskeleton reorganization and cytosolic Ca(2+) influx takes place. Increase in cytosolic Ca(2+) is sensed by CDPKs, phosphatase and MAPKs, which transduce the signals to switch on transcriptional cascades. Photosynthetic apparatus have also been thought to be responsible for low temperature perception and signal transduction. Many cold induced pathways are activated to protect plants from deleterious effects of cold stress, but till date, most studied pathway is ICE-CBF-COR signaling pathway. However, the importance of CBF independent pathways in cold acclimation is supported by few Arabidopsis mutants' studies. Cold stress signaling has certain pathways common with other abiotic and biotic stress signaling which suggest cross-talks among these. Most of the economically important crops are sensitive to low temperature, but very few studies are available on cold susceptible crop plants. Therefore, it is necessary to understand signal transducing components from model plants and utilize that knowledge to improve survival of cold sensitive crop plants at low temperature.

Cytoplasmic calcium increases in response to changes in the gravity vector in hypocotyls and petioles of Arabidopsis seedlings

Plants respond to a large variety of environmental signals, including changes in the gravity vector (gravistimulation). In Arabidopsis (Arabidopsis thaliana) seedlings, gravistimulation is known to increase the cytoplasmic free calcium concentration ([Ca(2+)](c)). However, organs responsible for the [Ca(2+)](c) increase and the underlying cellular/molecular mechanisms remain to be solved. In this study, using Arabidopsis seedlings expressing apoaequorin, a Ca(2+)-sensitive luminescent protein in combination with an ultrasensitive photon counting camera, we clarified the organs where [Ca(2+)](c) increases in response to gravistimulation and characterized the physiological and pharmacological properties of the [Ca(2+)](c) increase. When the seedlings were gravistimulated by turning 180 degrees, they showed a transient biphasic [Ca(2+)](c) increase in their hypocotyls and petioles. The second peak of the [Ca(2+)](c) increase depended on the angle but not the speed of rotation, whereas the initial peak showed diametrically opposite characters. This suggests that the second [Ca(2+)](c) increase is specific for changes in the gravity vector. The potential mechanosensitive Ca(2+)-permeable channel (MSCC) inhibitors Gd(3+) and La(3+), the Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), and the endomembrane Ca(2+)-permeable channel inhibitor ruthenium red suppressed the second [Ca(2+)](c) increase, suggesting that it arises from Ca(2+) influx via putative MSCCs in the plasma membrane and Ca(2+) release from intracellular Ca(2+) stores. Moreover, the second [Ca(2+)](c) increase was attenuated by actin-disrupting drugs cytochalasin B and latrunculin B but not by microtubule-disrupting drugs oryzalin and nocodazole, implying that actin filaments are partially involved in the hypothetical activation of Ca(2+)-permeable channels. These results suggest that the second [Ca(2+)](c) increase via MSCCs is a gravity response in the hypocotyl and petiole of Arabidopsis seedlings.

The externally derived portion of the hyperosmotic shock-activated cytosolic calcium pulse mediates adaptation to ionic stress in suspension-cultured tobacco cells

The influx of Ca(2+) into the cytosol has long been suggested to serve as a signaling intermediate in the acquisition of tolerance to hyperosmotic and/or salinity stresses. Here we use aequorin-transformed suspension-cultured tobacco cells to directly assess the role of cytosolic calcium (Ca(2+)(cyt)) signaling in salinity tolerance acquisition. Aequorin luminescence recordings and (45)Ca influx measurements using inhibitors of Ca(2+) influx (Gd(3+) and the Ca(2+)-selective chelator EGTA), and modulators of organellar Ca(2+) release (phospholipase C inhibitors U73122 or neomycin) demonstrate that hyperosmolarity, whether imposed by NaCl or by a non-ionic molecule sorbitol, induces a rapid (returning to baseline levels of Ca(2+) within 10 min) and complex Ca(2+)(cyt) pulse in tobacco cells, deriving both from Gd(3+)-sensitive externally derived Ca(2+) influx and from U73122- and neomycin-sensitive Ca(2+) release from an organelle. To determine whether each of the two components of this brief Ca(2+) signal regulate adaptation to hyperosmotic shock, the Ca(2+) pulse was modified by the addition of Gd(3+), U73122, neomycin, or excess Ca(2+), and then cells were treated with salt or sorbitol. After 10 min the cell culture medias were diluted with additional hyperosmotic media to reduce the toxic affects of the modulators, and the growth of cells was measured after 1 week. Gd(3+) treatment reduced growth in salt relative to control cells but not in sorbitol, and exposure to excess Ca(2+) increased growth in salt but not in sorbitol. In contrast, exposure to inhibitors of IP(3) formation had no effect on growth in salt or sorbitol. Therefore, although hyperosmotic treatment stimulates both Ca(2+) influx and Ca(2+) release from an internal Ca(2+) depot, only Ca(2+) influx has a measurable impact on ionic stress tolerance acquisition in tobacco cell suspensions. In contrast, osmoadaptation in these cells appears to occur independent of Ca(2+) signaling.

Effect of calcium and light on the germination of Urochondra setulosa under different salts

Urochondra setulosa (Trin.) C.E. Hubbard is a coastal halophytic grass thriving on the coastal dunes along the Pakistani seashore. This grass could be useful in coastal sand dune stabilization using seawater irrigation. The purpose of this investigation was to test the hypothesis that Ca(2+) (0.0, 2.5, 5.0, 10.0 and 50.0 mmol/L) alleviates the adverse effects of KCl, MgSO(4), NaCl and Na(2)SO(4) at 0, 200, 400, 600, 800 and 1000 mmol/L on the germination of Urochondra setulosa. Seed germination was inhibited with increase in salt concentration with few seeds germinated at and above 400 mmol/L concentration. No seed germinated in any of the KCl treatments. Inclusion of CaCl(2) substantially alleviated the inhibitory effects of all salts. Germination was higher under photoperiod in comparison to those seeds germinated under complete darkness. Among the CaCl(2) concentrations used, 10 mmol/L was most effective in alleviating salinity effects and allowing few seeds to germinate at 1000 mmol/L KCl, MgSO(4), NaCl and Na(2)SO(4) solution.

Calcium nutrition has a significant influence on wood formation in poplar

To test the effects of calcium on wood formation, Populus tremula x Populus tremuloides clones were supplied with Hoagland solution modified in its calcium contents. Energy-dispersive X-ray analysis (EDXA) revealed an increase in calcium in the phloem, the cambium and the xylem elongation zone with increasing Ca(2+) supply in the nutrient solution. Using light and electron microscopy, a strong impact was shown on the cambial and the elongation zones under calcium starvation. Using Fourier transform infrared (FTIR) spectroscopy on wood and bark cells formed under calcium starvation, we detected a reduction of some absorptions, such as carbonyl and methoxy groups from S-lignin. Also, a significant reduction in fiber length was detected with decreasing calcium supply in the nutrient solution. High-performance liquid chromatography (HPLC) analysis revealed a large increase in sugar concentrations in the leaves, but reduced concentrations in the bark under Ca(2+) deficiency. In conclusion, our results show a significant influence of calcium on the structure, chemistry and physiology of wood formation. Thus, efficient Ca(2+) supply has to be considered a decisive factor in wood formation.

Guard cell ABA and CO2 signaling network updates and Ca2+ sensor priming hypothesis

Stomatal pores in the epidermis of plants enable gas exchange between plants and the atmosphere, a process vital to plant life. Pairs of specialized guard cells surround and control stomatal apertures. Stomatal closing is induced by abscisic acid (ABA) and elevated CO(2) concentrations. Recent advances have been made in understanding ABA signaling and in characterizing CO(2) transduction mechanisms and CO(2) signaling mutants. In addition, models of Ca(2+)-dependent and Ca(2+)-independent signaling in guard cells have been developed and a new hypothesis has been formed in which physiological stimuli are proposed to prime Ca(2+) sensors, thus enabling specificity in Ca(2+)-dependent signal transduction.

Early signaling events induced by elicitors of plant defenses

Plant pathogen attacks are perceived through pathogen-issued compounds or plant-derived molecules that elicit defense reactions. Despite the large variety of elicitors, general schemes for cellular elicitor signaling leading to plant resistance can be drawn. In this article, we review early signaling events that happen after elicitor perception, including reversible protein phosphorylations, changes in the activities of plasma membrane proteins, variations in free calcium concentrations in cytosol and nucleus, and production of nitric oxide and active oxygen species. These events occur within the first minutes to a few hours after elicitor perception. One specific elicitor transduction pathway can use a combination or a partial combination of such events which can differ in kinetics and intensity depending on the stimulus. The links between the signaling events allow amplification of the signal transduction and ensure specificity to get appropriate plant defense reactions. This review first describes the early events induced by cryptogein, an elicitor of tobacco defense reactions, in order to give a general scheme for signal transduction that will be use as a thread to review signaling events monitored in different elicitor or plant models.

Detoxification of dissolved SO2 (bisulfite) by terricolous mosses

BACKGROUND AND AIMS

The widespread calcifuge moss Pleurozium schreberi is moderately tolerant of SO2, whereas Rhytidiadelphus triquetrus is limited to calcareous soils in regions of the UK that were strongly affected by SO2 pollution in the 20th century. The proposition that tolerance of SO2 by these terricolous mosses depends on metabolic detoxification of dissolved bisulfite was investigated.

METHODS

The capacities of the two mosses to accelerate loss of bisulfite from aqueous solutions of NaHSO3 were studied using DTNB [5, 5-dithio-(2-nitrobenzoic acid)] to assay bisulfite, and HPLC to assay sulfate in the incubation solutions. Incubations were performed for different durations, in the presence and absence of light, at a range of solution pH values, in the presence of metabolic inhibitors and with altered moss apoplastic Ca2+ and Fe3+ levels.

KEY RESULTS

Bisulfite disappearance was markedly stimulated in the light and twice as great for R. triquetrus as for P. schreberi. DCMU, an inhibitor of photosynthetic electron chain transport, significantly reduced bisulfite loss.

CONCLUSIONS

Bisulfite (SO2) tolerance in these terricolous mosses involves extracellular oxidation using metabolic (photo-oxidative) energy, passive oxidation by adsorbed Fe3+ (only available to the calcifuge) and probably also internal metabolic detoxification.

An early auxin-responsive Aux/IAA gene from wheat (Triticum aestivum) is induced by epibrassinolide and differentially regulated by light and calcium

The plant hormone auxin plays a central role in regulating many aspects of plant growth and development. This largely occurs as a consequence of changes in gene expression. The Aux/IAA genes are best characterized among the early auxin-responsive genes, which encode short-lived transcriptional repressors. In most plants examined, including Arabidopsis, soybean, and rice, the Aux/IAA genes constitute a large gene family. By screening the available databases, at least 15 expressed sequence tags (ESTs) have been identified from wheat (Triticum aestivum), which exhibit high sequence identity with Aux/IAA homologues in other species. One of these Aux/IAA genes, TaIAA1, harbouring all the four conserved domains characteristic of the Aux/IAA proteins, has been characterized in detail. The expression of TaIAA1 is light-sensitive, tissue-specific, and is induced within 15-30 min of exogenous auxin application. Also, the TaIAA1 transcript levels increase in the presence of a divalent cation, Ca(2+), and this effect is reversed by the calcium-chelating agent, EGTA. The TaIAA1 gene qualifies as the primary response gene because an increase in its transcript levels by auxin is unaffected by cycloheximide. In addition to auxin, the TaIAA1 gene is also induced by brassinosteroid, providing evidence that interplay between hormones is crucial for the regulation of plant growth and development.

Quantitative fluorescence microscopy: from art to science

A substantial number of elegant experimental approaches have been developed to image the distribution and dynamics of DNA, mRNA, proteins, organelles, metabolites, and ions in living plant cells. Although the human brain can rapidly assimilate visual information, particularly when presented as animations and movies, it is much more challenging to condense the phenomenal amount of data present in three-, four-, or even five-dimensional images into statistically useful measurements. This review explores a range of in vivo fluorescence imaging applications in plants, with particular emphasis on where quantitative techniques are beginning to emerge.

Calcium in plant defence-signalling pathways

In plant cells, the calcium ion is a ubiquitous intracellular second messenger involved in numerous signalling pathways. Variations in the cytosolic concentration of Ca2+ ([Ca2+]cyt) couple a large array of signals and responses. Here we concentrate on calcium signalling in plant defence responses, particularly on the generation of the calcium signal and downstream calcium-dependent events participating in the establishment of defence responses with special reference to calcium-binding proteins.