The physiological and molecular mechanisms of tolerance to osmotic and ionic components of salinity stress are reviewed at the cellular, organ, and whole-plant level. Plant growth responds to salinity in two phases: a rapid, osmotic phase that inhibits growth of young leaves, and a slower, ionic phase that accelerates senescence of mature leaves. Plant adaptations to salinity are of three distinct types: osmotic stress tolerance, Na + or Cl − exclusion, and the tolerance of tissue to accumulated Na + or Cl − . Our understanding of the role of the HKT gene family in Na + exclusion from leaves is increasing, as is the understanding of the molecular bases for many other transport processes at the cellular level. However, we have a limited molecular understanding of the overall control of Na + accumulation and of osmotic stress tolerance at the whole-plant level. Molecular genetics and functional genomics provide a new opportunity to synthesize molecular and physiological knowledge to improve the salinity tolerance of plants relevant to food production and environmental sustainability.

https://rodas5.us.es/file/c2a700e9-8b4a-1970-d343-4a269c302970/1/estres_salino_bibliografia_scorm.zip/files/estres_salino_bibliografia.pdf

Mechanisms of salinity tolerance

Salt and drought stress signal transduction consists of ionic and osmotic homeostasis signaling pathways, detoxification (i.e., damage control and repair) response pathways, and pathways for growth regulation. The ionic aspect of salt stress is signaled via the SOS pathway where a calcium-responsive SOS3-SOS2 protein kinase complex controls the expression and activity of ion transporters such as SOS1. Osmotic stress activates several protein kinases including mitogen-activated kinases, which may mediate osmotic homeostasis and/or detoxification responses. A number of phospholipid systems are activated by osmotic stress, generating a diverse array of messenger molecules, some of which may function upstream of the osmotic stress-activated protein kinases. Abscisic acid biosynthesis is regulated by osmotic stress at multiple steps. Both ABA-dependent and -independent osmotic stress signaling first modify constitutively expressed transcription factors, leading to the expression of early response transcriptional activators, which then activate downstream stress tolerance effector genes.

/pdf/salt-and-drought-stress-signal-transduction-in-plants-4bj87ki2ww.pdf

Salt and drought stress signal transduction in plants

▪ Abstract Plant responses to salinity stress are reviewed with emphasis on molecular mechanisms of signal transduction and on the physiological consequences of altered gene expression that affect biochemical reactions downstream of stress sensing. We make extensive use of comparisons with model organisms, halophytic plants, and yeast, which provide a paradigm for many responses to salinity exhibited by stress-sensitive plants. Among biochemical responses, we emphasize osmolyte biosynthesis and function, water flux control, and membrane transport of ions for maintenance and re-establishment of homeostasis. The advances in understanding the effectiveness of stress responses, and distinctions between pathology and adaptive advantage, are increasingly based on transgenic plant and mutant analyses, in particular the analysis of Arabidopsis mutants defective in elements of stress signal transduction pathways. We summarize evidence for plant stress signaling systems, some of which have components analogous to t...

Plant cellular and molecular responses to high salinity.

The reference human genome sequence set the stage for studies of genetic variation and its association with human disease, but epigenomic studies lack a similar reference. To address this need, the NIH Roadmap Epigenomics Consortium generated the largest collection so far of human epigenomes for primary cells and tissues. Here we describe the integrative analysis of 111 reference human epigenomes generated as part of the programme, profiled for histone modification patterns, DNA accessibility, DNA methylation and RNA expression. We establish global maps of regulatory elements, define regulatory modules of coordinated activity, and their likely activators and repressors. We show that disease- and trait-associated genetic variants are enriched in tissue-specific epigenomic marks, revealing biologically relevant cell types for diverse human traits, and providing a resource for interpreting the molecular basis of human disease. Our results demonstrate the central role of epigenomic information for understanding gene regulation, cellular differentiation and human disease.

Integrative analysis of 111 reference human epigenomes

Summary It is generally accepted that the functional compartmentalization of eukaryotic cells is reflected by the differential occurrence of proteins in their compartments. The location and physiological function of a protein are closely related; local information of a protein is thus crucial to understanding its role in biological processes. The visualization of proteins residing on intracellular structures by fluorescence microscopy has become a routine approach in cell biology and is increasingly used to assess their colocalization with well-characterized markers. However, imageanalysis methods for colocalization studies are a field of contention and enigma. We have therefore undertaken to review the most currently used colocalization analysis methods, introducing the basic optical concepts important for image acquisition and subsequent analysis. We provide a summary of practical tips for image acquisition and treatment that should precede proper colocalization analysis. Furthermore, we discuss the application and feasibility of colocalization tools for various biological colocalization situations and discuss their respective strengths and weaknesses. We have created a novel toolbox for subcellular colocalization analysis under Image J, named JACoP, that integrates current global statistic methods and a novel object-based approach.

A guided tour into subcellular colocalization analysis in light microscopy

Methods for measuring plant cytoplasmic calcium using microelectrodes or microinjected fluorescent dyes are associated with extensive technical problems, so measurements have been limited to single or small groups of cells in tissue strips or protoplasts. Aequorin is a calcium-sensitive luminescent protein from the coelenterate Aequorea victoria (A. forskalea) which is formed from apoaequorin, a polypeptide of relative molecular mass approximately 22,000, and coelenterazine, a hydrophobic luminophore. Microinjected aequorin has been widely used for intracellular calcium measurement in animal cells, but its use in plants has been limited to exceptionally large cells. We show here that aequorin can be reconstituted in transformed plants and that it reports calcium changes induced by touch, cold-shock and fungal elicitors. Reconstituted aequorin is cytoplasmic and nonperturbing; measurements can be made on whole plants and a calcium indicator can be constituted in every viable cell. Now that apoaequorin can be targeted to specific organelles, cells and tissues, with the range of coelenterazines with differing calcium sensitivities and properties available, this new method could be valuable for determining the role of calcium in intracellular signalling processes in plants.

Transgenic plant aequorin reports the effects of touch and cold-shock and elicitors on cytoplasmic calcium.

Changes in cytosolic free calcium concentration ([Ca2+]cyt) in response to mannitol (drought) and salt treatments were detected in vivo in intact whole Arabidopsis seedlings. Transient elevations of [Ca2+]cyt to around 1.5 microM were observed, and these were substantially inhibited by pretreatment with the calcium-channel blocker lanthanum and to a lesser extent, the calcium-chelator EGTA. The expression of three genes, p5cs, which encodes delta(1)-pyrroline-5-carboxylate synthetase (P5CS), the first enzyme of the proline biosynthesis pathway, rab18 and Iti78 which both encode proteins of unknown function, was induced by mannitol and salt treatments. The induction of all three genes by mannitol was inhibited by pretreatment with lanthanum. Salt-induced p5cs, but not rab18 and Iti78, expression was also inhibited by lanthanum. Induction of p5cs by mannitol was also inhibited by the calcium channel-blockers gadolinium and verapamil and the calcium chelator EGTA, further suggesting the involvement of calcium signalling in this response. Mannitol induced greater levels of p5cs gene expression than an isoosmolar concentration of salt, at both relatively high and low concentrations. However, calcium transients were of a similar magnitude and duration in response to both mannitol and isoosmolar concentrations of salt, suggesting that a factor other than calcium is involved in the discrimination between drought and salinity signals in Arabidopsis. In order to gauge the involvement of the vacuole as an intracellular calcium store in the response of Arabidopsis to mannitol, [Ca2+]cyt was measured at the microdomain adjacent to the vacuolar membrane. The results obtained were consistent with a significant calcium release from the vacuole contributing to the overall mannitol-induced [Ca2+]cyt response. Data obtained by using inhibitors of inositol signalling suggested that this release was occurring through IP3-dependent calcium channels.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-313X.1997.12051067.x

Calcium signalling in Arabidopsis thaliana responding to drought and salinity

Cold shock elicits an immediate rise in cytosolic free calcium concentration ([Ca2+]cyt) in both chilling-resistant Arabidopsis and chilling-sensitive tobacco (Nicotiana plumbaginifolia). In Arabidopsis, lanthanum or EGTA caused a partial inhibition of both cold shock [Ca2+]cyt elevation and cold-dependent kin1 gene expression. This suggested that calcium influx plays a major role in the cold shock [Ca2+]cyt response and that an intracellular calcium source also might be involved. To investigate whether the vacuole (the major intracellular calcium store in plants) is involved, we targeted the calcium-dependent photoprotein aequorin to the cytosolic face of the vacuolar membrane. Cold shock calcium kinetics in this microdomain were consistent with a cold-induced vacuolar release of calcium. Treatment with neomycin or lithium, which interferes with phosphoinositide cycling, resulted in cold shock [Ca2+]cyt kinetics consistent with the involvement of inositol trisphosphate and inositide phosphate signaling in this response. We also investigated the effects of repeated and prolonged low temperature on cold shock [Ca2+]cyt. Differences were observed between the responses of Arabidopsis and N. plum-baginifolia to repeated cold stimulation. Acclimation of Arabidopsis by pretreatment with cold or hydrogen peroxide caused a modified calcium signature to subsequent cold shock. This suggests that acclimation involves modification of plant calcium signaling to provide a "cold memory."

Cold calcium signaling in Arabidopsis involves two cellular pools and a change in calcium signature after acclimation.

STOMATAL pores at the leaf surface regulate water loss during transpiration and CO2 uptake for photosynthesis through changes in the turgor of the surrounding guard cells. Such regulation occurs in response to a wide range of environmental stimuli (such as light, CO2 level and abscisic acid). These are thought to be transduced through changes in cytosolic calcium levels1–3, and several treatments causing stomatal closure are accompanied by increases in cytosolic Ca2+ (ref. 4), probably from mobilization of intracellular Ca2+ stores. We report here the use of the fluorescent Ca2+ indicator Fluo-3 (refs 5,6) to follow changes in stomatal aperture and cytoplasmic Ca2+ concentration as Ca2+ or inositol 1,4,5-trisphosphate (InsP3) are released into the cell from their caged (photoactivatable) forms6–9. Increasing Ca2+ concentration to greater than ˜600 nM induced stomatal closure. Similarly, release of InsP3 initiated influx of Ca2+ into the cytosol which was followed by stomatal closure. These results suggest that Ca2+ and InsP3 may act as second messengers leading to guard cell closure.

Elevation of cytoplasmic calcium by caged calcium or caged inositol triphosphate initiates stomatal closure.

Tobacco (Nicotiana plumbaginifolia) seedlings genetically transformed to express apoaequorin were incubated in h-coelenterazine to reconstitute the calcium-sensitive luminescent protein aequorin. Treatment of these seedlings with hydrogen peroxide resulted in a transient burst of calcium-dependent luminescence lasting several minutes. Even though the hydrogen peroxide stimulus was persistent, the change in cytosolic free calcium concentration ([Ca2+]cyt) was transient, suggesting the presence of a refractory period. When seedlings were pretreated with hydrogen peroxide, there was no increase in [Ca2+]cyt upon a second application, which confirmed the refractory character of the response. Only when the two treatments were separated by 4 to 8 hr was full responsiveness recovered. However, treatment with hydrogen peroxide did not inhibit mobilization of [Ca2+]cyt induced by either cold shock or touching, suggesting that these three signals mobilize different pools of intracellular calcium. To examine whether [Ca2+]cyt is regulated by the redox state of the cytoplasm, we pretreated seedlings with buthionine sulfoximine (to modify cellular glutathione levels) and inhibitors of ascorbate peroxidase. These inhibitors modify the hydrogen peroxide-induced transients in [Ca2+]cyt, which is consistent with their effects on the cellular prooxidant/antioxidant ratio. Treatment with hydrogen peroxide that elicited [Ca2+]cyt increases also brought about a reduction in superoxide dismutase enzyme activity. This reduction could be reversed by treatment with the calcium channel blocker lanthanum. This indicates that there is a role for calcium in plant responses to oxidative stress.

Anthony J. Trewavas

Papers

Transgenic plant aequorin reports the effects of touch and cold-shock and elicitors on cytoplasmic calcium.

Calcium signalling in Arabidopsis thaliana responding to drought and salinity

Cold calcium signaling in Arabidopsis involves two cellular pools and a change in calcium signature after acclimation.

Elevation of cytoplasmic calcium by caged calcium or caged inositol triphosphate initiates stomatal closure.

Oxidative Signals in Tobacco Increase Cytosolic Calcium.