Halophytes, plants that survive to reproduce in environments where the salt concentration is around 200 mM NaCl or more, constitute about 1% of the worlds flora. Some halophytes show optimal growth in saline conditions; others grow optimally in the absence of salt. However, the tolerance of all halophytes to salinity relies on controlled uptake and compartmentalization of Na+, K+ and Cl- and the synthesis of organic compatible solutes, even where salt glands are operative. Although there is evidence that different species may utilize different transporters in their accumulation of Na+, in general little is known of the proteins and regulatory networks involved. Consequently, it is not yet possible to assign molecular mechanisms to apparent differences in rates of Na+ and Cl- uptake, in root-to-shoot transport (xylem loading and retrieval), or in net selectivity for K+ over Na+. At the cellular level, H+-ATPases in the plasma membrane and tonoplast, as well as the tonoplast H+-PPiase, provide the transmembrane proton motive force used by various secondary transporters. The widespread occurrence, taxonomically, of halophytes and the general paucity of information on the molecular regulation of tolerance mechanisms persuade us that research should be concentrated on a number of model species that are representative of the various mechanisms that might be involved in tolerance.

Salinity tolerance in halophytes

Plants are generally well adapted to a wide range of environmental conditions. Even though they have notably prospered in our planet, stressful conditions such as salinity, drought and cold or heat, which are increasingly being observed worldwide in the context of the ongoing climate changes, limit their growth and productivity. Behind the remarkable ability of plants to cope with these stresses and still thrive, sophisticated and efficient mechanisms to re-establish and maintain ion and cellular homeostasis are involved. Among the plant arsenal to maintain homeostasis are efficient stress sensing and signaling mechanisms, plant cell detoxification systems, compatible solute and osmoprotectant accumulation and a vital rearrangement of solute transport and compartmentation. The key role of solute transport systems and signaling proteins in cellular homeostasis is addressed in the present work. The full understanding of the plant cell complex defense mechanisms under stress may allow for the engineering of more tolerant plants or the optimization of cultivation practices to improve yield and productivity, which is crucial at the present time as food resources are progressively scarce.

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Membrane Transport, Sensing and Signaling in Plant Adaptation to Environmental Stress

Salt tolerance is an important economic trait for crops growing in both irrigated fields and marginal lands. The plant kingdom contains plant species that possess highly distinctive capacities for salt tolerance as a result of evolutionary adaptation to their environments. Yet, the cellular mechanisms contributing to salt tolerance seem to be conserved to some extent in plants although some highly salt-tolerant plants have unique structures that can actively excrete salts. In this review, we begin by summarizing the research in Arabidopsis with a focus on the findings of three membrane transporters that are important for salt tolerance: SOS1, AtHKT1, and AtNHX1. We then review the recent studies in salt tolerance in crops and halophytes. Molecular and physiological mechanisms of salt tolerance in plants revealed by the studies in the model plant, crops, and halophytes are emphasized. Utilization of the Na(+) transporters to improve salt tolerance in plants is also summarized. Perspectives are provided at the end of this review.

Physiological and molecular mechanisms of plant salt tolerance

The increasing seriousness of salinization aggravates the food, population and environmental issues. Ameliorating the salt-resistance of plants especially the crops is the most effective measure to solve the worldwide problem. The salinity can cause damage to plants mainly from two aspects: hyperosmotic and hyperionic stresses leading to the restrain of growth and photosynthesis. To the adverse effects, the plants derive corresponding strategies including: ion regulation and compartmentalization, biosynthesis of compatible solutes, induction of antioxidant enzymes and plant hormones. With the development of molecular biology, our understanding of the molecular and physiology knowledge is becoming clearness. The complex signal transduction underlying the salt resistance is being illuminated brighter and clearer. The SOS pathway is the central of the cell signaling in salt stress. The accumulation of the compatible solutes and the activation of the antioxidant system are the effective measures for plants to enhance the salt resistance. How to make full use of our understanding to improve the output of crops is a huge challenge for us, yet the application of the genetic engineering makes this possible. In this review, we will discuss the influence of the salt stress and the response of the plants in detail expecting to provide a particular account for the plant resistance in molecular, physiological and transgenic fields.

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Global plant-responding mechanisms to salt stress: physiological and molecular levels and implications in biotechnology

Over the last decades several efforts have been carried out to find out the mechanisms of salt homeostasis in plants and, more recently, to identify genes implicated in salt tolerance, with some plants being successfully genetically engineered to improve resistance to salt. It is well established that the efficient exclusion of Na+ excess from the cytoplasm and vacuolar Na+ accumulation are the most important steps towards the maintenance of ion homeostasis inside the cell. Therefore, the vacuole of plant cells plays a pivotal role in the storage of salt. After the identification of the vacuolar Na+/H+ antiporter Nhx1 in Saccharomyces cerevisiae, the first plant Na+/H+ antiporter, AtNHX1, was isolated from Arabidopsis and its overexpression resulted in plants exhibiting increased salt tolerance. Also, the identification of the plasma membrane Na+/H+ exchanger SOS1 and how it is regulated by a protein kinase SOS2 and a calcium binding protein SOS3 were great achievements towards the understanding of plant ...

https://www.tandfonline.com/doi/pdf/10.4161/psb.4.8.9236

Xiuling Ma

Papers

Coordinate up-regulation of V-H+-ATPase and vacuolar Na+/H+ antiporter as a response to NaCl treatment in a C3 halophyte Suaeda salsa