Morphological, Physiological and Biochemical Determinants of Halophyte Adaptive Strategies

Dear Colleagues,

The accumulation of salts in soil is one of the main environmental factors limiting the growth and productivity of plants. The expansion of the area of saline soils on the planet is associated with global climate change, spread of irrigation, and population growth, and it poses threats to human health, ecosystems, and national economies. Halophyte plants are capable of surviving on highly salinized soils throughout their entire life cycle. In the course of evolution, these plants developed the following special salinity tolerance mechanisms: (1) selective ions accumulation/exclusion; (2) control of ion uptake by roots and their transport into leaves; (3) prevention of Na+ and Cl– accumulation in the cytoplasm; (4) synthesis and accumulation of nontoxic (compatible) osmolytes in the cytosol; (5) change in photosynthetic pathway; (6) induction of antioxidative system; (7) stimulation of phytohormone production, such as abscisic and jasmonic acids. All these mechanisms are realized at the levels of the whole plant and plant tissue as well as at the cellular molecular level. The salinity tolerance of halophytes has, as a rule, a multigenic character, and, only in rare cases, one of the mechanisms is of predominant importance to be able to survive at a high concentration of NaCl. However, no whole spectrum of the adaptive mechanisms is equally realized in different halophytes. Among halophytes species with different metabolic types of photosynthesis are widespread (С3, С4, САМ- types). It is possible that plants with different types of photosynthetic metabolisms can differ significantly in mechanisms and the direction of changes in the structure and function of leaves, cells, chloroplast, as well as photosynthetic membranes with salinity. The fundamental basis for salinity adaptation in halophytes is the cell’s ability to control salt transport through membranes. The ion uptake control mechanisms are highly developed in the membranes of salt-accumulating halophytes (euhalophytes). Not only the plasma membrane is involved in the transport of Na+ ions in euhalophyte cells but also the membranes of individual subcellular compartments, including vacuoles, chloroplasts, and mitochondria. Lipids are the structural basis of cell membranes. Differences in the lipid composition of cell membranes, organelles, and individual microdomains (lipid rafts) are associated with the specifics of salt metabolism in halophytes. It can be assumed that the variability of the types and ratios of lipids take part in the adaptation of halophytes to growth conditions. It is important to note that halophytes of natural flora represent an important source of olive, ornamental, medicinal, and fodder plants and also of energy carriers and genes conferring salt tolerance to salt-sensitive plants. Halophytes are ideally suitable for the reclamation and remediation of saline land. Wider use of halophytes can help solve the problem of providing enough food for a growing world population, lowering the load on useable salt-sensitive plants and nonrenewable resources and reducing freshwater use in irrigating crops. This Special Issue of Plants will contribute to an in-depth understanding of the adaptation of halophytes to soil salinity and the formation of their ecological strategies.

Dr. Olga A. Rozentsvet
Guest Editor

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• halophytes
• adaptive strategies
• cell morphology
• membranes
• lipids