И. В. Деркач, Н. Д. Романюк
Львовский национальный университет имени Ивана Франко
ВЛИЯНИЕ ЗАСОЛЕНИЯ ПОЧВЫ НА РАСТИТЕЛЬНЫЕ ОРГАНИЗМЫ
В обзоре проанализированы и обобщены данные относительно механизмов адаптации растений к условиям NaCl засоления почвы с целью повышения их устойчивости к данному фактору. Проанализированы изменения в растительном организме, вызванные засолением почвы и приведены основные известные механизмы адаптации растений, в частности компартментализация, ионное исключение, устойчивость к осмотическому стрессу и роль антиоксидантных систем.
Ключевые слова: засоление, адаптационные механизмы, устойчивость, NaCl
I. V. Derkach, N. D. Romaniuk
Ivan Franko National University of Lviv, Ukraine
THE IMPACT OF SOIL SALINITY ON PLANTS
This article intends to examine the mechanisms of plant adaptation to soil salinity and describe avenues to increase salt tolerance of plants. The ways in which salt affects plants, through osmotic stress in particular, salt ions toxicity and levels of oxidative stress are analyzed. In Ukraine, according to the State Land Reports, saline soils occupy 1.71 mln hectares (arable land – 848.2,000 ha), including low salinized 1336.6,000 ha, medium salinized – 224.3,000 ha, severely salinized – 116.3,000 ha. The predominant salt is sodium chloride. Most of the negative effects of salinity are caused by an increase in the content of Na+ and Cl- ions, the latter being the most harmful. Direct and indirect methods of assessment of the plant salt tolerance are described, which include analysis of plant growth and productivity under salt environment in situ, as well as physiological, biochemical and biophysical methods that demonstrate changes of individual metabolic processes and their correlation with the direct methods. There is a direct dependence between the content of the NaCl in the environment and the growth and development of crops at the stage of vegetation. Salinity may also adversely affect the reproductive phase of plant growth because of the growing number of sterile flowers, reduced pollen viability, decreasing number of spikelets and seeds. Influence of different concentrations of salinity on the photosynthetic activity is described; low salt concentrations can enhance the photosynthetic activity, whereas high concentrations may impede it. The important role for the ions compartmentalization is played by membrane transporters regulating inter-cellular and intracellular distribution of ions. The function of vacuoles maintaining the optimum ratio of Na+/K+ in the cytosol is described. Ion exclusion, including Na+ exclusion, is another mechanism of plant adaptation. Na+ ions can reach toxic concentrations faster than ions of Cl-, because roots of tolerant plants are able to avoid absorption of these ions, and shoots are likely to avoid their accumulation too. The ability of plants to exclude the Na+ from the roots and thus to reduce the accumulation of Na+ is enhanced by the proteins encoded by Nax1 and Nax2 genes. The Na+ efflux from the root cells involves antiporters SOS1 and proton pump of plasma membrane. This antiporter is part of the mechanism, based on the level of salt stress, which entails an increase in cytosolic [Ca2+] reversible phosphorylation SOS1, together with SOS2 and SOS3, SOS2 coding SNF-kinases, SOS3 – Ca2+-binding protein. The role of micro-RNAs, particularly miR319 as a regulator of genes encoding transcription factors in stress tolerance is determined. Plants Resistant to osmotic stress plants are able to maintain turgor pressure under the influence of salinity. The important role in the osmotic tolerance is played by compatible osmolytes, low molecular organic compounds. Antioxidant systems are necessary to prevent damage from ROS, which are formed at high salt concentrations. Physiological and biochemical plant responses to salinity include the level of salt stress and salt signal transduction; responses implying changes in photosynthetic activity; production of phytohormones, antioxidant activities; acquisition, exclusion, transport and cellular compartmentalization of Na+ ions; modifying structural components of cell walls and membranes, etc. They are controlled by the interaction of hundreds of genes that also cross-react with other components of the stress signals transduction. Understanding these interactions is one of the prerequisites for creating salt-tolerant varieties of most important crops.
Keywords: salinity, adaptation mechanisms, tolerance, NaCl