Research Of Response To Salt Stress And Mechanism Of Salt-tolerant On Three Nitraria Species

Saline-alkali land is an important land resource. Biological control is an effective way to develop and utilize saline-alkali soil. To understand salt-tolerance mechanism of plants can breed better salt-tolerant plant varieties and look for ways and methods to improve the plants' salt tolerance, so it is propitious for development and comprehensive utilization of saline-alkali land. In this paper, three kinds of typical halophytes, Nitraria tangutorum Bobr, Nitraria sibirica Pall, Nitraria roborowskii Kom, as test materials, were planted in pots containing soils and subjected to salinity treatments. In order to explore its salt-tolerance mechanism, we studied the morphological characteristics, structural features, growth and the physiological responses, etc, then compared the differences in salt resistance of the three species by subordinate function. The main results were summarized as follows:1. All the three species of Nitraria had the typical salt-tolerant structures morphology and leaf anatomical structure, such as belonging to shrubby ecotype with many branches, small and a large number of succulent leaves, acanthoid stem apices, classical equilateral leaves with flourishing palisade tissue and parenchyma cells, cryptopore with deep substomatic chamber and so on. At the high salt concentrations, palisade cells of Nitraria tangutorum Bobr become looser compared with those of non-treated plants, but those of Nitraria sibirica Pall and Nitraria roborowskii Kom become compacter.2. Under salt stress, the plant height and biomass were increased at low salt concentration, while decreased at high salt concentration. When the concentration was 100 mmol/L, the height of plant and biomass reached the maximum. Attributed to the differences in varieties and salt tolerance the degree of damage was different from salt stress on a basis of aboveground and underground measurements, however, there was no apparent regular pattern in root/shoot ratios changings.3. Under salt stress, the chlorophyll content of 3 kinds of Nitraria was increased,it increased most at 100 mmol/L salt concentration. With the salt concentration increased, the activity of POD and SOD, the contents of MDA, proline, soluble sugar and soluble protein were all increased. The contents of Na+ and Cl- were also increased in the roots, stems and leaves. The content of Na+ and Cl- in leaves were highest and the content of Na+ was higher than Cl-. The changes of K+ content varied by different species, with the increase of salt concentration. The content of K+ in Nitraria tangutorum Bobr was initially increased and then decreased, while in Nitraria sibirica Pall was decreased and in Nitraria roborowskii Kom was increased, at the whole stage of experimental treatments. Except that K+/Na+ in the leaves of Nitraria roborowskii Kom was increased, K+/Na+ was reduced in various organs of three Nitraria. The absorption of Ca2+ was blocked, so that the contents of Ca2+ in roots, stems and leaves were all reduced. The contents of Na+ and Cl- in mesophyll cells were increased by X-ray microanalysis. Using the non-invasively ion-selective micro-electrode technique, the roots of Nitraria sibirica Pall had an enhanced Na+ and Cl- influx, under low salt concentration the roots retained a higher capacity for Na+ and Cl- absorption than that at high salt concentrations.4. According to the physiological responses to salt stress of the three Nitraria, as well as the comprehensive evaluation by the membership functions. The salt-tolerance sequence from high to low was:Nitraria sibirica Pall> Nitraria tangutorum Bobr> Nitraria roborowskii Kom.To sum up, the salt-tolerance mechanisms of Nitraria is that:they have the structure characteristics adapting to the saline environment. Under salt stress the capabilities for protecting and restoring the cytoplasmic membrane system were improved. Using the measures of increasing the contents of organic osmolytes and Na+ and Cl- which were absorbed by roots as inorganic osmotic substances, the plants reduced its intracellular water potential. On the other hand, they used the intracellular ion compartmentalization in leaves to reduce the damage to important organelles.