Study On Physiological Responses Mechanisms Of Rubus Crataegifolius Bge. Seedlings Under Saline Stress

Soil salinization is considered as a global problem, which influences agricultural production and ecological environment. Therefore, how to improve and use saline soil has become an important problem to be solved. Studies confirmed that the introduction of economic salt-tolerant plants to saline soil is one of the most effective biological measures to solve the problem of soil salinization and alkalinization. Rubus Crataegifolius Bge., a wild fruit tree widely distributed in Northeast China, having many excellent properties like strong adaptability, cold-resistant, drought-enduring, strong dust-retention ability and so on, is a favorable economic tree for fruit tree breeding, urban landscaping and ecological afforestation. In order to fully exploit the resource advantages of this tree and make clear its physiological adaptation features under saline-alkali stress, this paper, taking annual tissue culture seedlings of wild Rubus Crataegifolius as testing material, with potting stimulating saline stress environment, researched the effect of stresses of four single salts (NaCl, Na2SO4, NaHCO3, Na2CO3) and mixed salts of different proportion on the growth and physiological indices of Rubus Crataegifolius seedlings respectively; discussed the physiological adaptation features of Rubus Crataegifolius seedling’s antioxidant system and osmotic adjustment substances toward stresses of single salt and mixed salt, and expounded Rubus Crataegifolius Bge’s saline-alkali adaptation mechanism from the perspective of the absorption, transportation and distribution of ion; and made clear the leading factors of salt-alkaline mixed stress affecting Rubus Crataegifolius seedlings through statistical methods. The main research results are as follows:1. Grew in the treatment of alkaline salts (NaHCO3, Na2CO3) and mixed salt of a lower proportion of alkaline salts (NaCl:Na2SO4:NaHCO3:Na2CO3=1:2:1:0, pH=8.24), Rubus Crataegifolius seedling showed "promoted at low concentration and restrained at high concentration", while under the treatment of neutral salts (NaCl, Na2SO4) and mixed salts of other proportion, its growth was subject to different degrees of inhibition; Rubus Crataegifolius seedling’s tolerance threshold toward the four salts, namely, NaCl, Na2SO4, NaHCO3, Na2CO3 are 85.18 mmol·L-1 (0.50%, w/v),40.77 mmol·L-1 (0.58%, w/v),171.00 mmol·L-1 (1.44%, w/v),114.20 mmol·L-1 (1.21%, w/v) respectively.2. Under the stress of single salts (NaCl, Na2SO4, NaHCO3, Na2CO3) and mixed salts of different proportion, the relative conductivity of Rubus Crataegifolius seedling leaves showed an increasing trend with the increase of stress concentration, while the cell membrane permeability of Rubus Crataegifolius leaves were suffered serious damages under the treatment of high salinity (≥120 mmol.L-1) or high pH value (NaCl:Na2SO4:NaHCO3:Na2CO3=9:1:1:9,pH=10.58).3. Under the stress of NaHCO3 and mixed salts of different proportion, MDA content in Rubus Crataegifolius leaves increased or markedly increased compared to control group; under the stress treatment of four single salts, the activity of SOD in Rubus Crataegifolius leaves "raised first and then declined", but the activity of POD "declined first and then raised"; while under the stress treatment of mixed salts of different proportion, the activity of POD in Rubus Crataegifolius leaves markedly increased in all cases, but the activity of SOD declined overall. Researches showed that Rubus Crataegifolius seedling leaves, under the stress treatment of single salts, alleviated oxidative damage mainly through the supplementary effect of SOD and POD, while under saline mixed stress, it reduced the saline damage mainly by increasing POD activity, thus to maintain the normal physiological metabolism of the plant.4. Under the stress of single salt, with the increase of stress concentration, the content of soluble sugar, free proline, soluble protein in Rubus Crataegifolius seedling leaves all increased in different extents; under the stress treatment of monovalent single salts (NaCl, NaHCO3), Rubus Crataegifolius seedling exerted its osmotic adjustment function mainly through the alternately accumulation of soluble sugar, free proline and soluble protein; While under the stress treatment of divalent single salts (Na2SO4, Na2CO3), the accumulation trends of soluble sugar, free proline and soluble proteins were varied, among which, under Na2CO3 stress, the three accumulated synchronously and played their roles in osmotic regulatory function jointly, while under the treatment of Na2SO4 stress, Rubus Crataegifolius seedling reduced saline damage mainly through the synergistic effect of soluble sugar and soluble protein. Under saline mixed stress, with the increase of stress concentration, the content of both soluble sugar and soluble protein in Rubus Crataegifolius leaves were intermittently accumulated, while the content of free proline increased slowly first and then dramatically increased, playing a leading role in the whole process of osmotic adjustment.5. Under treatment of single salts and mixed salts stress, Na+ content in roots, stems and leaves of Rubus Crataegifolius seedling significantly increased, while the K+/Na+ and Ca2+/Na+ ratios in different organs showed an overall downward trend, but that in leaves remained relatively high, which had important implications for the maintenance of normal physiological function of blades; under the stress of neutral salts (NaCl, Na2SO4) and mixed salts of high concentration, Rubus Crataegifolius seedling preferentially retained Na+ in the stem, while under the stress of basic salts (NaHCO3, Na2CO3), Na+ was accumulated mainly in the stem and its content in the root and leaf was always at a low level, which may be an important way for Rubus Crataegifolius seedlings to adapt to saline stress.6. The multiple regression analysis showed that, salt concentration, [Cl-], pH value were the leading factors of saline mixed stress affecting Rubus Crataegifolius, and the salt-tolerance ability of Rubus Crataegifolius could be evaluated by indicators like plant height increment, relative conductivity, MDA content, chlorophyll content, soluble sugar content, proline content, soluble protein content, Na+, K+ content and K+/Na+ ratio in leaves and so on.