Study On The Physiological Response Of Cotton Under Salt Stress And Mechanism Of Salt Tolerance

Cotton is not only an important cash crop,but also a salt-tolerant pioneer crop in China.It has a certain salt-tolerant capacity and is one of the preferred crops for the development and biological improvement of saline-alkali land.This study analyzed the effects of salt stress on cotton seedling growth,photosynthetic physiology,and ion transport using cotton varieties with different salt tolerances as test materials by field micro-area control and hydroponic experiment.And it also reveals the mechanism of cotton salt tolerance from the perspectives of osmotic adjustment,antioxidant capacity,and membrane physiology of cotton,and provides a certain theoretical basis and scientific basis for the selection of salt-tolerant cotton varieties.The results are as follows:（1）Physiological responses of different salt-tolerant cotton varieties under saline-alkali land.Proline content in leaves of salt-tolerant varieties（Zhong H177,Zhong J0710）was significantly higher than that of salt-sensitive varieties（Zhong J0102,Xinluzao 74）（the former is 1.31⁴.14 times of the latter）,but malondialdehyde content was significantly lower than that of salt-sensitive varieties（the former is only52.73%⁶6.26%of the latter）;SPAD values and photosynthetic parameters were significantly greater than those of salt-sensitive varieties（the former is 1.02¹.48 times of the latter）;Na⁺,K⁺content of stems,and K⁺/Na⁺ratios in the shoots and roots of salt-tolerant varieties were higher than those of salt-sensitive varieties.Salt-tolerant varieties enhance cotton plant salt tolerance by slowing down the content of malondialdehyde,and are able to maintain high photosynthetic capacity and K⁺/Na⁺balance.According to the grey correlation degree,salt tolerance of Zhong H177 in cotton varieties is better.（2）Effects of salt stress on the growth of cotton seedlings with different salt-tolerant varieties.With the increase of salt concentration,the plant height,fresh dry weight and leaf area of cotton seedlings of different varieties gradually decreased.Under low salt environment（100 mmol/L）,cotton growth characteristics decreased less than high salt environment（150,200 mmol/L）;under salt stress,salt-tolerant varieties（Zhong 9806,Zhong 9807）fresh dry weight and leaf area The drop rate is less than that of salt-sensitive varieties（Zhong S9612,Xinluzao 74）.The growth of cotton was obviously inhibited by NaCl stress,especially high concentration NaCl stress;the salt stress resistance of salt-tolerant cotton was less than that of salt-sensitive cotton,and its cotton plant bioaccumulation was higher than salt-sensitive cotton.（3）Effects of salt stress on physiological characteristics of cotton seedlings with different salt-tolerant varieties.With the increase of salt concentration,the activity of antioxidant enzymes in cotton leaves increased first and then decreased,the content of malondialdehyde（MDA）increased,and the accumulation of superoxide dismutase（SOD）and peroxidase（POD）in leaves of salt-tolerant varieties was large,but the accumulation of MDA in salt-tolerant varieties（the former was only 2.82%²7.88%of the latter）lower than salt-sensitive varieties（the former is only 30.96%⁷7.34%of the latter）;under salt stress,the content of soluble protein（SP）,soluble sugar（SS）,and proline（Pro）in cotton leaves increased considerably,and SP and Pro increased significantly in salt-tolerant cotton species.Under salt stress,the peroxidation of cotton plants is accelerated,and salt-tolerant varieties have stronger ability to resist oxidation and adjust their own osmotic balance.（4）Effects of salt stress on ion balance of cotton seedlings with different salt-tolerant varieties.With the increase of salt concentration,the Na⁺content in roots and leaves increased significantly,the Na⁺content in stems increased first and then decreased,and the K⁺content and K⁺/Na⁺ratio both decreased.The Na⁺accumulation in the underground part of salt-tolerant cotton was lower Salt-sensitive cotton;under salt stress,the K⁺content decline in the leaves was slightly less than that in the roots,and the content of K⁺in leaves of salt-tolerant varieties is slightly higher than that of salt-sensitive varieties;the K⁺/Na⁺ratio of salt-tolerant varieties is slightly higher than that of salt-sensitive varieties;the K⁺/Na⁺ratio in leaves is always higher than the root K⁺/Na⁺ratio.The salt-tolerant varieties have a stronger transport capacity S_K?,_Na?from root to stem and leaf.Salt-tolerant varieties can effectively regulate the ion balance in the cell and improve salt-tolerance by trapping more Na⁺in the root and transporting K⁺to the leaves.（5）Effect of salt stress on intracellular enzyme activity of cotton with different salt-tolerant varieties.With the increase of salt concentration,the activities of H⁺-ATPase and Ca²⁺-ATPase of the plasma membrane and vacuolar membrane of salt-tolerant varieties showed an upward trend and then decreased,and the H⁺-ATPase activity of the salt-tolerant plasma membrane and vacuolar membrane is higher than those of salt-sensitive varieties;under salt stress,the Ca²⁺-ATPase activity of the plasma membranes and vacuole membranes of salt-sensitive varieties decreased,and salt damage disrupted the balance of H⁺and Ca²⁺in the cytoplasm of their roots,causing metabolic disorders.Compared to salt-sensitive cotton,salt-tolerant cotton can maintain high H⁺-ATPase activity,regulate osmotic pressure in vivo through H⁺,maintain cell homeostasis,and maintain Ca²⁺homeostasis to inhibit K⁺outflow and Na⁺inflow.