Effect Of Prohexadione-Calcium On Reducing The Growth Of Cotton Seedlings Under Salt Alkali Stress

The area of saline-alkali land in China is up to 99.13 million hm²,of which the area of saline-alkali soil accounts for one third of the total cultivated land area in Xinjiang,where cotton is concentrated in China.Facing the current situation of shortage of land resources,it is urgent to explore new ways to improve plant（cotton）resistance to saline alkali.Cotton seed germination,seedling growth,and related physiological indexes were examined in HM 3097 using Na Cl,Na₂SO₄,Na HCO₃,Na₂CO₃（9:1:1:9,molar ratio）at six concentrations（0,20,30,40,50,and 60 m M）;Prohexadione-calcium can improve plant disease resistance and stress resistance,Among them,50 m M was chosen to check the alleviating effect of prohexadione-calcium(5,10,50,100,200 mg L^-1)maceration.The results showed that:1.Saline alkali inhibited cotton seed germination and seedling growth,and the degree of inhibition was aggravated with increasing concentrations of saline alkali.When stressed:the germination rate of cotton seeds,seedling height,stem thickness,leaf area and biomass,growth rate,and so on decreased from 1.3%to 98.2%,but low concentrations of saline alkali can promote root growth;In cotton seedlings,the net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration,and transpiration rate decreased by 7.1%to74.6%;1.6-fold to 7.5-fold increase in Na⁺,12.3%to 77.4%decrease in K⁺and Ca²⁺,and2.8%to 352.1%increase in soluble proteins,soluble sugars and proline;Leaf O₂^-and H₂O₂,MDA content increased from 2.1%to 141.7%,relative conductivity increased from 11.8%to 125.9%,and SOD activity,CAT activity,and POD activity increased from 1.1%to390.1%;2.Prohexadione-calcium dip had a good effect of alleviating saline alkaline stress.Prohexadione-calcium(50 mg L^-1)infiltration,compared with conventional immersion,increased 10.3%to 73.8%of the following plants under saline alkaline（50 m M）stress conditions:cotton seed germination rate,seedling height,stem thickness,leaf area,root and biological quality,growth rate;The net photosynthetic rate,stomatal conductance,intercellular CO₂ content,transpiration rate of the seedlings increased significantly,with photosynthetic pigment contents increasing from 6.5%to 161%;Na⁺absorption decreased by 1.2%to 68.2%,and was more distributed in the root system and young stem,whereas K⁺and Ca²⁺absorption increased and the soluble sugar content increased;O₂^-and H₂O₂decreased by 0.1%to 68.8%,MDA content and relative conductivity decreased by 4.8%to51.9%,and SOD,CAT,and POD activities increased by 1.1%to 20.5%.It can be seen that saline alkaline stress disrupted ion balance in cotton seedlings,exacerbated the degree of peroxidation of the cytoplasmic membrane,inhibited leaf photosynthesis,and finally affected their normal growth and development.However,prohexadione-calcium seed soaking enhanced antioxidant enzyme activities and alleviated cytoplasmic membrane peroxidation in cotton seedlings;Increasing soluble sugar content and improving cotton osmoregulatory capacity;Decreasing the amount of Na⁺absorption,increasing the K⁺and Ca²⁺content,and maintaining cellular ion homeostasis;To improve the photosynthetic pigment content of leaves and enhance photosynthesis,and ultimately to improve the ability of cotton seedlings to resist saline alkaline stress.