Effect Of IAA On Cotton Seedlings Growth Under Drought Stress

In this study,the methods of indoor soil culture and hydroponics were used,and 10% PEG-6000 was used to simulate drought with 6 leaf stage of Yu nong Cotton 31 as material.Total nutrient solution treatment（CK1）,drought control（CK2）,10% PEG-6000+50 mg·L^-1 IAA,10% PEG-6000+100 mg·L^-1 IAA,10% PEG-6000+150 mg·L^-1 IAA were set.The effects of IAA on cotton seedlings under drought stress were investigated by analyzing the changes of morphology,physiology and drought-resistant gene expression of cotton with different concentrations of IAA,and the optimal concentration of IAA was screened out.Then,0.5 mmol·L^-1 SA and 40 mmol·L^-1 Ca Cl2 were sprayed on the leaves to analyze the effects of different exogenous substances on agronomic traits,physiological characteristics and differential expression of drought-resistant genes in cotton under drought stress.The main results are as follows:1.Effects of IAA and other exogenous substance treatment on the expression of drought resistance genes under drought stress.Compared with drought stress treatment,100 mg·L^-1 IAA treatment significantly increased germination potential and germination rate of cotton seeds under drought stress by 10.84% and 34.84%,respectively.The fresh weight,plant height,leaf area,root length,root surface area,root diameter and root volume increased by 46.47%,6.53%,17.00%,28.01%,13.71%,11.77% and 20.42%,respectively.The results showed that the germination rate,dry weight,root surface area and root volume of cotton seedlings were significantly improved by IAA combined with exogenous substances SA and Ca Cl2 under drought stress.The germination rate of seeds treated with 100 mg·L^-1 IAA+0.5 mmol·L^-1 SA,100 mg·L^-1 IAA+40 mmol·L^-1 Ca Cl2 and IAA+SA+Ca Cl2 increased by 6.71%,7.00% and 7.49%,respectively,reaching a significant level.The dry weight of seedlings under 100 mg·L^-1 IAA and 100 mg·L^-1 IAA+0.5 mmol·L^-1 SA+40 mmol·L^-1 Ca Cl2 increased by 14.17% and 13.69%,respectively.The root surface area and root volume of cotton seedlings treated with 0.5 mmol·L^-1 SA increased by 5.35% and 12.66%,respectively.2.Effects of IAA treatment and other exogenous substance treatment on microstructure of cotton stems under drought stress.Under drought stress,the transverse and medulla area of the stem decreases,and the proportion of the cortex in the cross-section becomes larger,and the cortical cells and vascular bundles are loosely arranged and easily separated.After external application of IAA treatments at different concentrations,cortical cells and vascular bundles are tightly arranged.3.Effects of IAA and other exogenous substance treatment on the expression of drought resistance genes under drought stress.Compared with drought stress treatment,100 mg·L^-1 IAA treatment significantly increased SOD,POD activities,proline and soluble sugar contents of cotton seedlings by 48.33%,23.02%,60.33% and 19.57% at 13 days,respectively;In addition,MDA content and leaf relative conductivity were significantly decreased by 28.79% and 3.93%.At 10 d,MDA content was significantly decreased by 12.86% and 10.00% when treated with 100 mg·L^-1 IAA+0.5 mmol·L^-1 SA and 100 mg·L^-1 IAA+40 mmol·L^-1 Ca Cl2,and soluble sugar content was significantly increased by 10.42% and 9.04%.4.Effects of IAA and other exogenous substance treatment on the expression of drought resistance genes under drought stress.Under drought stress,the relative expression of Gh RD22 and Gh DREB genes after the 100 mg·L^-1 IAA treatment was down-regulated by 37.08% and 25.00%,respectively,the relative expression of Gh PIP2;7 and Gh ABF1 genes was increased by 19.00% and 18.12%,respectively,and the relative expression of Gh ABF2 genes and Gh RD29 genes decreased significantly by 20.54% and 26.19% after the 40 mmol·L^-1 Ca Cl2 treatment and 0.5 mmol·L^-1 SA+ 40 mmol·L^-1 Ca Cl2 treatment.