Effects Of Low Temperature On Storage Substance Transformation During Cotton Seed Germination And Hormone Regulation

Low temperature inhibits cotton seed germination,causing cotton to lack seedlings and ridges,shortening the growth time,reducing seed cotton yield and deteriorating raw cotton quality.Therefore,it is of great significance to clarify the response mechanism of morphological characteristics,storage substances,enzyme activities and hormone content of cotton seeds to low temperature stress,to explore possible ways and technical measures to improve the low temperature resistance of cotton,and to ensure the efficient,safe and sustainable development of cotton in Xinjiang.In this study,upland cotton variety xinluzao 65?L65?and island cotton variety xinhai 35?H35?were used as test materials,and three temperature treatments were set:12-15? 18-21? and 25-28??CK?,study the germination in the process of cotton seed germination characteristics under different temperature conditions,germination potential,germination rate,germination index,mean germination time MTG),storage substance?protein,starch,fat,total sugar,glucose,fructose,sucrose?,a key enzyme?superoxide dismutase,peroxidase,catalase,amylase,lipase,hydrogen peroxide,proline,malondialdehyde?and endogenous hormones?abscisic acid,auxin,gibberellin,zeatin nucleotides?content such as indicators of change;Based on this,the effects of exogenous 100mg/L GA₃ regulation on the storage material,key enzyme activity and endogenous hormone content of cotton seeds during germination were investigated.The main findings are as follows:1.Effects of low temperature stress on germination characteristics and storage material contents of cotton seeds.With the decrease of temperature,the germination rate,germination potential,water absorption,germination index and germination index of cotton seeds decreased by 26.01%,11.67%,7.66%,12.64,1.48 on average compared with 25²8^oC?CK?.However,MTG increased by 3.94 d,respectively.Under low temperature stress,the contents of Pr,St,Ad,TS,Glu,Fru and Suc of cotton seeds were 2.88%,7.86%,3.64%,8.91%,7.61%,5.43%and2.71%lower than those of CK,respectively.There was a significant or extremely significant positive correlation between germination rate and germination potential,germination index and water absorption.There was an extremely significant positive correlation between Pr,Ad and water absorption,and TS,Glu,Fru and Suc were all significantly or extremely significantly positive correlation with the contents of Pr,St and Ad.The contents of Pr,St,Ad,TS,Glu,Fru and Suc in island cotton were 31.24%,5.35%,35.85%,10.66%,23.20%,20.93%and 18.05%respectively under low temperature stress.Therefore,under low temperature stress,island cotton seeds can increase water absorption,accelerate the decomposition and metabolism of protein and fat,and enhance the resistance of seed germination to low temperature.2.Effect of low temperature stress on membrane lipid peroxidation,metabolic enzyme activity and endogenous hormone content of cotton seedsWith the decrease of temperature,the activitiy of POD,SOD,CAT,LPS andcontent of ZR,GA₃,ABA,and IAA in cotton embryo were 8.68%,4.71%,3.81%,6.74%,15.16%,14.16%,21.88%and 3.28%lower than that of CK respectively.While Pro,MDA,H₂O₂,ZR/ABA,GA₃/ABA were 10.53%,7.59%,5.07%,16.11%and 8.33%respectively.The activity of SOD,POD,CAT,AMS and the contents of ZR,GA₃,ABA,IAA and Pro of island cotton were higher than those of upland cotton by 45.05%,20.53%,14.06%,4.85%,46.28%,103.93%,41.64%,38.79%,3.59%under low temperature stress,while the MDA content of upland cotton was 18.26%higher than that of island cotton.In addition,SOD,H₂O₂ and POD were significantly or extremely significantly positively correlated with ZR,IAA,GA₃ and ABA,while LPS was significantly or extremely significantly negatively correlated with ZR,IAA,GA₃ and ABA;all were positively correlated with ZR/ABA has a significant or very significant negative correlation,while Pro has a significant or very significant positive correlation with GA₃/ABA,IAA/ABA;Hoever,SOD,CAT,POD,H₂O₂,ZR,IAA,ABA,ZR/ABA were significantly or extremely significantly correlated with the contents of Pr,St,Ad,TS,Glu,Fru,Suc.The results of principal component analysis showed that ABA,Ad,GA₃,CAT,Pr,Fru,Suc and H₂O₂ were the key factors affecting seed germination.Therefore,sea-island cotton exhibits stronger cold resistance by enhancing the protective enzyme activity,increasing the content of storage substances and endogenous hormones,reducing the content of MDA,and reducing the accumulation of active oxygen,thereby accelerating the metabolism and conversion of substances.3.Effects of exogenous regulators on germination characteristics of cotton seeds during germination at low temperatureThe eight exogenous substances all increased the germination rate,germination potential,and germination index of cotton seeds under low temperature stress to varying degrees,and the MTG was shortened.Among them,GA₃ and FL were better.After 100 mg/L GA₃ treatment,the germination rate,germination potential and GI of GH35 and GL65 increased by 26.50%,7.75%and 4 on average at 12¹5?.The average increase was 5.25%,13%and 6.14 at25²8?,and the MTG decreased by 0.94 d.The germination rate,germination potential and GI of GH35 and GL65 increased by 19.75%,6.50%and 0.97 on average at 12¹5? after FL treatment of 3.29 mg/L,and MTG increased by 0.22.The average increase was 2%,9.25%and 2.87 at 25²8?,and the MTG decreased by 0.25 d respectively;However 20 mg/L of ABA and 5.88 mg/L of PA inhibited cotton seeds germination the most.After comprehensive comparison,it was found that exogenous GA₃ had a better effect on cotton seed germination at low temperature.4.Effects of GA₃ on storage substances and endogenous hormones during germination of cotton seeds under low temperatureAfter exogenous GA₃ treatment,the activity of SOD and LPS,the content of ZR,GA₃ and IAA were 3.81%,3.44%,4.52%,6.11%and 3.25%higher than the control respectively in the germination process of cotton under low temperature stress.The activity of POD,CAT,AMS,ABA,MDA and H₂O₂ and the content of St,TS and Pr were 4.06%,2.13%,3.27%,3.35%,11.51%,5.50%,1.296%,7.22%and 4.77%lower than the control.Correlation analysis showed that there were significant or extremely significant relationships between the storage substances,endogenous hormones and key enzymes,all of which were significantly negativeor extremelysignificantly negative correlated with GA₃ and GA₃/ABA.Principal component analysis showed that ABA,Ad,CAT,H₂O₂,POD,GA₃ and GA₃/ABA were the key factors affecting germination.Step-by-step analysis showed that GA₃ increased the germination rate of L65 by reducing the H₂O₂ content,increasing the CAT activity and fructose content;while reducing the GA₃/ABA ratio,increasing AMS,LPS activity and Suc content were the main factors for GA₃ to increase the germination rate of H35.