| The development of wheat endosperm cells is accompanied by endosperm PCD.It is easily affected by external environmental conditions and that is also determines the grain yield and quality of wheat to a large extent.During the grain-filling period in the wheat region of Xinjiang,frequent drought and high temperature,the acceleration of the PCD in endosperm,the insufficient development of the endosperm cells,and the shortening of the grain-filling period,which resulted in a reduction in grain yield and quality.The main winter wheat varieties in Xinjiang were used in this study.The characteristics of endosperm PCD under drought stress in wheat were investigated by histochemical staining,observation of endosperm cell structure by transmission electron microscopy,gel electrophoresis,real-time PCR detection of PCD-related gene transcription and so on.The aim is to reveal the regulatory mechanisms of the endogenous hormones Ethylene(ETH)and Abscisic Acid(ABA)on endosperm PCD.The damage of post-anthesis drought stress to wheat grain development was elucidated from the perspective of endosperm PCD,which provided a theoretical basis for wheat production in Xinjiang against drought stress.The main results are as follows:(1)The characteristics changes of PCD in wheat endosperm under post-anthesis drought stress.Affected by post-anthesis drought stress,in Xindong 18 and Xindong 22,the site of endosperm PCD was random,the nuclear degradation and deformation of endosperm cells were accelerated,and the mitochondria began to appear cavitation,the maximum number of endosperm cells decreased by 7.5% and 12.7%,respectively,the total DNA content decreased by 25.3% and 17.2%,respectively;the nuclease activity was significantly increased and the peak appearance time was advanced,the degree of genomic DNA fragmentation of endosperm cells was deepened and the maximization of fragmentation time was advanced.The contents of ACC and abscisic acid in the tested cultivars were significantly increased,and the relative expression levels of key enzyme genes(nced1,nced2,ao1,ao2)in ABA synthesis were significantly upregulated.Abscisic acid degradation key enzyme gene(aba1)was only expressed at late filling stage.The relative expression levels of ethylene receptor genes(ers1,ers2,etr1,etr2)were significantly down-regulated;the relative expression of dad1 gene was significantly decreased and the expression of bcl-2 gene was significantly up-regulated.Under the post-anthesis drought stress,the maximum grain filling rate of the two cultivars decreased significantly,which resulted in a significant decrease in grain weight at maturity,the grain weight in Xindong 18 decreased by 8.1%,and the grain weight in Xindong 22 decreased by 9.6%.(2)Effect of ETH on PCD in wheat endosperm under post-anthesis drought stressBy inhibiting ethylene treatment based on post-flower drought stress,the vigor of endosperm cells was significantly increased,and the nuclear deformation and disintegration of endosperm cells became slower.in Xindong 18 and Xindong 22,the maximum number of endosperm nuclei increased by 8.1% and 6.6%,respectively;the total DNA content increased by 12.6% and 12.5%,respectively;and the nuclease activity decreased significantly at the same time,the peak of nuclease activity was postponed.The degree of DNA fragmentation is reduced and the time to maximize fragmentation is delayed.In the tested cultivars,the content of ACC decreased significantly,and there was no significant difference in abscisic acid content and the expression of genes related to ABA synthesis and degradation.Affected by ETH inhibitors,the expression of ethylene receptor gene and dad1 gene was up-regulated,and bcl-2 gene was significantly down-regulated.The maximum grain filling rates of the two cultivars did not increase significantly,but the high-speed grouting rate keeping for a long time,and the grain weight increased significantly,the grain weight in Xindong 18 increased by 3.1%,and grain weight in Xindong 22 increased by 2.1%.(3)Effect of ABA on PCD in wheat endosperm under post-anthesis drought stressBy inhibiting ABA treatment based on post-flower drought stress,the viability of endosperm cells decreased significantly;the nuclear deformation and disintegration of endosperm cells accelerated.The maximum number of endosperm nuclei in Xindong 18 and Xindong 22 decreased by 11.9% and 5.2%,respectively;the maximum DNA content decreased by 7.9% and 10.4% respectively.At the same time,the nuclease activity increased significantly and the time of peak appearance advanced;the degree of fragmentation in endosperm genomic DNA increased,and the time to maximization fragment appearance was advanced.In the tested cultivars,the content of ACC increased significantly.In contrast,the ABA content and the expression of genes related to ETH receptor,ABA synthesis and degradation decreased significantly.Affected by ABA synthesis inhibitors,the relative expression of dad1 gene increased significantly,while the expression of bcl-2 gene significantly decreased.The maximum grain filling rates of both cultivars decreased significantly and the grain weight at maturity was also significantly decreased,the grain weight in Xindong 18 decreased by 2.9%,while that in Xindong 22 decreased by 8.0%.In summary,the wheat endosperm PCD is affected by the post-anthesis drought stress environment.External drought stress breaks the balance of endogenous hormones ETH and ABA,leading to a sharp increase in ETH and ABA content,and at the same time weakening the antagonism of ABA to ETH.Ultimately accelerated the process of endosperm PCD.The process of PCD in endosperm is closely related to grain filling rate and grain weight,and prolonging the process of the endosperm PCD can increase the grain weight.The research results can provide theoretical basis for artificial interventions which mitigate the damage caused by external drought stress in wheat production,and also provide new ideas for breeding drought-resistant,high-yield,high-quality wheat varieties. |
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