| Cotton is an important economic crop in China.The annual demand for cotton seeds in Xinjiang is about 200000 tons,with a value of nearly 3 billion yuan.The huge demand and non-standard market management lead to the perennial backlog of cotton seeds.Seed senescence will inevitably occur in the process of storage,resulting in gradual loss of vitality,which is one of the major problems in agricultural production and germplasm resources conservation.The study of seed senescence is helpful to the storage of seeds and the preservation of germplasm resources.Therefore,in this study,cotton variety Xinluzao 74 was aging at 45℃ for 1,2,3,4 and 5 days,respectively.The effects of artificial aging treatment on cotton seed vigor,ROS content,antioxidant enzyme activity,seed embryo ATP content and ATP synthase subunit mRNA integrity were determined in order to provide a basis for revealing the mechanism of seed senescence.The results are as follows:1.The vigor of cotton seeds treated by artificial aging was evaluated:the results of standard germination test,TTC staining and dehydrogenase activity showed that with the artificial aging treatment,the seed germination rate and radicle elongation length decreased,the seed embryo staining became lighter,and the dehydrogenase activity decreased,indicating that artificial aging treatment reduced the seed germination ability and vitality.The results of microscopic and submicroscopic observation showed that after artificial aging treatment,the mitotic ability of seed root tip cells decreased and the structure of mitochondria was destroyed.2.The results of electrical conductivity and MDA content of cotton seeds showed that with the artificial aging treatment,the electrical conductivity of seed soaking solution and the content of MDA in seed embryos increased,indicating that artificial aging treatment caused cell membrane damage.3.The results of ROS content determination of cotton seed embryos showed that the production rate of O2-· in seed embryo cells of artificial aging treatment increased on the 1st and 3rd day of artificial aging treatment,and decreased after 5 days of aging,and the change trend of H2O2 content was similar to that of O2-·.The results of antioxidant enzyme activity determination showed that after artificial aging treatment,the activities of SOD and POD in seed embryos decreased.The results showed that artificial aging treatment decreased the scavenging ability of antioxidant enzymes in seed embryos,resulting in a large number of production and accumulation of ROS.4.The results of ATP content determination of cotton seed embryos showed that after artificial aging treatment,cotton seed respiration rate decreased,seed embryo ATP content and ATP synthase activity decreased,imbibition could increase cotton seed respiration rate,seed embryo ATP content and ATP synthase activity,but the deeper the aging degree,the weaker the increase.5.The integrity of ATP synthase subunit mRNA of cotton seed embryo was detected by reverse transcription blocking-double primer amplification method.The results showed that after artificial aging treatment,the R value of ATP synthase βsubunit mRNA was higher than that of the control,and the R value of α,δ,γ and εsubunit mRNA decreased in different degrees,indicating that the mRNA of these subunits were damaged in different degrees,resulting in the inhibition of seed embryo ATP synthase protein synthesis.Conclusion:under the condition of artificial aging,the antioxidant enzyme system of seed embryo is damaged and a large amount of O2-· and H2O2 are produced,which results in the destruction of the integrity of cell membrane system,the damage of mitochondrial structure and function,the mRNA oxidation damage of ATP synthase subunits α,γ,ε and δ in mitochondria,the decrease of translation protein efficiency,the hindrance of ATP synthase protein synthesis and insufficient energy supply,which leads to the decrease of seed vigor.This may be one of the main reasons for seed senescence. |
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