Germination And Morphogenesis Of Pelleted Rice Seeds Under Hypoxic Adversity

Hypoxia stress inhibits the germination of rice seeds,resulting in low and uneven seedling emergence in direct-seeded rice,which severely limits the high and stable yield of rice.Studies have shown that seed pelleting is an effective way to improve seed germination and seedling vigour.Therefore,it is important to investigate the effect of seed pelleting on seed germination and seedling morphology under low oxygen stress to alleviate the damage caused by flooding to rice seeds.In this experiment,rice varieties Wankennuo No.1 and Huanghuazhan were selected as test materials,and the anaerobic/low-oxygen environment in the field was simulated by sand culture in artificial climate incubator,The effects of the pelleting treatment with three active ingredients,namely ABT3,calcium cyclamate and Ca O₂,on the hypoxic germination and seedling growth of rice seeds were investigated,and the physiological mechanisms underlying the ability of the pelleting treatment to promoter the hypoxic germination of rice seeds were further investigated.The main results showed that:1.Among the 12 pelleting treatments,the quality indexes of pelleting rice seeds from Wankennuo No.1 and Huanghuazhan were better than the other treatments in terms of clarity,uniformity,single seed rate,splitting rate and compressive strength,etc.The pelleting seeds were of uniform size,with a smooth surface and no lumps,and were suitable for sowing.Therefore,in the subsequent pelleting of rice seeds,a ratio of clay:bentonite=6:4 was used for the pelleting treatment without active ingredient,and a ratio of clay:bentonite:active ingredient=6:3:1 was used for the pelleting treatment with active ingredient.2.The promotion effect of the active ingredient pelleting treatment on the germination of rice seeds with hypoxia was clarified.Compared with the normal germination control,seed germination was significantly inhibited under flooding conditions,and the active ingredient pelleting treatment could effectively alleviate flooding stress,significantly improve seed vitality and promote seed germination.Compared with the naked species control,the germination rate of Wankennuo No.1 and Huanghuazhan accounted for 13.4%and 20%,the vitality index increased by 47%and 60.6%,the germination index increased by 28.2%and28.5%,and the germination potential increased by 23.0%and 23.9%after the granulation treatment of ABT3 pelleting.After granulation treatment,the germination rate of calcium cyclic acid pelleting increased by 16.7%and 23.3%,the vitality index increased by 72%and75.3%,the germination index increased by 40.3%and 39.1%,and the germination potential increased by 39.1%and 32.7%.After granulation of Ca O₂ pelleting,the germination rate of Ca O₂ pelleting increased by 15.7%and 26.7%,the vitality index increased by 60.3%and82.6%,the germination index increase by 32.7%and 41.5%,and the germination potential increased by 34%and 37.5%.In summary,it is shown that for the varieties of Wankennuo No.1 and Huanghuazhan,the pelleting treatment of the three active ingredients can alleviate the inhibition of rice seed germination by hypoxic stress to varying degrees,significantly improve the germination rate,vitality index,germination index and germination potential,and enhance the germination vitality of rice seeds.In addition,there were differences between the varieties between Huanghuazhan and Wankennuo No.1 seeds to the pelleting treatment of active ingredient pelleting,Huanghuazhan had the best response to Ca O₂pelleting granulation treatment,while Wankennuo No.1 had the best response to calcium cyclic acid pelleting granulation treatment.3.The effect of pelleting granulation treatment on hypoxic germination and seedling growth of rice seeds was studied.Using Wankennuo No.1 and Huanghuazhan as test materials,the growth of seedlings was inhibited in a flooded environment.Through the granulation treatment of the active ingredient pelleting,the growth of seedlings was promoted,and the plant height,mesocotyl shaft and germ sheath length of seedlings were significantly improved.Under flooded environment,the average plant height,mesocotyl and germ sheath length of Wankennuo No.1 seedling increased by 35.9%,26.4%and 30.9%percent respectively compared with the naked species control.The average plant height,mesocotyl shaft and germ sheath length of Huanghuazhan accounted for seedlings increased by 38.1%,37.2%and 35.5%respectively compared with the naked species control,and the increase of various morphological indicators of Huanghuazhan in seedlings was greater than that of Wankennuo No.1,indicating that Huanghuazhan was more sensitive to the promotion response of the active ingredient pelleting treatment.4.Using Wankennuo No.1 and Huanghuazhan as test materials,the antioxidant enzyme activity of rice seeds in flooded environment was determined respectively.Compared with the naked species control,the active ingredients ABT3 pelleting Wankennuo No.1 and Huanghuazhan accounted for 8.7%and 9.1%percent of seed POD activity,CAT activity increased by 15.9%and 10.4%,and SOD activity by 5.9%and 3.7%.The active ingredients Calcium Cyclic Acid pelleting granulated Wankennuo No.1 and Huanghuazhan accounted for 13.2%and 16.3%percent of seed POD activity,25.4%and 21.4%of CAT activity,and13.2%and 10.1%percent of SOD activity.The active ingredients Ca O₂ pelleting Wankennuo No.1 and Huanghuazhan accounted for 14.5%and 17.3%percent of seed POD activity,25.4%and 22%percent of CAT activity,and 14.7%and 9.2%percent of SOD activity.Among them,the POD and CAT activities of Wankennuo No.1 and Huanghuazhan both peaked on the 4th day after sowing,and the SOD activities of Wankennuo No.1 and Huanghuazhan peaked on the 7th day after snowing.The results showed that under flooding stress,the pelleting granulation treatment of the three active ingredients could significantly improve the antioxidant enzyme activity of rice seeds and enhance the flood tolerance of rice seeds.Overall,Ca O₂ pelleting granulation had the best promotion effect on various physiological indexes of rice seeds,followed by ABT3 and calcium cyclic acid pelleting granulation.5.Physiological mechanism of active ingredient pelleting treatment to promote rice seed germination and early growth under low oxygen stress:（1）Active ingredient pelleting can alleviate flooding stress and promote rice seed germination and seedling growth.This is mainly attributed to the fact that the granulation of the active ingredient pelleting can significantly increase theα-amylase activity in seeds,promote the degradation of endosperm starch,accelerate the internal glucose metabolism process of seeds,and increase the soluble sugar content,thereby promoting the rapid germination of rice seeds and the growth of seedlings.Under flooded conditions,theα-amylase activities of Wankennuo No.1 seeds were increased by 137.8%,178.4%and 191.9%,respectively,by granulation of the active ingredients ABT3,Prohexadione calcium,Ca O₂ pelleting.Theα-amylase activity of Huanghuazhan accounted for seeds increased by 148%,191.3%and 226.8%,respectively.It can be seen that among the three active ingredient pelleting granulation,the active ingredient Ca O₂ pelleting has the most obvious effect on promoting theα-amylase activity of rice seeds.（2）Compared with naked species control,the ADH activity of Wankennuo No.1 and Huanghuazhan treated with ABT3 pelleting decreased by 67.3%and 78.8%,and the PDC activity decreased by 65%and 66.7%.The active ingredients calcium cyclic acid pelleting granulated Wankennuo No.1 and Huanghuazhan accounted for 70.8%and 72.8%percent of the seed ADH activity and 66%and 68.5%percent of PDC activity.The active ingredients Ca O₂ pelleting Wankennuo No.1 and Huanghuazhan accounted for 76.7%and78.3%percent of the seed ADH activity and 66%and 69.4%of the PDC activity.The results showed that under hypoxic stress,the pelleting of the three active ingredients could effectively reduce the ADH and PDC activities of rice seeds,weaken anaerobic respiration during germination,and promote rice seed germination and seedling growth.In summary,the germination and seedling morphological growth of the seeds of Wankennuo No.1 and Huanghuazhan were significantly improved by the pelleting treatment of three effective ingredients,ABT3,calcium cyclamate and Ca O₂,under low oxygen stress environment,and the antioxidant enzyme and amylase activities of the seeds were significantly increased,while the activities of ADH and PDC were significantly reduced,which effectively improved the flooding tolerance of rice and promoted the germination and seedling growth of rice seeds,and played an important role in alleviating the problems of low seedling emergence and poor seedling morphology of direct-seeded rice.