Effects Of Drought During Flowering And Boll-Forming Stage On Cotton Pollen Fertility And Related Physiological Metabolism In Pollen

Cotton during the flowering and boll stage is the most sensitive to water stress.Water shortage during this period will seriously impact cotton yield and fiber quality.Drought during this period can significantly reduce boll weight,resulting in yield loss.The fertilization rate of cotton is positively correlated with boll weight.A pot experiment was carried out in greenhouses with a drought-sensitive variety Yuzaomian 9110 and a drought-resistant variety Dexiamian 1 in Nanjing Agricultural University campus(32°02’N and 118°50’E)in 2017-2018.Two water regimes:a well-watered treatment with soil relative water content of 75±5%(CK),and a drought stress tredatment with soil relative water content of 45±5%,donated as CK and drought,were imposed at the beginning of flowering stage.The effects of soil drought during flowering and boll-forming stage on pollen fertility,related carbohydrate metabolism and antioxidant metabolism in pistil and boll weight were investigated to reveal the physiological mechanism of drought stress during flowering and boll period affecting cotton pollen fertility.The main results are as follows:1.Drought effects on boll weight and pollen fertilityDrought stress significantly reduced the pollen viability,in vitro pollen germination rate and in vivo pollen germination rate of the two cultivars.Drought stress also increased the infertility seed rate and reduced the number of fertilized seeds,which ultimately reduced boll weight.Under drought treatment,compared with Yuzaomian 9110,the higher pollen vitality of Dexiamian 1 resulted in higher number of fertilized seeds and lower seed abortion rate,which eventually led to higher boll weight.2.Drought effects on physiological metabolism on antherUnder drought stress,the carbon assimilation ability of the leaves decreased.Drought stress also down-regulated the GhSUT-1 expression,which affected the carbohydrate transport ability to the anthers,affecting energy supply in the anthers,so reduced ATP content in the anthers was measured under drought stress.Drought stress reduced the sucrose hydrolysis into hexose in anthers by reducing the activity of sucrose synthetase and acid invertase.Drought stress led to a decrease in ADP-glucose py-rophosphorylase polypetide(AGPase)activity,which limited the production of UDP-glucose.Despite the activity of Granule-bound starch synthase increased,the lack of substrate inhibited the synthesis of starch,which ultimately led to a significant decrease in anther starch of the two varieties.Under drought treatment,the higher expression of SuSC and INV1 genes in the anthers of Dexiamian 1 than Yuzaomian 9110 resulted in less changed acrivities of SuSy and acid invertase,which ensured the rate of hydrolysis of sucrose into hexose.Moreover,under drought stress,the AGPase activity in the anther was significantly higher for Dexiamian 1 than Yuzaomian 9110,which also provided sufficient reaction substrate for GBSSase and SSSase to ensure the starch synhesis.Eventually,droughted anther of Dexiamian 1 had a higher starch content than that of Yuzaomian 9110.Drought stress reduced the activities of superoxide dismutase(SOD),peroxidase,catalase and antioxidant catalase(APX)in the anthers of the two varieties,and increased the content of hydrogen peroxide(H2O2)and malonaldehyde(MDA)in the anthers.Compared with Yuzaomian 9110,Dexiamian 1 had higher SOD and APX activities in anthetrs,which resulted in higher active oxygen scavenging ability of anthers,and smaller damage of active oxygen to anther cells in Dexiamian 1 than Yuzaomian 9110.Eventually resulted in less MDA and H2O2 in the anthers.This was one of the reasons for stronger pollen fertility in Dexiamian 1 than Yuzaomian 9110.