| Rice(Oryza Sativa L.)is main food crop in our country.Taking advantages of subspecies heterosis on indica and japonica rice was always considered as effective path way and important trend in further advance of rice yield.Many spikelets per panicles,variation components of indica and japonica compatible and some low temperature sensitive variety groups were observed in indica-japonica hybrid rice,which would easily lead to seed-set obstacle after flowering.Therefore,it is vitally important for high yield and stable yield through improving grain filling and seed-setting rate of indica-japonica hybrid rice.In present,many studies on indica-japonica hybrid rice were mainly focus on the cultivation of high yield&super high yield and the genetic theory of heterosis on indica-japonica hybrid,but the the study on the effects of low temperature(LT)on the obstacle of grain filling and seed-setting rate of indica-japonica hybrid rice needs to be further strengthened and improved.To understand the character of grain filling and seed-setting rate and its the mechanism induced induced by LT of indica-japonica hybrid,a pot experiment in greenhouse and a field experiment were conducted to study on the obstacle of grain filling and seed-setting rate induced by LT of indica-japonica hybrid rice in China National Rice Research Institute(CNRRI)in 2013 and 2014.Variety of Yongyou series,which were planted with large area in Zhejiang province were collected and grown,and indica rice Qianyou2,Zhongzheyoul and japonica rice Zhejing88 which were applied with large area in rice production were also used as control.In the studies,we investigated the variety difference of Yongyou series with cold resistance,the mechanism of seed-setting rate on resistance to LT at anthesis,the characteristics of grain growth and development induced by LT after flowering and the obstacle mechanism of grain filling and seed-setting rate on protein expression,and the effects of sowing date on the characteristic of seed-setting rate.It will provide theoretical and technical support for the cultivation of high and stable yield and breeding for stress tolerance.The primary results were listed as follows:(1)A pot experiment under LT with 17?for 4 duration days and 7 duration days at anthesis was carried out to analyze the difference on seed-setting rate of Yongyou series varieties with number of 9 of indica-japonica hybrid rice and Qianyou 2 of hybrid Indica rice,Zhejing 88 of inbred Japonica rice as control materials.The results showed that seed-setting rate and grain weight per panicle of Yongyou series was decreased significantly with LT,and the LT stress effects were higher during 7 duration days than 4 duration days.Based on the results of clustering analysis,Yongyou 538,Yongyou 10,Yongyou 6,Yongyou 15,Zhejing 88 and Yongyou 17,Yongyou 9,Yongyou 8,Yongyou 12 were divided into chilling tolerance lines,chilling sensitivity lines,respectively,and the others were divided into intermediate type lines.There was no significant difference with the ratio of indica and japonica blood between chilling tolerance lines and chilling sensitivity lines in Yongyou series variety.(2)With the aim of understanding the mechanism of seed-setting rate to resist LT at anthesis of indica-japonica hybrid rice,we observed the difference on anther dehiscence,pollen grain germination on the stigma and spikelets reached anthesis under LT with the five duration days.The results showed that LT decreased significantly spikelets fertility(SF)in cold-sensitive cultivars compared with the chilling-tolerance cultivar,particularly influence on the upper spikelet of panicles.SF under LT was decreased by 12.5%in Yongyoul7 and 9.5%in Yongyou9 contrast to control treatment,respectively.Moreover,microscopic analyses revealed significant differences in anther width and volume between genotypes and treatments,but such differences were not found for anther dehiscence.The number of grains of pollen and of germinated pollen on stigmas with high pollen viability and diameter was observed to be higher on Yongyou538 and Zhejing88 compared with Yongyou9 and Yongyou 17,although the cold-sensitive cultivars could reach a high number of spikelets at anthesis with five days duration under LT.The number of germinated pollen on stigmas was positively associated with SF,but it could not be related to spikelets reached anthesis.Therefore,the improvement of SF was mainly based on the excellent reception of pollen grain on the stigmas.(3)At different days after flowering(from 0 to 15 duration days,early stage;from 15to 30 duration days,middle stage;from 30 to maturity,late stage),the effects of LT(i.e.early stage,20 ?;middle stage,17?;late stage,14?)on grain growth and development of indica-japonica hybrid rice of Yongyou variety were investigated through plant growth chamber.Results showed that effects of LT of different days after flowering on grain filling and seed-setting rate of different genotypes followed the trends early stage>middle stage>later stage,and there was no difference between middle stage,later stage and control.LT at early stage significantly reduced grain filling initiation and grain filling speed and prolonged grain filling time of Yongyou 17,resulted in poor of seed-setting rate and the reduction grain weight per panicle,and that trend was higher on inferior grains than super grains.It was the reduction of 41.41%in seed-setting rate and 35.61%in grain weight per panicle,respectively,contrasting to control,but no difference was found in Yongyou538and Zhejing88.Compared with Yongyou538,LT at early stage after flowering reduced the content of IAA and ZR in the grain,but increased the content of GA3 and ABA in the grain;it could affect the accumulation and transfer of sucrose in the grain,and reduce the starch synthesis;and also it could reduce chlorophyll fluorescence parameters of flag leaf.Therefore,grain filling and seed-setting rate of Yongyou17 under LT at early stage after flowering were affected by significant changes of hormone content in the grain,the carbohydrate accumulation and transportation impeded and the reduction of photosynthesis.(4)The effects of LT on grain characteristic and grain quality of indica-japonica hybrid rice of Yongyou variety under different days after flowering were studied.It showed that LT at early stage after flowering significantly reduced grain width,area,equivalent diameter and ratio of grain weight to area(RGWA)of Yongyoul7.Compared with control,RGWA was the reduction of 66.08%in super grains and 59.65%in inferior grains of Yongyou17,respectively,and it was higher than Zhongzheyoul in super and inferior grain(52.43%,18.37%).Meanwhile,LT at early stage significantly reduced head rice rate and amylose content,but raised protein content,and also reduced the chalkness of Yongyou 17and Yongyou538.Besides,it significantly affected peak viscosity,hot paste viscosity,breakdown and setback,and decreased breakdown of Yongyou 17,led to affect cooking and eating quality of rice.(5)Protein expression mechanism on grain development under LT was studied to understand the characteristic of grain filling and seed-set obstacle of indica-japonica hybrid rice.It showed that LT at early stage after flowering significantly reduced grain protein content by 40.42%of Yongyou 17,compared with Yongyou538.2-DE results showed that there were 117 and 6 up-regulated-expression protein in Yongyou17 and Yongyou538,41and 36 down-regulated-expression protein in Yongyou17 and Yongyou538.We found 33different proteins based on mass spectrometric analysis and protein database search,their biological functions were involved in grain development(12 proteins),energy metabolism(5 proteins),pathogenesis reaction(3 pathogenesis related proteins),protein metabolism(2proteins),stress response(2 resistance related proteins)and oxidation(2 proteins).Most of proteins were over expressed to the different degrees of Yongyou 17,which could be observed negative damage function on the expression of protein level.Two new proteins related to response stress resistance,called Sgtl protein and hypothetical KAB24 protein were also observed in our study.(6)A field experiment was conducted to investigate the effect of sowing date(i.e.14June,early sowing;21 June,suitable sowing;28 June and 5 July,late sowing)on the characteristics of seed-setting rate of indica-japonica hybrid rice,and mitigative effects of exogenous spermidine(Spd)on indica-japonica hybrid rice under LT was studied.The results showed that growth duration period of Yongyou varieties were shortened with sowing date delaying,but grain filling duration after flowering was prolonged,especially in indica rice Zhongzheyoul.Compared with suitable sowing,early&late sowing could affect grain yield of rice.The fluctuation on grain yield of Yongyou varieties under sowing date was difference on growth duration period and stress resistance,but they were lower than indica rice.The decreasing amplitude from 0.91%to 8.85%of grain yield of Yongyou538 was lower than Yongyou8 that from 2.25%to 14.81%and Yongyou 15 that from 17.38%to 25.42%under late sowing.In addition,sowing date delaying,seed-setting rate was reduced significantly,which was positively correlated with day mean temperature of first,second and forth week after flowering;it could reduce chalkness of Yongyou varieties,but result in forming poor grain quality of indica rice Zhongzheyoul.Besides,with sowing delayed,grain length,area,and perimeter were enhanced of Yongyou varieties,and RGWA could be improved by suitable sowing of all genotypes.Under LT treatment,exogenous Spd treatment decreased significantly the levels of MDA of rice seedlings,increased SOD activity,and alleviated the extent of injury.Meanwhile,later sowing(5 July)treatment could retard the degree of senescence of rice leaves and increase grain weight,particularly on inferior grain. |
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