Study On The Characteristics And Physiological Mechanism Of Rice Quality Formation In Dry Cultivation

In recent years,frequently regional and seasonal droughts,underdeveloped agricultural mechanization and decreasing number of agricultural workers year by year limit the production of rice and stimulate the development of rice dry cultivation.However,low rice yield and poor grain quality in dry cultivation lead to the lack of economic and social attraction.At present,grain yield in dry cultivation has been raised,but the research on rice quality in dry cultivation has been marginalized.Therefore,exploring the mechanism of grain quality formation in dry cultivation had great significance to relieve the conflict between high-yield,high-quality and water-saving and to improve the economic and social benefits of dry cultivation.At the research farm in Wuhan and Zaoyang of Huazhong Agricultural University during 2017 – 2019,field and pot experiments were carried out.Five rice varieties were selected as the research materials,including high-yield and high-quality indica conventional rice cultivar Huanghuazhan(HH),high-yield and drought resistant three-line hybrid indica rice cultivar Hanyou 73(HY),drought resistant indica conventional rice cultivar IRAT109(IR),high-yield and drought sensitive three-line hybrid indica rice cultivar Yueyou 9113(YY)and drought sensitive indica conventional rice Zhenshan 97(ZS).Two water treatments including conventional flooding irrigation(F)and rice dry cultivation(D)were set up in this study.By analyzing the relationship between rice grain metabolome,starch,fatty acid and amino acid metabolism,physicochemical traits of starch and grain processing,appearance,cooking and nutritional quality,and by comparing the characteristics of rice quality formation in different panicle parts under dry cultivation and in dry cultivation of ratooning rice system,to clarify the physiological mechanism of high-quality formation in dry cultivation.The main results are showed as follows:(1)The relationship between grain metabolome and high rice quality traits in dry cultivation showed that: The rice quality traits of YY and HY under dry cultivation were significantly reduced compared with them in flooding irrigation,while the quality traits of HH variety under dry cultivation conditions were not significantly reduced than that in flooding irrigation and still maintained at a high rice quality.The HH in dry cultivation increased or improved some metabolites and metabolic pathways to maintain higher grain quality traits.These metabolic pathways mainly included starch and sucrose metabolic pathway(osa00500),anthocyanin biosynthesis(osa00942),arginine and proline metabolic pathway(osa00330),galactose metabolism pathway(osa00052),serine,glycine and threonine metabolic pathway(osa00260),phenylpropanoid biosynthesis(osa00940),ubiquinone and another terpenoid-quinone biosynthesis(osa00130)and flavonoid biosynthesis(osa00941).The HH in dry cultivation mainly increased 16 metabolites,which could be classified into flavones,carboxylic acids and derivatives,quaternary ammonium salts,anthocyanidins and anthocyanins,flavonoid glycosides,indolyl carboxylic acids and derivatives,and amines.(2)The experiment on the relationship between starch,fatty acid and amino acid metabolism and the physicochemical traits of starch and rice quality showed that:The synthesis of starch,fatty acids and amino acids of HY,YY and IR varieties in dry cultivation was weak,especially 12-27 d after anthesis,which limited the development of endosperm cells and the improvement of starch granules traits,resulting in a greater decline in the rice quality traits of HY,YY and IR varieties in dry cultivation compared with these cultivar in flooding irrigation;compared with other treatments,HH in低容易cultivation maintained higher soluble starch synthase(SSSase),starch branching enzyme(SBE)during 2-12 d after anthesis,which tended to synthesize short branched amylopectin and to competitively reduce the synthesis of amylose.During 12-27 d after anthesis,HH in dry cultivation increased the activities of SSSase and granular bound starch branching enzyme(GBE),supporting the formation of long branched amylopectin.The HH in dry cultivation maintained high crystallites size,interplanar spacing and micro strain,increased C16:0,C16:1,C18:1,C18:2,Glu,Asp,Lys and Thr,and decreased glutelin and prolamine in head rice.In addition,HH in dry cultivation maintained high C=O bonds in esters and ketones,C-O bonds in carboxylic acids,esters,alcohols and ethers and OH bonds in alcohols before pasting,and reduced C-O bonds and C=O bonds in carboxylic acids and aldehydes after pasting.The accumulation of starch,fatty acid and amino acid and the physicochemical traits of starch before or after pasting maintained the high cooking quality in HH in dry cultivation.(3)The experiment on the formation of rice quality in lower and upper panicle under dry cultivation showed that: Except for HH in flooding irrigation,the upper panicle of HH variety in dry cultivation had higher rice quality traits and still maintained at a high-quality level;the upper panicle and lower panicle of IR and ZS varieties in dry cultivation remained higher soluble sugar content and lower starch content during 12-27 d after anthesis.That leaded to higher soluble sugar in grains or endosperm cells during12-27 d after anthesis,which promoted the polymerization of soluble sugar,protein and lipid to increases the accumulation of polymers between starch granules,resulting in a larger gap between starch granules to reduce the appearance and processing quality.Except FHH treatment,upper panicle of HH in dry cultivation maintained high rice quality traits.Upper panicle of HH in dry cultivation had higher soluble sugar content than that in other treatments during 2-12 d after anthesis,but it decreased the soluble sugar content and increased the starch content during 12-27 d after anthesis.Compared with other treatments,upper panicle of HH in dry cultivation maintained higher activities of granular bound starch synthase(GBSSase),ADP-glucose pyrophosphorylase(ADPGase)and UDP-glucose pyrophosphorylase(UDPGase)during 2-12 d after anthesis to increase the synthesis of amylose;upper panicle of HH in dry cultivation also maintained high Su Sase,ADPGase,SSSase and SBE activities during 2-27 d after anthesis,which promoted the synthesis of short and long breached amylopectin.The traits of starch synthesis supported the high rice quality.In addition,higher starch content and lower soluble sugar in upper panicle of HH in dry cultivation during 17-27 d after anthesis limited the accumulation of glutenin and prolamine,respectively.Glutelin and prolamine content had positive relationship with chalkiness and chalky grain rate.Glutelin,prolamine and total flavonoids contents in upper panicle had negative correlation with gelatinization temperature.In addition,upper panicle of HH in dry cultivation before pasting increases the ordered structure of carbon chain and crystalline region of starch granules,as well as many hydrophilic functional groups(intramolecular and intermolecular OH bonds,C=O bonds in anhydrides,Ar-O bonds in phenols,C-O bonds in esters and carboxylic acids and C=O bonds in aldehydes)and hydrophobic functional groups(C-N bonds in amines and C-C bonds in hydrocarbons).This supported higher cooking quality in upper panicle of HH in dry cultivation.(4)The study on the formation of rice quality of different rice cultivar in dry cultivation under ratooning rice system showed that: Compared with the main season,ratoon season had higher processing and appearance quality,but reduced cooking quality.In ratoon season,compared with HY variety in flooding irrigation and dry cultivation,HH variety decreased chalkiness,gelatinization temperature,setback value and retrogradation value,but increased head rice rate,breakdown value and amylose content.Compared with other treatments in main and ratoon seasons,HH of dry cultivation in ratoon season had higher GBE and GBSSase activities during 2-12 d after anthesis,higher SSSase and SBE activities during 2-27 d after anthesis,which tended to synthesize long or short branched amylopectin for constructing the crystalline regions.The HH of dry cultivation in ratoon season has higher crystallinity,crystallites size,interplanar spacing and dislocation density,but it reduces micro strain in brown rice and head rice.The HH of dry cultivation in ratoon season also increased C16:1,C18:0,C18:1,C18:2,C18:3 and starch lipid in head rice and Glu,Thr and Lys in brown and head rice,but decreased the accumulation of C15:0,C16:0,C18:0 and C18:3 in brown rice and glutelin and Asp in brown and head rice.In addition,HH of dry cultivation in ratoon season increased the content of main functional groups(C-N bond in amines,C=O bond in anhydride and carboxylic acid,Ar-O bond in phenols,C-O bond in ether,alcohol,anhydride and carboxylic acid)in brown rice before pasting,and maintained the diversity of functional groups in head rice(C≡C bond,C=C bond,C=O bond in ketones and carboxylic acids,C-O bond in carboxylic acid,ether,alcohol and anhydride,C-N bond in amines,intermolecular OH bond,Ar-O bond in phenols,OH bond in carboxylic acids and phenols).After pasting,HH of dry cultivation in the ratoon season reduced the relative content of some functional groups in starch colloids(including intramolecular and intermolecular OH bonds,C-O bonds in esters,carboxylic acids and alcohols,C=O bonds in carboxylic acids and esters and NH bonds in amines).The starch,fatty acid and amino acid accumulation traits and starch physicochemical traits maintained the higher processing,appearance and cooking quality in HH of dry cultivation in ratoon season.In summary,rice quality traits in rice dry cultivation showed a decreasing trend compared with flooding irrigation,but the high-quality rice variety in dry cultivation did not decrease much and remained at the high-quality level;the high-quality and high-yield rice variety under dry cultivation compared to the high-yield rice variety,the water-saving and drought-resistant rice varieties and drought-sensitive variety ZS have higher rice quality characteristics,while the rice quality traits of the upper panicle of high-quality and high-yield rice variety under dry cultivation were better than those of the lower panicle,and rice quality traits of dry cultivation in ratoon season were significantly higher than rice quality traits of dry cultivation in main season.Therefore,the application of high-quality rice varieties in dry cultivation can obtain high-quality traits.To improve the quality traits of lower panicle and to learn from the physiological mechanism of maintaining the high-quality traits in upper panicle of high-quality rice varieties in dry cultivation or dry cultivation in ratoon season could further raise the rice quality traits in dry cultivation.