| Rice is an important food crop.The high and stable yield of rice is of great significance to the food security to our country.However,in actual production,the phenomenon of rice stem lodging occurs sometimes,becoming an important limiting factor for rice yield and quality improvement.In recent years,because of the lowering solar radiation,the inadequate light resources have become an adverse factor in crop growth and development.At the same time,chemical control technology is an important cultivation for controlling crop lodging resistance.Therefore,it is of great practical significance to carry out the mechanistic study on the impacts of shading and exogenous regulating substances on the lodging resistance of japonica rice.Field experiments were conducted in 2015～2016 at Nanjing Agricultural University Experimental Base in Danyang county,Jiangsu Province.Two lodging difference japonica rice varieties(Wuyunjing 23,lodging resistance;W3668,lodging susceptible)were used as test materials.Normal light and shading treatment with black shade net were set up from jointing to heading stage.The shading treatment was used with black shading net and the shading rate was 60%.In 2015,GA:(Gibberellin acid 3)and Uni:(Uniconazole)were treated under normal light and shading treatment.In 2016,GA:(Gibberellin acid 3)and Uni(Uniconazole)were treated under normal light;Uni(Uniconazole)were treated under shading treatment.The yield and yield components,field apparent lodging rate,stem morphology and mechanical properties,endogenous phytohormones content,anatomical characteristics,stem carbohydrates content and the biosynthesis dynamics changes of structural carbohydrates genes expression were analyzed and compared.The aim of this study was to reveal the impacts of shading and exogenous regulating substances on lodging resistance and its regulation mechanisms of japonica rice.On the basis of the above,RNA-seq and iTRAQ sequencing analysis were carried out on the stem samples with exogenous regulating substances treatment under normal light at key stage.The main results were as follows:(1)Shading and exogenous regulating substances significantly affected the yield of japonica rice.Shading reduced grain yield.Gibberellin acid reduced grain yield under shading condition,however,the response of yield between Wuyunjing 23 and W3668 were different under normal light condition.Exogenous uniconazole had no significant effects on grain yield.Lodging reduced the yield of japonica rice,but the effects of lodging on yield was not only related to the occurrence of lodging period but also related to the lodging type.In addition,variety,light and exogenous regulating substances had significant interactions on yield and yield components.(2)Analysis of stem mechanical indices showed that,shading and exogenous regulating.substances significant influenced stem mechanical characteristics of japonica rice.Because of the higher breaking strength(M),the lodging index(LI)of Wuyunjing 23 was lower than that of W3668.Shading increased lodging index,and resulted in risk increased lodging.Exogenous gibberellin acid increased stem lodging index under both normal light and shading conditions,which was due to the increased of bending moment of the whole plant(WP),the length from the broken point to the panicle top(SL),the fresh weight from the broken point to the panicle top(FW),and the reduction of M and bending stress(BS).The actual lodging time of gibberellin acid treatment under shading occuered earlier than that of gibberellin acid treatment under normal light,and the actual lodging rate was higher than that of gibberellin acid treatment under normal light.Exogenous uniconazole treatment reduced stem lodging index,and decreased the risks of lodging under normal light and shading conditions,this was because of the M and section modulus(SM)were significantly increased,as well as the WP reduced.(3)Shading and exogenous regulating substances significantly affected morphological and structural characteristics of japonica rice stem.Compared with normal light,the culm diameter and culm wall thickness decreased under shading treatment.Exogenous gibberellin acid treatment significantly increased plant height,gravity centre height and internode length,especially the basal internode length,due to the content of endogenous GA3 increased,resulting in rapid cell length elongation.Plant height,gravity centre height and the length of the basal internodes were significantly shortened.However,the culm diameter and the culm wall thickness were increased significantly,due to increase the content of endogenous ZR(Trans zeatin),causing cell division accelerated,resulted in culm diameter,culm wall thickness increased significantly.(4)Shading and exogenous regulating substances significantly affected the formation of stem cell wall of japonica rice.The culm cell walls were developed dysplasia with shading or gibberellin acid treatments,the thickness of mechanical tissues were decreased and arranged loosen,and thus the stem mechanical strength reduced.The thickness of mechanical tissues increased and arranged dense with uniconazole treatment,and the filling materials in parenchyma tissues increased,then the mechanical strength of the stem enhanced.These were the anatomical reasons of the mechanical strength of stem changes.The lignin and primary cell wall cellulose biosynthesis genes in the early and middle stage after the intemode elongation were down-regulated under shading,the accumulation of cellulose and lignin in the culms were inadequate,and decreased the plumpness in addition,leading to the stem mechanical strength reduced eventually.Gibberellin treatment significantly reduced the non-structural carbohydrates content,so the synthesis substrates of structural carbohydrates were inadequate;the cellulose and lignin genes expression up-regulated in the early stage was a feedback regulation mechanism of lacking synthesis substrate.In addition,due to the rapid elongation of intemodes,therefore the lignin accumulation of per unit length culms in the later stage was insufficient.Uniconazole treatment significantly increased content of non-structural carbohydrates,so the synthesis substrates of structural carbohydrates were adequate,thus the related genes expression down-regulated was a feedback regulation mechanism of sufficient synthesis substrates.Atthe same time,because of the significantly shortened intemodes,therefore the cellulose and lignin accumulation of per unit length culms increased significantly.(5)RNA-seq and iTRAQ analysis showed that:shading and exogenous regulating substances significantly affected lignin and cellulose related metabolic pathways of japonica rice stem.Gibberellin acid treatment enhanced the aromatic amino acids metabolism,phenylpropanoid metabolism,and turned to lignin biosynthesis,promoted the lignin biosynthesis pathways;but inhibited the cellulose catabolism and starch synthesis.Uniconazole treatment inhibited the lignin biosynthesis at the transcriptional level,but had no significant effects on the protein level.In addition,uniconazole treatment inhibited the cellulose catabolism. |
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