Effects Of Exogenous Allantoin On Root Growth And Carbon And Nitrogen Metabolism Of Rice Under Low Temperature Stress At Booting Stage

Heilongjiang Province,as the main rice producing area in China,its cultivation area and total yield rank among the top in China,which is an important guarantee for China’s food security.However,low temperature and cold damage occur frequently,which seriously affects the growth and yield formation of rice and restricts the development of rice.The booting stage is not only the key period of rice yield formation,but also the most sensitive period to temperature response.During this period,it is subjected to low temperature and cold damage,which seriously affects the growth and development process and yield formation process of rice,resulting in a significant reduction or no yield.As an important substance of plant nitrogen cycle system,allantoin plays an important role in stress response.In this experiment,Songjing21 was used as the test material,and the normal temperature treatment was used as the control,and the natural cold damage was simulated by cold water irrigation,set different concentrations of allantoin gradient(0 kg/hm~2、5 kg/hm~2、10 kg/hm~2、15 kg/hm~2、20 kg/hm~2、25 kg/hm~2),the effects of exogenous allantoin on root characteristics and carbon and nitrogen metabolism of rice under low temperature stress at booting stage were studied.The effects of exogenous allantoin on root architecture,nitrogen metabolism,allantoin metabolism,nitrogen absorption and transport,photosynthetic characteristics,non-structural carbohydrate formation and accumulation of rice under low temperature stress at booting stage and their internal relations were clarified.The relationship between root characteristics and nitrogen formation and accumulation,non-structural carbohydrate formation and accumulation and yield formation was revealed,which laid a foundation for the development of rice stress-resistant,synergistic and yield-preserving cultivation techniques.The main results of this experiment are as follows:1.Exogenous allantoin had a significant effect on rice root growth under low temperature stress at booting stage.Compared with normal temperature control,low temperature stress at booting stage significantly reduced root length,root volume,root surface area,root bleeding intensity,root oxidation force and root absorption area.Compared with the low temperature stress at booting stage,the application of exogenous allantoin can improve the root morphology and root activity,and with the increase of the application level of exogenous allantoin,the trend of increasing first and then decreasing.The root morphology and root activity of C15treatment increased significantly and reached the maximum,but still lower than the normal temperature control.2.Exogenous allantoin had a significant effect on the key enzyme activities of nitrogen metabolism in rice under low temperature stress at booting stage.Compared with the normal temperature control,low temperature stress at booting stage significantly reduced the activities of NR and GABA-T in roots and functional leaves,and increased the activities of GS,GOGAT,GDH,GAD,XOD and UE.Compared with low temperature stress at booting stage,the application of exogenous allantoin could increase the activity of key enzymes of nitrogen metabolism(except GABA-T),and increased first and then decreased with the increase of exogenous allantoin application level.The activity of key enzymes of nitrogen metabolism(except GABA-T)in C15 treatment increased significantly and reached the maximum,and was significantly higher than that in normal temperature control(NR activity in roots at full heading stage and NR activity in leaves at booting stage were significantly higher than that in normal temperature control,and the rest were significantly lower or not significantly different).The application of exogenous allantoin could significantly reduce the activity of GABA-T(there was no significant difference between C5 treatment of functional leaves at wax ripening stage and full ripening stage).With the increase of exogenous allantoin application level,the activity of GABA-T decreased first and then increased.3.Exogenous allantoin had a significant effect on nitrogen accumulation and distribution in rice under low temperature stress at booting stage.Compared with the normal temperature control,the nitrogen accumulation of each organ decreased significantly under low temperature stress at booting stage,the nitrogen distribution ratio of stem sheath and leaf increased,and the nitrogen distribution ratio of panicle decreased.Compared with low temperature stress at booting stage,the application of exogenous allantoin could increase the nitrogen accumulation of each organ,and with the increase of allantoin application level,the nitrogen accumulation of each organ increased first and then decreased.The nitrogen accumulation of each organ in C15 treatment(C20 treatment at stem sheath full heading stage)increased significantly and reached the maximum.Among them,the nitrogen accumulation of leaves in C15 treatment at full heading stage,C15 and C20 treatments at full heading stage and C15 treatment from wax maturity stage to full maturity stage was higher than that of normal temperature control,and the rest were lower than that of normal temperature control.The application of exogenous allantoin could reduce the nitrogen distribution ratio of stem sheath and leaf,and increase the nitrogen distribution ratio of panicle.The nitrogen distribution ratio of panicle in C15treatment was the largest,but it was still lower than that of normal temperature control,indicating that the application of appropriate amount of allantoin under low temperature stress could promote the transport of nitrogen from various organs to panicle.4.Exogenous allantoin had a significant effect on photosynthetic characteristics of rice under low temperature stress at booting stage.Compared with normal temperature control,low temperature stress at booting stage significantly reduced chlorophyll content,net photosynthetic rate(Pn),transpiration rate(Tr),intercellular carbon dioxide concentration(Ci),maximum photochemical efficiency(Fv/Fm),potential photochemical efficiency of PSII(Fv/Fo)and leaf area index(LAI)of functional leaves.Compared with the low temperature stress at booting stage,the application of exogenous allantoin could increase the chlorophyll content,Pn,Tr,Ci,Fv/Fm,Fv/Fo and LAI of functional leaves,and with the increase of allantoin application level,the trend of increasing first and then decreasing.The photosynthetic characteristics of C15 treatment were significantly increased and reached the maximum,but still lower than the normal temperature control.5.Exogenous allantoin had a significant effect on sucrose metabolism of rice under low temperature stress at booting stage.Compared with the normal temperature control,the sucrose content and soluble sugar content of functional leaves increased significantly at different growth stages under low temperature stress at booting stage.The fructose content increased significantly from booting stage to milk stage,and decreased significantly at wax stage and full maturity stage,which was related to the significant increase of sucrose synthase(SS)and sucrose phosphate synthase(SPS)activities from booting stage to milk stage,and the significant decrease of SS and SPS activities at wax stage and full maturity stage.The sucrose content and soluble sugar content(except full heading stage and milk stage)of grains at wax maturity stage and full maturity stage increased significantly,while the sucrose content,fructose content and soluble sugar content of grains at full heading stage and milk stage decreased significantly.Compared with the low temperature stress at booting stage,the application of exogenous allantoin could increase the sucrose content and soluble sugar content,fructose content and SS activity and SPS activity of functional leaves from booting stage to full heading stage,and the sucrose content and fructose content from full heading stage to milk ripening stage,and the soluble sugar content at full heading stage.With the increase of allantoin application level,the trend of increasing first and then decreasing,and the indexes of C15 treatment increased significantly and reached the maximum.The application of exogenous allantoin could reduce the content of sucrose in functional leaves after full heading stage and soluble sugar from wax maturity stage to full maturity stage.The sucrose content and soluble sugar content of the grains from the dough stage to the full maturity stage decreased first and then increased with the increase of the allantoin application level,and the C15 treatment significantly decreased and the content was the lowest.Compared with the normal temperature control,the sucrose content and soluble sugar content of the exogenous allantoin treatment were significantly increased at the wax maturity stage and the full maturity stage.The sucrose content and fructose content from full heading stage to milk ripening stage and the soluble sugar content at full heading stage were significantly reduced.6.Exogenous allantoin had a significant effect on starch formation in rice grains under low temperature stress at booting stage.Compared with the normal temperature control,the amylopectin content,total starch content,soluble starch synthase(SSS)activity,adenosine diphosphate glucose pyrophosphorylase(AGPase)activity,starch branching enzyme(SBE)activity,amylose content and granule starch synthase(GBSS)activity were significantly decreased under low temperature stress at booting stage.Grain amylose content and GBSS activity were significantly increased at dough stage and ripening stage.Compared with the low temperature stress at booting stage,the application of exogenous allantoin could increase the amylopectin content,total starch content,SSS activity,AGPase activity,SBE activity,amylose content and GBSS activity at full heading stage and milk ripening stage,and with the increase of allantoin application level,the trend of increasing first and then decreasing.The above indexes of C15 treatment increased significantly and reached the maximum,but still lower than the normal temperature control.The application of exogenous allantoin significantly reduced the amylose content and GBSS activity of grains at wax ripening and full ripening stages,and decreased first and then increased with the increase of allantoin application level.The C15treatment was significantly reduced,but still higher than the normal temperature control.7.Exogenous allantoin had a significant effect on rice yield under low temperature stress at booting stage.Compared with the normal temperature control,the dry matter accumulation,panicle length,primary branch number,secondary branch number,primary branch grain number,secondary branch grain number,grain number per panicle,seed setting rate,1000-grain weight and yield of each organ were significantly decreased under low temperature stress at booting stage.The difference of effective panicle number in 2021 was not significant but lower than that of normal temperature control,and the effective panicle number in 2022 was significantly lower than that of normal temperature control.Compared with the low temperature stress at booting stage,the application of exogenous allantoin could improve the above indexes,and with the increase of allantoin application level,the above indexes increased first and then decreased.The above indexes(except the number of effective panicles)of C15treatment increased significantly and reached the maximum,but still lower than the normal temperature control.