Effects Of Copper Content On Grain Filling Properties,Yield And Quality Of Rice In Paddy Fields

Grain filling is an important stage for rice yield and quality formation.On the base of the"source-sink-transportation"theory of crop yield formation,this study investigated the effects of copper content on the metabolism of rice assimilates and the grain filling properties of superior and inferior grains.To clarify the effects and mechanisms of superior and inferior grain filling on rice yield and quality formation under copper contamination in paddy fields.This experiment was conducted in pot experiments in the greenhouse of the Science and Technology Park of Jiangxi Agricultural University in 2019（pre-experiment）and 2021.And the test soil was copper uncontaminated paddy field cultivated layer soil,and the test variety was Super Rice Wufeng You 286.Three treatments were set up by adding exogenous Cu for control（i.e.,original soil）,Cu content of 100 and 200 mg·kg^-1,denoted as CK,Cu₁₀₀,and Cu₂₀₀,respectively.This experiment aimed to study the effects of the copper content in rice fields on the photosynthetic effect,assimilate synthesis,assimilate transport in stem sheath（source）,superior and inferior grain filling properties,key enzyme activities such as sucrose synthase（SS）,soluble starch synthase（SSS）,ADPG pyrophosphorylase（AGPase）and starch branching enzyme（SBE）in grains during sucrose-starch metabolism,and yield quality during the filling period of rice in paddy fields,to provide a theoretical basis for further rational use of Cu-contaminated soil.The main findings are as follows:1.The results of the 2019 and 2021 trials in this study showed that the rice yields were decreased at Cu₂₀₀ treatment,which was decreased by 31.2%and 39.5%compared with the control（CK）respectively,and the pattern was the same.However,rice yield in both years was only significantly or highly significantly positively correlated with the effective number of spikes.In addition,the copper content of grain hulls and brown rice increased with the increasing copper content of the paddy field,as shown by brown rice>grain hulls,and the copper content of brown rice exceeded the critical value of food quality copper(<10 mg·kg^-1)at Cu₂₀₀ treatment.The key enzyme activities during grain filling of both superior and inferior grains were positively correlated with yield,processing quality,and cooking quality,and negatively correlated with appearance quality,nutritional quality,and hygienic quality.In contrast,sucrose synthase（SS）,soluble starch synthase（SSS）and starch branching enzyme（SBE）were the more critical enzymes affecting the quality of rice during the filling process of superior and inferior grains.2.At the sources organ:The results of this study found that at Cu₁₀₀ treatment,the flag leaves could still maintain good photosynthesis without significant inhibition on the synthesis and production of leaf assimilates,but even promoted the synthesis of leaf photosynthetic assimilates to a certain extent.In contrast,assimilates in the stem sheath tended to accumulate significantly in the late filling stage,and the stem sheath dry matter quality increased by 3.9%to 15.6%compared to the control（CK）.However,compared with the control（CK）,the photosynthetic characteristics（SPAD value of flag leaf,leaf area index,photosynthetic potential,net assimilation rate,and population growth rate）,photosynthetic assimilate content,and the dry matter mass of the stem sheath was significantly decreased in the leaves at soil Cu₂₀₀ treatment.3.At the sink organ:the carbohydrate content of grains and the related enzyme activities measured decreased significantly with increasing copper content,with the inferior grains being more significantly affected.At Cu₁₀₀ treatment,the SS,SSS,AGPase,and SBE activities of the superior grains were transiently increased,which prolonged the duration of the active period of grain filling and increased the final growth A value of the superior grains.However,the SS,SSS,and SBE activities of the inferior grains were significantly decreased,both the maximum and average filling rates were significantly reduced,and the active period of filling and the time to reach the maximum filling rate were also significantly shortened,resulting in a significantly lower final growth A value than the control（CK）.At Cu₂₀₀ treatment,both superior and inferior grains were significantly shortened in the active period of filling and the time to reach the maximum filling rate,and SS,SSS,AGPase,and SBE activities were significantly decreased,which resulted in a significantly lower final growth A value for both superior and inferior grains than the control（CK）.In conclusion,rice leaves could maintain a high photosynthetic production capacity under the lower copper content,and although the translocation capacity of stem sheath assimilates was reduced,which might lead to a decrease in the amount of assimilates transported to the seeds,there was no significant inhibition on the accumulation of starch synthesis in the superior grains.In addition,although lower copper content inhibited starch synthesis in the inferior grains,it could increase the grain weight and effective spike number of the superior grains by promoting the filling of the superior grains,which could compensate for the lack of filling of the inferior grains to some extent,and there was no significant decrease in yield.