Effects Of Low Temperature Stress At Flowering And Grain Filling Stages On Micronutritional Quality Of Rice

Rice grain quality is not only determined by varieties,but also affected by environmental factors.Temperature is the key climate factor affecting rice quality.Rice is main source of mineral element(Fe,Zn,P,K,Ca)for human,and the content of mineral element in rice grain have significant effects on crop development and growth,as well as on human health.In addition,the content of amino acids and the composition of essential amino acids and its balance play important roles in determining rice grain nutritional quality.Under the background of global climate change,the frequency and intensity of extreme low temperature stress during rice critical growth period are increasing,which seriously threatens rice yield and quality,especially micronutrients.Therefore,it is of great significance to determine the effects of different levels of low temperature stress at flowering and grain filling stages on rice grain nutritional elements for quantitative prediction of rice quality productivity,and ensuring food nutritional security under future climate conditions.In this study,Huaidao 5 and Nanjing 46 which have different sensitivities to cold stress,were used to quantitatively analyze the effects of low temperature stress at different stages(early flowering,mid-flowering and grain filling)with different duraitons(3,6,and 9 days)and diffrerent temperature levels(27/21 ℃,23/17 ℃,19/13 ℃ and 15/9 ℃)on 5 kinds of mineral elements and 17 kinds of amino acids in mature rice grains.The main results are as follows:(1)In terms of micro-mineral elements,the content of Fe and Zn in Huaidao 5increased first and then decreased with the decrease of temperature level at early flowering stage,increasred under low temperature stress at mid-flowering stage,but decreased under low temperature stress at grain filling stage.The content of Fe and Zn in Nanjing 46 decreased under low temperature stress at all three stages.The relative content of Fe and Zn in Nanjing 46 decreased significantly with the increase of ACDD at all three stages,while the relative content of Fe and Zn in Huaidao 5 increased significantly with the increase of ACDD only at the mid-flowering stage.For massive mineral elements,after low temperature treatment at all three stages,with the decrease of temperature level,the content of P and K in Huaidao 5 decreased,and negatively correlated to ACDD.The content of P and K in Nanjing 46 increased after low temperature treatment at early flowering stage,and positively correlated to ACDD,but decreased after low temperature treatment at grain filling stage.The content of Ca in Huaidao 5 and Nanjing 46 increased under low temperature stress at early flowering and grain filling stage.Under low temperature stress at mid-flowering stage,the content of Ca decreased in Huaidao 5,but increased in Nanjing 46.Generally,the correlation between relative content of Ca and ACDD was not significant.At the same temperature level,the content and accumulation of most mineral elements did not change significantly with the duration of low temperature.There were significant positive correlations among the content of five mineral elements in Huaidao 5,but no significant correlation between content of five mineral elements and content of protein,total starch,amylose and amylopectin;The grain protein content of Nanjing 46 was significantly negatively correlated with content of micro-mineral elements,significantly positively correlated with content of massive mineral elements,and there was a significant positive correlation between starch content and Fe.In general,the content of mineral elements in grains of Huaidao 5 was more sensitive to low temperature stress at mid-flowering stage than at grain filling stage and early flowering stage;Compared with Nanjing 46,the content of mineral elements in grains of Huaidao 5 was more sensitive to low temperature stress.(2)Among the essential amino acids,methionine in Huaidao 5 was sensitive to all three stages of low temperature stress,in addition,threonine and leucine were sensitive to low temperature stress at grain filling stage,the content of methionine,threonine and leucine increased with the decrease of temperature treatment at corresponding stage;Phenylalanine and lysine in Nanjing 46 were sensitive to low temperature stress at early flowering stage,isoleucine was sensitive to low temperature stress at mid-flowering stage,the content of phenylalanine,lysine and isoleucine increased with the decrease of temperature treatment at corresponding stage,lysine was more sensitive to low temperature stress at grain filling stage,and its content decreased with the decrease of temperature.Among the non-essential amino acids,serine in Huaidao 5 was sensitive to low temperature stress at flowering stage,cystine was sensitive to low temperature stress at early flowering and grain filling stage,tyrosine was sensitive to low temperature stress at grain filling stage,these three amino acids showed an increasing trend with the decrease of temperature treatment at corresponding stage;Histidine content in grain of Nanjing 46 was more sensitive to early flowering and grain filling stage,and increased after low temperature treatment at flowering stage,but the opposite was true at grain filling stage.Cystine and tyrosine were more sensitive to low temperature stress at mid-flowering stage.With the decrease of temperature,cystine content decreased,while tyrosine content was on the contrary.The total amino acid content,total essential amino acid content,total non-essential amino acid content and relative content in grains increased with the decrease of treatment temperature at different stages and different low temperature levels.The contents of total amino acids,total essential amino acids and total non-essential amino acids of Huaidao 5and Nanjing 46 increased by 0.17%,0.18%,0.16% and 0.09%,0.10%,0.05% respectively,with 1 ℃·d increase in ACDDa.The effect of low temperature stress on essential amino acids was greater than that of total amino acids and non-essential amino acids.The sensitivity to low temperature stress was in the order of mid-flowering stage > early flowering stage > grain filling stage.After low temperature treatment at early flowering stage,the accumulation of total amino acids showed a decreased trend,but it was different at mid-flowering stage and grain filling stage.From the amino acid score,amino acid ratio coefficient and essential amino acid index,although the total amino acid,essential amino acid and non-essential amino acid contents in grains were increased by low temperature treatment at different stages,the amino acid nutritional value of the two varieties were decreased.Huaidao 5 was more significantly affected by low temperature than Nanjing 46.The effect of low temperature at grain filling stage on the composition and balance of essential amino acids was less than that at flowering stage.