| Cd is a kind of heavy metal with strong biological toxicity and widely distributed.Cd will not only affect the growth and development of plants,but also can enter the human body and animals through the food chain,which will cause harm to human and animals health to a certain amount.Cd is easily absorbed,transported and accumulated by rice and can be accumulated in large amounts in brown rice.Heavy metal pollution,especially Cd pollution,in paddy is serious in China.Cultivating low-accumulation Cd rice varieties is one of the most economical and effective methods to solve the Cd pollution hazard in rice.Trace elements such as Cu,Fe,Mn,and Zn have many functions in the human body,which is lack can cause human body dysfunction and thus affect human health.Improving the above trace element content in the edible parts of food crops can effectively alleviate human mineral element deficiency.Rice is one of the most important food crops for humans.Therefore,it is very important to carry out Cd stress response mechanisms in rice and the genetic mechanisms of Cd,Cu,Fe,Mn,and Zn for improving the efficiency of Cd low-accumulation rice varieties and the improvement of trace elements in rice.This study was to investigate the effect of Cd stress on rice growth,physio-biochemical and gene expression analysis,and to carry out QTL mapping for five trace metals including Cd.The specific results are as follows:1.The results showed that the longest root length,seedling height,fresh weight per plant and dry weight per plant of the six varieties were significantly affected by the water cultured seedlings of six rice varieties treated with 25 μΜ,50 μΜ and 100 μΜ concentrations of Cd for 5 d.Inhibition,inhibition effect size is longest root length> fresh weight of single plant> dry weight of single plant> high seedling height,and the inhibitory effect is enhanced with the increase of Cd stress concentration;It was more economical and reasonable to identify the Cd resistance of rice seedlings with 50 μΜ Cd stress concentration;Under stress conditions,it is more scientific to evaluate Cd tolerance ability of seedlings using the four indicators of longest root length,seedling height,single plant fresh weight and dry weight per plant.2.Three Cd concentrations of 25 μΜ,50 μΜ and 100 μΜ were used to treat the water cultured seedlings of Zhenyang 97 B and Miyang 46 for 1 d,3 d and 5 d.The results showed that there are differences in processing concentration and processing time on SOD,POD and CAT enzymes of two varieties.The three enzymes showed a trend of decreased 25 μM Cd stress activity,50 μM Cd stress activity and 100 μMCd stress activity,which better reflected the Physiological response mechanism of the two varieties under Cd stress.3.The Cd stress treatment of 7 rice cultivars was conducted at the whole growth period with 5.88 μg/g concentration.The results showed that there was a significant difference in Cd accumulation between the cultivars regardless of the control(Cd concentration of 0.53 μg/g)or Cd stress,among which Cd accumulation was extremely significant greater than the control under Cd stress.Under Cd stress,the Cd accumulation of all varieties was significantly higher than that of the control,the accumulation ability of 906 Cd was the highest,and that of Zhenshan 97 B was relatively weakest.Under the Cd stress condition,the contents of Cd in stems,leaves and brown rice of Mingzhu 1,Aizhen and Zhenshan 97 B was stems>brown rice>leaves,which is different with the control’s situation of stems>leaves>brown rice,suggesting that high concentration of Cd stress will change the Cd accumulation characteristics of brown rice and leaves in some rice varieties.4.The water cultured seedlings of YZX and Xiangwanxian 12 was treated with 50 μΜ Cd for 5 d.The results showed that the relative expression of OsNramp1 was significantly up-regulated in both above-ground parts and roots of YZX and Xiangwanxian 12 under Cd stress and the increase was greater in the former than in the control;OsLCT1 was only significantly up-regulated in the above-ground part of YZX than that of the control,while the expression level in the above-ground part of the Xiangwanxian 12 was significantly lower than that of the control.OsHMA3 and OsPDR17 were significantly different in the above-ground and root systems of YZX and Xiangwanxian 12.In a comprehensive analysis,OsNramp1 and OsLCT1 may be two major genes that regulate the accumulation of Cd in grains of YZX and Xiangwanxian 12.5.QTLs for five trace metals were analyzed using recombinant inbred lines derived from hybrids Zhenshan 97 B and Miyang 46 by field and pot experiments.The results showed that 37 QTLs controlling the contents of Cd,Cu,Fe,Mn,and Zn were detected in brown rice,hulls,and stems and leaves,distributed on chromosomes other than 3 and 10,and the phenotypic variation of qZnHR7 contributed the highest rate(14.4%),and the favorable alleles of the remaining 27 QTLs were derived from the female parent Zhenshan 97 B with the exception of qCd2,qCu7,qFe7,qMn7,qZn1-1,qZn4,qCuCL6,qMnCL6,qZnCL4 and qZnCL6.22 QTLs controlled the contents of Cd,Cu,Fe,Mn and Zn in brown rice.Thirteen QTLs and 9 QTLs were identified in field and pot experiments.Among them,qCd5 was repeatedly detected in two experiments and was a new QTL controlled Cd content in brown rice;4 QTLs controlled contents of Fe and Zn in husk;11 QTLs controlled contents of Cd,Cu,Fe,Mn and Zn in stems and leaves. |
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