外源半胱氨酸对铜胁迫下小麦幼苗生长、铜积累量及抗氧化系统的影响

Effects of exogenous cysteine on growth,copper accumulation and antioxidative systems in wheat seedlings under Cu stress

采用滤纸培养法,研究了不同浓度的L-半胱氨酸(L-Cys)对200μmol/L铜离子胁迫下小麦幼苗生长、铜积累量和抗氧化系统的影响。结果表明,(1)200μmol/L的铜离子可抑制小麦幼苗生长,使根长、生物量、总叶绿素含量极显著下降,可溶性蛋白和还原性谷胱甘肽(GSH)含量,超氧化物歧化酶(SOD)和抗坏血酸氧化酶(APX)活性略微上升,丙二醛(MDA)含量和细胞膜透性极显著上升。(2)外源Cys在1.0—5.0mmol/L时,受铜胁迫的小麦幼苗生长势与对照无差异,在1.0和2.5mmol/L下,根长、生物量、叶绿素a和总叶绿素含量与对照无显著差异,与Cu处理组差异显著(P<0.01)。(3)高于1.0mmol/L的外源Cys可极显著增加铜胁迫下小麦叶片和根系中的铜积累量。(4)外源Cys极显著提高了铜胁迫下小麦幼苗可溶性蛋白和GSH含量,并使SOD和APX活性持续维持在较低水平;外源Cys浓度低于2.5mmol/L时,MDA含量极显著下降,低于5.0mmol/L时,细胞膜透性极显著升高;多酚氧化酶(PPO)活性先上升后下降,除Cys为0.5mmol/L处理外,其它各处理间PPO活性均无显著差异。综合来看,喷施1.0—2.5mmol/L的外源Cys可提高小麦幼苗对铜胁迫的耐受性。

Cysteine （Cys） is one of the twenty basic amino acids and is converted to glutathione （ GSH）, phytochelatins （PCs） and other variety of metabolites in the body. GSH is an enzymatically synthesized tripeptide in which Cys is linked via peptide bonds to the y-carboxyl group of glutamic acid （Glu） and the c^-amino group of glycine （Gly） depending on peptide bonds. GSH serves as the first line of the organism defense against the products of oxygen metabolism, reactive oxygen species, and other electrophilic compounds such as toxins （herbicides）, xenobiotics, and heavy metals. PCs are a family of heavy metal-inducible peptides important in the detoxification of heavy metals and can chelate the metals, have been identified in plants and some microorganisms. The inactive toxic metal ions of metal-PCs chelatins are subsequently transported from cytosol to vacuole before they poison the enzymes of life-supporting metabolic routes, and transiently store in vacuole to reduce the heavy metal concentration in cytosol. Thus, heavy metal detoxification is attained. When one considers that Cys plays a central role, it is perhaps understandable that the effects of exogenous Cys have been less well studied in higher plants. In this paper, the effects of exogenous Cys on growth, copper accumulation and antioxidative systems in wheat seedlings under 2001μol/L copper stress culture method. The results showed that the growth of wheat seedlings were inhibited under 200μmol/L copper stress, and that the radical elongation, biomass and total chlorophyll content decreased highly significantly, （SOD） and aseorbate peroxidase （ the contents of soluble protein and GSH, the activities of superoxidase dismutase APX ） increased slightly. Malondialdehyde （MDA） content and the membrane permeability enhanced significantly. At 1.0-5.0mmol/L exogenous Cys level, the seedling growth was similar to that of the control ones, and at 1.0 and 2.5mmol/L exogenous Cys level, the radical elongation, biomass, chlorophyll a and total chlorophyll content were no significantly different compared with those of the control ones, while significantly different from those with Cu treatments （P〈0.01）. Above 1.0mmol/L exogenous Cys level, copper accumulation increased continuously in wheat leaves and roots. Exogenous Cys significantly enhanced the contents of soluble protein and GSH, and maintained the activities of SOD and APX at a low level continuously. In contrast, MDA content decreased significantly at the level of less than 2.5mmol/L Cys, while t he membrane permeability increased significantly. Polyphenol oxidase （PPO） activity increased firstly and then decreased, showing no significant differences from control ones except with 0.5mmol/L treatment. On the whole, spraying 1.0-2.5mmol/L exogenous Cys can enhance the tolerance of wheat seedlings to copper.