不同耐性水稻幼苗根系对镉胁迫的形态及生理响应

Root morphological and physiological responses of rice seedlings with different tolerance to cadmium stress

采用水培试验,以两个耐镉性不同的水稻品种为材料,研究了不同浓度镉胁迫对水稻幼苗根系形态、根系活力、游离脯氨酸含量及抗氧化酶活性的影响。结果表明:低于5μmol/L Cd胁迫对2个水稻品种总根长、根表面积、根体积、根干重、根系活力无明显影响,在1μmol/L Cd时,甚至起促进作用。随Cd浓度增加表现出一定的抑制效应,秀水63在10μmol/L Cd胁迫下根系形态、根系活力明显受到抑制,而秀水09在25μmol/L Cd胁迫下明显受抑。随Cd胁迫浓度的增加,游离脯氨酸含量、丙二醛(MDA)含量、超氧化物歧化酶(SOD)、过氧化物酶(POD)活性均呈上升趋势,两品种相比,秀水09的游离脯氨酸含量、SOD和POD增幅大于秀水63,而MDA含量增幅小于秀水63;过氧化氢酶(CAT)活性变化表现为先上升后下降,10—100μmol/L Cd胁迫下秀水63根系中CAT活性明显低于秀水09。总之,水稻对Cd毒害响应存在明显的品种差异,且Cd胁迫下根系生理响应的差异是品种间耐性差异的重要原因之一。

Heavy metal pollution has received increasing attention duo to the public awareness of environmental issues.Cadmium（Cd）,a divalent heavy metal cation,is one of the most toxic environmental pollutants with noknown physiological function,which could cause serious problems to plants,animals and human being.Toxic levels of Cd may be come up by contaminated soil containing abundant Cd,by agricultural manufacturing,mining,smelting,atmospheric deposition and other waste disposal practices,or by use of metal-containing pesticides and fertilizers in agricultural soils.In higher plants,roots may be the first organs contacting to the toxic metal ions during their absorbing process,therefore,roots usually response firstly to the toxic metal ions if there is any than do shoots.However,there are little studies dealing with the toxicity and mechanisms behind Cd tolerance concerning the root.The objective of the present study was to investigate the root morphology,physiological and ecological responses of rice root to cadmium stress.Two rice（Oryza sativa L.） cultivars,differing markedly in Cd tolerance,Xiushui 09（Cd-tolerant genotype） and Xiushui 63（Cd-sensitive genotype）,were adopted in the solution culture experiments.Seedlings were selected for uniformity and cultivated in IRRI′s nutrient solution.Cadmium with 7 concentrations of 0（the control）,1,5,10,25,50,and 100 μmol/L Cd in the form of CdCl2（calculated according to pure Cd） was added to the nutrient solution（pH 5.0） at 5-leaf stage of rice seedling.In the experiments,each treatment was replicated three times,and the nutrient solution was renewed every 4 days.After 12 days of cultivation,rice roots were sampled and root morphology,root biomass,root activities,content of proline and malondialdehyde（MDA）,the activities of superoxide dismutase（SOD）,peroxidase（POD） and catalase（CAT） were determined.The results showed that Cd concentration higher than 5 μmol/L in the solution inhibited root growth,while Cd concentration lower than 5 μmol/L in the solution did not affect the total root length,root surface area,root volume,root dry weight and root activities.And Cd of 1 μmol/L showed a slight stimulatory effects.Compared to Xiushui 09,cultivar Xiushui 63 had more pronounced inhibition effect in root growth and root activity under Cd supply.These root morphology parameters,root dry weight and root activities of Xiushui 63 and Xiushui 09 were significantly decreased under 10 μmol/L and 25 μmol/L Cd,respectively.In both cultivars compared with their corresponding control,the proline content and activities of SOD and POD were significantly enhanced with the increasing of Cd concentrations from 0 to 100 μmol/L in the nutrient solution.Meanwhile,as Cd concentration varied from 0 to 100 μmol/L,MDA accumulation was enhanced notably,and the activity of CAT in roots increased at first and then decreased as the Cd concentration beyond 10 μmol/L,and being more pronounced effect in Xiushui 63 than in Xiushui 09.As an index of lipid peroxidation,the higher MDA content in the cultivar Xiushui 63 indicated the occurrence of more severe oxidative stress under Cd stress.In conclusion,Cd had obvious toxicity to rice roots,and there was significant different response to Cd between Xiushui 09 and Xiushui 63.The physiological characteristics of rice root responding to Cd might be important factors for the tolerance of cultivars.