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The Effects of H₂O₂ Pretreatment on Antioxidative System, Uptake and Translocation of Cd in Rice Seedlings

Author: HuYanLing
Tutor: GeZuo
School: Nanjing Agricultural College
Course: Environmental Science
Keywords: rice antioxidative system Cd H2O2 translocation
CLC: S511
Type: Master's thesis
Year: 2009
Downloads: 15
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Abstract

Cd is one of the toxic heavy metals in environment, threatening animals and plants growth as well as human’s heath. With the development of agriculture and industry, Cd pollution becomes more and more serious. Rice is the main crop in China. However, it is also relatively tolerant to heavy metal pollution, and can accumulate Cd to a high level. Therefore, two problems must be solved in order to produce rice safely in the farm land contaminated by low concentration of Cd:One is to improve the tolerance of rice seedlings, and the other is to reduce the Cd translocation from roots to shoots. It has been known that the application of exogenous chemicals such as salicylic acid (SA) to pretreat crop seeds or seedlings can enhance Cd tolerance. Yet little is known about the effect of H2O2 pretreatment on rice under Cd stress.In this paper, a hydroponic experiment was carried out to study the role of H2O2 (1,10 and 100μM) in improving tolerance and reducing translocation of Cd in rice seedlings. Results showed that, Cd significantly repressed rice growing and dry matter accumulation, involving reduced heights, biomass of shoots and roots. The activities of antioxidative enzymes decreased. GST activity and antioxidant contents (ascorbic acid and glutathione) increased, which was more apparent in rice roots. These caused accumulated H2O2 and MDA contents, indicating oxidative stress. On the other hand, when the seedlings were pretreated by different levels of H2O2, Cd toxicity was variously alleviated. Details are given in the following sections.Compared to the Cd-stressed only, the height and biomass of shoot and root significantly increased. The 1 and 10μM H2O2-stressed only had no impact on rice growth, while 100μM demonstrated an unfavorable effect. There was no marked difference among Cd-H2O2 groups, despite a better effect obtained by 100μM level.The inhibition of enzyme activities including CAT, GPX, APX and leaf SOD was variously mitigated. The GPX activity enhanced with the increased H2O2 pretreatment level, similar with the trends of root CAT and leaf APX activity. Moreover, leaf GPX activity was even higher than the control. However, in roots,1 and 10μM H2O2 caused a decrease in APX activity, the result opposite with 100μM treatment. The pretreatment improved root SOD activity and it was higher than the Cd-stressed only at 100μM H2O2 level. The activity of GST involving detoxification increased either by Cd stress or H2O2, and it was more distinguished in roots. The pretreatment resulted in higher GST activity both than the control and the Cd-stressed only. In addition,100μM H2O2 was the best for promoting the enzyme activities, especially in roots. In addition to CAT, other enzyme activities were higher in roots than in leaves.In response to Cd, antioxidants including AsA and glutathione (GSH, GSSG) synthesized more in rice seedlings. The pretreatment increased leaf AsA and root GSH contents, as well as total glutathione content in roots and GSH/GSSG. Leaves had more AsA and GSH contents than roots under normal condition. However, when stressed by Cd or H2O2, roots had more GSH. There was no apparent difference of GSSG amount between roots and leaves. H2O2 pretreatment reduced endogenous H2O2 and MDA level, contributing to alleviated oxidative damage.The pretreatment enhanced Cd uptake and accumulation in roots compared with the Cd-stressed only, and the effect was less apparent concomitant with pretreatment levels. Meanwhile, a reduction happened in relate with the ability of Cd translocation, resulting in lower S/R.In conclusion, H2O2 pretreatment enhanced Cd tolerance of rice seedlings, partly because of the improved antioxidative system, which in turn effectively prevented the accumulation of endogenous H2O2 and acceleration of lipid peroxidation. On the other hand, it may be associated with elevated Cd sequestration in vacuole.

The Effects of H2O2 Pretreatment on Antioxidative System, Uptake and Translocation of Cd in Rice Seedlings

Abstract

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The Effects of H₂O₂ Pretreatment on Antioxidative System, Uptake and Translocation of Cd in Rice Seedlings