作 者 ：郑国红,周楠,刘鹏*,徐根娣,张健平
期 刊 ：生态学报 2010年 30卷 20期 页码：5585~5591
Keywords:iron toxicity, potassium, cell-wall polysaccharide, root, rice,
摘 要 ：以耐铁毒型水稻品种协优9308和铁毒敏感型水稻品种Ⅱ优838为实验材料，采用溶液培养法研究250 mg?L-1 Fe2+（EDTA-Fe2+）胁迫下，不同钾水平对两种水稻的生长特性、酸性磷酸酶(APA)、果胶甲酯酶(PME)、根系果胶含量、半纤维素1含量以及半纤维素2含量的影响。结果表明，经250 mg?L-1 Fe2+ 处理7d和14d后，协优9308和Ⅱ优838的相对根长明显下降，APA、PME的活性显著升高，果胶含量、半纤维素1含量、半纤维素2含量显著增加，Ⅱ优838酶活性及细胞壁多糖含量提高幅度较大，表现出其铁毒敏感性,并且随着处理时间的延长，铁胁迫对两种水稻相对根长，PME活性,HC1含量及HC2含量的影响越显著，但APA活性和果胶含量则没有明显变化。加入外源钾可以不同程度的降低酶活性及细胞壁多糖含量，外源钾浓度为200 mg?L-1,对水稻相对根长，APA活性，HC1含量缓解效果较好；外源钾浓度为400 mg?L-1，对PME活性，果胶含量缓解效果较好。随着外源钾浓度升高，水稻铁毒症状得到不同程度的缓解，但钾浓度高于200 mg?L-1又会对水稻造成新的胁迫。由此推测，水稻通过提高根系细胞壁多糖含量来增加根尖铁的结合位点，以及细胞壁的厚度和刚性，并降低细胞壁的伸展性，使根细胞的伸长受抑，从而提高其铁耐性。
Abstract:A hydroponic experiment was conducted to study the effects of potassium on growth character, acid phosphatase enzyme (APA) and pectin methylisterase enzyme (PME) activity, root pectin, hemicellulose 1（HC1) and hemicellulose 2 (HC2) contents of rice under 250mg ? L-1 Fe2+（EDTA-Fe2+) toxicity. The results showed that the growth of rice was inhibited in both Fe-resistant genotype of xieyou9308 and Fe-sensitive genotype of Ⅱyou838 when the two cultivars were exposed to 250mg?L-1 Fe2+ solution for 7d and 14d. The activities of acid phosphatase enzyme and pectin methylisterase enzyme were enhanced for both two rice genotypes, the contents of root pectin, hemicellulose 1 and hemicellulose 2 were increased under iron toxicity. Ⅱyou838 always showed a higher enzyme activity and cell-wall polysaccharide contents than xieyou9308, and its root cell-wall pectin, hemicellulose 1 and hemicellulose 2 contents were increased by a large margin, showing its sensitivity to iron toxicity. With the extension of processing time, the effects of iron toxicity on the relative root length, root pectin methylisterase enzyme activity, hemicellulose 1 and hemicellulose 2 contents of both two genotypes were more significant, but the acid phosphatese enzyme activity and pectin content did not change significantly. The root length was an important indicator of iron toxicity, and had an important relationship with the cell-wall polysaccharide content; High iron toxicity led to accumulation of cell-wall polysaccharide pectin and high pectin methylisterase enzyme activity, increased the number of free carboxyl groups which have more iron-binding sites; The skim membrane increased seriously when the acid phosphatase activity became high, then the membrane structure and function were destructed. The different potassium concentrations could decrease the enzyme activity and the cell-wall polysaccharide content to some extent. When the exogenous potassium concentration was 200 mg?L-1, the relative root length, acid phosphatese enzyme activity, hemicellulose 1 content of both two genotypes and hemicellulose 2 content of Ⅱyou838 were relieved close to the control group value; When the exogenous potassium concentration was 400 mg?L-1, pectin methylisterase enzyme activity, root cell-wall pectin content of both two genotypes and hemicellulose 2 content of xieyou9308 were relieved close to the control group value. As the concentration of exogenous potassium increased, the iron toxicity to both two genotypes of rice was relieved in different degrees. Exogenous potassium decreased the enzyme activity and the cell-wall polysaccharide contents significantly, While the exogenous potassium concentration was higher than 200 mg?L-1, the potassium would also create new form of toxicity to rice, the relative root length began to decrease, the acid phosphatese enzyme activity, hemicellulose 1 and hemicellulose 2 contents were enhanced again, which suggested that exogenous potassium could alleviate iron toxicity of rice to some extent, but just a limited capacity to alleviate iron toxicity not complete remission. Our study suggested that iron tended to modify the metabolism of cell-wall polysaccharides and thus made cell-wall more thick and rigid, inhibited the elongation of root cells and the growth of rice roots, thereby improved their tolerance to iron toxicity.
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