| Rice provide for more than half of the world's population as staple food, occupies an important position in agricultural production. It's common to find iron toxicity in tropical, subtropical region, and iron toxicity is considered one of the important limiting factor for rice growth, with the expanding of global acidic soil area, how to seek economic and efficient path to relieve iron toxity and how to improve the production of rice has become one of the hot fields of biology. This experiment chose Fe-resistant genotype of xieyou9308 and Fe-sensitive genotype ofⅡyou838 as the research materials, use the hydroponic experiment to study the rice seed germination, growth character, characteristics of antioxidant enzymes system and the influence of iron toxicity on chlorophyll fluorescence characteristics on physiological level:From the cellular level we researched the effects of exogenous potassium on the cell-wall polysaccharides components and the activity of rice root pectin acidic phosphatase enzyme and pectin methylisterase enzyme; we also research the influence of the interaction of iron and potassium on elements uptake, transportation and on accumulation and distribution regularity inside rice on nutritional level, in order to provide suitable method for rice growth under stress environment and increase the production of rice. The results are as follows:(1) We use solution culture experiment to study the effects of different concentration of potassium on radicle and shoot elongation, Vigour index, Germination Index, the activity of catalase, peroxides, superoxide dismutase, total amylolytic and a-amylase under 250mg·L-1 Fe2+ toxicity. The result indicated that the percenttage of seed germination, the elongation of radicle and shoot were enhanced as well as the activities of CAT, POD, SOD, and a-amylase. The most suitable concentration of potassium is about 200 mg·L-1 for bothⅡyou838 and xieyou9308, under this concentration the exgenous potassium could alleviate the iron toxicity very well. The influence of iron toxicity on seed germination ofⅡyou 838 is more than Xieyou 9308.(2) The results of rice antioxidant system and the transformation of chlorophyll fluorescence indicated that under 250mg-L-1 Fe2+ stress, the antioxidant enzymes activity of two different genotypes of rice were decreased, MDA content increased, chlorophyll content decreased, initial fluorescent rised, the biggest fluorescence (Fm) droped and the maximum photochemistry efficiency of PhotosystemⅡalso was decreased, which indicated that the PhotosystemⅡresponse center had been harmed, inhibited the primal reaction of photosynthesis and obstructed the electronic transfer process. Exert exogenous potassium, chlorophyll content of two cultivars increased significantly compared with iron-stress group, Fv/Fm value rised slightly and Fo value decreased. All of above indicated that exogenous potassium can alleviate the harm of iron toxicity on photosynthesis and photosynthetic organ.(3)Study on the effects of different kalium strength on rice growth characteristics, elements absorption and transportation of different organs and subcellular of xieyou9308 andⅡyou838 under high content iron stress indicated that the growth of rice were inhibited seriously, the content of Fe increased, and the absorption and transportation of K, Ca, Zn, Na were inhibited. Exogenous potassium can alleviate iron toxicity on rice, and alleviate the inhibition of plant height and root length, the content of iron in rice decreased and the absorption and transportation of nutritional were increased. In the subcellular fraction, Fe, K is mainly distributed in the cell-wall component and the soluble fraction. In conclusion, appropriate concentration of potassium can change the absorption and transportation of elements in rice under high content iron stress, which can alleviate iron toxicity and promote the rice growth.(4)A solution experiment was conducted to study the effects of potassium on rice growth character, the activity of pectin methylisterase enzyme and acid phosphatase enzyme, the contents of root pectin, hemicellulose 1 and hemicellulose 2 of rice under 250mg·L-1 Fe2+ toxicity. The results showed that the rice growth was inhibited in both Fe-sensitive genotype ofⅡyou838 and Fe-resistant genotype of xieyou9308 after the two cultivars exposed to 250mg·L-1 Fe2+ solution. The activities of pectin methylisterase enzyme and acid phosphatase enzyme were enhanced for both two rice cultivars, the contents of root pectin, HC1 and HC2 were increased under high iron toxicity.Ⅱyou838 always expressed a higher enzyme activity and cell-wall polysaccharide contents than xieyou9308, and under iron toxicity its root cell-wall pectin, HC1 and HC2 contents were increased by a large margin, showing its sensitivity to iron toxicity. The effects of iron toxicity were more significant on the relative root length, the activity of root pectin methylisterase enzyme, the contents of HC1 and HC2 of both two genotypes with the extension of processing time, but the acid phosphatese enzyme activity and pectin content did not change significantly. Root length was an important indicator for iron toxicity, and had important relationship with the cell-wall polysaccharide content; High content iron toxicity lead to cell-wall polysaccharide pectin accumulation and high PME activity, increased the number of free carboxyl groups; The skim membrane increased seriously when the acid phosphatase activity increased, then the membrane structure and function were destructed seriously. Different potassium concentration decreased the activity of enzyme and the content of cell-wall polysaccharide to some extent. When the exogenous potassium concentration was 200 mg·L-1, the relative root length, acid phosphatese enzyme activity, HC1 content of both two cultivars and HC2 content ofⅡyou838 were relieved close to the control group value; When exogenous potassium concentration was 400 mg·L-root cell-wall pectin content and pectin methylisterase enzyme activity of both two genotypes and HC2 content of xieyou9308 were relieved close to the control group value. With the increase of exogenous potassium, the high iron toxicity on both two genotypes of rice was relieved to some extent. Exogenous potassium decreased the activity of enzyme and the contents of cell-wall polysaccharide significantly, While the concentration of exogenous potassium was higher than 200 mg·L-1, the potassium would also make another form of toxicity to rice, the relative root length began to decrease, and the acid phosphatese enzyme activity, HC1 and HC2 contents were enhanced again, which suggested that exogenous K+ can alleviate iron toxicity of rice to some extent, but just a limited capacity not complete. Our study suggested that hign concentration of iron tended to modify the metabolism of cell-wall polysaccharides and then made cell-wall more thick and rigid, inhibited the growth of rice roots and the elongation of root cells, thereby improved tolerance of rice to iron toxicity. (5)To examine the effects of potassium (K) on the organic acid metabolism of rice plants experiencing iron (Fe) stress, we conducted a hydroponic study to measure the physiological and biochemical characteristics associated with organic acid metabolism including plant morphology, enzyme activities (citrate synthase, aconitase, phosphoenolpyruvate carboxylase, and malate dehydragenase), and organic acid contents (malic acid and citric acid). We found that Fe stress in both of the rice varieties studied in this experiment—Fe-sensitiveⅡyou838 and Fe-resistant Xieyou9308—caused an increase in organic acid contents and a decrease in the following growth indices:plant height, root length, biomass, and enzyme activities. Except for the citric acid contents, the other observed changes were statistically significant. When K was added to the hydroponic solution containing Fe, however, the negative effects of Fe stress were alleviated but not completely mitigated. TheⅡyou838 variety showed larger changes in plant morphology, enzyme activities, and organic acid contents than Xieyou9308, thus confirming its Fe-sensitive characteristics. The findings regarding the ability of K to decrease Fe toxicity symptoms may be used to prevent Fe damage in crops, especially in Fe-sensitive strains, and is of economic and agricultural interests. |
PDF Full Text Request