Evaluation of biochemical indicators of Fe and Mn nutrition for soybean plants. II. Superoxide dismutases, chlorophyll contents and photosystem II activity

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Abstract
The evaluation of nutritional status of plants through the use of biological indicators has been found useful when chemical analysis of the leaf nutrient concentrations does not reveal certain nutrient imbalances. In this work, the responses of Superoxide dismutases (SOD) isoenzymes, chlorophylls and photosystem II activity of leaves from soybean plants grown under different Fe and Mn nutrient levels were studied. Soybean plants, cv. Williams, were cultivated under growth chamber conditions in aerated nutrient solutions until the second trifoliate stage. At this time, first trifoliate leaves were sampled for biochemical analysis. Manganese and iron levels brought about modifications in the total SOD activity and in chlorophyll a and b contents. Isozyme Mn‐SOD and photosystem II activities, and the ratios chlorophyll a/b were clearly modified by Mn nutrient levels suggesting the specificity of these biochemical indicators for the appraisal of the Mn nutritional status of soybean plants. Correlation studies between enzyme activities and leaf nutrient concentrations or leaf growth were performed, and the validity of using biochemical markers for the evaluation of the Mn nutrient status is discussed in relation to other reports described for different plants species.