Electron microprobe analysis of zinc and other elements within and around rice root grown in flooded soil

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Abstract
Electron microprobe analysis was applied to the localization of zinc, phosphorus, sulfur, and calcium within and around the rice root grown in the flooded soil of high zinc content (300 ppm). A method for the preparation of the section of the undisturbed soil with the rice root in place is described. Having been dehydrated with ethanol, the sample became free of water soluble ions and, therefore, the insoluble fractions of the elements were mainly localized. The results obtained were as follows: 1) A longitudinal view of the root in the soil was successfully shown as a secondary electron image. 2) The compaction effect of the expanding root on the orientation of the soil particles was not observed. 3) The distribution patterns of the elements in the apical region of the root differed distinctly from those in the basal region. In the latter region, the elements were accumulated in the cells of the epidermis, exodermis, endodermis, and marginal layers of stele. Zinc and phosphorus appeared to be in particles at the same sites in this region. In the apical region, all the elements but calcium were highly and evenly distributed in the central part of the root and scarcely found in marginal layers. Calcium was not significantly detected anywhere in this region. 4) In the basal region, all the elements, whether they were actively absorbed or not, were found to be accumulated at the same sites. 5) Flooding of the soil seemed not to affect the distribution of the elements within the root.