Entry and distribution of aluminum in Zea mays

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Abstract
The electron microprobe X-ray analyzer (microprobe) has been used to determine the mode of entry of aluminum (Al) and its distribution and localization in the corn plant. Microprobe analysis is a non-destructive method allowing for multiple element analysis in the same tissues, cells or cell organelles. Al was found to be precipitated on the surface of the epidermal cells of the root with no penetration into the cortex as long as the root surface remained intact. The root cap was freely permeable and contained the highest concentration of Al. The epidermal layer behind the root cap prevented movement into the cortex and conductive tissue. The penetration of a lateral root through the endodermis, cortex and epidermis provided a channel of entry for Al into the cortex and conducting tissues of both the lateral and main root. Essentially no Al was found in the transition zone and only small quantities were present in the above-ground plant parts. The localization of phosphorus was exactly the same as that of Al. This suggested that there was a precipitation of P by Al. A similar analysis for calcium and phosphorus on control plants did not reveal such a precipitation. The method of sample preparation was critical in retaining and localizing the elements in question and is discussed in that light.