Entry and distribution of aluminum in Zea mays

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.

Aluminium uptake sites in the primary root of Zea mays L.

“…The results of this investigation differ principally from previous research on Zea (Rasmussen, 1968;Kalovoulos & Misopolinos, 1983) and Triticum (Wright & Donahue, 1953), with respect to the identification of the chronological pattern of Al uptake by the cell populations of the primary root. This information is a useful basis for speculating on the probable location of the site of AI injury in the root and, indeed, on the mechanism of AI toxicity.…”

“…While AI concentration may be relevant, this investigation has clearly shown that with prolonged exposure, AI can enter the root through the epidermis and, in this respect, results differ from the findings of Rasmussen (1968). Furthermore, morphological disturbances of the root apex leading to fracture of the epidermis as noted in Experiment I and also in Triticum (Hecht-Buchholz, 1983) are not a pre-requisite for the entry of AI into the cells of the root apex.…”

“…Mobility of Al in the root cells is also low and penetration does not extend beyond the outer cortical layers. These observations may explain the association between Al accumulation sites and the outer surface of the root (Rasmussen, 1968;McCormick & Borden, 1974). These factors also suggest that the presence of AI in these tissues does not represent a primary site of Al toxicity.…”

“…Published research on the sites of Al uptake is infrequent (McLean & Gilbert, 1927;Wright & Donahue, 1953;Rasmussen, 1968;Kalovoulos & Misopolinos, 1983), and the function of the root epidermis in controlling entry of AI into the root is controversial (Wright & Donahue, 1953;Rasmussen, 1968). Nevertheless, the identification of the sites of Al uptake and accumulation in the root is fundamental to the elucidation of the mechanism of AI toxicity.…”

“…Earlier researchers (Wright & Donahue, 1953;Rasmussen, 1968) have differed with respect to the effectiveness of the epidermis in preventing entry of AI into the root meristem. While AI concentration may be relevant, this investigation has clearly shown that with prolonged exposure, AI can enter the root through the epidermis and, in this respect, results differ from the findings of Rasmussen (1968).…”