Electron-probe microanalysis of silicon in the adventitious roots and terminal internode of the culm of Zea mays

The adventitious roots and terminal internode of the culm of mature, field-grown specimens of five cultivars of Zea mays L. were investigated with relation to silicon, using electron-probe microanalysis. No silicon was detected above the background level within the endodermis or any other tissues within the adventitious roots. In contrast, however, in the terminal internode silicon was present in the outermost layers of cells, the highest levels being detected in the outer epidermal wall. It was also present in the internal epidermal cell wall, as well as in the walls of underlying tissues of the outer region of the culm, in the sclerenchyma, and at a low level in the parenchyma forming the ground tissue. Thus, the culms displayed a decreasing gradient of silicon content, probably in the form of amorphous silica gel, in cell walls, proceeding from the outermost layer, the epidermis, to the centrally located ground parenchyma, a result generally consistent for all five cultivars. The results are discussed in relation to the anatomy of these tissues and their silicification.