Observations on the development of the silica cells of the leaf sheath of wheat (Triticum aestivum)

Abstract

The formation of silica cells in the sheath epidermis of wheat is described. These cells are of two types, unpaired rod-shaped cells and isodiametric cells paired with basal cork cells. When the leaves have expanded fully, the potential silica cells have reached their mature shape, with thin, usually concave outer walls. At this stage, the nucleus and cytoplasm of these cells are suddenly lost, producing apparently empty cells. After this, silica appears to accumulate and precipitate in these empty cells. Very early stages of silica accumulation could not be detected, but later, refractive granular masses of precipitated silica gel can be seen in fixed, dehydrated preparations. In aqueous mounts the accumulating silica appears as a translucent peripheral mass, surrounding vesicular contents. Further silica accumulation produces the mature, glassy silica bodies containing small vesicles which probably represent some remnant of the disintegrated cytoplasm. The young silica cells did not seem to have the low pH levels sometimes suggested as initiating silica precipitation. Enzyme localization tests did not distinguish potential silica cells from their immediate neighbors.