The fine structure of fern root cells showing apospory

Abstract

Isolated roots of the fern, Pteridium aquilinum were grown on growth-supporting medium (White's plus 5% coconut milk) and on apospory-promoting medium (Knudson's inorganic salts with or without 10 −7 M kinetin). In the latter medium growth of the root ceased and diploid gametophytes were formed in 8 to 10 weeks from outer cells of the root. These became green, bulged outward, and divided to form first a filament and then a two-dimensional plate. With kinetin more root cells became green and more gametophytes were formed per root. The fine structure of cells in roots growing normally and in roots in the apospory-inducing medium was compared, concentrating on the region several millimeters behind the apex where most gametophytes formed. No differences among the normal root cells were observed which would explain why only a few cells were capable of gametophyte formation. Most of the root cells degenerated on aposporypromoting medium. Some cells, however, remained viable and showed increases in the internal complexity and size of the plastids, and in the size of the mitochondria. Ribosomes and endoplasmic reticulum became more conspicuous. It is inferred that these cells were regaining the capacity to divide and were the source of the gametophytes.