Semipermeable Layer in Seeds

Abstract

Semipermeability may be defined as the ability of seed coverings to allow water uptake and gas exchange, while solute diffusion is restricted or prevented. The presence and location of a semipermeable layer was studied in seed coats of cabbage, leek, onion, tomato, and pepper. Morphological studies did not reveal a semipermeable layer in cabbage seed coats, and all subsequent research was performed on seeds of the other four species. Electron microscopy studies revealed that the semipermeable layer is located at the innermost layer of the seed coat just next to the endosperm. Ultrastructurally, the layer was similar for the four species, typically amorphous, highly compact, but easily distinguished from the remainder of the seed coat and endosperm tissue. The layer was permeable to water while inhibiting uptake of lanthanum salts. Histochemical analysis revealed that the semipermeable layer in seed coats of leek and onion was composed primarily of cutin, while in tomato and pepper the layer was composed of suberin.