The Fine Structure of Dehydrated and Reviving Leaves of Borya nitida Labill.—A Desiccation-tolerant Plant

Abstract

The dry viable leaves of Borya nitida show degeneration of the protoplasm: bounding membranes of chloroplasts and mitochondria are vague and the former display extensive gaps, starch and grana are lost, while thylakoids and cristae are considerably reduced in number. The nucleus and nucleoli retain their integrity, as does also the tonoplast, even though the vacuole is fragmented. It appears that stress-induced degeneration of organelles is similar to that in desiccation-sensitive plants but occurs to a controlled level, at which a sufficient residual structure is still present to initiate the reconstruction of the cell fine structure on rehydration.

During the recovery of the cell on rehydration, the degraded plastids appear to repair the bounding membranes and produce new thylakoids which, at the start of regreening, begin to form grana and starch grains. Mitochondria are fewer but better structured in the regreened leaf.

It is suggested that the induction of desiccation tolerance in the initial stages of drying may be associated inter alia with the production of additional mitochondria and of additional sugar by starch hydrolysis; both processes would tend to ensure a supply of respiratory ATP to support reconstruction of the metabolic system during rehydration.