Some ultrastructural and enzymatic effects of water stress in cotton (gossypium hirsutum L.) leaves.

Water stress induced by floating discs cut from cotton leaves (Gossypium hirsutum L. cultivar Stoneville) on a polyethylene glycol solution (water potential, -10 bars) was associated with marked alteration of ultrastructural organization of both chloroplasts and mitochondria. Ultrastructural organization of chloroplasts was sometimes almost completely destroyed; peroxisomes seemed not to be affected; and chloroplast ribosomes disappeared. Also accompanying water stress was a sharp increase in activity of acid phosphatase [orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2], and acid and alkaline lipase [glycerol ester hydrolase EC 3.1.1.3] within chloroplasts. Only acid lipase activity was detected inside mitochondria of stressed discs. These alterations in cell organization and enzymology may account for at least part of the previously reported effects of water stress on the CO(2) compensation point, photochemical reactions, and photorespiration.