Plants and water

Abstract

The major thrusts of water-related plant physiology are concerned with the strong interactions with plant production. These emphasise the reciprocal exchange of water and carbon dioxide at the wetted mesophyll cell wall and the exchange control exerted by stomatal behaviour. Metabolic economy of water use is also well studied, with the C—4 metabolic pathway for photosynthesis now being interpreted as a familar feature of tropical and arid-zone species. The ‘crassulacean acid metabolism’ (CAM) pathway is an even more extreme metabolic device for conservation of water. It permits photosynthetic energy capture during the day to be separated from gas exchange at night. Obligate water loss from open stomata is thus minimised, and the stored water of succulents conserved. This system is known to operate not only in the Crassulaceae, but also in succulent members of the Cactaceae, Aizoaceae, Asclepiadaceae, Bromeliaceae, Orchidaceae and Liliaceae.