THE GENUS CLUSIA AS AN EXAMPLE OF STUDIES ON PLANT RESPONSES TO STRESS IN TROPICAL ENVIRONMENTS

Abstract

The genus Clusia is characterized by a great diversity of life forms and the presence of C₃ , C₃ -­CAM and CAM species. Moreover, for some species ali these patterns of carbon metabolism can be reversibly induced in a single plant, by changing light levels, temperature or water regime. Another physiological characteristic of this genus is the nocturnal accumulation of both malic and citric acids. While the role of day/night changes in malic acid leveis is well established as a mechanism to save water and carbon, the ecophysiological importance of day/night changes in the leveis of citric acid are still unclear. It was proposed that for low light plants, which show no day/night changes in malic acid levels, the nocturnal accumulation of citric acid functions as an energy and carbon saving mechanism. In plants exposed to full sunlight, the breakdown of citrate and malate in the presence of light increases the internal CO₂ levels and may prevent photoinhibition especially under drought conditions, when stomatal opening is substantially reduced. This metabolic flexibility allows these plants to rapidly respond to changes in environmental conditions and may have contributed to the successful invasion by Clusia of a wide range of tropical habitats.