XVI International Botanical Congess

The trivial names of several of the cyclic polyols already mirror their wide distribution in the plant kingdom including gymnosperms (pinitol, sequoyitol), broad-leaved species (quercitol, quebrachitol) and members of the Fabales (ononitol). In temperate climate trees cyclitols accumulated in needles, buds and phloem tissue during the cold season. Their function as antifreeze substances was tested by in vitro experiments with thylakoid membranes. In several cultivated plants (e.g. soybean, chickpea) and a number of prominent tree species (e.g. Acacias) pinitol increased markedly under drought conditions. Besides a function as organic osmolyte the ameliorating effect in this stress situation might lie in the hydroxyl radical scavenging capacity of pinitol and other cyclitols. In a number of herbaceous halophytes as well as in all mangrove species belonging to the Rhizophoraceae cyclic polyols accumulated with increasing salt stress. Although information on the subcellular compartmentation is scarce it can be assumed that cyclitols are mainly localized in the cytoplasm to maintain intracellular osmotic adjustment. Projects are followed up to improve drought and salt resistance of crop plants by introducing the genes for cyclitol synthesis.