ABSCISIC-ACID (ABA) RELATIONS IN THE AQUATIC RESURRECTION PLANT CHAMAEGIGAS-INTREPIDUS UNDER NATURALLY FLUCTUATING ENVIRONMENTAL-CONDITIONS

The resurrection plant Chamaegigas intrepidus Dinter (Scrophulariaceae ) grows as a typical hydrophyte in shallow rock pools on granitic outc rops in arid areas of Namibia. During the rainy season, the rock pools are temporarily filled with water. When the pools dry up, C. intrepid us desiccates and survives in an air-dry condition for at least 8 mont hs. After rewatering, the plants regain their metabolic activity in un der 2 h. The desiccation of the vegetative organs is accompanied by a dramatic accumulation of abscisic acid (ABA). Beyond this, desiccation of roots is accompanied by the occurrence of specific dehydration-rel ated proteins, whereas the leaves of C. intrepidus show high levels of dehydrins in the dehydrated as well as in the hydrated state. Investi gations in Namibia showed drastic diurnal fluctuations in the pH of th e rock pools. The pH value increased from slightly acidic or neutral c onditions during the morning to alkaline conditions (up to pH 12) duri ng late afternoon. Since compartmental ABA distribution depends strong ly on pH gradients across membranes, the external pH would be expected to affect the ABA relations in the plant. According to the anion trap concept, an alkaline pH in the surrounding medium should cause a rele ase of ABA from the roots, although C. intrepidus appeared to release less ABA than the terrestrial rosettes of Valerianella locusta.