INTRACELLULAR PH STABILITY IN THE AQUATIC RESURRECTION PLANT CHAMAEGIGAS-INTREPIDUS IN THE EXTREME ENVIRONMENTAL-CONDITIONS THAT CHARACTERIZE ITS NATURAL HABITAT

Chamaegigas intrepidus Dinter (syn. Lindernia intrepidus (Dinter) Ober m.) is a poikilohydric aquatic plant that lives in rock pools on grani tic outcrops in Central Namibia. The pools are only filled intermitten tly during the summer rains, and the plants can pass through 15-20 reh ydration/dehydration cycles during a single wet season. Rehydrated pla nts also have to cope with substantial diurnal fluctuations in the poo l pH as a result of photosynthetic CO, uptake. We have used in vivo P- 31 NMR spectroscopy to investigate the effect of external pH and dehyd ration (low water potential) on intracellular pH in the roots and subm erged leaves of C. intrepidus. Increasing the external pH from 6 to 10 had no effect on the steady state cytoplasmic and vacuolar pH values of submerged leaves, but caused a slight alkalinization of the root cy toplasm. Similarly dehydration with PEG-600 at either pH 6 or pH 10 ha d no effect on the cytoplasmic pH of the leaves, but it did cause a sm all alkalinization of the leaf vacuoles at pH 10. These results imply an unusually effective regulation of intracellular pH, consistent with the adaptation of C. intrepidus to the extreme environmental conditio ns of its habitat. The NMR analysis also showed that dehydration had n o effect on the inorganic phosphate and phosphocholine pools, and this was taken to indicate that the cell membranes were well protected fro m the effects of the low water potential.