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 outcrops in arid areas of Namibia. During the rainy season, the rock pools are temporarily filled with water. When the pools dry up, C. intrepidus desiccates and survives in an air-dry condition for at least 8 months. After rewatering, the plants regain their metabolic activity in under 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-related proteins, whereas the leaves of C. intrepidus show high levels of dehydrins in the dehydrated as well as in the hydrated state. Investigations in Namibia showed drastic diurnal fluctuations in the pH of the rock pools. The pH value increased from slightly acidic or neutral conditions during the morning to alkaline conditions (up to pH 12) during late afternoon. Since compartmental ABA distribution depends strongly 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 release of ABA from the roots, although C. intrepidus appeared to release less ABA than the terrestrial rosettes of Valerianella locusta.