Borya nitida Labill.—An Australian Species in the Liliaceae With Desiccation-tolerant Leaves

Abstract

Borya nitida, a perennial tufted herb, grows in south Western Australia as a pioneer plant codominant with lichens on exposed rock outcrops, and on bare sands with low water-holding capacity and rapid drainage. The mature leaves of the plant are capable of reviving after desiccation; they develop drought tolerances of 0% relative humidity (RH) under field conditions. The rate of drying is critically important for the development of desiccation tolerance. Drought-avoidance mechanisms (possibly related to the xeromorphic features of the plant) slow the rate of dehydration sufficiently for the development of full drought tolerance which requires completion of a time-dependent tolerance-endowing process in the range of water potential around 96% RH (90-98%), as well as avoidance of a slower time-dependent injurious process at water potentials of 75% RH and above. Non-senescent leaves that fulfil both requirements remain viable at water potentials below 50% RH for years. Dry viable leaves are yellow, owing to the loss of chlorophyll during the former process. Induction of drought tolerance at moderate water stress has been reported in other species, but Borya is remarkable for the extreme rapidity of the process and the degree of tolerance developed.