The atmospheric epiphyte Tillandsia ionantha is capable of surviving drought stress for 6 months or more without any exogenous water supply via an as of yet to be determined mechanism. When plants were soaked in water for 3 h, leaves absorbed a remarkably large amount of water (30-40% on the basis of fresh weight), exhibiting a bimodal absorption pattern. Radiolabeled water was taken up by the leaves by capillary action of the epidermal trichomes within 1 min (phase 1) and then transported intracellularly to leaf tissues over 3 h (phase 2). The removal of epidermal trichome wings from leaves as well as rinsing leaves with water significantly lowered the extracellular accumulation of water on leaf surfaces. The intracellular transport of water was inhibited by mercuric chloride, implicating the involvement of a water channel aquaporin in second-phase water absorption. Four cDNA clones (TiPIP1a, TiPIP1b, TiPIP1c, and TiPIP2a) homologous to PIP family aquaporins were isolated from the leaves, and RT-PCR showed that soaking plants in water stimulated the expression of TiPIP2a mRNA, suggesting the reinforcement in ability to rapidly absorb a large amount of water. The expression of TiPIP2a complementary RNA in Xenopus oocytes enhanced permeability, and treatment with inhibitors suggested that the water channel activity of TiPIP2a protein was regulated by phosphorylation. Thus, the high water uptake capability of T. ionantha leaves surviving drought is attributable to a bimodal trichome- and aquaporin-aided water uptake system based on rapid physical collection of water and subsequent, sustained chemical absorption.

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1984. AlPase activity associated with vaeuoles and tonoplast vesicles isolated from the CAM plant. Kalanchoe daivremontiana. -Phvsiol. Plant. 6tl: 21-25.Inlaet vacuoles were isolated from leaves of the CAM plant, Kalanchoe daigrcmontiana Hamet et Perr. Both ATPase and acid phosphatase activities were found in the vacuoles. Purified lonoplast vesicles showed only ATPase activity with a pH optimum of 8.0. This activity was Mg-*-depcndcnt and KCl or NaCl caused a further stimulation. N,N'-dieyelolicxyIcarbodiimide, dietbylstilbesirol and quercetin inhibited the A TPase almost completely at concentrations well below I mM. NaVOj, l-ethyl-3(3diniethylaminopropyi)earb(idiimidc, oligomyein and NaNj had little or no effect. Carbonyl cyanide w-ehlorophenylliydrazone stimulated ihe ATPase about 40% at 5 X 10^ A/. Ttie K^ for AlP was found to be 0.55 niA/. These results indicate that the ATPa.se found in the tonoplast membrane of Kalanchoe dciigremoniianti is qualitatively similar to that of other plant species.Additional key words -Aeid phosphatase, protoplast.

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