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.

Analyzing the intracellular contents and enzymatic activities of single cells is important for studying the physiological and pathological activities at the cellular level. For this purpose, we developed a simple single-cell lysis method by using a dense array of microwells of 10-30-pL volume fabricated by poly(dimethylsiloxane) (PDMS) and a commercially available cell lysis reagent. To demonstrate the performance of this single-cell lysis method, we carried out two different assays at the single-cell level: detection of proteins by antibody conjugated microbeads and measurement of protease activity by fluorescent substrates. The results indicated that this method readily enabled us to monitor protein levels and enzymatic activities in a single cell. Because this method required only an array of PDMS microwells and a fluorescence microscope, the simplicity of this platform opens a way to explore the biochemical characteristics of single cells even by those who are not familiar with microfluidic technology.