Ion transport in salt glands and bladders in halophyte species

Salt secretion via salt glands is found in more than 50 species in 14 angiosperm families and represents a highly efficient way of dealing with excessive salt load in photosynthetically active mesophyll tissues. Equally efficient is the storage of cytotoxic NaCl in external structures such as epidermal bladder cells (salt bladders). In this chapter, we briefly summarize the current knowledge of physiological and molecular basis of salt sequestration and secretion through bladders and glands. First, the anatomical structure of three major types of secretory organs-salt bladders, salt glands, and secretory microhairs-is described. Then, the mechanistic basis of ion transport and metabolism in secretory structures are examined. The major focus is on five model species widely used in halophyte research: salt bladder-bearing Chenopodium quinoa and Mesembryanthemum crystallinum; Limonium bicolor and mangrove species possessing salt glands; and Oriza coarctata (wild rice) bearing secretory microhairs.