Plant growth under low K + availability or salt stress requires tight control of K + and Na + uptake, long-distance transport, and accumulation. The family of membrane transporters named HKT (for High-Affinity K + Transporters), permeable either to K + and Na + or to Na + only, is thought to play major roles in these functions. Whereas Arabidopsis (Arabidopsis thaliana) possesses a single HKT transporter, involved in Na + transport in vascular tissues, a larger number of HKT transporters are present in rice (Oryza sativa) as well as in other monocots. Here, we report on the expression patterns and functional properties of three rice HKT transporters, OsHKT1;1, OsHKT1;3, and OsHKT2;1. In situ hybridization experiments revealed overlapping but distinctive and complex expression patterns, wider than expected for such a transporter type, including vascular tissues and root periphery but also new locations, such as osmocontractile leaf bulliform cells (involved in leaf folding). Functional analyses in Xenopus laevis oocytes revealed striking diversity. OsHKT1;1 and OsHKT1;3, shown to be permeable to Na + only, are strongly different in terms of affinity for this cation and direction of transport (inward only or reversible). OsHKT2;1 displays diverse permeation modes, Na + -K + symport, Na + uniport, or inhibited states, depending on external Na + and K + concentrations within the physiological concentration range. The whole set of data indicates that HKT transporters fulfill distinctive roles at the whole plant level in rice, each system playing diverse roles in different cell types. Such a large diversity within the HKT transporter family might be central to the regulation of K + and Na + accumulation in monocots.Although it is not clear what levels of Na + are toxic in the plant cell cytosol and actually unacceptable in vivo, the hypothesis that this cation must be excluded from the cytoplasm is widely accepted. The most abundant inorganic cation in the cytosol is K + , in plant as in animal cells. This cation has probably been selected during evolution because it is less chaotropic than Na + (i.e. more compatible with protein structure even at high concentrations; Clarkson and Hanson, 1980). Its selection might also be due to the fact that in primitive cells, which originated in environmental conditions (seawater) where Na + was more abundant than K + , a straightforward process to energize the cell membrane was to accumulate the less abundant cation and to exclude the most abundant one.In the cell, K + plays a role in basic functions, such as regulation of cell membrane polarization, electrical neutralization of anionic groups, and osmoregulation. Concerning the latter function, K + uptake or release is the usual way through which plant cells control their water potential and turgor. Although toxic at high concentrations, Na + can be used as osmoticum and substituted for K and tissue levels have actually been shown to be essential in plant adaptation to salt stress (Greenway and Munns, 1980;Flowers, 1985;Hasegawa...

Salt-tolerant plants grow in a wide variety of saline habitats, from coastal regions, salt marshes and mudflats to inland deserts, salt flats and steppes. Halophytes living in these extreme environments have to deal with frequent changes in salinity level. This can be done by developing adaptive responses including the synthesis of several bioactive molecules. Consequently, several salt marsh plants have traditionally been used for medical, nutritional, and even artisanal purposes. Currently, an increasing interest is granted to these species because of their high content in bioactive compounds (primary and secondary metabolites) such as polyunsaturated fatty acids, carotenoids, vitamins, sterols, essential oils (terpenes), polysaccharides, glycosides, and phenolic compounds. These bioactive substances display potent antioxidant, antimicrobial, anti-inflammatory, and anti-tumoral activities, and therefore represent key-compounds in preventing various diseases (e.g. cancer, chronic inflammation, atherosclerosis and cardiovascular disorder) and ageing processes. The ongoing research will lead to the utilisation of halophytes as a new source of healthy products as functional foods, nutraceuticals or active principles in several industries. This contribution focuses on the ethnopharmacological uses of halophytes in traditional medicine and reviews recent investigations on their biological activities and nutraceuticals. The work is distributed according to the different families of nutraceuticals (lipids, vitamins, proteins, glycosides, phenolic compounds, etc.) discussing the analytical techniques employed for their determination. Information about the claimed health promoting effects of the different families of nutraceuticals is also provided together with data on their application.

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