Assessment of the relevance of osmolyte biosynthesis for salt tolerance of halophytes under natural conditions

Abstract

[EN] The study of the mechanisms of response to salt stress is one of the most active research topics in plant biology, not only due to its unquestionable academic interest but also because of its economic implications, since high soil salinity is together with drought one of the major causes of reduction of crop yields worldwide. These studies have shown a series of basic mechanisms of response to abiotic stress, which include, among others, the synthesis and accumulation in the cytoplasm of `compatible solutes or osmolytes', used for osmotic balance and as `osmoprotectants'. Today, there is overwhelming evidence that osmolyte, and especially proline accumulation, represents a general and reliable biochemical marker for salt stress. However, and despite the large amount of data available regarding this response mechanism, our knowledge of the importance of osmolyte biosynthesis for salt tolerance of any given species under natural conditions, is still very limited. This is partly due, in our opinion, to the approaches commonly used in these studies, which rely on experiments performed with salt-sensitive plants (glycophytes) instead of halophytes, plants naturally adapted to high soil salinities under artificial laboratory or greenhouse conditions. In this review, we describe and comment on data supporting these ideas, and point out that extreme caution should be taken when assessing the biological relevance of laboratory results.