Drought and soil salinity are at present the major factors responsible for the global reduction of crop yields, and the problem will become more severe in the coming decades because of climate change effects. The most promising strategy to achieve the increased agricultural production that will be required to meet food demands worldwide will be based on the enhancement of crop stress tolerance, by both, traditional breeding and genetic engineering. This, in turn, requires a deep understanding of the mechanisms of tolerance which, although based on a conserved set of basic responses, vary widely among plant species. Therefore, the use of different plant models to investigate these mechanisms appears to be a sensible approach. The genus Portulaca could be a suitable model to carry out these studies, as some of its taxa have been described as tolerant to drought and/or salinity. Information on relevant mechanisms of tolerance to salt and water stress can be obtained by correlating the activation of specific defence pathways with the relative stress resistance of the investigated species. Also, species of the genus could be economically attractive as ‘new’ crops for ‘saline’ and ‘arid’, sustainable agriculture, as medicinal plants, highly nutritious vegetable crops and ornamentals.
Genetic improvement of crop drought tolerance has become an urgent need for increasing agricultural yields and food production, to feed a growing human population in the context of global climate change. To get insights into the most relevant mechanisms underlying drought resistance in beans, we have analysed the responses to water deficit of three Phaseolus vulgaris (common bean) and one P. coccineus (runner bean) cultivars, focusing on the accumulation of specific osmolytes, a conserved response to abiotic stress in plants. Changes in osmolyte levels were correlated with the relative tolerance to water stress of the studied cultivars. Drought tolerance in Phaseolus largely depends on the accumulation of myo-inositol; glycine betaine may also contribute to tolerance in P. coccineus (but not in P. vulgaris). Proline, another common osmolyte, is a reliable marker of the level of stress affecting bean plants, but is not directly involved in tolerance mechanisms, as its drought-dependent accumulation is lowest in the most tolerant cultivar. We suggest that, by measuring the levels of proline and myo-inositol in water-stressed plants, a large number of cultivars could be easily and rapidly screened to select promising candidates to be used in breeding programmes for improving drought tolerance in beans.