Introduction to the Special Issue: Halophytes in a changing world.

Climate change will bring about rising sea levels and increasing drought, both of which will contribute to increasing salinization in many regions of the world. There will be consequent effects on our crops, which cannot withstand significant salinization. This Special Issue looks at the roles that can be played by halophytes, extremophiles that do tolerate salinities toxic to most plants. In an ecological context, papers deal with the conservation of a rare species, the effects of rising concentrations of CO2 and flooding on coastal vegetation, and the consequences of tree planting in inland plains for salinization. Physiological studies deal with the different effects of chlorides and sulfates on the growth of halophytes, the ability of some parasitic plants to develop succulence when growing on halophytic hosts and the interesting finding that halophytes growing in their natural habitat do not show signs of oxidative stress. Nevertheless, spraying with ascorbic acid can enhance ascorbic acid-dependent antioxidant enzymes and growth in a species of Limonium. Enzymes preventing oxidative stress are expressed constitutively as is the case with the vacuolar H-ATPase, a key enzyme in ion compartmentation. A comparison of salt-excreting and non-excreting grasses showed the former to have higher shoot to root Na(+) ratios than the latter. A particularly tolerant turf grass is described, as is the significance of its ability to secrete ions. A study of 38 species showed the importance of the interaction of a low osmotic potential and cell wall properties in maintaining growth. From an applied point of view, the importance of identifying genotypes and selecting those best suited for the product required, optimizing the conditions necessary for germination and maximizing yield are described. The consequence of selection for agronomic traits on salt tolerance is evaluated, as is the use of halophytes as green manures. Halophytes are remarkable plants: they are rare in relation to the total number of flowering plants and they tolerate salinities that most species cannot. It is clear from the papers published in this Special Issue that research into halophytes has a distinct place in aiding our understanding of salt tolerance in plants, an understanding that is likely to be of importance as climate change and population growth combine to challenge our ability to feed the human population of the world.