Plants have adapted to life in saline environments in a myriad of ways, some more broadly successful than others. These adaptations involve the integration of all activities at levels ranging from genes to physiology to life cycles. With the availability of new ‘-omic’ resources, the tools of systems biology and perhaps forgotten tools of physiology and biophysics, we may now be poised to decipher the complexities of the integration of organismal activities as never before.

Proteome studies can provide important insights into plant responses to salinity stress and thier mechanism of tolerance. In this review, recent knowledge of proteome response to salinity is summarised with a focus on comparative studies revealing similarities and differences between related plant species with contrasting salinity tolerance – glycophytes and halophytes. The contribution of proteomic studies to a complex picture of plant salinity response is discussed.

Proteomic approaches allow the analysis of salt-induced changes in protein patterns at any given moment in time. Here we summarise such data from halophytes and closely related plants differing in salt resistance and physiology respectively. Results indicate that, in general, keeping structural integrity in the presence of salt is of the highest priority, but plants differ in their strategies of how to tune metabolism and reach a new equilibrium subsequent to exposure to salt.

Soil salinity is one of the most important environmental factors that reduce crop yields in agriculture and limit plant distribution in nature. In this review, we discuss evidence supporting a functional role of soluble carbohydrates in salt tolerance mechanisms, although their ecological relevance remains largely unknown. We propose that more effort should be invested in field studies of salt-tolerant plants, as a complement to more common experimental approaches based on the analysis of salt-sensitive models under artificial laboratory conditions.

The halophyte Thellungiella salsuginea has been used as a model for studying plant salt tolerance. In this review, T. salsuginea and the glycophyte Arabidopsis thaliana are compared with regards to their biochemical, physiological and molecular responses to salinity. Recent developments are presented for improvement of salinity tolerance in glycophytic plants using genes from halophytes.

Halophytes deploy a range of responses to salinity that confers on them more tolerance to salt than seen in glycophytes. Induction of an antioxidant defence system is one of these responses, which protects plants against reactive oxygen species and regulates their level for stress signalling. An understanding of these mechanisms in halophytes may provide information for increasing stress tolerance of crop plants.

Surprisingly little is known about the effects of salt stress upon seeds given their pivotal role in plant reproduction and dispersal. This review provides information on redox control in seeds, detoxification mechanisms and tolerance in relation to seed metabolism and performance. Implications of redox control in seeds on the physiological, biochemical and molecular level are discussed; the review concludes with a perspective on future research in relation to salt stress and seed biology.

To investigate the role of compartmentation and secretion rate in the avoidance of Na⁺ toxicity in the halophyte Aeluropus lagopoides, we report that Na⁺ was successfully compartmentalised at salinities up to 373 mM NaCl by upregulating the gene expression of membrane linked transport proteins V-NHX and PM-NHX. At higher salinity a reduction in the expression of V-NHX and PM-NHX in leaves without any change in the rate of salt secretion is a possible cause of toxicity of NaCl.

Salinity and waterlogging (oxygen deficiency around the roots) are plant stresses that often occur together on saltland. This combination of stresses impacts on plant growth by decreasing the concentration of potassium and increasing the concentrations of sodium and chloride in shoots. The synchronicity between these changes in ion concentrations has important implications for our understanding of the mechanisms of ion regulation in plants.

Saline lands are often affected by a wide range of constraints rather than salinity alone. Often, only halophytes are able to survive in these conditions by amplifying the mechanisms of salt tolerance, mainly proline accumulation, K : Na homeostasis and antioxidant defence. Cross-tolerance, anticipation and memory are also involved in the tolerance of halophytes to combined stresses.

Some stem-succulent halophytes inhabit areas of very high salinity, such as inland salt lakes. Tolerance and physiological responses to extreme salinity (2000 mM NaCl) were evaluated for two Tecticornia species; both were highly tolerant. Growth patterns of halophytic species on the margins of salt lakes are likely influenced both by soil salinity and water availability (periodic floods and water deficits).

Heavy metal pollution is a major environmental problem that is rapidly gaining importance due to its impact on human health through the food chain. Phytoremediation is considered an effective, low cost, preferred cleanup option for moderately contaminated areas. In this context, the available literature on heavy metal bioaccumulation by Spartina sp. was compiled and compared.

In contaminated estuaries, halophytes can be subjected to high levels of metal contamination that inevitably affect their metabolism, namely, their anti-oxidant systems. Considering the more abundant halophyte species in Tagus estuary salt marshes, Spartina maritima proved to be potentially efficient biomonitor species. Also its enzymatic anti-oxidant system revealed a substantial increase of activity under contaminated conditions. Considering this, Spartina maritima and its anti-oxidant enzymatic defences arise as potential biomonitor species and biomarker for heavy metal contamination studies.

In this work the metal concentration in three plant species (Scirpus maritimus, Spartina maritima and Zostera noltii) of the Mondego Estuary in Portugal was analysed. From the concentration of metals in the aboveground and belowground organs and in the sediment it was possible to conclude that the Mondego Estuary, although having a low level of contaminants, could be a source of metals for nearby aquatic systems.

A broad variety of secondary compounds of economic interest is present in halophytes, with potential uses in various fields such as pharmaceuticals and nutraceuticals. Salt-tolerant plants are potential sources of valuable products that are largely unexploited. Our overview identifies open research questions and gives suggestions for future applications of secondary compounds of halophytes.

In an attempt to develop Aster tripolium L. as a halophyte vegetable for saline irrigation on dune sand, it was observed that sequential harvesting resulted in leaf chlorosis, yield reduction, reduced nitrate reductase activity (NRA) and enhanced nitrate concentration. Application of suitable Fe-chelates restored leaf colour, NRA and nitrate content indicating that NRA can be an indicator for iron deficiency in A. tripolium.