The effect of hyper-osmotic salinity on protein pattern and enzyme activities of halophytes

Studies of the convergence of the expression of enzymes and the physiology of salt resistance are rare, and give the general impression of a jigsaw puzzle with many missing pieces. To date, only minor responses of plasma membrane and tonoplast proteins of halophytes have been reported. Mostly, subunits of the catalytic portions of ATPases were found to change. In succulent plants such as Salicornia europea the abundance of V-type ATPase subunits has been correlated with growth performance. This stresses the physiological strategy to sequester incoming salt into vacuoles, which may also benefit osmotic regulation and further promote growth. A considerable amount of information is available on the responses of proteins involved in photosynthesis and detoxification of reactive oxygen species (ROS) under saline conditions. Two aspects deserve special attention: (i) salt responsive multiple spot patterns of individual proteins (due to protein modification, phosphorylation, for instance); and (ii) correlations between salt-mediated protein abundance and plant performance. Relevant observations underline that there exists a tightly knit metabolic network underlying physiological observations. Although the exact functioning of control and signalling sequences remains elusive, another aspect becomes very obvious from the publications analysed: stress responses of halophytes are multi-variant and include not only an increase in abundance of enzymes, but also of chaperones and proteins controlling organisation of the cytoplasm.