Review article. Molecular biology of salt tolerance in the context of whole-plant physiology

Abstract

nical ability for plant transformation increases daily, the practicality of using transgenic plants in complex The halobacteria are the only organisms that are tolerbreeding programmes seems rarely to be given enough ant of salinity at the molecular level. All other bacteria, thought. If intervention at the molecular level is to lead all fungi, all plants, and all animals avoid the need for to salt-tolerant crop plants then it will be essential to salt tolerance for most of their macromolecules by view this in the contexts of whole plants and of plant maintaining defined and conserved conditions in the breeding. Recent indications that a relatively small cytoplasm. These conditions favour potassium over number of quantitative trait loci (QTL) may govern comsodium, the limitation of total inorganic ion activity, plex physiological characters offer the most hope for and the supplementation of this where necessary with the future. organic solutes which are metabolically neutral osmolytes that may also be osmoprotectant. The salt toler-Key words: Salt tolerance, molecular biology, breeding ance of an organism depends upon the range of programmes, QTL, whole-plant physiology. external salinity over which it is able to sustain these conditions in the cytoplasm. There is substantial and increasing knowledge of the molecular biology and

Responses of freshwater biota to rising salinity levels and implications for saline water management: a review

“…Salt tolerance in plants and animals depends on their ability to maintain defined conditions in the cytoplasm of their cells over a range of external salt concentrations (Greenway and Osmond 1972;Yeo 1998). Elevated salinity can result in reduced growth or death in plants, as a result of either the toxic effect of excess ions in the cells and/or water deficiency caused by the difficulty of extracting water from the saline external medium (Greenway and Munns 1980).…”

“…This compartmentalisation of ions also prevents osmotic withdrawal of water from the cell, low cell turgor and consequent water deficiency. Plants may avoid excess ion concentration by controlling the uptake of ions and their transport to the shoot (Greenway and Munns 1980;Yeo 1998).…”

“…In plants, salt-tolerant and salt-intolerant species differ in the degree to which ion concentration can be regulated within cellular compartments to maintain defined conditions in the cytoplasm, rather than in the mechanisms available for regulation (Greenway and Osmond 1972;Yeo 1998). An exception are those species that possess salt-excreting glands.…”

Changes in free polyamine concentration induced by salt stress in seedlings of different species

“…Salinity results in a reduction of K + and Ca 2+ concentration and an increased concentration of Na + and Cl -, which has ionic effects. The osmotic adjustment in plants exposed to saline stress can occur by accumulation of high concentrations of inorganic ions or low molecular weight organic solutes (Yeo 1998). Both mechanisms play important roles under saline conditions, but their relative contribution varies between species, varieties and even between different compartments within the same plant (Ashraf and Harris 2004).…”

Aging and some physiological and biochemical characteristics of two Aelorupus species

“…According to the results of this study, although sodium ion content in A. littoralis was more stable in different sections when compared with A. lagopoides species, the ratio of sodium to potassium ion in A. littoralis showed severe reduction with age compared with A. lagopoides. According to Yeo (1998), ratio of sodium to potassium ion is considered as a key factor in improving performance of plants under drought stress. Increasing NaCl concentration and salinity occurrence results in membrane depolarization and replacement of sodium ions instead of potassium ions which ultimately lead to potassium deficiency in the plant (Cramer et al, 1991).…”