Salinity is a major abiotic stress affecting approximately 7% of the world's total land area resulting in billion dollar losses in crop production around the globe. Recent progress in molecular genetics and plant electrophysiology suggests that the ability of a plant to maintain a high cytosolic K+/Na+ ratio appears to be critical to plant salt tolerance. So far, the major efforts of plant breeders have been aimed at improving this ratio by minimizing Na+ uptake and transport to shoot. In this paper, we discuss an alternative approach, reviewing the molecular and ionic mechanisms contributing to potassium homeostasis in salinized plant tissues and discussing prospects for breeding for salt tolerance by targeting this trait. Major K+ transporters and their functional expression under saline conditions are reviewed and the multiple modes of their control are evaluated, including ameliorative effects of compatible solutes, polyamines and supplemental calcium. Subsequently, the genetic aspects of inheritance of K+ transport 'markers' are discussed in the general context of salt tolerance as a polygenic trait. The molecular identity of 'salt tolerance' genes is analysed, and prospects for future research and breeding are examined.

Potassium transport and plant salt tolerance.

VIVO 273 EFFECTS OF FC IN VITRO: MODEL OF MECHANISM OF ACTION 275 FC AND THE INTERDEPENDENCE OF TRANSPORT PROCESSES 277 METABOLIC CHANGES ASSOCIATED WITH FC-INDUCED H+ EXTRUSION .... 279 MECHANISM OF FC ACTION ON CELL ENLARGEMENT 280 FC AND THE REGULATION OF CELL TURGOR: THE EFFECT ON STOMATAL OPENING 282 FC, CELL MULTIPLICATION, AND THE BREAKING OF SEED DORMANCY ... .. .. 282 FC AS A TOOL TO UNDERSTAND HORMONE ACTION 283 CONCLUSIONS 284

Fusicoccin: A Tool in Plant Physiology

The molecular basis of cytoplasmic male sterility and fertility restoration

Cell wall strength is decreased by both auxin treatment and low pH. In a recently proposed model of the plant cell wall, xyloglucan polymers are hydrogen-bonded to cellulose fibrils, forming the only noncovalent link in the network of polymers which cross-link the cellulose fibers. The decreased strength of the cell wall seen upon lowering the pH might be due to an effect of hydrogen ions on the rate of xyloglucan creep along cellulose fibers. This paper investigates binding of xyloglucan fragments to cellulose. At equilibrium, the per cent of nine- and seven-sugar xyloglucan fragments which are bound to cellulose is sensitive to both temperature and the concentration of nonaqueous solvents. However, neither the per cent of xyloglucan fragments bound to cellulose at equilibrium, nor the rate at which the xyloglucan fragments bind to cellulose, is sensitive to changes in hydrogen ion concentration. These results support the hypothesis that, within the cell wall, xyloglucan chains are connected to cellulose fibers by hydrogen bonds, but these results suggest that this interconnection between xyloglucan and cellulose is unlikely to be the point within the wall which regulates the rate of cell elongation.

The Structure of Plant Cell Walls: I. The Macromolecular Components of the Walls of Suspension-cultured Sycamore Cells with a Detailed Analysis of the Pectic Polysaccharides.

On a global basis, water is a paramount factor in determining the distribution of species, and the responses and adaptations of a species to water stress are critical for its success in any environmental niche. Numerous studies have reported a myriad of changes elicited by water stress. The changes observed are dependent on the species under study and on the severity, duration, and time course of the stress. Before reviewing the changes in detail, we will first present an overview of stress and responses using the stress-strain concept of physics. Next, we will discuss specific water-related parameters for quantifying plant water status and briefly consider how changes in the parameters may affect plant functions. This is followed by the main body which first reviews and analyzes selected responses to water stress and then examines the integrated adaptive behavior of whole plants.

Physiological Responses to Moderate Water Stress

Correlation between cell enlargement in pea internode segments and decrease in the pH of the medium of incubation: I. Effects of fusicoccin, natural and synthetic auxins and mannitol

Evidence for the coupling of proton extrusion to K+ uptake in pea internode segments treated in fusicoccin or auxin

Transmembrane potential increase induced by auxin, benzyladenine and fusicoccin. Correlation with proton extrusion and cell enlargement

Brassinolide, a plant hormone newly isolated from pollen, promotes growth of the stem of a number of plant species. Similar effects are induced by a brassinosteroid (BR), the synthetic 24-epibrassinolide. In this paper the effects of BR on acid secretion and transmembrane electrical potential difference in Azuki bean (Vigna angularis, Ohwi and Ohashi cv. Takara) epicotyls were determined in short term experiments and compared with the effects on growth. At concentrations between 10-7 to 10-5M, BR stimulates, similarly to indole-3-acetic acid (IAA), growth and H+ extrusion and hyperpolarizes the transmembrane electric potential (PD). These effects of BR, as well as those of IAA, are suppressed by inhibitors of RNA and protein synthesis. All these effects of BR and IAA appear roughly additive, even when both hormones are present at their optimal concentrations. The data are interpreted as showing that the action of BR on growth is at least in part mediated by its capability to activate electrogenic proton extrusion. The additivity of the effects of BR and IAA suggests that the primary mechanism of action of the two hormones is different.

Effects of a brassinosteroid on growth and electrogenic proton extrusion in Azuki bean epicotyls

Correlation between proton extrusion and stimulation of cell enlargement effects of fusicoccin and of cytokinins on leaf fragments and isolated cotyledons

P. Lado

Papers

Correlation between cell enlargement in pea internode segments and decrease in the pH of the medium of incubation: I. Effects of fusicoccin, natural and synthetic auxins and mannitol

Evidence for the coupling of proton extrusion to K+ uptake in pea internode segments treated in fusicoccin or auxin

Transmembrane potential increase induced by auxin, benzyladenine and fusicoccin. Correlation with proton extrusion and cell enlargement

Effects of a brassinosteroid on growth and electrogenic proton extrusion in Azuki bean epicotyls

Correlation between proton extrusion and stimulation of cell enlargement effects of fusicoccin and of cytokinins on leaf fragments and isolated cotyledons