Inhibition of root growth by salinity stress: Toxicity or an adaptive biophysical response?

Abstract

This review considers mechanisms underlying the inhibition of root elongation growth by salinity stress. The first section considers effects of salinity on quasi steady state elongation growth, morphology and mature cell size, in maize (Zea mays L) primary roots. The following sections review evidence indicating that the inhibition of root elongation growth by salinity need not be a toxic consequence, e.g. of competitive displacement of essential Ca2+ from plasmamembrane binding sites in the expanding tip tissues. Thus growth inhibitory levels of salinity did not compete with Ca2+ for initial attachment to plasmamembrane binding sites, did not reduce capacity for trans-membrane proton transport, and did not reduce capacity for osmotic adjustment or turgor maintenance in growing root tips supplied with adequate external calcium. As an alternative to the ion toxicity hypothesis, it is suggested that salinity induces regulated biophysical restraints to cell wall expansion, which in turn inhibit root expansion growth. Finally, the possibility that regulated reductions in cell, root and overall plant size, have adaptive advantages for prolonging plant survival in drying salinized soils, is considered.

Effects of Salt Stress on Plant Growth, Nutrient Partitioning, Chlorophyll Content, Leaf Relative Water Content, Accumulation of Osmolytes and Antioxidant Compounds in Pepper (Capsicum annuum L.) Cultivars

“…It affects more than 10% of arable land and salinization is rapidly increasing on a global scale, declining average yield for most major crop plants by more than 50% (Bray et al, 2000). Salt stress occurs in areas where soils are naturally over salted and precipitation is low and/or where irrigation, hydraulic lifting of salty underground water, or invasion of sea water in coastal areas brings salt to the surface soil that inhabit plants (Neumann, 1995). Globally compatible solutes, have shown that increases in SS and/or other osmolytes provide optimism to increase plant tolerance to abiotic stresses such as drought, salinity and cold (Cusido et al, 1987;Rathinasabapathi, 2000).…”

Salinity reduced growth PS2 photochemistry and chlorophyll content in radish

“…There have been numerous reviews of the effects of salinity on plant physiological processes and subsequent effects on yield (Greenway & Munns, 1980;Shannon et al, 1994;Neumann, 1995). In spite of this extensive literature there is still a controversy with regard to the mechanisms of salt tolerance in plants (Neumann, 1995).…”

Application of Root Growth Endpoint in Toxicity Tests With Lettuce (Lactuca sativa)

“…Salinity in the soil and irrigation water is a problem mainly in arid and semi-arid regions, and can severely limit crop yields or even make it impossible to grow certain plants (Shannon, 1998). However, despite extensive studies, there is still a good deal of controversy over plants' salt tolerance mechanisms (Neumann, 1995).…”