EXPANSIVE GROWTH, WATER-STRESS AND OSMOTIC ADJUSTMENT OF CROPS - A REVIEW

The expansion of a growing plant cell can be described as following a cyclic process of wall loosening, a decline in turgor pressure and total water potential followed by water uptake and solute accumulation. Both cell wall properties and hydraulic conductance play a role in controlling cell expansion. The method used for recording osmotic and total water potential can influence the measurements when made on growing cells. Wall stress relaxation is associated with a reduction in turgor pressure during the 5- to 10-min period immediately following excision of the cell sample from the plant and cessation of growth due to the lack of water supply. Osmotic adjustment is a change in osmotic potential resulting in a maintenance of turgor pressure despite water-deficit or salinity conditions. The actively growing zone of the leaf has a greater capacity for osmotic adjustment than does the mature portion of the leaf. For a complete representation of the osmotic adjustment, the associated change in volume of the leaf tissue and the water content must also be considered. Solute concentration should therefore be calculated in addition to osmotic potential measurements. Osmotic adjustment properties can be used as a selection criterion for breeders, especially in areas subject to drought.