Osmotic Adjustment in Sorghum

Abstract

Osmotic adjustment, defined as a lowering of osmotic potential (*In) due to net solute accumulation in response to water stress, has been considered to be a beneficial drought tolerance mechanism in some crop species. The objective of this experiment was to determine the relative contribution of passive versus active mechanisms involved in diurnal 'II changes Loss of water from turgid leaf tissue in response to transpiration results in not only a significant decline in 'I',' but also a decline in 'In, to a lesser extent. As the leaf tissue 'I,, declines even more in response to soil water deficits, 'I' declines accordingly as reported in a large number of crop species (2,(13)(14)(15)(16)19). A decline in measured 'I' can result from a simple passive concentration of solutes due to dehydration or due to net solute accumulation. The lowering of 'n by net solute accumulation is termed OA. OA has been considered a beneficial drought tolerance mechanism in some 'Abbreviations: I', water potential (MPa); 'n, osmotic potential (MPa); Ip, turgor potential (MPa); In°"°, 'n at full hydration (MPa); RWC, relative water content (%); OA, osmotic adjustment (MPa); E, modulus of elasticity (MPa); TW, turgid weight (g); DW, dry weight (g); WC, water content (g).field crop species (6,9,20,22). Processes such as cell expansion are dependent on the influx of water driven by the maintenance of lower T' by net solute increase in the expanding cell. The lowering of Tr, by OA also minimizes the opportunity for significant water loss to occur from leaftissue.Passive concentration of solutes due to dehydration can arise from a decrease in WC per unit DW, reduced leaf tissue volume due to cellular shrinkage, change in leaf tissue elasticity, or relative partitioning of water between the symplastic and apoplastic fractions.

Osmotic Adjustment in Sorghum

“…Details concerning cultural practices and experimental site description are given in the preceding paper (8). The experimental design was a randomized complete block with four irrigation treatments and four replications.…”

“…Methods for the measurement of T'I', tn, calculated 'Ip, RWC, and OA are given in the preceding paper (8).…”

“…We have defined the relative contribution of passive and active solute potential change in sorghum leaves subject to diurnal water stress imposed during the preflowering period and also the grain-filling period (8). The results indicated the occurrence of OA, but it accounted for <50% of the total change in r,n.…”

The olive tree: a paradigm for drought tolerance in Mediterranean climates

“…Cell contents were extracted by squeezing leaf and root tissues in sterilized plastic syringes and the extract was used to determine osmolarity by an osmometer (Wescor model 2000, Logan, UT, USA) calibrated against a salt solution. Osmotic adjustment was calculated as reported by Girma and Krieg (1992) whereas elastic modulus was determined after Tyree and Jarvis (1982). Antioxidant enzymes and lipoxygenase were extracted and their activities were evaluated following the methods proposed by Sofo et al (2004a).…”

In vitro selection of sorghum (Sorghum bicolor (L) Moench) for polyethylene glycol (PEG) induced drought stress

“…Plant responses to drought is a complex physical-chemical process, in which many biological macromolecules and small molecules are involved, such as nucleic acids (DNA, RNA, microRNA), proteins, carbohydrates, lipids, hormones, ions, free radicals and mineral elements (Ingram and Bartels, 1996). Identification and understanding the mechanisms of drought tolerance in sorghum have been major goals of plant physiologists and breeders which includes prolific root system, ability to maintain stomatal opening at low levels of leaf water potential and high osmotic adjustment (Turner, 1974;Fekade and Daniel, 1992;Cabelguenne and Debaeke, 1998;Rajendran et al, 2011). Water stress affects almost every developmental stage of the plant.…”