Leaf water relations and solute accumulation in two grain sorghum lines exhibiting contrasting drought tolerance

A drought-tolerant grain sorghum line (K886) maintained significantly higher relative water content (RWC), osmotic potential at full turgor (ψx(100)) and turgor pressure (ψp) than did a drought-susceptible line (CS3541) when the two genotypes were grown in containers and subjected to severe water stress prior to anthesis. Leaf area expansion was inhibited to a greater extent by water deficit in line CS3541 than in K886. Both the basal ψx(100) and the capacity to accumulate solutes upon exposure to stress appear to play important roles in the measured genotypic differences in leaf water relations. Sap osmolarity was greater in line K886 than in CS3541 throughout the entire range of water potential induced. With the exception of proline, the baseline concentrations of each of eight solutes were higher in K886 than in CS3541. Further, when water deficit was imposed, K886 exhibited larger increases in sap osmolality than did CS3541. The concentrations of Kplus;, sugars, Cl− and P, predominant solutes contributing to osmotic adjustment, increased with increasing stress in K886, but essentially remained constant in CS3541. The two lines exhibited large differences in the relative contributions of individual solutes to osmotic adjustment, and these contributions changed markedly during stress development both within and between lines. The most notable differences between genotypes were with respect to the contributions of sugars and K+ ions. The capacity to accumulate K+ ions and to minimize stress-induced reductions in water content, turgor and leaf expansion appear to be useful traits for inclusion in germplasm screening programmes for improved drought tolerance in sorghum.