Wheat plants, 22d. old, were exposed to wide range of soil water osmotic potential (Psi(s) = 0 to -1.2 MPa) induced by NaCl and CaCl2 treatments in combination with roots maintained under aerobic (drained at field capacity) or nonaerobic (flooded) conditions in the soil, and sprayed with 10 mg L-1 kinetin solution. In drained plants, not receiving kinetin, increased soil salinity resulted in appreciable inhibition of shoot growth and reduction in chlorophyll (Ch1.), soluble sugars (SS) contents and grain yield. Shoot growth, Ch1. content, soluble sugars and grain yield were significantly lower for flooded plants than unflooded analogues over the entire Psi s range. Both salinity and waterlogging synergize to increase Na+, Ca2+ and Cl- accumulation in shoot tissues and to decrease the stability of leaf membranes to either dehydration (40% polyethylene glycol 6000) or heat (51 degrees C) stress. The ratio of K+/Na+ transported to shoots under aerobic and anaerobic conditions decreased progressively on salinization. The association between the internal mineral element concentrations was largely affected by kinetin treatment. Kinetin application ameliorated the deleterious effects of salinity and oxygen deficiency. It reduced Na+, Ca2+ and Cl- accumulation and improved K+ uptake under salinity and waterlogging stresses. Increased K+/Na+ ratio helped the plants to avoid Na+ toxicity and enhanced shoot growth and grain yield. Kinetin also reduced membrane injury by dehydration and heat stresses and improved the water status of plants under both aerobic and anaerobic conditions. The effects of single factors (Soil salinity `Psi s', soil waterlogging `WL' and Kinetin `Kin') and their interactions (Psi s x WL, Psi s x Kin, WL x Kin and Psi s x WL x Kin) were shown by analysis of variance to be statistically significant for most parameters tested. Calculation of the coefficient of determination (eta(2)) led to three important findings. (1) Salinity (Psi s) was dominant in affecting leaf relative water content (RWC), shoot dry mass, grain yield, stability of leaf membranes to dehydration stress and the contents of Na+, Ca2+, Mg2+ and Cl-. (2) Kinetin (Kin) had a dominant effect on the stability of leaf membranes to heat stress as well as on chlorophyll and soluble sugars contents. (3) The share of waterlogging (WL) was dominant for K+ content. It can be concluded that kinetin application helped wheat plants to grow successfully in the areas subjected to combined effects of salinity and oxygen deficiency, such as in salt marshes.
