Salinity-Induced Modifications in the Response of Maize to Water Deficits

In many crop species, salinity induces physiological and morphological adjustments which assist in the maintenance of a favorable water balance. Adjustments such as these may also be effective in modifying the response of salinized plants to drought. This study was designed to evaluate the effect of salinity pretreatment on the response of maize to matric water stress. Maize (Zea mays L.) was grown in sand culture tanks at four levels of nutrient solution salinity, produced with an equivalent mixture of CaCl₂ and NaCl: −0.4, −2.4, −4.4, and −6.4 bar osmotic potentials. When the plants were 35 days old, irrigation was stopped and a period of drought stress began. When predawn leaf xylem water potentials (ᴸΨₜ in all but the highest salinity treatment had dropped below −15 bar, irrigation was resumed. Prior to, during, and after the drought period, rates of leaf blade elongation, ᴸΨₜ, and relative water content (RWC) were measured. The lowest rates of leaf blade elongation prior to drought occurred in the high salinity treatments. However, 5 days after discontinuing irrigation, leaf blade elongation in the −0.4 bar treatment had nearly ceased, while the rate for the −6.4 bar treatment slowed considerably but continued to be measurable for 9 days. Plants from the high salinity treatment also did not show the rapid decreases in ᴸΨₜ exhibited in the other treatments. This response was presumed to be due primarily to salinity-induced reductions in the transpiration rate which prolonged the period of adequate water supply. Elongation rates partially recovered after the plants were rewatered, but the plants from the high salinity treatment again resisted rapid change. Salinity pretreatment altered the relationship between longation and ᴸΨₜ indicating that loss of turgor during drought may be partially moderated by preconditioning with osmotic stress. The water desorption characteristics of maize were significantly modified by any increase in salinity above that of the control solution.