Changes in Yield and Chloroplast Mg^2+-ATPase Activity of Wheat (Triticum aestivum L.) in Response to Soil Salinity and Nutrient Supply

Under stress conditions such as salinity and drought, plant tolerance depends on upregulating ATPase activity. A greenhouse and a field experiments were conducted to investigate the regulation of chloroplast Mg^+2-ATPase activity in wheat in response to soil salinity and nutrient supply. In the greenhouse, plants were imposed irrigation with three water salinities; 0.4, 4.0, and 8.0 dSm^-1 with different sub-treatments of nutrient applications. Wheat yield was negatively correlated with soil salinity, presenting threshold at 6 dsm^-1 followed by yield reduction with slope 7.4 % per unit dsm^-1. Salt stress decreased Mg^+2-ATP activity from 0.32 to 0.28 μmole Pi min^-1 mg^-1chl. Application of mixed fertilizers M.F. (compost, Gypsum, P, and K) for the non stressed plants resulted in increasing both Mg^2+-ATPase from 0.32 to 0.40 and the relative grain yield to 120%, suggesting anabolic metabolism. At soil salinity above the threshold level, application of nutrients sharply increased Mg^2+-ATPase activity up to 1.06 μmole Pi min^-1 mg^-1chl accompanying yield reduction; suggesting catabolic metabolism. In the field experiment, the soil salinity was 12.3 dSm^-1 at planting and only drainage water (EC 3.9 dSm^-1) was available for irrigation. The soil EC steeply reduced to 5.0 dSm^-1 before the productive growth stages. Mg^+2-ATPase activity was up-regulated at flowering and was low late in the season at the grain filling stage. Foliar spray with K+ and a biostimulant enhanced ATPase activity as well as grain yield compared to the control. Under the field condition Mg^2+-ATPase activity was correlated with the grain yield, which reached 8.7 Mg ha^-1. The variation in wheat response in the greenhouse to that in the field may be attributed to the greenhouse conditions that impaired photosynthesis activity and induced catabolic ATP hydrolysis.