Response of wheat seedlings to short-term drought stress with particular respect to nitrate utilization

Abstract. The effect of short-term changes in the water potential (from 0 to – 2.5 MPa) by addition of PEG 4000 to the nutrient solution was investigated with respect to nitrate uptake and reduction in 3-week-old wheat plants ( Triticum aestivum , cv Fidel). Plants were harvested at the end of 12-h treatments in the dark. The water potential of the mature leaves was similar to that of the medium down to – 0.8 MPa and was maintained at this level even though the external water potential was much lower. The medium water potential of 0.8 was a threshold level below which elongation of the youngest leaf was inhibited. Increase of the PEG concentration in the medium brought about a decrease of evapotranspiration and enhancement of nitrate uptake. No difference in the rate of nitrate reduction was observed, although the in vitro nitrate reductase activity was lowered. Nitrate accumulation in the shoot was ascribed both to the stimulation of net uptake from the medium, and to the mobilization and translocation of nitrate from the root. It is suggested that increase in the storage pool of nitrate in shoots was related to the role of NO₃⁻ as an osmoticum.