Nitrate Reductase Acivity in Leaves of Barley (Hordeum vulgare) and Durum Wheat (Triticum durum) during Field and Rapidly Applied Water Deficits

Abstract

The effect of field and rapidly applied water deficits on nitrate reductase activity in the leaves of two barley varieties and one durum wheat variety was investigated. In field experiments plants were subjected to irrigation at different rates in three Mediterranean environments by means of a line source sprinkler irrigation system. The environments differed in rainfall and nitrogen fertility. Plant water potentials decreased from −1.5 MPa to between −2.5 and −3.0 MPa as the irrigation rate decreased. Nitrate reductase activity in the leaves of these plants during heading was either unaffected or sometimes increased where the least water was supplied. Nitrate reductase activity was highest in the plants growing with an ample nitrogen supply irrespective of water regime. In contrast, seedlings subject to rapidly applied water stress over 6 d lost 30-85% of their nitrate reductase activity when leaf water potential fell from between −0.33 and −0.75 MPa to between −O.93 and −2.04 MPa. The decrease was less in the young leaves than in the old leaves. Polyethylene glycol induced osmotic stress resulted in a drop in leaf water potential from −0.20 MPa to between −1.05 and −1.20 MPa along with a loss of 40-85% of leaf nitrate reductase activity after 48 h.

It is suggested that maintenance of nitrate reductase activity in field grown barley and durum wheat plants reflects an acclimation to water deficit Maintenance of nitrate assimilation during water stress may allow continued synthesis of nitrogenous compatible solutes using the excess photochemical energy available during stomatal closure.