Nitrate reductase in wheat plants grown under water stress and inoculated with Azospirillum spp.

The present investigation has been performed to evaluate nitrate reductase (NR) and nitrogenase activities as well as growth and mineral nutrition of wheat plants grown under drought stress and inoculated with different Azospirillum strains (NR- and NR+). Fresh, dry mass and water content decreased with decreasing soil moisture content, which was accompanied with low soluble sugars and soluble protein content and increase in the total amino acids content. Azospirillum inoculation with either bacterial strain (NR- and NW) significantly increased the above characteristics even at 40 % moisture content. NR activity decreased in both the shoots and roots by decreasing soil moisture content. NR+ strain exhibited increased root NR activity compared with uninoculated plants or inoculated with NR- strain. However, plants inoculated with NR- strain increased NR activity in the shoot more than in the root of the same plant and in the shoot of control plants. Inoculation with either NR- and NR+ Azospirillum strains gave higher nitrogenase activity than uninoculated control plants. The low N supply (0.5 mM) did not affect nitrogenase activity. NR- strain was less effective than NR+ strain in promoting total N-yield, spike numbers and their mass per pot. Azospirillum inoculation exhibited no significant changes in wheat Mg2+ content. However, K+ and Ca2+ have shown significantly increased values. Azospirillum beneficial effect on plant N balance and growth are most probably composed of multiple mechanisms and beneficial NR is one of them. The importance of Azospirillum NR+ strains for increasing wheat resistance to water stress is also supported by the obtained data.