The response of nitrate reductase activity and nitrate assimilation in maize roots to growth regulators at acidic pH

Nitrate and total nitrogen contents, and nitrate reductase (NR) activity of the excised maize roots in buffered or unbuffered nitrate solution (at pH 6.5 or 4.5) as affected by putrescine (PUT), abscisic acid (ABA) and salicy lic acid (SA) were investigated. In unbufferred solution, the NR activity w as lower at pH 4.5 as compared to that at pH 6.5, but in bufferred solution the activity was higher at lower pH. Supply of 100 muM PUT or 500 muM SA, promoted NR activity and 50 muM ABA inhibited the activity at pH 6.5. Howev er, at pH 4.5, PUT and SA inhibited NR activity and ABA had no effect. In m ost cases, the increase in NR activity was positively correlated with total organic nitrogen and a negatively with nitrate content. A reverse situatio n was found when NR activity was inhibited by the growth regulators.