Nitrate Uptake, Efflux, and In Vivo Reduction by Pima and Acala Cotton Cultivars

Nutrient assimilation by seedlings is an early indicator of subsequent plant growth and development. This study was conducted to compare NO−3 assimilation (net uptake, efflux and in vivo reduction) by 8‐d‐old seedlings of three Pima (S‐7, Oro Bianco, Conquistador) (Gossypium barbadense L.) and four Acala (Maxxa, GC‐510, Royal, SJ‐2) (Gossypium hirstum L.) cotton cultivars. The seedlings were grown hydroponically in a growth chamber and induced with 0.05, 0.1, or 1.0 mM NO−3 for 24 h. Net NO−3 uptake rates were determined by following its depletion from uptake solutions that initially contained the same concentration of NO−3 as the induction solutions. Efflux was measured by following NO−3 accumulation in an external solution. At 0.05 mM NO−3, net uptake rates for the Acala cultivars were about 40% lower than those for Pima cultivars. These differences disappeared as the NO−3 concentration in the growth mediumw as increased to 1.0 mM. In contrast, efflux from Acala roots was 40 to 50% lower than that from Pima roots at all NO−3 levels. Although NO−3 concentration of roots increased about three fold as the NO−3 level in the induction mediumin creased, efflux increased only 20 to 30%. In vivo NO−3 reduction by Pima and Acala cultivars was similar when the seedlings were supplied with 1.0 mM NO−3. However, at 0.05 mM NO−3 the Pima cultivars reduced NO−3 more effectively than did the Acala cultivars. The results indicate that Pima cultivars are better able to utilize available NO−3 at lower concentrations even though they efflux greater amounts of NO−3.