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

Dep. of Agronomy and Range Science, Univ. of California, Davis, CA 55616-8515

^* Corresponding author (rltravis{at}ucdavis.edu).

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.

Received for publication August 6, 1996.

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