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 NO3 - assimilation (net uptake, efflux and in vivo reduction) by 8-d-old s eedlings of three Pima (S-7, Oro Blanco, Conquistador) (Gossypium barb adense L.) and four Acala (Maxxa, GC-510, Royal, SJ-2) (Gossypium hirs tum L.) cotton cultivars. The seedlings were grown hydroponically in a growth chamber and induced with 0.05, 0.1, or 1.0 mM NO3- for 24 h. N et NO3- uptake rates were determined by following its depletion from u ptake solutions that initially contained the same concentration of NO3 - as the induction solutions. Efflux was measured by following NO3- ac cumulation in an external: solution. At 0.05 mM NO3-, net uptake rates for the Acala cultivars were about 40% lower than those for Pima cult ivars. These differences disappeared as the NO3- concentration in the growth medium was increased to 1.0 mM. In contrast, efflux from Acala roofs was 40 to 50% lower than that front Pima roots at all NO3- Level s. Although NO3- concentration of roots increased about three fold as the NO3- level in the induction medium increased, efflux increased onl y 20 to 30%. In vivo NO3- reduction by Pima and Acala cultivars was si milar when the seedlings were supplied with 1.0 mM NO3-. However, at 0 .05 mM NO3- the Pima cultivars reduced NO3- more effectively than did the Acala cultivars. The results indicate that Pima cultivars are bett er able to utilize available NO3- at lower concentrations even though they efflux greater amounts of NO3-.