The effect of NaCl concentration on NO₃^-, K⁺ and orthophosphate-P influx to peanut roots

The effect of relatively low concentrations of NaCl on the vegetative growth of peanut (Arachis hypogaea L.) plants appeared to be due to its disruption to nutrient uptake. The specific effect of NaCl on the uptake rate of NO₃^-, K⁺ and orthophosphate-P was studied in solution culture. The influxes of the nutrients were calculated according to their depletion in the solution, and the parameters for the Hill Kinetics for low concentrations were calculated as: I_n = I_maxC^h (K^h + C^h), where I_n = net influx, I_max = maximal influx, C = concentration, K = the apparent Michaelis-Menten coefficient, and h = the Hill cooperativity index. The reduction in ion influx was greatest for K⁺, followed by NO₃^-, while phosphate influx was not affected by NaCl. All three parameters of the Hill equation for K⁺ influx were affected by NaCl concentration: I_max decreased to about one-third, while the value of K tripled and h doubled, when NaCl concentration increased from 0 to 75 mM. I_max of NO₃^- influx was reduced by 40% because of the same increase in NaCl concentration. The other two parameters were unaffected. The results confirm previous results that low concentrations of NaCl disturb the nutritional balance of plants, mainly by Na⁺-K⁺ competition in uptake, and to a smaller degree, by Cl^--NO₃^- interaction. The possible implications about the nature of ion interaction in uptake by the roots, derived from the differential effect of NaCl on the parameters of the Hill equation are discussed.