Internal Factors Regulating Nitrate and Chloride Influx in Plant Cells

The primary factor determining the observed decrease in activeC1^– influx during salt accumulation in carrot and barleyroot cells has been shown to be the concentration of C1^–+ NO₃^– in the vacuole. The relationship between C1^– influx and the vacuolar concentrationsof various substances was examined after the tissues had accumulatedions from various salt solutions. After accumulating K⁺ malate,C1^– influx was not reduced, but after accumulating C1^–or NO₃^– salts, C1^– influx was reduced by up to 90per cent. Considering all treatments, C1^– influx was notcorrelated with the vacuolar concentration of K⁺, Na⁺, (K⁺+Na⁺),reducing sugars, malate, C1^–, or NO₃^–, nor withthe cellular osmotic pressure. The correlation coefficient betweenCl^– influx and log (C1^– + NO₃^– concentrationin the vacuole) was highly significant, and accounted for allthe variation in C1^– influx in this experiment. Net NO₃^– influx is similarly reduced by a high C1^–concentration in the vacuole. External Cl^– and NO₃^–have quantitatively different, apparently competitive, effectson C1^– influx. These differ from the apparently negative-feedbackeffects of C1^– and NO₃^– in the vacuole, which arequantitatively similar. Decreasing the internal hydrostatic pressure by raising theexternal osmotic pressure increased active K⁺ influx in Valoniaventricosa, but had no effect on C1^– or K⁺ influx in carrotor maize root cells. Cl^– influx is not related to thereducing sugar concentration during ageing drifts in excisedcarrot root tissue. Acetazolamide did not inhibit C1^– influx to carrot tissue. The implications of this type of negative feedback regulation,and the relationship between C1^– and NO₃^– transportare discussed.