Characterization of Orthophosphate Absorption by Pea Root Protoplasts

Root protoplasts were isolated from 4 d old seedlings of Pisum sativum. Viability was verified by fluorescin diacetate, direct blue and neutral red vital staining techniques. Phosphate influx of the protoplasts was similar to that of roots with respect to phase 1 affinity for orthophosphate /{Km = 99 mmol m−3) and sensitivity to pH and metabolic inhibitors. Carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone decreased uptake to 4% of the control and diethyl-stilboestrol induced leakiness in the protoplasts. Influx was only slightly less than that in plasmolysed roots which in turn was 3.6 times lower than that of normal roots. Efflux from the protoplasts was high with a value of approximately 2% of the cellular phosphate content per hour. The elevated leakage indicated an essential difference between the effects of protoplast isolation on influx and efflux of phosphate.