Nitrate uptake into Pisum sativum L. cv. Feltham First seedlings: commonality with nitrate uptake into Chara corallina and Hordeum vulgare through a substrate cycling model

Abstract

Abstract Net NO3−, uptake into Pisum sativum L. seedlings temporarily ceased in the presence of very low NH4 concentrations (δmmol m−3). The sensitivity to NH4+ was apparent for seedlings grown in nitrogen‐free conditions with or without NO3− pretreatment, although in the latter case the inhibitory effects were more obvious because net NO3− uptake was higher. NO3− influx, measured using 36ClO3− tracer, was unaffected by NH4+ though pretreatment with NO3− for 24 h slightly stimulated influx. The inhibitory effects of NH4+ were attributed to its effects on stimulating NOJ efflux, which, under certain conditions, was moving against its electrochemical gradient.A theoretical model has been devised that involves NO3− cycling across the plasmalemma, with distinct parallel influx and efflux pathways, which improves the sensitivity to substrate and effectors and provides a means for control of internal pool size. The sensitivity of net flux (J) to effectors of the influx step (I) is a function of (1 +E/J), and the sensitivity of J to effectors of the efflux step (E) is a function of ‐ E/J. The model has been used to quantify the relative sensitivity of nitrate influx and efflux processes to nitrate and ammonium for Pisum sativum, Chara corallina and Hordeum vulgare. As steady state is reached, sensitivity of net flux (J) to NO3− increases, whereas sensitivity to NH4+ decreases.