EFFECT OF ROOT PERTURBATION AND EXCISION ON NITRATE INFLUX AND EFFLUXIN BARLEY (HORDEUM-VULGARE) SEEDLINGS

The effects of perturbation and excision on net NO3- uptake, influx an d efflux in roots of 8-day-old barley (Hordeum vulgare L.) seedlings i nduced with NO3- or NO2- were determined. Perturbation was simulated b y mechanically striking the intact roots with a glass rod. Perturbatio n or excision of roots and subsequent division into small segments had little effect on NO3- influx, but briefly inhibited net uptake which recovered within a few min. While in perturbed roots net uptake rates recovered to the same level as in control roots, full recovery did not occur in excised roots. Inhibition of net uptake was due to stimulati on of NO3- efflux. The recovery time and level of inhibition of net NO 3- uptake and/or stimulation of efflux were a function of extent of pe rturbation, or the number of segments following excision, and root NO3 - concentration. NO3- efflux was further stimulated when roots were pe rturbed after cytoplasmic NO3- had been depleted, indicating that both the plasmalemma and tonoplast may be affected. In excised roots both NO3- influx and efflux decreased with age due to depletion of energy s ources. The results indicate that root perturbation and excision had n o effect on NO3- influx but inhibited net uptake by stimulating efflux .