A THEORETICAL-MODEL FOR EXPLAINING THE EFFECT OF PHYSICAL MANIPULATION ON NITRATE UPTAKE IN SPINACH (SPINACIA-OLERACEA L)

Experiments with spinach (Spinacia oleracea L., cv. Subito) plants in which net nitrate uptake rate (NNUR) and nitrate influx and efflux wer e measured showed that handling the plants affected the results consid erably. Both nitrate influx and efflux changed after physical manipula tion of the plants, even when they were gently transferred from one be aker to another, as is usually done in nutrient uptake studies. The sa me was observed after more severe physical manipulations, mimicking pr etreatments that involve more handling of the plants prior to uptake m easurements. Physical handling, however, did not always necessarily re sult in an alteration of the NNUR. The impact of, the handling and the time course of the recovery depended on the severity of the disturban ce. In order to explain the observed effects, a model for physical per turbation-generated signals and the control of NNUR is presented, with a key role played by stretch-activated ion channels and changes in th e cytoplasmic Ca2+ concentration.