CHARACTERIZATION OF THE NITRATE TRANSPORTER IN ROOT PLASMA-MEMBRANES OF CUCUMIS-SATIVUS L

Nitrate uptake in right-side out plasma membrane vesicles isolated fro m cucumber roots was characterized. Nitrate uptake into vesicles was d riven by an artificially imposed pH gradient. The uptake was strongly inhibited by phenylglyoxal, an arginyl residue modificator. Only a sli ght repression of NO3- transport in vesicles was observed in the prese nce of NEM, a thiol group reagent. pCMBS, an other thiol reagent and D EPC, an effector of histidine residue, had no effect on the nitrate tr ansport in plasma membranes. ATP-driven proton transport in vesicles w as not significantly affected in the presence of both, phenylglyoxal a nd DEPC, whereas pCMBS and NEM abolished it almost completely. The pos sible role of the particular amino acids residues in the active nitrat e transport is discussed. NO3- uptake into vesicles isolated from both , nitrate-induced and nitrate-depleted plant material was higher than that observed in the vesicles obtained from uninduced plants. Thus, is olated vesicles reflect the well-known in vivo response of intact plan ts on the exogenous nitrogen regime.