Nitrate supply decreases uptake and accumulation of ciprofloxacin in Brassica parachinensis

How nitrate (NO 3 − ) fertilization influences ciprofloxacin (CIP) uptake by crops remains unsolved. Here, two Brassica parachinensis cultivars differing in CIP accumulation were cultivated to investigate the effects of NO 3 − supply on CIP uptake and the underlying mechanism. The results showed that NO 3 − supply effectively reduced CIP toxicity and accumulation in the two cultivars, especially in the low CIP cultivar. Moreover, NO 3 − supply induced different mechanisms of coping with CIP stress in the two cultivars through influencing subcellular distribution of CIP. The uptake of CIP by root was demonstrated to be a carrier-mediated, energy-consuming, and proton motive force-dependent influx process. Consequently, a mechanism of nitrate supply decreasing CIP uptake was proposed that uptake of CIP and NO 3 - into root cell would compete for the proton motive force and share a common energy source provided by plasma membrane H + -ATPase. Besides, regulating the concentration balances of cytoplasmic NO 3 - and proton by inhibiting the activities of NRase and two tonoplast proton pumps (V-ATPase and V-PPase) led to opposite effect on CIP uptake, further supporting this inference. Our results provide a novel insight into CIP uptake by plant roots, and improve the strategy of minimizing CIP accumulation in crops for food safety by fertilization management.