Kinetics of phosphate uptake by cells of maize mature leaf

Phosphate uptake by plasma membrane vesicles was studied with 32P labeled phosphate and the results indicated that phosphate uptake capacity (Vmax) of cells of maize (Zea mays L.)mature leaf was enlarged (P<0.01) under phosphorus starvation. Local application of 32P labeled phosphate solutions on mature leaf revealed that a close relationship existed between phosphate uptake by leaf cells from the apoplasts and phosphorus export of the leaf. Furthermore, the investigation on variations of phosphorus contents in the xylem saps and phloem exudates of mature leaf during phosphorus starvation showed that phosphorus which was imported to mature leaf through xylem flows decreased markedly, while the phosphorus export of the leaf through phloem was enhanced relatively. It is proposed that enhancement of phosphate uptake capacity of cells of maize mature leaf under phosphorus deficiency might benefit the absorption of phosphate from leaf apoplasts including xylem and P output of mature leaf. (authors)