COMPARISON OF DEVELOPMENTAL GRADIENTS FOR GROWTH, ATPASE, AND FUSICOCCIN-BINDING ACTIVITY IN MUNG BEAN HYPOCOTYLS

A comparison has been made of the developmental gradients along a mung bean (Vigna radiata L.) hypocotyl of the growth rate, plasma membrane ATPase, and fusicoccin-binding protein (FCBP) activity to determine w hether they are interrelated. The hook and four sequential 7.5 millime ter segments of the hypocotyl below the hook were cut. A plasma membra ne-enriched fraction was isolated from each section by aqueous two-pha se partitioning and assayed for vanadate-sensitive ATPase and FCBP act ivity. Each gradient had a distinctive and different pattern. Endogeno us growth rate was maximal in the second section and much lower in the others. Vanadate-sensitive ATPase activity was maximal in the third s ection, but remained high in the older sections. Amounts of ATPase pro tein, shown by specific antibody binding, did not correlate with the a mount of vanadate-sensitive ATPase activity in the three youngest sect ions. FCBP activity was almost absent in the first section, then incre ased to a maximum in the oldest sections. These data show that the gro wth rate is not determined by the ATPase activity, and that there are no fixed ratios between the ATPase and FCBP.