EFFECTS OF G-PROTEIN PROBES ON INTERACTIONS BETWEEN AUXIN EFFLUX CARRIERS AND PHYTOTROPIN RECEPTORS IN ZUCCHINI (CUCURBITA-PEPO L) MICROSOMAL-MEMBRANES

Microsomal vesicles prepared from etiolated hypocotyl tissue of zucchi ni (Cucurbita pepo L. cv. All Green Bush) exhibited saturable N-1-naph thylphthalamic acid ([H-3]NPA) binding, NPA-stimulated association of indol-3yl-acetic acid ([H-3]IAA), and saturable binding of guanosine 5 '-O-[3-thiotriphosphate] (GTP-gamma-[S-35]). These vesicles were used to test the possibility that NPA receptors might interact with IAA-ani on efflux carriers by coupling through a GTP-binding protein (G-protei n). Unlabelled GTP-gamma-S or guanosine 5'-O-[2-thiodiphosphate] (GDP- beta-S) had no effect on saturable NPA binding or on the NPA-stimulate d association of IAA with microsomes. NPA did not affect saturable bin ding of GTP-gamma-[S-35] to microsomes, either in the presence or abse nce of saturating concentrations of unlabelled GTP-gamma-S or GDP. It is concluded that the occupancy of phytotropin receptors is not transd uced to auxin efflux carriers by a GTP-binding protein.