Intracellular Sites ofSynthesis andStorage of 1-(Malonylamino)cyclopropane-1-C

Vacuoles wereisolated fromAcerpseudoplatanus cells thatwere incubated with[14Cl-aminocyclopropane-l-carboxylic acid (ACC). The kinetics of['4Cll-(malonylamino)cyclopropane-l-carboxylic acid (MACC)formation areconsistent withtheinterpretation that MACC is synthesized inthecytosol, transported through thetonoplast, andaccumulated inthevacuole. Twenty hours after chasing thelabeled ACCwith unlabeled ACCandadding 1millimolar unlabeled MACC,allthe[4Cq MACCsynthesized islocated inthevacuole. Wholecells preloaded with ['4CMACC andthensubmitted toa continuous washing out, readily release their cytosolic MACCuntil complete exhaustion. Thehalf-time ofMACC efflux fromthecytosol, calculated bythetechnique ofcompartmental analysis, isabout 22minutes. Incontrast, vacuolar MACC remains sequestered within thevacuole. Thetransport oflabeled MACC into thevacuole isstimulated bythepresence ofunlabeled MACCinthe suspension medium, probably asaresult ofareduced efflux ofthelabeled MACCfromthecytosol into thesuspending medium.