PROTEIN SYNTHESIS AND GOLGI-MEDIATED VESICLE TRAFFIC IS NOT REQUIRED TO MAINTAIN A POLARISED MEMBRANE VOLTAGE IN THE PRESENCE OF AUXIN

摘要

The contribution of protein synthesis and secretion to indol acetic acid (IAA) induced polarisation of the plasma membrane voltage (V-M) was investigated. The V-M of coleoptiles from Zea mays was measured in the presence of known inhibitors of protein- and RNA synthesis, as well as those of Golgi-mediated vesicle secretion. Inhibitors were applied under conditions at which they are known to abolish IAA stimulated H+ secretion and cell elongation effectively. Cycloheximide (CHI), an inhibitor of protein synthesis, caused depolarisation of V-M with a half maximal concentration of approximately 20 mu M. At 100 mu M CHI, V-M depolarised to a new stable voltage with a half time of 9.8 +/- 0.6 min. The temporal similarity of CHI-induced depolarisation and cessation of coleoptile elongation suggests that the induced change in V-M underlies inhibition of elongation. CHI evoked membrane depolarisation to a final voltage of about -100 mV irrespective of the presence or absence of auxin in the external medium. Thus, CHI probably affected constitutive membrane transport properties independently of IAA-induced modulation of transport proteins. Cordycepin (COR), an inhibitor of RNA synthesis, had no significant effect at 400 mu M on V-M of IAA-treated cells, suggesting that gene transcription for transport- or regulatory protein synthesis was not essential for IAA-generated polarisation of V-M. Brefeldin-A (BFA), an inhibitor of Golgi-mediated vesicle secretion in maize coleoptiles, had no perceivable effect at 20 mg/l on V-M of IAA-treated coleoptile cells, demonstrating that constitutive or IAA-stimulated protein secretion was not essential for the mechanism underlying IAA-evoked V-M polarisation. Hence, IAA-stimulated and COR/BFA-depressed H+ extrusion in elongating coleoptiles may not be entirely mediated by auxin-enhanced ATPase activity. [References: 25]