UNITARY EXOCYTOTIC AND ENDOCYTOTIC EVENTS IN ZEA-MAYS L. COLEOPTILE PROTOPLASTS

Cell-attached capacitance measurements were used to detect unitary exo cytotic and endocytotic events in protoplasts from Zea mays L. coleopt iles with a high-frequency lock-in amplifier. A background noise level of around 70 aF permitted the detection of interacting vesicles with a diameter as small as 60 nm. The distribution of discrete on-steps (e xocytosis) was similar to that of off-steps (endocytosis) with a modal values at about 200 aF for both events. From the frequency of endocyt otic events (1.5 +/- 1.4 min(-1)) it is estimated that 200 min are req uired for the whole membrane to be ingested in a non-stimulated protop last.