Unitary exocytotic and endocytotic events in Zea mays L. coleoptile protoplasts

Cell-attached capacitance measurements were used to detect unitary exocytotic and endocytotic events in protoplasts from Zea mays L. coleoptiles 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 (exocytosis) was similar to that of off-steps (endocytosis) with a modal values at about 200 aF for both events. From the frequency of endocytotic events (1.5 +/- 1.4 min(-1)) it is estimated that 200 min are required for the whole membrane to be ingested in a non-stimulated protoplast.