Synthesis of vesicle cargo determines amplitude of Ca(2+)-sensitive exocytosis.
Here we examine the potential coupling between the synthesis of secretory proteins and the sensitivity of exocytosis to the concentration of free Ca(2+) in the cytosol ([Ca(2+)](i)) in plant cell. We therefore monitor in tobacco protoplasts the excursion of the membrane capacitance in response to an elevation of [Ca(2+)](i) as a measure for exocytotic activity. The data show that a ramp like elevation of [Ca(2+)](i) generates in protoplasts from wild type plants and from transgenic plants, which overexpress the secreted α-amylase, an exocytotic burst with an initial steep and a subsequent slow phase. The largest capacitive burst is obtained in α-amylase producing plants and the amplitude of the [Ca(2+)](i) evoked C(m) excursion is a function of the amylase synthesis of the plants. The data support a model according to which plant cells have at least two serial [Ca(2+)](i) sensitive processes in the final steps of their exocytotic pathway. The overproduction of a secreted cargo does not affect the kinetics of this process but the number of vesicles in pools upstream of the [Ca(2+)](i) sensitive steps.
University of Strathclyde, 107 Rottenrow East, Glasgow G4 0NG, UK.
Jens-Uwe
JU
Sutter
Jürgen
J
Denecke
Gerhard
G
Thiel
D002118:Calcium / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000378:metabolism; D011523:Protoplasts / Q000201:enzymology / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*; D014026:Nicotiana / Q000378:metabolism; D000516:alpha-Amylases / Q000096:biosynthesis / Q000378:metabolism
D010940:Plant Proteins; D000516:alpha-Amylases; D002118:Calcium