Sl. Jackson et Ar. Hardham, A TRANSIENT RISE IN CYTOPLASMIC FREE CALCIUM IS REQUIRED TO INDUCE CYTOKINESIS IN ZOOSPORANGIA OF PHYTOPHTHORA-CINNAMOMI, European journal of cell biology, 69(2), 1996, pp. 180-188
We studied the role of cytoplasmic free Ca2+ concentration ([Ca2+](i))
in cytokinesis of zoosporangia of the water mold Phytophthora cinnamo
mi. In these cells cytokinesis is separated from nuclear division and
can be triggered at precisely determined times by cold shock. Changes
in [Ca2+](i) were monitored by ratiometric fluorescence imaging of pre
ssure microinjected Fura-2 dextran. Two increases in [Ca2+](i) always
occurred in sporangia that underwent cytokinesis in response to cold s
hock. Within the first minute of cold shock, [Ca2+](i) rose rapidly an
d transiently to levels 25 to 131% higher than the resting level of 10
4 +/- 54 nM. By 10 min, [Ca2+](i) had decreased and was near the initi
al resting level. The second increase in [Ca2+](i) was gradual and pro
longed, accompanying cell division. Near completion of cytokinesis, [C
a2+](i) had risen to 231 +/- 165 nM. The initial brief rise in [Ca2+](
i) was absent in sporangia that did not undergo cleavage. Microinjecti
on of the Ca2+ buffer 5,5'-dibromo-BAPTA before cold shock, blocked cy
tokinesis suggesting that the transient rise in [Ca2+](i) may be neces
sary for induction. The subsequent gradual increase in [Ca2+](i) may n
ot be critical because microinjection of 5,5'-dibromo-BAPTA during cle
avage plane development did not always perturb division.