Ve. Franklintong et al., RATIO-IMAGING OF CA-I(2-INCOMPATIBILITY RESPONSE IN POLLEN TUBES OF PAPAVER RHOEAS() IN THE SELF), Plant journal, 12(6), 1997, pp. 1375-1386
The data presented here describe ratio-imaging of in intracellular fre
e calcium (Ca-i(2+)) during the self-incompatibility (SI) response in
pollen. Use of the ratiometric indicator, fura-2 dextran, in pollen tu
bes of Papaver rhoeas has provided new, detailed information about the
spatial-temporal alterations in Ca-i(2+), and has permitted calibrati
on of alterations in the concentration of intracellular free calcium (
[Ca2+](i)) in the SI response. Ratio images demonstrate that, like oth
er pollen tubes, normally growing P. rhoeas pollen tubes exhibit a tip
-focused gradient of Ca-i(2+bf), with levels reaching 1-2 mu M at the
extreme apex of the pollen tube. Non-growing pollen tubes did not exhi
bit this tip-focused gradient. Basal levels of Ca-i(2+) in the shank o
f the pollen tube were fairly consistent and had a mean value of 210 n
M, with low-level fluctuations +/- 50 nM observed. Challenge with inco
mpatible S proteins resulted in S-specific, rapid and dramatic alterat
ions in [Ca2+](i) within a few seconds of challenge. Increases in [Ca2
+](i) were visualized in the subapical/shank regions of the pollen tub
e and alterations in [Ca2+](i) in this region subsequently increased f
or several minutes, reaching >1.5 mu M. At the pollen tube tip, a dimi
nution of the tip-focused gradient was observed, which following some
fluctuation, was reduced to basal levels within similar to 1 min. Our
data suggest that some of these alterations in [Ca2+](i) might be inte
rpreted as a calcium wave, as the changes are not global. Although the
increases in [Ca2+](i) in the subapical/shank region are very rapid,
because tip [Ca2+](i) oscillates during normal growth, it is difficult
to ascertain whether the increases in the shank of the pollen tube pr
ecede the decreases in [Ca2+](i) at the pollen tube tip.