Agriculture Reference
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Fig. 6.1.
Self-incompatibility (
SI
) induces dramatic rearrangements of actin cytoskeleton
organization in
Papaver
pollen.
a
The actin cytoskeleton of a normally growing pollen tube
haslongitudinalarraysofF-actininthepollentubeshank,adensesub-apicalnetworkof
F-actin and a fine array of dynamic filaments at the tip.
b
Following SI induction rapid
reorganization is observed. Within 1 min, F-actin accumulates in the tip of the pollen tube.
c
,
d
By 20 min after SI induction, the F-actin has disappeared from the cortex and is localized
to the periphery of grains and pollen tubes and “punctate foci” of F-actin begin to appear.
e
,
f
The punctate foci persist for greater than 60 min and increase in size over time.
a
,
b
,
d
-
f
are epifluorescence microscope images of rhodamine-phalloidin-labelled pollen tubes.
c
is a single optical section from confocal microscope imaging of rhodamine-phalloidin-
labelled pollen grain.
Bars
represent 10 µm
6.2.3
Self-Incompatibility Stimulates Rapid
and Sustained Depolymerization of F-Actin
Because the actin reorganization observed during the early stages of the SI
response suggested that actin depolymerization had occurred, a quantita-
tiveapproachwasusedtoinvestigatethisfurther.Atechniquebasedon
the number of fluorescent-phalloidin binding sites (Howard and Oresajo
1985; Lillie and Brown 1994) was used to determine the concentration of
actin in filamentous form in pollen (Gibbon et al. 1999; Snowman et al.
2002). We found that the levels of F-actin in pollen throughout hydration,
germination and early growth were constant (Snowman et al. 2002). Upon
SI induction, a rapid and sustained decrease in F-actin levels was induced.
Within 1 min there was a significant reduction in F-actin. These levels con-
tinued to decrease, so that by 5 min after SI induction, F-actin levels were
less than 50% of the controls and by 1 h were reduced by 74% (Snowman et
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