Actin is bundled in response to Al3+ in
grapevine cells
To address the role of actin in defence, we used aluminium as tool to
induce actin remodeling based on our previous work demonstrating
aluminium-dependent actin bundling in tobacco (Ahad & Nick, 2007). We
therefore tested, whether this response can also be evoked in grapevine
cells. In control cells, actin was organised as meshwork of fine
filaments (Figure 1A ). Between these filaments, few punctate
signals were seen as well, for instance, in the perinuclear region.
These punctate structures presumably represent nucleation complexes
(Maisch et al., 2009). When the cells were incubated with
AlCl3 (200 µM), the actin filaments had, after 2 h,
reorganised into dense bundles, often aligned with the long axis of the
cell and detached from the membrane (Figure 1B ). In addition,
the punctate signals had increased in abundance. To statistically
validate this phenomenon, actin bundling was quantified using a
quantitative image analysis strategy (Figure 1C ). Compared to
the control, the aluminium treatment increased the degree of bundling
significantly (by more than 60%).
In order to get insight into the base for the observed bundling, we used
Latrunculin B (LatB), a drug that
irreversibly sequesters G-actin and prevents F-actin assembly, such that
actin polymerisation is blocked. In response to 1 µM LatB (2 h), only
short rods of actin were observed, accompanied by increased diffuse
fluorescence in the cytoplasm and a higher incidence of punctate signals
(Suppl. Figure S1A ). The fine filaments prevalent in control
cells (Figure 1A ) were completely eliminated, such that the
quantification of actin bundling produced a slightly increased value
(compare white bars in Suppl. Figure S1C with those inFigure 1C ). When LatB (1 µM) was administered in presence of
AlCl3 (200 µM), the actin filaments were significantly
longer (Suppl. Figure S1B ), and the degree of actin bundling
was also slightly, but significantly (P = 0.05), increased
compared to the situation without AlCl3 (Suppl.
Figure S1C ). Aluminium could rescue the effect of Latrunculin B, albeit
only partially. This would indicate that a part of the actin response to
aluminium is due to a reduced turnover of actin filaments.