Biology Reference
In-Depth Information
microspores turned 180° until the pollen aperture sites faced each other (Figure
3B). The remaining PMC cellulosic wall, which persisted for some time, together
with the confined space provided by the tapetal chamber, appear to contribute
towards keeping the microspore tetrad together. Subsequently the PMC cellulosic
wall disappeared completely (Figure 3C) and the tapetum degenerated as the mi-
crospores increased in size. They remained in their new orientation attached by
their apparently sticky aperture sites that now faced each other (Figure 3D).
Figure 3.
Pollen development within the tapetal chamber in Annona cherimola.
(A) Two
young microspores in a tetrad which still keeps the pollen mother cell wall. Aperture sites are located
towards the outside facing the pollen mother cell wall. (B) Pollen is shed free, within the PMC wall, in the
tapetal chamber. Within this confined space the young microspores turn (C) with their aperture sites facing now
each other as the PMC cellulosic wall is digested. (D) The pollen grains regroup sticking through the aperture
sites, and enlarge as the tapetum degenerates. Longitudinal anther 2
µ
m resin sections stained with calcofluor
and auramine. Bar = 20
µ
m.
At this stage, both the cell walls of the somatic cells of the anther and the inner
wall of microspores (intine) reacted similarly for methyl-esterified pectins (Figure
4A), while unesterified pectins were present just in the microspore intine (Figure
4B). The exine showed a low unspecific autofluorescence but in a different fluo-
rescence wavelength (yellowish color) than the fluorescent marker of the antibod-
ies, AlexaFluor 488, which emitted green fluorescence. As a consequence, exine
autofluorescence was clearly differentiated from the immunofluorescence signals.
