Biology Reference
In-Depth Information
Immunocytochemical essays revealed the localization of various cell wall com-
ponents (Figure 2). Callose surrounded the PMC wall and, following meiosis I,
an additional furrow of callose developed inwards (Figure 2A) forming a callose
positive band between the dyad cells (Figure 2B, 2C). Successive cytokinesis fol-
lowed (Figure 2C), resulting in a tetrad (2D), each separated by callose. Dyad and
tetrad stages coexist in the flower as centripetal maturation progresses. The PMC
wall also reacted positively to JIM7 (Figure 2E) and JIM5 (Figure 2F) staining,
indicating the presence of methyl-esterified and unesterified pectins respectively.
However, while the walls of the anther somatic and tapetal cells also reacted posi-
tively to the JIM7 for methyl-esterified pectins (Figure 2E), they showed only a
faint staining for the presence of unesterified pectins (Figure 2F).
Figure 2.
Callose and pectins during microsporogenesis in Annona cherimola.
(A-D) Anticallose
in dyad/tetrad phases. (A) A furrow of callose developed inwards, forming a wall between
the dyad cells. (B) Dyad phase, showing (B) an incipient, and (C) a well developed callose wall. (D) Tetrad
microspore showing in the section plane three of the microspores separated by callose walls. (E) PMC and other
anther tissue walls showing methyl-esterified pectins. (F) PMC wall also shows unesterified pectins. Specific cell
components were localized using antibodies against callose (A, B, C, D), methyl-esterified pectin (JIM7) (E),
and unesterified pectin (JIM5) (F). A-D Bar = 10
µ
m. E-F: Bar = 20
µ
m.
Pollen Cohesion
Following tetrad formation, callose disappeared but the microspores remained
within the PMC calcofluor-positive cellulosic wall (Figure 3A). At this devel-
opmental stage, an interesting event was detected: the microspores within each
tapetal chamber, which initially had their pollen aperture sites facing outward
towards the PMC wall (Figure 3A), appeared to float and rotate within their
individual chambers (Figure 3B). This movement was not random, but the
