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(Figure 6B). However, mature pollen tetrads resisted separation during acetolysis,
showing the permanence of joint sporopollenin (Figure 6C).
Figure 6. Mature pollen of Annona cherimola.
(A) Intine (black arrow) is similar all around the pollen grain, but exine (white arrow) is thinner in the pollen
aperture site. Longitudinal section stained with a 3:1 mixture of Auramine and Calcofluor. (B) Sibling pollen
grains have a faint cohesion that showed with JIM 5 antibody the presence of unesterified pectins. (C) Mature
pollen tetrad following acetolysis. (D, E, F) Mature pollen observed with scanning electron microscopy (SEM).
(D) Mature pollen grains with a globose shape and a radiosymmetric disposition. (E) Exine cohesion helps
keeping sibling pollen grains together. (F) Pollen exine shows a tectate perforate appearance. A, B, D: Bar = 20
µ m; C: Bar = 10 µ m; E, F: Bar = 2 µ m.
Scanning electron micrographs revealed that mature pollen had a radiosymet-
ric globose shape, was inaperturated, tectate perforate, and with a diameter of 40
µm (Figure 6D, 6E, 6F). Mature pollen was shed in groups of four sibling pollen
grains that stick together having an exine cohesion, clearly visible with high mag-
nification scanning electron microscopy images (Figure 6E).
Tapetum Degeneration
A. cherimola has a secretory tapetum with tapetal-type septa similar to those de-
scribed in other species of the genus Annona such as A. squamosa [26] and A.
glabra [27]. Prior to meiosis, septal initials formed tapetal chambers that host the
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