Seven different stages
(tetrads, young, mid, and late (vacuolate) microspores,
and young, mid and late, mature pollen) were established
based on morphological criteria such as cell size
and shape, and number, type and position of the
nucleus. Briefly, post-meiotic tetrads were identified
by the presence of four cells enclosed within a thick,
callose envelope (Fig. 1a0). Young microspores, just
released from the tetrad, by their reduced size, their
polygonal shape and when visible, a centered nucleus
(Fig. 1b0). Mid microspores had a slightly increase in
size and a more rounded profile (Fig. 1c0). In some
instances, the onset of vacuolization is visible. In
addition to this, vacuolate microspores presented a
large, central and clearly visible vacuole which