Thursday 30 April 2020
45. Discuss the various mechanisms that hinder self-pollination and self-fertilisation in plants
Protandry and protogyny; these are mechanisms
where either the male or female parts of the reproductive organs ripen at
different times in some flowers; Protandry is a case where stamens ripen
earlier; and anthers release their pollen grains before the stigma is mature;
while protogyny refers to a case where the stigma matures earlier; and hence
becomes ready to receive pollen grains before the anthers are ready/ripe to
shed the pollen grains; common in plants of the grass family; Self-sterility or
incompatibility; is a case where pollen grains cannot germinate on stigma of
the same plant; but only germinate on a different plant of the same species;
hindering self-pollination; Heterostyly; condition of having different
arrangements of style and stigma; for instance flowers could have shorter
stamens than pistils; hence becomes impossible for the pollen to land,
germinate and fertilise the ovules of the same flower; pistils on some flowers
could also be shorter than the stamens therefore other mechanisms that hinder
self-pollination are utilized; Dioecius and monoecius plants; dioecius plants
have reproductive parts located separately on different plants of the same
species; discouraging self-pollination; while monoecius plants have the parts
located at different parts of the same plant body; encouraging
cross-pollination;
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