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What happens after a pollen grain reaches a receptive stigma?
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Pollination
Common carder bumblebee (Bombus pascuorum) pollinating a honeysuckle (Lonicera species) flower.
Once a pollen grain lands on a receptive stigma, it germinates to produce a pollen tube. This tube grows down through the style, nourished by secretions from the plant's transmitting tissue. If mitosis in the generative cell has not yet occurred, it takes place during this elongation.12
The pollen tube eventually reaches the ovule through the micropyle and penetrates a synergid cell, where it discharges two male gametes. This leads to a process known as double fertilization:31
- One male gamete fuses with the egg cell to form a diploid zygote, which develops into the embryo.32
- The second male gamete fuses with the two polar nuclei in the central cell to form a triploid primary endosperm nucleus, which initiates the development of nutritive tissue.32
Many plants employ self-incompatibility systems to prevent fertilization by pollen from the same plant, thereby promoting genetic diversity.1