Pollination is the process which plants depend on to transfer pollen grains from anther to stigma/pistil. It can be either cross pollination or self pollination. Most of the plants are bisexual/ hermaphrodite which promote self pollination. Is this self pollination desirable? What are the factors promoting cross pollination ? What is pollen-pistil interaction?
Self pollination is common and more likely to happen in case of hermaphrodite flowers but a successive series of self pollination affects negatively and causes inbreeding depression. This also results in homozygous genes. Thus plants are adapted to promote cross pollination. This is known as outbreeding. Factors which encourages cross pollination are as follow:
- Unisexual flower: If a flower is unisexual i.e., contain only one sex either female or male, cross pollination is the only choice.
- Non-Synchronization: Timing is important for successful pollination. Pollen release and receptivity of stigma should happen simultaneously. Sometimes, pollen matures and releases before stigma is open which leads to loss of pollen vitality or vice-versa. This prevents self pollination; even though flower is hermaphrodite.
- Self-incompatibility: Incompatibility within a flower (or plant) includes self-sterility; structural barrier .Self-sterility means even though pollination takes place it can’t proceed to fertilization due to further pollen growth failure. Structural barriers include height difference between gynoecium and androecium and some structures which hinder the stigma from receiving pollen. These are more or less genetic mechanism.
All pollinations do not lead to a successful fertilization because for a successful fertilization, pistil of a flower has to recognize the pollen of same species. Therefore, interaction between pollen grains and stigma needs to be understood properly. Once compatible pollen is accepted by pistil, events for fertilization proceed, whereas incompatible pollens are rejected. This interaction where a pistil is capable of recognizing its pollen is the result of long term pollen-pistil interaction and chemicals released by pollen.
Events of pollen-pistil interaction proceeds as follows:
- Landing of true pollen on compatible pistil.
- Germination of pollen and formation of pollen tube where pollen grains release its contents.
- Pollen tube growth through style of the pistil towards the ovary.
- Entry of male gametes into the ovule and then to synergid.
Knowledge about outbreeding devices and pollen-pistil interaction helped in economical and financial development. To more about the topic please download Byju’s –The Learning App.