. What are the stages of Pre-Pollination development of pollen grain
It occurs in following stages.
1.Size of pollen grain nucleus increases in size and then shifts to one side near the wall.
2.Now protoplast pides into two unequal cells – small generative cell and large tube cell or vegetative cells.
3.Generative cell is separated from the pollen grain wall, due to development of a layer of callose.
4.Later on, due to dissolution of callose naked generative cell comes to lie freely in the cytoplasm of the tube cell. The generative cell is lenticular to spherical in outline.
5.In some species the generative cell pides into two male gametes, prior to the dehiscence of anther and release of the pollen grains. Hence at the time of pollination, the pollen grain is either two celled or 3 celled. In two celled pollen grain, there are one tube cell and one generative cell. In three celled pollen grain, there are one tube cell and two male gametes.
6.Pollen grains are called monosiphonous when each pollen grain produces single pollen tube found in monocots.
7.Pollen grains are called polysiphonous when each pollen grain produces more than one pollen tubes usually found in dicots. E.g. Malva, Althaea (Malvaceae) and members of cucurbitaceae.