NOVEL THINKING

The tube cell enlarges and comes out of the pollen grain through one of the germ pores to form a pollen tube. In Amentiferae, the tube shows branches. The tube or vegetative cell enlarges. The pollen tube then moves downwards from the stigma to the pistil, along with the sperm cells. When the pollen contacts the sticky surface of the stigma, it may germinate and create a pollen tube which reaches an ovary of the flower where it fuses with an ovule to create a seed. When the pollen grain reaches a stigma, it undergoes a process called germination (which is not the same as seed germination). It comes out of the pollen grain through one of the germ pores or germinal furrows to form a pollen tube. On favourable conditions, pollen grains germinate and forms a germ tube refers as “Pollen tube”. On the stigma the pollen grain absorbs water and nutrients from the stigmatic secretion through its germs pores. On the stigma, the germination of pollen grains begins by absorption of water and nutrients and the pollen grain produces a tiny pollen tube through the style to the ovary. This, in turn, stimulates the formation of the fruit. The interaction is primarily between the pollen and the stigma epidermal cells. It is composed of a special type of structures known as stigmatic papillae, cells that are receptive to mature pollen grains. A large number of pollen grains come to germinate over the papillose stigmatic surface. In some plants, like cabbage, the pollen is rejected at the surface of the stigma, and the unwanted pollen does not germinate. In other plants, pollen tube germination is arrested after growing one-third the length of the style, leading to pollen tube death. In other plants, pollen tube germination is arrested after growing one-third the length of the style, leading to pollen tube death. The stigma is normally present at a lower level in comparison to the anther. Once the pollen tube penetrates the outer layer of the stigmatic cell wall, it grows in the apoplastic space down to the ovary for fertilization. Previously, with small fields and rich habitats, the pollination was done by wild bees. The complete process of pollination is as listed below: Once the pollen grains are deposited on the stigma, it starts to germinate … The stigma forms the distal portion of the style or stylodia. During pollen germination, the tube cell forms a pollen tube through the style to the bottom of the ovary, the generative cell migrates through it to enter the ovary for fertilization. The stigma, together with the style and ovary comprises the pistil, which in turn is part of the gynoecium or female reproductive organ of a plant. When pollen grains are released from anthers and then captured on the surface of the stigma, they obtain water and other resources from the stigma for germination and pollen tube elongation. Most pollen grains are monosiphonous, i.e., only a single pollen tube emerges from each pollen grain; others, like those of the Malvaceae, Cucurbitaceae and Campanulaceae, are polysiphonous. In some plants, like cabbage, the pollen is rejected at the surface of the stigma, and the unwanted pollen does not germinate. Pollen grains may also germinate on other parts of the flower besides the stigma. Shedding of pollen grains onto the platform of stigma. The interaction is primarily between the pollen and the stigma epidermal cells. As pollen tubes germinate from the grains, a final stage of adhesion begins in which the pollen tube passes through the foot into the stigma surface, tethering the emptying pollen grain to the stigma via the tube (Zinkl et al., 1999; Dickinson et al., 2000; Heizmann et al., 2000). The pollen tube … Pollination refers to the transfer of pollen grains from the anther of a flower to the stigma of the same or different flower through biotic or abiotic means. The stigma is a sticky structure and allows germination of pollen grains.

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