angiorepro213-page18

angiorepro213-page18 - that have many ovules must also have...

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Flowering Plant Reproduction - 18 Pollen Germination Successful pollination is just one step in the process of reproduction and development in flowering plants. If pollen of the correct type is deposited on the receptive stigma of a carpel (one which contains at least one ovule with a mature egg), chemicals secreted by the surface stigmatic tissue of the stigma will stimulate the pollen grain to "germinate". A receptive stigma can often be discerned visually, because its surface will be coated with a sugary, sticky secretion. Pollen germination itself involves uptake of water from surrounding stigma cells by the pollen grain, swelling it until it splits open. As pollen germinates, it grows a pollen tube that grows through the length of the style, through a special tissue called the transmitting tissue that forms a path to the ovary with its ovule(s). The style may have mechanisms to facilitate the growth of the tube. Each ovule must be fertilized by separate sperm, so flowers
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Unformatted text preview: that have many ovules must also have many germinated pollen grains. For example, each corn silk is a single style. An average corn on the cob may have 400-500 grains. That is the result of 400-500 pollinations (and fertilizations and embryo developments). Each pollen grain contains two sperm that migrate down the pollen tube. Ultimately, the sperm will migrate to the embryo sac at a region called the micropyle, which is at the base of the synergids and egg. The pollen tube enters one of the two synergids, which has been degenerating during the growth of the pollen tube. The tube nucleus and both sperm are discharged into the synergid. Chemical signals from the synergid are critical for this function, as are signals and cytoplasmic connections from the egg, central cell of the embryo sac and the sperm cells for successful fertilization....
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This note was uploaded on 01/08/2012 for the course BIO 213 taught by Professor Makina during the Fall '09 term at SUNY Stony Brook.

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