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Lecture 15 - 6:13 - Biology 172 Lecture 15 Monday Todays...

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1 Lecture 15: Monday, June 13, 2011 Biology 172 Today’s Outline Plant development Embryogenesis Meristems Announcements
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Figure 23-00 8 cell stage of plant
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Figure 23-1 Mustard bead, drosophila, short generation time to go from seed to seed, small genome
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Figure 23-2 GAMETOGENESIS GAMETOGENESIS Pollen grains produce sperm cells Many ovules— each contains an egg cell REPRODUCTIVE DEVELOPMENT VEGETATIVE DEVELOPMENT Cotyledons Pollen grain Sperm cells move down pollen tube, toward egg Embryo Hypocotyl Root Seedling GERMINATION Seed (mature ovule) EMBRYOGENE SIS Fertilized egg (zygote) inside ovule Haploid ( n ) Diploid (2 n ) FERTILIZATION Embryogenesis – multiple embryos made
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Pollination and Fertilization In plants, sperm and egg cells are produced from haploid cells via mitosis, not from diploid cells by meiosis as in animals. Plant sperm develop from multicellular pollen grains . Pollen grains have a protective coat and are carried to flowers by wind, water, or insects or other animals. In the process of pollination , the pollen grain interacts with the stigma , which is the top of the carpel. The carpel is the female reproductive structure containing the ovules. If the interaction is successful, a pollen tube begins to grow and extend down toward the egg cells in the ovules.
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Figure 23-3a Pollen grains are microscopic but multicellular. This nucleus and cytoplasm (pink material) manage growth of the pollen tube This cell will divide to form sperm Tough coat There are two cells here, one inside the other: Pollen interacts with pistel/carpel (female part – stigma) through pollination by wind, etc – have species-specific interactions (similar to bindin-fertilizin interactions) (egg w/ sperm)
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Figure 23-3b Pollen grains interact with the stigma. Pollen grain Stigma Proteins on surface of stigma Protein on surface of pollen grain
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Figure 23-3c Plant sperm move to the egg through a pollen tube. Pollen tube Germinated pollen grain Sperm cells Pollen tube nucleus Ovule Final division through mitosis
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Pollination and Fertilization One sperm fuses with the egg to form the diploid zygote. The other fuses with the maternal cell with two haploid nuclei to form a triploid cell in an event known as double fertilization . The triploid cell divides repeatedly to form a nutritive tissue called endosperm . This tissue (like the yolk in animal eggs) stores nutrients inside the seed for embryonic development, seed germination, and early seedling growth.
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Endosperm is nutritive part (provides food, etc)
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Endosperm provides nutrients for embryonic development, germination (resumption of seed growth), and early seedling growth.
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What Happens during Embryogenesis? After fertilization, the zygote undergoes an asymmetric cell division, producing a large basal cell and a small apical cell .
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Fertilized egg Apical cell Basal cell Descendants of apical cell Descendants of basal cell Globular stage Suspensor Basal cell Hypocotyl Root Cotyledons Shoot apical meristem (SAM) Root apical meristem (RAM) Cotyledons
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