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PLANT GROWTH AND DEVELOPMENT - zygote  multicellular embryo - embryo  a seedling - seedling  mature plant - l

PLANT GROWTH AND DEVELOPMENT - zygote  multicellular embryo - embryo  a seedling - seedling  mature plant - leaves? - stem branches? - root branches? - flowers? . all formation of plant organs, and growth, results from three processes: cell division cell expansion

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PLANT GROWTH AND DEVELOPMENT - zygote  multicellular embryo - embryo  a seedling - seedling  mature plant - l

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  1. PLANT GROWTH AND DEVELOPMENT - zygote  multicellular embryo - embryo  a seedling - seedling  mature plant - leaves? - stem branches? - root branches? - flowers?

  2. all formation of plant organs, and growth, results from three processes: cell division cell expansion cell differentiation controlled by (a) internal factors and (b) external factors

  3. the direction of growth of a plant organ, and the shape of the organ, is determined by 1) the location of, and direction of, cell division 2) the extent of, and direction of, cell wall expansion 1) cell division: anticlinal cell division periclinal cell division

  4. FOR EXAMPLE (1) an anticlinal division, followed by (2 – 5) a series of periclinal divisions results in the formation of a glandular hair on the surface of this leaf

  5. 2) cell expansion a) diffuse growth b) tip growth

  6. primary cell wall structure cellulose microfibrils hemicelluloses pectins

  7. direction of cell expansion - determined by arrangement of cellulose microfibrils in cell wall isotropic (random) arrangement anisotropic (nonrandom) arrangement

  8. during cell expansion: stretching of existing wall requires 1) an internal force to cause stretching 2) "loosening" of cell wall wall extensibility = measure of wall's ability to undergo plastic change

  9. acid growth of cell walls: cell walls expand faster at low pH; slower at higher pH involves expansins CELLS WITH SECONDARY CELL WALLS ARE NO LONGER ABLE TO EXPAND

  10. Growth occurs at the shoot tip (shoot meristem) and root tip (root meristem) - both usually indeterminate - shoot meristem is responsible for (a) elongation of the stem (b) leaf production (c) branch production - flowers develop from an altered shoot meristem (floral meristems - often determinate) - root meristem is responsible for elongation of the root

  11. Cell Differentiation - establishes each cell's unique structure and metabolic features - the process may be reversible dedifferentiationandredifferentiation totipotency

  12. cell differentiation controlled by: - genes - hormones - environmental signals

  13. Senescence -normal developmental process, either - occurring in a timed fashion OR - in response to environmental cues -may include programmed cell death = apoptosis - e.g. xylem cell development, hypersensitivity response - senescence often visible as chlorosis

  14. INTERNAL AND EXTERNAL FACTORS CONTROLLING PLANT GROWTH - LIGHT 1) photomorphogenesis 2) photoperiodism 3) phototropism

  15. each requires 1) that light absorbed by a photoreceptor 2) a mechanism to convert the photoreceptor's light absorption into developmental changes photoreceptors 1) phytochromes 2) cryptochromes 3) phototropins 4) zeaxanthin

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