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Regulation of Plant Growth and Development

Regulation of Plant Growth and Development. Growth in Animals. Animals grow throughout the whole organism many regions & tissues at different rates. Growth in Plants. Specific regions of growth: meristems stem cells: perpetually embryonic tissue regenerate new cells

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Regulation of Plant Growth and Development

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  1. Regulation of Plant Growth and Development

  2. Growth in Animals • Animals grow throughout the whole organism • many regions & tissues at different rates

  3. Growth in Plants • Specific regions of growth: meristems • stem cells: perpetually embryonic tissue • regenerate new cells • apicalshoot meristem • growth in length • primary growth • apical root meristem • growth in length • primary growth • lateral meristem • growth in girth • secondary growth

  4. Apical meristems shoot root

  5. Root structure & growth protecting the meristem

  6. Shoot growth • Apical bud & primary growth of shoot • region of stem growth • axillary buds • “waiting in the wings” protecting the meristem Young leaf primordium Apical meristem Older leaf primordium Lateral bud primordium Vascular tissue

  7. Primary xylem Growth in woody plants Primary phloem • Woody plants grow in height from tip • primary growth • apical meristem • Woody plants grow in diameter from sides • secondary growth • lateral meristems • vascular cambium • makes 2° phloem & 2° xylem • cork cambium • makes bark Epidermis Lateral meristems Secondary xylem Primary phloem Primary xylem Secondary phloem Annual growth layers Bark

  8. Secondary growth • Secondary growth • growth in diameter • thickens & strengthens older part of tree • cork cambium makes bark • growing ring around tree • vascular cambium makes xylem & phloem • growing ring around tree

  9. corkcambium vascularcambium Why are early & late growth different? Vascular cambium • Phloem produced to the outside • Xylem produced to the inside bark phloem xylem late early last year’s xylem

  10. Woody stem cork cambium How old is this tree? vascular cambium late early 3 2 1 xylem phloem bark

  11. Aaaargh! Murderer! Arborcide! Tree trunk anatomy tree girdling What does girdling do to a tree?

  12. Plant hormones • auxin • gibberellins • abscisic acid • ethylene • cytokinins

  13. Auxin (IAA) • Effects • controls cell division & differentiation • phototropism • growth towards light • asymmetrical distribution of auxin • cells on darker side elongate faster than cells on brighter side • apical dominance

  14. Auxin on roots Used as “rooting hormone”

  15. Cytokinins -made in roots and travel upwards Effect of cytokinins and lack of auxin

  16. Gibberellins • Family of hormones • over 100 different gibberellins identified • Effects • stem elongation • fruit growth • seed germination plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

  17. Gibberellins - Made in apical meristems (roots and shoots) and developing seeds -shows effect of ‘”bolting” of flower producing stem

  18. Gibberellins - Made in apical meristems (roots and shoots) and developing seeds -shows effect of ‘”bolting” of flower producing stem

  19. Abscisic acid (ABA) • Effects • slows growth • stimulates closing of stomata (K+transport out of guard cells) • seed dormancy • high concentrations of abscisic acid • germination only after ABA is inactivated or leeched out • survival value: seed will germinate only under optimal conditions • light, temperature, moisture

  20. Ethylene • Hormone gas released by plant cells • Effects • fruit ripening • leaf drop • like in Autumn • apoptosis

  21. Fruit ripening • Adaptation • hard, tart fruit protects developing seed from herbivores • ripe, sweet, soft fruit attracts animals to disperse seed • Mechanism • triggers ripening process • breakdown of cell wall • softening • conversion of starch to sugar • sweetening • positive feedback system • ethylene triggers ripening • ripening stimulates more ethylene production

  22. Tropisms

  23. Negative gravitropism Positive gravitropism Unequal distribution of organelles

  24. Thigmotropism

  25. Sudden movements caused by sudden release of K+ Response is transmitted to other leaves via action potentials

  26. Circadian Rhythms May be related to cyclic concentrations in a transcription factor

  27. Photoperiod and control of flowering Relative length of day and night

  28. Red is most effective in interrupting flowering A flash of far red can reverse the effect of red

  29. Phytochromes photoreceptors that function in a plants response of flowering, germination Have 2 forms: 1 absorbs red light (Pr), the other far red light (Pfr) Sunlight has high amount of red light cytochrome in Pfr by sunset Need minimum amount of night to covert back to Fr to trigger flowering

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