chapter 37 Plant Growth and Development

chapter 37 Plant Growth and Development - Plant Growth and...

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Plant Growth and Development Tropisms · Tropism - Directional growth in response a stimulus, results in a change of the position of a plant, irreversible and can be positive or negative · Phototropism- change in the direction of a plant caused by light · Plant must have a photoreceptor, light-sensitive substance to absorb light. Photoreceptors for blue light are phototropins , family of yellow pigments. They are light-activated kinases , enzymes that transfer phosphate groups · Gravitropism- growth in response to the direction of gravity, most stems exhibit negative gravitropism while roots exhibit positive gravitropism · Root cap is the site of gravity perception in roots, special cells possess starch-containing amyloplasts that collect at the bottom of the cells in response to gravity · Thigmotropism- growth in response to a mechanical stimulus, such as contact with a solid object (climbing of vines) Plant Hormones and Development · Hormone- organic compound that acts as a chemical signal eliciting a variety of responses that regulate growth and development · Produced close to where they take effect Plant Hormones and Signaling Molecules Hormone Site of Production Principal Actions Auxins Shoot apical meristem, young leaves, seeds Stem elongation, apical dominance, root initiation, fruit development Gibberellins Young leaves and shoot apical meristems, embryo in seed Seed germination, stem elongation, flowering, fruit development Cytokinins Roots Cell division, delay of leaf senescence, inhibition of apical dominance, flower development, embryo development, seed germination Ethylene Stem nodes, ripening fruit, damaged or senescing tissue Fruit ripening, responses to environmental stressors, seed germination, maintenance of apical
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