Growth and development in plants

1. Growth and development in plants

2. Response  Stimulus • Results in survival of species • respond by changing their growth pattern • Tropism – growth toward or away from a unidirectional stimulus, toward +, away - • Phototropism - light • Gravitropism - gravity • Thigmotropism – touch • Reception  transduction  response

3. Nastic movements • Movements that do not involve growth, not dependent on direction of stimulus • Seismonastic movements – touching, shaking, light or thermal stimulation • Mimosa plant, prayer plant • Changes in turgor pressure, K+ • Circadian rhythm – biological rhythm with 24 hours cycle • Biological clock – mechanism by which the biological rhythm is maintained

4. Plant Hormones • Chemical signals produced in very low concentrations for communication

5. Auxin • affect many aspects of plant growth and development • Indoleacetic acid(IAA) most common occurring • Apical dominance – prevents lateral buds • Promotes root growth if applied • Promotes growth of fruit • Induce development of fruit without pollination • Weed control (Agent Orange) • Gravitropism and phototropism • moves to shady side, 2nd messengers lead to production of growth factors, elongation of stem on shady side, bends toward light

6. Gibberellins • Growth promoting hormones • Gibberellic acid (GA) • Stem elongation (bush beans to pole beans) • Used to break dormancy, bring on onset of flowers • Induce growth of plants and increase size of flowers

7. cytokinins • Promote cell division, derivative of adenine • Occur n actively dividing tiwwues of roots, seeds and fruits • Used to prolong life of flower cuttings and vegetables in storage • Senescence – aging process, loss of leaves • Can be prevented by applying cytokinins

8. Abscisic Acid (ABA) • Stress hormone • initiates and maintains seed and bud dormancy • Stimulates closure of stomata when in water stress • Natural progression in Fall for plants, levels decrease in spring (gibberellins increase) • Abscission – dropping of leaves, fruit, flowers if applied externally, not naturally

9. Ethylene • Involved in abscission, stimulates enzymes which cause leaves, fruit or flowers drop • Used to speed up ripening of fruit • Applied to citrus to keep color • Release gas at wound, speeds up ripening of fruit around fruit

10. Photoperiodism • Physiological response prompted by changes of length of day or night • Germination – breaking of bud dormancy • Can influence flowering • 3 groups of flowering plants • Short day – day length 14 hours or shorter • Long day – 14 hours or longer • Day neutral - not dependent on day length • If dark period is interrupted, flowering will not result, not the same result if reversed

11. Phytochrome • blue/green leaf pigment, • has 2 forms that absorbs red light at different wavelengths • Phytochrome red – 660 nm • Phytochrome far-red – 730 nm • Allows a plant to detect photoperiod changes • Other functions of phytochrome • Promotes seed germination • Inhibits stem elongation