Growth and development in plants Response Stimulus n

Growth and development in plants

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

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

Plant Hormones n Chemical signals produced in very low concentrations for communication

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

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

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

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

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

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

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