EXTERNAL REGULATION OF PLANT GROWTH Plants like all

EXTERNAL REGULATION OF PLANT GROWTH

Plants, like all other living organisms, exhibit all the characteristics of life. They even respond to stimuli or stresses in their environment. PHOTOTROPISM � When plants grow towards the light GRAVITROPISM � Tendency of roots to grow in the direction of gravity

MORE TROPISMS � THIGMOTROPISM � PHOTOPERIODISM � Movement � Growth in response to touch � E. g. Mimosa fern or blooming at specific times of day � E. g. Morning glory

INTERNAL REGULATION OF PLANT GROWTH �Plants contain specific chemical substances (analogous to hormones in animals) which are called plant growth regulators.

AUXINS �Stimulate cell division and cell enlargement in apical (tip) meristems. �Auxins regulate root formation on stems and fruit growth. �They are present in low quantities but exhibit profound responses. This is due to their intentional uneven distribution in plants.

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CYTOKININS �Promote cell division and differentiation �Stimulate the proteins needed for mitosis and cytokinesis �Delay the ageing of leaves and fruit

GIBBERILLINS �Plant growth regulators involved in cell division and elongation (increase in plant size), stop dormancy in seeds. �Used in commercial crops to increase fruit size and to increase cluster size in grapes �Unlike auxins, these hormones are evenly distributed throughout the plant

MORE HORMONES!! � ETHYLENE � ABSCISIC ACID � Important in fruit ripening. Fruits can be harvested prematurely for marketing and can be artificially treated with ethylene gas to induce ripening. Refrigeration suppresses ethylene gas which explains why fruit lasts longer when refrigerated � Influences the shedding of leaves and the seasonal slowing down of plant growth

BOZMAN BIOLOGY CLIP � http: //www. bozemans cience. com/plantcontrol