PHOTOTROPISMGRAVITROPISM  When plants grow towards the light  Tendency of roots to grow in the direction of gravity

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

 Plants contain specific chemical substances (analogous to hormones in animals) which are called plant growth regulators.

 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.

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

 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

 ETHYLENE  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  ABSCISIC ACID  Influences the shedding of leaves and the seasonal slowing down of plant growth

 science.com/plant- control