PLANT HORMONES Hormones Chemical messenger that stimulates or

PLANT HORMONES

Hormones • Chemical messenger that stimulates or suppresses the activity of cells • Produced in one location of an organism and causes a response in another

Gibberellins • Dramatic increase in size • End seed dormancy, start germination. And promote rapid growth of seedlings. • Big fruit, long stems

Ethylene • Causes ripening • Naturally produced by the plant

Cytokinins • Stimulate cytokinesis ( last stage of cell division) • Produced in growing roots, seed, and fruits • Lateral growth- side branches

Auxins • Lengthening of plant- apical meristem • Stimulate growth of the primary stem-preventing growth of new branches. • Controls some forms of tropism

PLANT RESPONSES

Tropisms are a plant’s response to conditions in the environment. The responses can be affected by gravity, light, touch, and seasonal changes.

TROPISMS – Gravitropism – Phototropism – Thigmotropism

Gravitropism - Up and down growth of a plant - Plant responding to gravity - Down ( +) – with gravity - Up (-)- against gravity

Phototropism A phototropic response is when a plant grows toward a source of light. Stems may bend toward a window or nearest source of light. This growth allows their leaves to capture the most sunlight for the process of photosynthesis.

Thigmotropism • When plants respond to touch • Climbing plants/vines

Thigmotropism Examples: – A plant that is touched regularly may be stunted in its growthsometimes quite dramatically – Vines and climbing plants-tips wrap around objects

Rapid Responses • Some responses do not involve growth; they are not tropisms • Examples: – Mimosa pudica: the “sensitive plant” – The Venus flytrap