Question

Introduction to plant stimuli and primary plant development

• Know all of the plant tropisms covered in class. Please focus on: Phototropism, Thigmotropism, Geotropism/Gravitropism, Hydrotropism, Chemotropism, and plagiotropism.

• Remember the signal transduction pathway

Answer 1

Like all organisms, plants detect and respond to stimuli in their environment. Unlike animals, plants cannot away from danger as they are stationary . They are usually rooted to the soil. Instead, a plant's primary means of response by showing certain movements (tropic movements) or growth patters in response to environmental stress.

Tropic movements: The directional movements in plants that occurs in response to directional stimulus.

Phototropism: The tropic response to unidirectional light.

Thigmotrophism: The movement or response is triggered by touch.

Geotropism: The movement of plant parts in response to gravity. Roots are positively geotropic (growing towards gravity) and stem is negatively geotropic (growing against the force of gravity).

Hydrotropism: The tropic response to the availability of water. For example, roots are directed towards the well hydrated region in soil.

Chemotrophism: This is a special trophic movement that is seen in response to the chemicals produced by plants to communicate with eachother, especially during reproduction and fertilization.

Plagiotropism: A tropism in which the plant part is aligned at some angle to the direction of the stimulus. A plagiotropic response to gravity (plagiogeotropism) is exhibited by lateral shoots and roots.

Singnal transduction pathway: This can be initiated by number of signalling molecules like hormones, chemicals etc. When the signaling molecules bind to their respective receptors on the cell membrane, they initiate a transduction cascade, which ultimately give out the respective cellular response.