environmental hort. phys. CH. 13 signals from sunlight

solar tracking

the movement of leaves or flowers in response to the sun's movement across the sky

Photomorphogenesis

growth and development of plants in response to light

Phototropism

Growth of a plant shoot toward or away from light.

Nyctinasty

movements based on time of day

Photonasty

A flower (or stomata) opens or shuts according to whether it is light

Photoperiodism

A plant's response to seasonal changes in length of night and day

Photoreceptors

respond to light

Chromophore

the light-catching part of the visual pigments

Phytochromes

A type of light receptor in plants that mostly absorbs red light and regulates many plant responses, such as seed germination and shade avoidance.

Cryptochromes

Pigment used to detect blue light that regulate germination, elongation aPigment used to detect blue light that regulate germination, elongation and photoperiodismnd photoperiodism

Phototropins

photoreceptors that detect blue light and initiate phototropic responses

ZEITLUPE

circadian photoreceptor

Photoreversibility

The ability of a pigment to undergo conformational change to switch from absorbing red to far-red light

Fluence

energy delivered per unit area, measured in J/cm2

Irradiance

the level of light intensity, often measured as photon flux density

Phytochrome exist in two forms. Explain the process of converting between the two forms of phytochrome. In addition, explain what happens when cycling between red and far-red light..

due to photoreversibility, when Pr is exposed to red light, some is absorbed and converted to Pfr, while the Pfr absorbs some of the red light and converts back to Pr. equilibrium is achieved through this constant converting.

Explain the three levels of light requirement for some phytochrome responses.

UV-A, blue, far-red