Light and Photoperiod Flashcards
What is light to plants?
Wavelengths of the electromagnetic spectrum including those that humans can see (visible light) and some of the wavelengths that humans can’t see (e.g. infrared light). These are important for a range of processes.
What is light to humans?
A transverse electromagnetic wave of radiant energy. Wavelengths of radiant energy in the electromagnetic spectrum activate light receptors in eyes. When activated impulses are interpreted by the brain and vision is experienced.
What do animals use light for?
Transferring information about position, movement, shape and colour of material objects.
Animal light perception is centred around food, prey acquisition, concealment from predators, reproduction.
What do plants use light for?
An information medium and producing food through photosynthesis.
When light intercepts pigment systems in a leaf, the plant receives information on the directional and spectral composition of light.
This affects the morphological composition and phenology of the plant.
Define light quality.
The composition of light regarding wavelengths that are useful for photosynthesis and other plant growth processes.
Define light intensity.
The amount of light a plant receives. Plants normally grow in proportion to light intensity.
Define light saturation point.
The relative light requirement of a plant. Light intensity exceeding this point will not increase the photosynthetic rate.
What is PAR?
Photosynthetic active radiation- the amount of light energy within the 400nm (violet) - 700nm (red) used by plants for photosynthesis (umol.m.2s1 of PAR, quanta of light in PAR range).
Who concluded that day length/ night length controlled flowering, introducing the theory of photoperiodism?
Garner and Allard, 1920’s
What are the two types of photoperiodism?
Short day plants,
Long day plants.
Explain obligate or qualitative long-day plants.
Plants that require day length to exceed a minimum period to flower.
Explain facultative or quantitative long-day plants.
These plants flower under any day length, but flower earlier with long days.
What is florigen?
Florigen is generated in leaves that are exposed to a suitable photoperiodic cycle, transmitted through the phloem, and activates flowering genes at the shoot apex.
What is phytochrome?
A single blue pigment, that is an important photoreceptor for the perception of light.
In what forms does phytochrome exist?
Photo-chemically inconvertible forms.
Red (600-700nm peak at 660nm)
Far-red (700-800nm peak at 730nm)
What type of phytochrome is synthesised in the dark?
The red-absorbing form.
What type of phytochrome is synthesised in light?
The far-red-absorbing form.
What are the 3 principles of phytochrome response?
When PR form of the pigment absorbs red light (660nm), it is converted into PFR form.
When PFR form of the pigment absorbs far-red light (730nm), it is converted into PR form.
The PFR form of the pigment gradually changes into PR form in dark.
What happens when PR absorbs red light?
It is converted into PFR which inhibits flowering in short-day plants.
