How do plants know when to flower?

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Presentation transcript:

How do plants know when to flower? The Phytochrome System

Flowering of plants is determined in part by the length of the day. long days & short nights short days & long nights

Plants are of three general types: Example strawberry short-day spinach long-day day-neutral sunflower

Short-day plants flower in spring or autumn when the day lengths are shorter than the critical day length.. For example, the common cocklebur (Xanthium strumarium) is induced to flower only when exposed to 16 hours or less of light.

Examples of short-day plants : poinsettias strawberries primroses.

Long day plants flower chiefly in the summer and will flower only when exposed to light for longer than a critical length. Spinach has a critical daylength of 13 hours.

Examples of long-day plants spinach lettuce henbane

What determines if plants are long or short-day is not so much the length of the exposure time but whether it is longer or shorter than some critical interval.

Day-neutral plants flower without respect to daylength. Examples of day-neutral plants corn cucumber sunflower

cucumber

Plants contain a photoreceptor called phytochrome (P) which comes in two forms which are interconvertible, Pr and Pfr. Pr Pfr

Pr absorbs red light and Pfr absorbs far-red light.

Visible light lies between 400 and 700 nm.

Red light Far Red light 730nm 660 nm

The Electromagnetic spectrum

Light induced synthesis Physiological response Pr Dark reversion Red light Far-red light Physiological response Slowly reverts during the night. Straight away Pfr Straight away