Three major classes of animal-cell junctions: 

1. Anchoring junctions

2. Tight junctions

3. Gap junctions

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#Unit 6. System Physiology – Plant

In dark-grown or etiolated plants, phytochrome is present in a red light–absorbing form, referred to as Pr because it is synthesized in this form.

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#Unit 6. System Physiology – Plant

Pr, which to the human eye is blue, is converted by red light to a far-red light–absorbing form called Pfr, which is bluegreen.

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#Unit 6. System Physiology – Plant

Pfr, in turn, can be converted back to Pr by far-red light. Known as photoreversibility, this conversion/reconversion property is the most distinctive property of phytochrome.

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#Unit 6. System Physiology – Plant

Lettuce seed germination is a typical photo reversible response controlled by phytochrome

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#Unit 6. System Physiology – Plant

The initial observation was that the germination of lettuce seeds is stimulated by red light and inhibited by farred light.

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#Unit 6. System Physiology – Plant

Typical photoreversible responses induced by phytochrome in variety of higher and lower plants