Lysosomes are membrane-enclosed organelles filled with soluble hydrolytic enzymes that digest macromolecules.

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Bacterial phytochrome-like proteins (BphPs) regulate the biosynthesis of the photosynthetic apparatus in Rhodopseudomonas

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In dark-grown or etiolated plants, phytochrome is present in a red light–absorbing form, referred to as Pr. Pr, which to the human eye is blue, is converted by red light to a far-red light–absorbing form called Pfr, which is blue-green. 

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Pfr, in turn, can be converted back to Pr by far-red light known as photoreversibility

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When Pr molecules are exposed to red light, most of them absorb it and are converted to Pfr, but some of the Pfr also absorbs the red light and is converted back to Pr because both Pr and Pfr absorb red light. 

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Proportion of phytochrome in the Pfr form after saturating irradiation by red light is only about 85%. 

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Very small amount of far-red light absorbed by Pr makes it impossible to convert Pfr entirely to Pr by broad spectrum far-red light. An equilibrium of 97% Pr and 3% Pfr is achieved. This equilibrium is termed the photostationary state.