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Old 01-13-2019, 01:16 AM #31

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I found a better explanation of phytochrome red/far red and wanted to share to help explain it better and clear up any confusion:

The phytochromes are a family of chromoproteins with a linear tetrapyrrole chromophore, similar to the ringed tetrapyrrole light-absorbing head group of chlorophyll. Phytochromes have two photo-interconvertible forms: Pr and Pfr.

Pr absorbs red light (~660nm - ~729nm) and is immediately converted to Pfr.

Pfr absorbs far-red light (~730nm - ~800nm) and is quickly converted back to Pr.

Pfr naturally converts to Pr in darkness over time.

Absorption of red or far-red light causes a massive change to the shape of the chromophore, altering the conformation and activity of the phytochrome protein to which it is bound. Pfr is the physiologically active form of the protein; therefore, exposure to red light yields physiological activity. Exposure to far-red light inhibits phytochrome activity. Together, the two forms represent the phytochrome system.

Unfiltered sunlight is rich in red light but deficient in far-red light. Therefore, at sunrise, all the phytochrome molecules in a leaf quickly convert to the active Pfr form, and remain in that form until sunset. In the dark, the Pfr form takes hours to slowly revert back to the Pr form. By sensing the Pr/Pfr ratio at sunrise, a plant can determine the length of the day/night cycle. In addition, leaves retain that information for several days, allowing a comparison between the length of the previous night and the preceding several nights. If the night is long (as in winter), all of the Pfr form reverts. If the night is short (as in summer), a considerable amount of Pfr may remain at sunrise.

Link to source:

So to clear up any confusion:

Its the ratio of how much time either Pr or Pfr is the active phytochrome that dictates the flowering response in short day plants like cannabis.

Red light between 660nm - 729nm converts Pr in the plant to Pfr which helps the plant remain in veg.

Infra red light between 730nm - 800nm converts Pfr in the plant to Pr which helps the plant begin flowering.
Originally Posted by Dirt Bag View Post
The beauty of science is that it works whether you believe in it or not. - NdT
Originally Posted by Ibechillin View Post
Sadly Pseudoscience works the same way, and dunning kruger aint helping much either...
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Last edited by Ibechillin; 01-13-2019 at 01:32 AM..
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