Difference between Phi2, PhiNO, PhiNPQ?

Technical Support and Questions

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Saket Navlakha

Mar 2016

Hi, I've been looking at the forums and blog and was unable to find the difference between Phi2, PhiNO, PhiNPQ? Can you please help clarify?

Thanks.

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Greg Austic

Mar 2016

Also, the paper which best describes many of these parameters is here:

http://www.ncbi.nlm.nih.gov/pubmed/16228395

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Saket Navlakha

Mar 2016

Thanks everyone -- this was very helpful!

Dynamics of "PhiNPQ" "NPQt" is similar, a positive correlation. "PhiNO" and "NPQt" - a negative correlation. "PhiNO" and "Phi2" - a positive correlation. Is it true?

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Dan TerAvest

Mar 2016

The dynamics of PhiNPQ and NPQt will always be similar. However, the relationship between PhiNPQ (and NPQt) and Phi2 and PhiNO is not always similar.

If PhiNPQ increases, then there must be a corresponding decrease in either Phi2 or PhiNO, because the sum of PhiNPQ + Phi2 + PhiNO =1. However, it could be that only Phi2 goes down to compensate for increased PhiNPQ and PhiNO doesn't change, or vice versa. So we cannot assume a positive or negative correlation.

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Greg Austic

Mar 2016

Put another way, while we've seen some general trends so far for Phi2 PhiNPQ and PhiNO, exploring these relationships remains an open and very compelling path - there is science to be done here!!!

:)

Greg

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Dan TerAvest

Mar 2016

Briefly, these 3 parameters describe the destination of captured light, and the sum of all 3 parameters should equal 1.0:

Phi2: Quantum yield of Photosystem II. This measurement is essentially the percentage of incoming light (excited electrons) that go into Photosystem II (photosynthetic processes). Photosystem II is where most light energy is converted into food.

PhiNPQ: Ratio of incoming light (excited electrons) that goes towards non-photochemical quenching. The plant regulating excess energy in such a way as too reduce damage to the plant.

PhiNO: Ratio of incoming light that is lost via non-regulated processes. PhiNO is the combination of a number of unregulated processes whose by products can inhibit photosynthesis or be harmful to the plant.