Oleg V. Moskvin OMEGA at
Sun Oct 27 05:43:45 EST 1996

Harold Weger wrote: 

>I have been following the anthocyanin/red colouration discussion, and have
>read with interest many of the ideas/hypotheses advanced to date. However, I
>have consistently wondered whether anthocyanin synthesis in the fall is
>simply a mechanism to reduce the effective light intensity (PFR), i.e. that
>anthocyanin functions as a sun screen (cytosolic carotenoids have been
>postulated to function in the same manner in the green alga Haematococcus).

>Why would a maple turn red in the fall? Is it simply to decrease the degree
>of photoinhibition induced by low temperature? That is, as temperatures
>decrease proportionally more than PFR in the fall, synthesis of anthocyanins
>would serve to screen the photosynthetic apparatus, and thus minimize the
>degree of photoinhibition. I don't know if there are experiments or data
>that support this idea, but it should be easy enough to test using a
>chlorophyll a fluorescence measurements. Does anyone know of such experiments?

>Harold Weger

>Harold G. Weger            tel: 306-585-4479
>Department of Biology      fax: 306-585-4894
>University of Regina       e-mail: Harold.Weger at
>3737 Wascana Parkway
>Regina, Saskatchewan               
>S4S 0A2

It seems to be a fresh idea. I do not beleive that plants "do it specially", 
however, as a side effect of partial destruction of photosynthetic pigment 
system, the rest of chlorophyll could be really "shielded" thus being kept 
in an active state under limited utilization of excitation energy (i.e. at 
low temperatures). 
As to chlorophyll a fluorescence, this approach became extreamly popular 
after PAM-type portable devices became available. You can monitor the 
fluorescence quenching coefficients, the efficiency of PSII photochemistry... 
Unfortunately, you cannot see the item "degree of photoinhibition" on the 
screen of your fluorometer... If you discover that in certain conditions, 
the PSII quantum yield decreases, it may be due to either photoinhibition or 
the increase of non-radiative energy dissipation SAVING FROM photoinhibition. 
You may see the photoinhibition more or less directly if you measure the dark 
relaxation of chlorophyll fluorescence quenching. 
As far as I know, chlorophyll a fluorescence has not been applied to the 
autumn leaves. You may be the first! 

Oleg Moskvin. 

Oleg V. Moskvin 
Lab. of Photosynthetic Electron Transport 
Inst. of Soil Sci. & Photosynthesis 
Russian Academy of Sciences 
142292 Russia 
E-mail: omega at  

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