quantum yield

Jonathan B. Marder MARDER at agri.huji.ac.il
Tue Sep 3 10:58:43 EST 1996


In article <506o1f$671 at mserv1.dl.ac.uk>,
   "Kromkamp, Jacco" <kromkamp at cemo.nioo.knaw.nl> wrote:
>
>hello,
>
>I'm working with eukaryotic marine microalgae and investigating how
oxygen
>evolution and PSII quantum efficiency is regulated in nutrient rich,
light
>limited continuous cultures. The maximum PSII quantum efficiency
(Fv/Fm) I
>seem to be able to get using PAM measurements (and saturating multiple
>turnover flashes) seems to be around 0.65, but never as high as
0.8-0.85, as
>found for higher plants.

The higher ratio for land plants occurs when pretty much all of Fo comes
from "open" PSII and all of Fmax from closed PSII. As soon as there is
some extra fluorescence in Fo, the ratio falls. Since you are looking at
algae, I would suspect that antenna fluorescence is involved (e.q.
phycobiliproteins can be highly fluorescent).


> Any suggestions for possible causes? Might it be due to the fact that
>the
>excitation light (standard red LED for measuring ligh) is poorly
>absorbed?
Definitely not! Light not absorbed isn't going to elicit fluorescence.

>Or is it due to the fact that I use chlorophyll a/c containing species
>(diatoms, Prymnesiophytes), which do not show stacking in the
>chloroplasts?
Worth considering. However, barley mutants with vastly reduced antenna
and stacking often show normal variable fluorescence.


We address some of these issues in the last Photosynthesis Congress:
Marder, Caspi & Raskin (1995) In: Photosynthesis: from Light ro
Biosphere (ed. P. Mathis), Vol III pp 305-8 (Kluwer press).


I hope that this helps.


Jonathan B. Marder             ,      Department of Agricultural Botany
E-mail: MARDER at agri.huji.ac.il |      The Hebrew University of Jerusalem
Phone: (08 or +9728) 9481918   | /\/  Faculty of Agriculture
Fax:   (08 or +9728) 9467763   |/  \  P.O.Box 12, Rehovot 76100, ISRAEL
     http://www.agri.huji.ac.il/~marder





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