In article <506o1f$671 at mserv1.dl.ac.uk>, "Kromkamp, Jacco"
<kromkamp at cemo.nioo.knaw.nl> wrote:
>> 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.
> 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?
> 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?
Perhaps you have more PSI in the light limited cultures. PSI seems to
contribute an approximately constant amount to the apparent Fo. The
quantum efficiency you get by using Fv/Fm in a mix of PSII and PSI centers
would be lower than if you had isolated PSII.
See Genty et al. (1990) Photosynth. Res. 26: 133-139
They didn't *prove* that it was due to PSI, but the data is quite
suggestive of that. If anybody knows of a better reference on this
subject, I would like to know about it.
Idle time is not idle! See above why.