Impact of dimeric organization of enzyme on its function: the case of photosynthetic water splitting.

MOTIVATION: It is a question of whether the supramolecular organization of the protein complex has an impact on its function, or not. In the case of the photosystem II (PSII), water splitting might be influenced by cooperation of the PSIIs. Since PSII is the source of the atmospheric oxygen and because better understanding of the water splitting may contribute to the effective use of water as an alternative energy source, possible cooperation should be analyzed and discussed. RESULTS: We suggest that the dimeric organization of the PSII induces cooperation in the water splitting. We show that the model of monomeric PSII is unable to produce the oxygen after the second short flash (associated with the double turnover of the PSII), in contrast to the experimental data and model of dimeric PSII with considered cooperation. On the basis of this fact and partially from the support from other studies, we concluded that the double turnover of the PSII induced by short flashes might be caused by the cooperation in the water splitting. We further discuss a possibility that the known pathway of the electron transport through the PSII might be incomplete and besides D1-Y161, other cofactor which is able to oxidize the special chlorophyll pair (P680) must be considered in the monomeric PSII to explain the oxygen production after the second short flash. AVAILABILITY: Commented SBML codes (.XML files) of the monomeric and dimeric PSII models will be available (at the time of publication) in the BioModels database (www.ebi.ac.uk/biomodels).

A Monte Carlo study of the chlorophyll fluorescence emission and its effect on the leaf spectral reflectance and transmittance under various conditions.

Spectral hemispherical reflectance R(lambda) and transmittance T(lambda) are affected by chlorophyll (Chl) fluorescence which may complicate the evaluation of optical parameters of leaves. Measured Chl a fluorescence spectral emission F(lambda) is itself affected by several distortion effects on the leaf level (fluorescence reabsorption, secondary fluorescence, inner filter, surface and subsurface reflections etc.). In this work we propose a Monte Carlo photon transport (MCPT) model capable for treating a variety of optical distortion effects on the leaf level. In the forward mode the model decouples R(lambda), T(lambda) and their fluorescence contributions FR(T)(lambda). To obtain the absorption and scattering spectra of the leaf, utilized in the forward modeling, we have suggested an inversion procedure employing the experimental R(lambda), T(lambda). The attention was paid on the correction of the leaf absorption and scattering spectra caused by the optical effects on the sample level including Chl fluorescence contribution to measured R(lambda), T(lambda).

Early detection of plant stress from changes in distributions of chlorophyll a fluorescence parameters measured with fluorescence imaging.

In this work, we used barley leaves suffering from a stress, for measurements of chlorophyll a fluorescence with an imaging fluorometer. We compared selected fluorescence parameters (FP) determined from the measurements of control (no stress) and afterwards stressed sample by classical statistical comparison (Mann-Whitney test) and by statistical comparison of shapes of distributions of the FPs (two-sample Smirnov test). We have found that there exist examples where statistically significant difference is not revealed using the classical statistical comparison (for given critical level), but statistically significant difference is revealed using comparisons of distributions (for the same critical level). It implies that the shape of statistical distribution of a FP is more sensitive to a stress of a sample than median of the FP. Further, the comparison of changes in shapes of statistical distributions of FPs is therefore more suitable for early detection of plant stress than a classical statistical comparison. The observed changes in the distributions of FPs are discussed.