Comparative Time-Resolved Photosystem II Chlorophyll a Fluorescence Analyses Reveal Distinctive Differences between Photoinhibitory Reaction Center Damage and Xanthophyll Cycle-Dependent Energy Dissipation*

Abstract— The photosystem II (PSII) reaction center in higher plants is susceptible to photoinhibitory molecular damage of its component pigments and proteins upon prolonged exposure to excess light in air. Higher plants have a limited capacity to avoid such damage through dissipation, as heat, of excess absorbed light energy in the PSII light-harvesting antenna. The most important pho-toprotective heat dissipation mechanism, induced under excess light conditions, includes a concerted effect of the trans-thylakoid pH gradient (ΔpH) and the carotenoid pigment interconversions of the xanthophyll cycle. Co-incidentally, both the photoprotective mechanism and photoinhibitory PSII damage decrease the PSII chlorophyll a (Chi a) fluorescence yield. In this paper we present a comparative fluorescence lifetime analysis of the xanthophyll cycle- and photoinhibition-dependent changes in PSII Chi a fluorescence. We analyze multifrequency phase and modulation data using both multicomponent exponential and bimodal Lorentzian fluorescence lifetime distribution models; further, the lifetime data were obtained in parallel with the steady-state fluorescence intensity. The photoinhi-bition was characterized by a progressive decrease in the center of the main fluorescence lifetime distribution from ～2 ns to ～0.5 ns after 90 min of high light exposure. The damaging effects were consistent with an increased nonra-diative decay path for the charge-separated state of the PSII reaction center. In contrast, the ΔpH and xanthophyll cycle had concerted minor and major effects, respectively, on the PSII fluorescence lifetimes and intensity (Gilmore et ah, 1996, Photosynth. Res., in press). The minor change decreased both the width and lifetime center of the longest lifetime distribution; we suggest that this change is associated with the ΔpH-induced activation step, needed for binding of the deepoxidized xanthophyll cycle pigments. The major change increased the fractional intensity of a short lifetime distribution at the expense of a longer lifetime distribution; we suggest that this change is related to the concentration-dependent binding of the deepoxidized xanthophylls in the PSII inner antenna. Further, both the photoinhibition and xanthophyll cycle mechanisms had different effects on the relationship between the fluorescence lifetimes and intensity. The observed differences between the xanthophyll cycle and photoinhibition mechanisms confirm and extend our current basic model of PSII exciton dynamics, structure and function.     

The impact of preventive voice care programs for training teachers: A longitudinal study

The teaching profession puts vocal health at a higher risk than other professions, causing what is referred to as "occupational dysphonia." There is a need for primary prevention of "occupational dysphonia" among the teaching profession, where good vocal health is promoted before a problem occurs. To investigate the primary prevention of occupational dysphonia among teachers, this study uses a sample population of 55 training teachers, in the postgraduate certificate of education (PGCE) course at the University of Ulster, Northern Ireland, who were randomly assigned to three training groups: control, indirect, and direct. The vocal performance of the three groups was measured at two points over the year of the PGCE course: first before any teaching or training began, and again after the first teaching practice. The training for the indirect and direct groups was provided before the teaching practices. Acoustic and self-perceptual measurements were used to assess the multidimensional outcomes. The results demonstrate interesting trends, that although not found to be significant, are approaching significance. Their voices will be reevaluated at a third point of measurement. The acoustic measurement reflects deterioration from time 1 to time 2 for the control group, improvement for the direct group, and no change for the indirect group, indicating that the training has proved beneficial. The self-rating scores vary in agreement with the acoustic results, presenting interesting findings. The findings of this study will be of benefit to teachers, their educators, voice therapists, health promoters, and human resource personnel.     

Simulation of capillary-dominated displacements in microtomographic images of reservoir rocks

Displacement simulation in realistic pore networks, such as those derived from X-ray microtomography, is presented for the regime where capillarity controls fluid motions and spatial distributions. Complex displacement sequences involving both imbibition and drainage are constructed to extract wettability indices. The percolation properties of predicted equilibrium phase distributions are analyzed. Equilibrium fluid distributions are used to model transport properties for each phase.     

Solution structural characterization of an array of nanoscale aqueous inorganic Ga13–xInx (0 ≤ x ≤ 6) clusters by 1H-NMR and QM computations

NMR spectroscopy is the go-to technique for determining the solution structures of organic, organometallic, and even macromolecular species. However, structure determination of nanoscale aqueous inorganic clusters by NMR spectroscopy remains an unexplored territory. The few hydroxo-bridged inorganic species well characterized by ¹H Nuclear Magnetic Resonance spectroscopy (¹H-NMR) do not provide enough information for signal assignment and prediction of new samples. ¹H-NMR and quantum mechanical (QM) computations were used to characterize the NMR spectra of the entire array of inorganic flat-Ga_13–xIn_x (0 ≤ x ≤ 6) nanoscale clusters in solution. A brief review of the known signals for μ₂-OH and μ₃-OH bridges gives expected ranges for certain types of protons, but does not give enough information for exact peak assignment. Integration values and NOESY data were used to assign the peaks of several cluster species with simple ¹H-NMR spectra. Computations agree with these hydroxide signal assignments and allow for assignment of the complex spectra arising from the remaining cluster species. This work shows that ¹H-NMR spectroscopy provides a variety of information about the solution behavior of inorganic species previously thought to be inaccessible by NMR due to fast ligand and/or proton exchange in wet solvents.