Localization of the mechanism of pH-dependent non- photochemical fluorescence quenching in thylakoid membranes

Higher plants have evolved a well-conserved set of photoprotective mechanisms, collectively designated Non-Photochemical Quenching of chlorophyll fluorescence (qN), to deal with the inhibitory absorption of excess light energy by the photosystems. Their main contribution originates from safe thermal deactivation of excited states promoted by a highly-energized thylakoid membrane, detected via lumen acidification. The precise origins of this energy- or LlpH-dependent quenching (qE), arising from either decreased energy transfer efficiency in PSII antennae (~ Young & Frank, 1996; Gilmore & Yamamoto, 1992; Ruban et aI., 1992), from alternative electron transfer pathways in PSII reaction centres (~ Schreiber & Neubauer, 1990; Thompson &Brudvig, 1988; Klimov et aI., 1977), or from both (Wagner et aI., 1996; Walters & Horton, 1993), are a source of considerable controversy. In this study, the origins of qE were investigated in spinach thylakoids using a combination of fluorescence spectroscopic techniques: Pulse Amplitude Modulated (PAM) fluorimetry, pump-probe fluorimetry for the measurement of PSII absorption crosssections, and picosecond fluorescence decay curves fit to a kinetic model for PSII. Quenching by qE (,..,600/0 of maximal fluorescence, Fm) was light-induced in circulating samples and the resulting pH gradient maintained during a dark delay by the lumenacidifying capabilities of thylakoid membrane H+ ATPases. Results for qE were compared to those for the addition of a known antenna quencher, 5-hydroxy-1,4naphthoquinone (5-0H-NQ), titrated to achieve the same degree of Fm quenching as for qE. Quenching of the minimal fluorescence yield, F0' was clear (8 to 130/0) during formation of qE, indicative of classical antenna quenching (Butler, 1984), although the degree was significantly less than that achieved by addition of 5-0H-NQ. Although qE induction resulted in an overall increase in absorption cross-section, unlike the decrease expected for antenna quenchers like the quinone, a larger increase in crosssection was observed when qE induction was attempted in thylakoids with collapsed pH gradients (uncoupled by nigericin), in the absence of xanthophyll cycle operation (inhibited by DTT), or in the absence of quenching (LlpH not maintained in the dark due to omission of ATP). Fluorescence decay curves exhibited a similar disparity between qE-quenched and 5-0H-NQ-quenched thylakoids, although both sets showed accelerated kinetics in the fastest decay components at both F0 and Fm. In addition, the kinetics of dark-adapted thylakoids were nearly identical to those in qEquenched samples at F0' both accelerated in comparison with thylakoids in which the redox poise of the Oxygen-Evolving Complex was randomized by exposure to low levels of background light (which allowed appropriate comparison with F0 yields from quenched samples). When modelled with the Reversible Radical Pair model for PSII (Schatz et aI., 1988), quinone quenching could be sufficiently described by increasing only the rate constant for decay in the antenna (as in Vasil'ev et aI., 1998), whereas modelling of data from qE-quenched thylakoids required changes in both the antenna rate constant and in rate constants for the reaction centre. The clear differences between qE and 5-0H-NQ quenching demonstrated that qE could not have its origins in the antenna alone, but is rather accompanied by reaction centre quenching. Defined mechanisms of reaction centre quenching are discussed, also in relation to the observed post-quenching depression in Fm associated with photoinhibition.

Mindfulness: An Ancient Wisdom for the Reconceptualisation of Modern Education in the Complex World

Exploring the new science of emergence allows us to create a very different classroom than how the modern classroom has been conceptualised under the mentality of efficiency and output. Working on the whole person, and not just the mind, we see a shift from the epistemic pillars of truth to more ontological concerns as regards student achievement in our post-Modern and critical discourses. It is important to understand these shifts and how we are to transition our own perception and mentality not only in our research methodologies but also our approach to conceptualisations of issues in education and sustainability. We can no longer think linearly to approach complex problems or advocate for education and disregard our interconnectedness insofar as it enhances our children’s education. We must, therefore, contemplate and transition to a world that is ecological and not mechanical, complex and not complicated—in essence, we must work to link mind-body with self-environment and transcend these in order to bring about an integration toward a sustainable future. A fundamental shift in consciousness and perception may implicate our nature of creating dichotomous entities in our own microcosms, yet postmodern theorists assume, a priori, that these dualities can be bridged in naturalism alone. I, on the other hand, embrace metaphysics to understand the implicated modern classroom in a hierarchical context and ask: is not the very omission of metaphysics in postmodern discourse a symptom from an education whose foundation was built in its absence? The very dereliction of ancient wisdom in education is very peculiar indeed. Western mindfulness may play a vital component in consummating pragmatic idealism, but only under circumstances admitting metaphysics can we truly transcend our limitations, thereby placing Eastern Mindfulness not as an ecological component, but as an ecological and metaphysical foundation.

Metabolite changes during Riesling icewine fermentation when yeast micronutrients are used /

Icewine is an intensely s\veet dessert \vine fermented from the juice of naturally frozen grapes. Icewine fermentation poses many challenges such as failure to reach desired ethanol levels and production of high levels of volatile acidity in the fonn of acetic acid. This study investigated the impact of micronutrient addition (GO-FERM® and NATSTEP®) during the rehydration stage of the commercial \vine yeast Saccharomyces cerevisiae KI-VIII6 during Ice\vine fermentation. Sterile-filtered and unfiltered Riesling Ice\vine juice was inoculated \vith yeast rehydrated under four different conditions: in water only; with GO-FERM®; with NATSTEP®; or the combination of both micronutrient products in the rehydration water. Using sterile-filtered Icewine juice, yeast rehydration had a positive impact of reducing the rate of acetic acid produced as a function of sugar consumed, reducing the ratio of acetic acid/ethanol and reducing the ratio of acetic acid/glycerol. In the sterile-filtered fermentation, yeast rehydrated with micronutrients generated 9-times less acetic acid per gram of sugar in the first 48 hours compared to yeast rehydrated only \vith water and resulted in a 17% reduction in acetic acid in the final \vine \vhen normalized to sugar consumed. However, the sterile-filtered fermentations likely became stuck due to the overc1arification of the juice as evidenced from the low sugar consumption (117 gIL) that could not be completely overcome by the micronutrient treatments (144 gIL sugar consumed) to reach a target ethanol of IO%v/v. Contrary to \vhat \vas observed in the sterile-filtered treatements, using unfiltered Ice\vine juice, yeast micronutrient addition had no significant impact of reducing the rate of acetic acid produced as a function of sugar consumed, reducing the ratio of acetic acid/ethanol and reducing the ratio of acetic acid/glycerol. However, in the unfiltered fermentation, micronutrient addition during yeast rehydration caused a reduction in the acetic acid produced as a function of sugar consumed up to 150 giL sugar consumed.. In contrast to the sterile-filtered fermentations, the unfiltered fermentations did not become stuck as evidenced from the higher sugar consumption (l47-174g1L). The largest effects of micronutrient addition are evident in the first two days of both sterile and unfiltered fermentations.