A PSII photosynthetic control is activated in anoxic cultures of green algae following illumination

Abstract

Photosynthetic hydrogen production from microalgae is considered to have potential as a renewable energy source. Yet, the process has two main limitations holding it back from scaling up; (i) electron loss to competing processes, mainly carbon fixation and (ii) sensitivity to O2 which diminishes the expression and the activity of the hydrogenase enzyme catalyzing H2 production. Here we report a third, hitherto unknown challenge: We found that under anoxia, a slow-down switch is activated in photosystem II (PSII), diminishing the maximal photosynthetic productivity by three-fold. Using purified PSII and applying in vivo spectroscopic and mass spectrometric techniques on Chlamydomonas reinhardtii cultures, we show that this switch is activated under anoxia, within 10 s of illumination. Furthermore, we show that the recovery to the initial rate takes place following 15 min of dark anoxia, and propose a mechanism in which, modulation in electron transfer at the acceptor site of PSII diminishes its output. Such insights into the mechanism broaden our understanding of anoxic photosynthesis and its regulation in green algae and inspire new strategies to improve bio-energy yields.

Visible Organic Thermoluminescence above Room Temperature in Small Molecule Crystals

“…Nuclear magnetic resonance (NMR) spectra were acquired on a JNM-ECZ600R/S1 spectrometer (600 MHz). Proton chemical shifts are reported in parts per million (ppm, δ scale), and are referenced by using tetramethylsilane (TMS) as an internal standard or residual protium in the NMR solvent (CDCl3: 1 H, δ = 7.26 ppm; 13 C, δ = 77.00 ppm). Splitting patterns are designated as s (singlet), d (doublet), t (triplet), q (quartet), and m (multiplet).…”

“…The results demonstrate that the trap depths of the TL materials are distributed within the range of 0.77 eV to 0.93 eV (Supplementary Section 2, Supplementary Tables 5 and 6, Supplementary Figs. [12][13][14][15][16]. Analysis of the isothermal decay curves reveals that Bp-PTZe and Dp-PTZe exhibit the longest (1761.78 s) and shortest (1357.17 s) afterglow lifetimes (Fig.…”

“…For instance, the temperature-induced recombination of charge-separated states in the photosystem II (SPII) serves as the primary source of thermoluminescent emission in the photosynthetic system (plants/algae). Since this type of luminescence involves a series of electron transfer reactions centered around metal complexes, such as chlorophyll, it deviates from the strictly defined realm of organic thermoluminescence 12,13 . To date, thermoluminescence research has primarily focused on polymer among pure organic compounds.…”

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Thermoluminescence (TL) is commonly observed in inorganic luminescent materials at elevated temperatures [1][2][3][4][5] , with applications in radiation dosimetry, archaeology, geological dating, and defect studies [6][7][8][9][10][11] . However, the understanding of TL in organic small molecules above room temperature is still limited [12][13][14][15][16][17][18][19][20][21][22][23][24] . Here, we experimentally discovered and theoretically analyzed the unusual TL exhibited by organic scintillation crystals in air.

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Photosynthetic H2 production: Lessons from the regulation of electron transfer in microalgae

“…Unfortunately, most of these methods substantially impair PSII activity (Figure 2), which significantly reduces the rate of photosynthetic H 2 production in microalgae compared to the dark‐to‐light transition method (Table 2), thus hampering its potential for future commercial applications. Moreover, even in the dark‐to‐light transition method, PSII electron output is diminished through a photosynthetic control mechanism, consequently reducing the rate of photosynthetic H 2 production in microalgae (Milrad et al., 2023).…”