Synthesis of a new furan-bearing triazine dichloride compound

Donor-acceptor compounds have been receiving increased attention lately, especially in opto-electronic applications. In this work, a novel compound named triazine-furan, comprised of a triazine acceptor moiety and a furan donor side group, was designed and synthesised for the first time. The influences of temperature and the feeding proportion of cyanuric chloride to furfurylamine were investigated to optimise the reaction yield and purification process. The synthesised compound was characterised using thin-layer chromatography (TLC), Fourier-transform infrared spectroscopy (FTIR), and proton nuclear magnetic resonance (1H-NMR) spectroscopy.

An amino residue that guides the correct photoassembly the water-oxidation complex but not required for high affinity Mn2+ binding

The assembly of the Mn4O5Ca cluster of the photosystem II (PSII) starts from the initial binding and photooxidation of the first Mn2+ at a high affinity site (HAS). Recent cryo-EM apo-PSII structures reveal an altered geometry of amino ligands in this region and suggest the involvement of D1-Glu189 ligand in the formation of the HAS. We now find that Gln and Lys substitution mutants photoactivate with reduced quantum efficiency compared to the wild-type. However, the affinity of Mn2+ at the HAS in D1-E189K was very similar to the wild-type (~2.2 μM). Thus, we conclude that D1-E189 does not form the HAS (~2.9 μM) and that the reduced quantum efficiency of photoactivation in D1-E189K cannot be ascribed to the initial photooxidation of Mn2+ at the HAS. Besides reduced quantum efficiency, the D1-E189K mutant exhibits a large fraction of centers that fail to recover activity during photoactivation starting early in the assembly phase, becoming recalcitrant to further assembly. Fluorescence relaxation kinetics indicate on the presence of an alternative route for the charge recombination in Mn-depleted samples in all studied mutants and exclude damage to the photochemical reaction center as the cause for the recalcitrant centers failing to assemble and show that dark incubation of cells reverses some of the inactivation. This reversibility would explain the ability of these mutants to accumulate a significant fraction of active PSII during extended periods of cell growth. The failed recovery in the fraction of inactive centers appears to a reversible mis-assembly involving the accumulation of photooxidized, but non-catalytic high valence Mn at the donor side of photosystem II, and that a reductive mechanism exists for restoration of assembly capacity at sites incurring mis-assembly. Given the established role of Ca2+ in preventing misassembled Mn, we conclude that D1-E189K mutant impairs the ligation of Ca2+ at its effector site in all PSII centers that consequently leads to the mis-assembly resulting in accumulation of non-catalytic Mn at the donor side of PSII. Our data indicate that D1-E189 is not functionally involved in Mn2+ oxidation\binding at the HAS but rather involved in Ca2+ ligation and steps following the initial Mn2+ photooxidation.

Fast enzymatic HCO3- dehydration supports photosynthetic water oxidation in Photosystem II from pea

Carbonic anhydrase (CA) activity, associated with Photosystem II (PSII) from Pisum sativum, has been shown to enhance water oxidation. But, the nature of the CA activity, its origin and role in photochemistry has been under debate, since the rates of CA reactions, measured earlier, were less than the rates of photochemical reactions. Here, we demonstrate high CA activity in PSII from Pisum sativum, measured by HCO3- dehydration at pH 6.5 (i.e. under optimal condition for PSII photochemistry), with kinetic parameters Km of 2.7 mM; Vmax of 2.74·10-2 mM·sec-1; kcat of 1.16·103 sec-1 and kcat/Km of 4.1·105 M-1 sec-1, showing the enzymatic nature of this activity, which kcat exceeds by ~13 times the rate of PSII, as measured by O2 evolution. The similar dependence of HCO3- dehydration, of the maximal quantum yield of photochemical reactions and of O2 evolution on the ratio of chlorophyll/photochemical reaction center II demonstrate the interconnection of these processes on the electron donor side of PSII. Since the removal of protons is critical for fast water oxidation, and since HCO3- dehydration consumes a proton, we suggest that CA activity, catalyzing very fast removal of protons, supports efficient water oxidation in PSII and, thus, photosynthesis in general.

Polymer-Modified Single-Walled Carbon Nanotubes Affect Photosystem II Photochemistry, Intersystem Electron Transport Carriers and Photosystem I End Acceptors in Pea Plants

Single-walled carbon nanotubes (SWCNT) have recently been attracting the attention of plant biologists as a prospective tool for modulation of photosynthesis in higher plants. However, the exact mode of action of SWCNT on the photosynthetic electron transport chain remains unknown. In this work, we examined the effect of foliar application of polymer-grafted SWCNT on the donor side of photosystem II, the intersystem electron transfer chain and the acceptor side of photosystem I. Analysis of the induction curves of chlorophyll fluorescence via JIP test and construction of differential curves revealed that SWCNT concentrations up to 100 mg/L did not affect the photosynthetic electron transport chain. SWCNT concentration of 300 mg/L had no effect on the photosystem II donor side but provoked inactivation of photosystem II reaction centres and slowed down the reduction of the plastoquinone pool and the photosystem I end acceptors. Changes in the modulated reflection at 820 nm, too, indicated slower re-reduction of photosystem I reaction centres in SWCNT-treated leaves. We conclude that SWCNT are likely to be able to divert electrons from the photosynthetic electron transport chain at the level of photosystem I end acceptors and plastoquinone pool in vivo. Further research is needed to unequivocally prove if the observed effects are due to specific interaction between SWCNT and the photosynthetic apparatus.

Properties of Photosystem II lacking the PsbJ subunit

Photosystem II (PSII), the oxygen-evolving enzyme, consists of 17 trans-membrane and 3 extrinsic membrane proteins. Other subunits bind to PSII during assembly, like Psb27, Psb28, Tsl0063. The presence of Psb27 has been proposed (Zabret et al. 2021; Huang et al. 2021; Xiao et al. 2021) to prevent the binding of PsbJ, a single transmembrane α-helix close to the quinone QB binding site. Consequently, a PSII rid of Psb27, Psb28 and Tsl0034 prior to the binding of PsbJ would logically correspond to an assembly intermediate. The present work describes experiments aiming at further characterizing such a ΔPsbJ-PSII, purified from the thermophilic Thermosynechococcus elongatus, by means of MALDI-TOF spectroscopy, Thermoluminescence, EPR spectroscopy and UV-visible time-resolved spectroscopy. In the purified ΔPsbJ-PSII, an active Mn4CaO5 cluster is present in 60-70 % of the centers. In these centers, although the forward electron transfer seems not affected, the Em of the QB/QB- couple increases by ≈120 mV thus disfavoring the electron coming back on QA. The increase of the energy gap between QA/QA- and QB/QB- could contribute in a protection against the charge recombination between the donor side and QB-, identified at the origin of photoinhibition under low light (Keren et al. 1997), and possibly during the slow photoactivation process.

PROTECTION WITH A BIOACTIVE COMPOSITION BASED ON PLUMBAGIN (CERATOSTIGMA PLUMBAGINOIDES BUNGE) AND NA-ASCORBATE PIGMENTS AND PSII IN OXIDATIVE STRESS

The protective properties of Na-ascorbate and a bioactive composition (BAC) obtained on the basis of plumbagin from roots (Ceratostigma plumbaginoides Bunge) under the toxic effect of Zn2+ and Ni2+ on wheat seedlings (Triticum aestivum L.) were studied. The change in the characteristics of millisecond delayed fluorescence (msec DF Chl a) reflecting the state of PS II shows a decrease in the blocking of the activity of the electron transport chain (ETC) on the acceptor side under the action of Zn2+ and Ni2+ and on the donor side under the action of Ni2+. The resistance of Chl b 650 decreases and the resistance of carotenoids to this stress increases. The action of Na-asс and BAC changes the ratio of pigments. Na-asc restores the activity of the donor side and increases the work of the acceptor side of the ETC upon sequential action with Zn2+. The activity of the acceptor side of the ETC is restored with the simultaneous action of Na-asc with Ni2+. The effect of the BAC is manifested in the restoration of the activity of the donor side of the ETC PS II with sequential action with metals. The corrective effect of Na-asc and LHC is determined by their ability to neutralize reactive oxygen species formed under stress and to support the redox reactions of photosystems.

Why Does Aid Not Target the Poorest?

Foreign-aid projects typically have local effects, so they need to be placed close to the poor if they are to reduce poverty. I show that, conditional on local population levels, World Bank (WB) project aid targets richer parts of countries. This relationship holds over time and across world regions. I test five donor-side explanations for pro-rich targeting using a pre-registered conjoint experiment on WB Task Team Leaders (TTLs). TTLs perceive aid-receiving governments as most interested in targeting aid politically and controlling implementation. They also believe that aid works better in poorer or more remote areas, but that implementation in these areas is uniquely difficult. These results speak to debates in distributive politics, international bargaining over aid, and principal-agent issues in international organizations. The results also suggest that tweaks to WB incentive structures to make ease of project implementation less important may encourage aid to flow to poorer parts of countries.

Effects of phosphorus deficiency on the absorption of mineral nutrients, photosynthetic system performance and antioxidant metabolism in Citrus grandis

Phosphorus (P) is an essential macronutrient for plant growth, development and production. However, little is known about the effects of P deficiency on nutrient absorption, photosynthetic apparatus performance and antioxidant metabolism in citrus. Seedlings of ‘sour pummelo’ (Citrus grandis) were irrigated with a nutrient solution containing 0.2 mM (Control) or 0 mM (P deficiency) KH2PO4 until saturated every other day for 16 weeks. P deficiency significantly decreased the dry weight (DW) of leaves and stems, and increased the root/shoot ratio in C. grandis but did not affect the DW of roots. The decreased DW of leaves and stems might be induced by the decreased chlorophyll (Chl) contents and CO2 assimilation in P deficient seedlings. P deficiency heterogeneously affected the nutrient contents of leaves, stems and roots. The analysis of Chl a fluorescence transients showed that P deficiency impaired electron transport from the donor side of photosystem II (PSII) to the end acceptor side of PSI, which showed a greater impact on the performance of the donor side of PSII than that of the acceptor side of PSII and photosystem I (PSI). P deficiency increased the contents of ascorbate (ASC), H2O2 and malondialdehyde (MDA) as well as the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in leaves. In contrast, P deficiency increased the ASC content, reduced the glutathione (GSH) content and the activities of SOD, CAT, APX and monodehydroascorbate reductase (MDHAR), but did not increase H2O2 production, anthocyanins and MDA content in roots. Taking these results together, we conclude that P deficiency affects nutrient absorption and lowers photosynthetic performance, leading to ROS production, which might be a crucial cause of the inhibited growth of C. grandis.