Rubisco activities, properties, and regulation in three different C4 grasses under drought

In C4 plants, water deficit may decrease photosynthetic CO2 assimilation independently of changes in stomatal conductance, suggesting decreased turnover by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The activity and biochemistry of Rubisco was studied in three different C4 grasses: Paspalum dilatatum, Cynodon dactylon, and Zoysia japonica. The objectives were to characterize the C4 Rubisco in these species and to identify factors associated with decreased photosynthetic rates caused by drought. Rubisco isolated from each of the three C4 grasses was characterized by smaller specificity factors (SC/O), larger Michaelis–Menten constants for CO2 (Kc) and O2 (Ko), and larger maximum carboxylation velocities (Vc) than Rubisco from wheat, which can be rationalized in terms of the CO2-rich environment of C4 Rubisco in the bundle sheath. During leaf dehydration the quantity and maximum activity of Rubisco remained unchanged but the initial and total activities declined slightly, possibly due to increased inhibition. Tight-binding inhibitors were present in the light but were more abundant in the dark, especially in Z. japonica, and increased in quantity with drought stress. The inhibitor from darkened leaves of Z. japonica was identified as 2-carboxyarabinitol-1-phosphate (CA1P). Consistent with the presence of CA1P, the total activity of Rubisco was decreased after 12 h darkness in Z. japonica. Ribulose-1,5-bisphosphate (RuBP) in the leaves decreased with drought stress, to quantities approximating those of Rubisco catalytic sites. The magnitude of the decrease in RuBP suggested that, at least in C. dactylon and Z. japonica, it could contribute to the drought-induced decrease in photosynthesis

[60]PCBM Single Crystals: Remarkably Enhanced Band-like Charge Transport, Broadband UV-Visible-NIR Photo-responsivity and Improved Long-term Air-stability

We report the charge transport mechanism, long-term stability and UV-Visible-NIR photo-responsivity of single crystals of [60]PCBM (phenyl-C61-butyric acid methyl ester) – the dominant acceptor material in organic photovoltaics. Despite [60]PCBM’s paramount role in such device, its intrinsic properties was largely unknown because of highly disordered solution-processed films, the electron transport mechanism remained ill-defined, and the long-term stability was poor – posing a major bottleneck for advancing cell efficiency and stability. We employed a liquid−liquid interfacial precipitation strategy to grow single crystals of [60]PCBM, which allowed us to experimentally elucidate its electron transport properties, long-term stability and photo-responsivity. Temperature-dependent mobility studies enabled us to reveal its charge transport mechanism. Promisingly, [60]PCBM single crystals were found to exhibit a more favorable band-like charge transport mechanism at room temperature and present electron mobility exceeding their thin-film counterparts by two orders of magnitude. Photodetectors based on single crystals show broadband photo-responsivity from UV, Visible to NIR regions. Long-term stability test showed the performance of devices based on single crystals remained 80% after 480-hour aging, whereas the performance of thin film devices dropped by over 80% under the same condition. Our findings underscore single crystals as a key strategy to achieve breakthroughs in highly efficient and stable devices

Glyphosate-dependent effects on photosynthesis of Solanum lycopersicum L. an ecophysiological, ultrastructural and molecular approach

This study aimed to assess the toxicity of glyphosate (GLY; 0, 10, 20 and 30?mg?kg-1) in Solanum lycopersicum L., particularly focusing on the photosynthetic metabolism. By combining ecophysiological, ultrastructural, biochemical and molecular tools, the results revealed that the exposure of tomato plants to GLY led to alterations in leaf water balance regulation [increasing stomatal conductance (gs) and decreasing water use efficiency (WUEi) at higher concentrations] and induced slight alterations in the structural integrity of cells, mainly in chloroplasts, accompanied by a loss of cell viability. Moreover, the transcriptional and biochemical control of several photosynthetic-related parameters was reduced upon GLY exposure. However, in vivo chlorophyll fluorometry and IRGA gas-exchange studies revealed that the photosynthetic yield of S. lycopersicum was not repressed by GLY. Overall, GLY impacts cellular and subcellular homeostasis (by affecting chloroplast structure, reducing photosynthetic pigments and inhibiting photosynthetic-related genes transcription), and leaf structure, but is not reducing the carbon flow on a leaf area basis. Altogether, these results suggest a trade-off effect in which GLY-induced toxicity is compensated by a higher photosynthetic activity related to GLY-induced dysfunction in gs and an increase in mesophyll thickness/density, allowing the viable leaf cells to maintain their photosynthetic capacity.FCT -Fundação para a Ciência e a Tecnologia(SFRH/BD/115643/2016)info:eu-repo/semantics/publishedVersio

Glycolate Oxidase Isozymes Are Coordinately Controlled by GLO1 and GLO4 in Rice

Glycolate oxidase (GLO) is a key enzyme in photorespiratory metabolism. Four putative GLO genes were identified in the rice genome, but how each gene member contributes to GLO activities, particularly to its isozyme profile, is not well understood. In this study, we analyzed how each gene plays a role in isozyme formation and enzymatic activities in both yeast cells and rice tissues. Five GLO isozymes were detected in rice leaves. GLO1 and GLO4 are predominately expressed in rice leaves, while GLO3 and GLO5 are mainly expressed in the root. Enzymatic assays showed that all yeast-expressed GLO members except GLO5 have enzymatic activities. Further analyses suggested that GLO1, GLO3 and GLO4 interacted with each other, but no interactions were observed for GLO5. GLO1/GLO4 co-expressed in yeast exhibited the same isozyme pattern as that from rice leaves. When either GLO1 or GLO4 was silenced, expressions of both genes were simultaneously suppressed and most of the GLO activities were lost, and consistent with this observation, little GLO isozyme protein was detected in the silenced plants. In contrast, no observable effect was detected when GLO3 was suppressed. Comparative analyses between the GLO isoforms expressed in yeast and the isozymes from rice leaves indicated that two of the five isozymes are homo-oligomers composed of either GLO1 or GLO4, and the other three are hetero-oligomers composed of both GLO1 and GLO4. Our current data suggest that GLO isozymes are coordinately controlled by GLO1 and GLO4 in rice, and the existence of GLO isozymes and GLO molecular and compositional complexities implicate potential novel roles for GLO in plants