Photosynthesis Research最新文献

Mg²⁺, the most abundant divalent cation in living cells, plays a pivotal role in numerous enzymatic reactions and is of particular importance for organisms performing oxygenic photosynthesis. Its significance extends beyond serving as the central ion of the chlorophyll molecule, as it also acts as a counterion during the light reaction to balance the proton gradient across the thylakoid membranes. In this study, we investigated the effects of Mg²⁺ limitation on the physiology of the well-known model microorganism Synechocystis sp. PCC6803. Our findings reveal that Mg²⁺ deficiency triggers both morphological and functional changes. As seen in other oxygenic photosynthetic organisms, Mg²⁺ deficiency led to a decrease in cellular chlorophyll concentration. Moreover, the PSI-to-PSII ratio decreased, impacting the photosynthetic efficiency of the cell. In line with this, Mg²⁺ deficiency led to a change in the proton gradient built up across the thylakoid membrane upon illumination.

Cyanobacteria play a crucial role in global carbon and nitrogen cycles through photosynthesis, making them valuable subjects for understanding the factors influencing their light utilization efficiency. Photosynthetic microorganisms offer a promising avenue for sustainable energy conversion in the field of photovoltaics. It was demonstrated before that application of an external electric field to the microbial biofilm or cell improves electron transfer kinetics and, consequently, efficiency of power generation. We have integrated live cyanobacterial cultures into photovoltaic devices by embedding Limnospira indica PCC 8005 cyanobacteria in agar and PEDOT:PSS matrices on the surface of boron-doped diamond electrodes. We have subjected them to varying external polarizations while simultaneously measuring current response and photosynthetic performance. For the latter, we employed Pulse-Amplitude-Modulation (PAM) fluorometry as a non-invasive and real-time monitoring tool. Our study demonstrates an improved light utilization efficiency for L. indica PCC 8005 when immobilized in a conductive matrix, particularly so for low-intensity light. Simultaneously, the impact of electrical polarization as an environmental factor influencing the photosynthetic apparatus diminishes as matrix conductivity increases. This results in only a slight decrease in light utilization efficiency for the illuminated sample compared to the dark-adapted state.

Changes in rainfall patterns are important environmental factors affecting plant growth, especially when larger precipitation events and prolonged drought periods occur in subtropical regions. There are many studies on how drought reduces plant biomass through drought-sensitive functional traits, but how excess water affects plant growth and ecophysiology is still poorly understood. Therefore, a greenhouse experiment was conducted on Schima superba (Theaceae), a dominant tree species in subtropical forests and commonly used in forestry, in a closed chamber under control (25% soil water content (SWC) as in local forests), drought stress (D, 15% SWC) and moisture stress (W, 35% SWC). Plant growth and ecophysiological traits related to morphology, leaf gas exchange, water potential and structural traits were measured. Compared to control, S. suberba under dry conditions significantly decreased its aboveground biomass, photosynthetic rate (A), leaf water potential and nitrogen use efficiency, but increased intrinsic water use efficiency, root to shoot ratio and specific root length. S. superba under wet conditions also significantly decreased its total biomass, aboveground biomass and specific root length, while W had no effect on A and leaf water potential. Our results indicate that S. superba shows a decrease in carbon gain under drought stress, but less response under wet conditions. This emphasizes the need to consider the strength and frequency of rainfall pattern changes in future studies because rainfall may either alleviate or intensify the effects of drought stress depending on the moisture level, thus suitable water conditions is important for better management of this tree species in subtropical China.

Aquatic plants are a crucial component of the aquatic ecosystem in the Tibetan Plateau region. Researching the adaptability of plateau aquatic plants in photosynthesis to the plateau environment can enhance understanding of the operational mechanisms of plateau ecosystems, thereby providing a scientific basis for the protection and management of plateau aquatic ecosystems. This study presents an investigation of photosynthetic inorganic carbon utilization strategies and photosynthetic efficiency of 17 aquatic plants under natural growing conditions in Niyang River basin on the Tibetan Plateau. In pH-drift experiments, 10 of 17 species were able to utilize HCO₃^-, and environmental factors like water pH were shown to have a significant effect on the ability of the tested species to utilize HCO₃^-. Titratable acidity in the leaves of Stuckenia filiformis, Zannichellia palustris, Batrachium bungei, and Myriophyllum spicatum showed significant diurnal fluctuations at certain sampling sites, indicating the presence of CAM. In B. bungei, water pH positively correlated with CAM activity, while CO₂ concentration negatively correlated with CAM activity. The chlorophyll fluorescence analysis revealed that aquatic plants inhabiting the Tibetan Plateau exhibited photosynthetic adaptations. In conclusion, the aquatic plants on the Tibetan Plateau employ diverse strategies for utilizing inorganic carbon during photosynthesis, exhibiting their flexible adaptability to the native high-altitude habitats of the Tibetan Plateau.

Photosystem II (PSII) uses light energy to oxidize water and to reduce plastoquinone in the photosynthetic electron transport chain. O₂ is produced as a byproduct. While most members of the PSII research community agree that O₂ originates from water molecules, alternative hypotheses involving bicarbonate persist in the literature. In this perspective, we provide an overview of the important roles of bicarbonate in regulating PSII activity and assembly. Further, we emphasize that biochemistry, spectroscopy, and structural biology experiments have all failed to detect bicarbonate near the active site of O₂ evolution. While thermodynamic arguments for oxygen-centered bicarbonate oxidation are valid, the claim that bicarbonate is a substrate for photosynthetic O₂ evolution is challenged.

Understanding the stability of photosynthetic pigments is crucial for developing crop cultivars with high productivity and resilience to the environmental stresses. This study leveraged GGE biplot, WAASB, and MTSI indices to assess the stability of content and composition of photosynthetic pigments in leaves and siliques of 286 Brassica juncea (L.) Czern. genotypes across three environments. The GGE biplot analysis identified NRCQR-9901 as the best genotype in terms of chlorophyll 'a' under conditions of high irradiance and long days (E1). For chlorophyll 'b' and total chlorophyll, NC-533728 performed the best. AJ-2 and NPJ-208 had the maximum total carotenoids levels in leaves. RLC-2 was characterized by maximum values for chlorophyll a, chlorophyll b, and total chlorophyll in the siliques. The low irradiance, short days, and moderate to high temperatures (E2) seemed perfect for the synthesis of photosynthetic pigments. NPJ-182 shows the maximum concentrations of chlorophyll 'a', total chlorophyll, and total carotenoids in leaves. Conversely, IC-597869, RE-389, and IC-597894 exhibited the highest concentrations of chlorophyll 'b' under an environment characterized by low light intensity, shorter daylights, and low temperatures (E3) during flowering and siliqua formation stages. The combined analysis found NPJ-182, NC-533728, CN-105233, RLC-2, CN-101846, JA-96, PBR-357, JM-3, and DTM-34 as top performers with high stability. Comparative transcriptome analysis with two stable and high-performing genotypes (PBR-357 and DTM-34) and two average performers revealed upregulation of critical photosynthesis-related genes (ELIP1, CAB3.1, ELIP1.5, and LHCB5) in top performers. This study identified promising trait donors for use in breeding programs aimed at improving the mustard crop's photosynthetic efficiency, productivity, and stability.

In the next 10–20 years, several observatories will aim to detect the signatures of oxygenic photosynthesis on exoplanets, though targets must be carefully selected. Most known potentially habitable exo-planets orbit cool M-dwarf stars, which have limited emission in the photosynthetically active region of the spectrum (PAR, (400< lambda < 700) nm) used by Earth’s oxygenic photoautotrophs. Still, recent experiments have shown that model cyanobacteria, algae, and non-vascular plants grow comfortably under simulated M-dwarf light, though vascular plants struggle. Here, we hypothesize that this is partly due to the different ways they harvest light, reflecting some general rule that determines how photosynthetic antenna structures may evolve under different stars. We construct a simple thermodynamic model of an oxygenic antenna-reaction centre supercomplex and determine the optimum structure, size and absorption spectrum under light from several star types. For the hotter G (e.g. the Sun) and K-stars, a small modular antenna is optimal and qualitatively resembles the PSII-LHCII supercomplex of higher plants. For the cooler M-dwarfs, a very large antenna with a steep ’energy funnel’ is required, resembling the cyanobacterial phycobilisome. For the coolest M-dwarfs an upper limit is reached, where increasing antenna size further is subject to steep diminishing returns in photosynthetic output. We conclude that G- and K-stars could support a range of niches for oxygenic photo-autotrophs, including high-light adapted canopy vegetation that may generate detectable bio-signatures. M-dwarfs may only be able to support low light-adapted organisms that have to invest considerable resources in maintaining a large antenna. This may negatively impact global coverage and therefore detectability.

The ring-like peripheral light-harvesting complex 2 (LH2) expressed by many phototrophic purple bacteria is a popular model system in biological light-harvesting research due to its robustness, small size, and known crystal structure. Furthermore, the availability of structural variants with distinct electronic structures and optical properties has made this group of light harvesters an attractive testing ground for studies of structure-function relationships in biological systems. LH2 is one of several pigment-protein complexes for which a link between functionality and effects such as excitonic coherence and vibronic coupling has been proposed. While a direct connection has not yet been demonstrated, many such interactions are highly sensitive to resonance conditions, and a dependence of intra-complex dynamics on detailed electronic structure might be expected. To gauge the sensitivity of energy-level structure and relaxation dynamics to naturally occurring structural changes, we compare the photo-induced dynamics in two structurally distinct LH2 variants. Using polarization-controlled 2D electronic spectroscopy at cryogenic temperatures, we directly access information on dynamic and static disorder in the complexes. The simultaneous optimal spectral and temporal resolution of these experiments further allows us to characterize the ultrafast energy relaxation, including exciton transport within the complexes. Despite the variations in PPC molecular structure manifesting as clear differences in electronic structure and disorder, the energy-transport and-relaxation dynamics remain remarkably similar. This indicates that the light-harvesting functionality of purple bacteria within a single LH2 complex is highly robust to structural perturbations and likely does not rely on finely tuned electronic- or electron-vibrational resonance conditions.

Low iron (Fe) bioavailability can limit the biosynthesis of Fe-containing proteins, which are especially abundant in photosynthetic organisms, thus negatively affecting global primary productivity. Understanding cellular coping mechanisms under Fe limitation is therefore of great interest. We surveyed the temporal responses of Chlamydomonas (Chlamydomonas reinhardtii) cells transitioning from an Fe-rich to an Fe-free medium to document their short and long-term adjustments. While slower growth, chlorosis and lower photosynthetic parameters are evident only after one or more days in Fe-free medium, the abundance of some transcripts, such as those for genes encoding transporters and enzymes involved in Fe assimilation, change within minutes, before changes in intracellular Fe content are noticeable, suggestive of a sensitive mechanism for sensing Fe. Promoter reporter constructs indicate a transcriptional component to this immediate primary response. With acetate provided as a source of reduced carbon, transcripts encoding respiratory components are maintained relative to transcripts encoding components of photosynthesis and tetrapyrrole biosynthesis, indicating metabolic prioritization of respiration over photosynthesis. In contrast to the loss of chlorophyll, carotenoid content is maintained under Fe limitation despite a decrease in the transcripts for carotenoid biosynthesis genes, indicating carotenoid stability. These changes occur more slowly, only after the intracellular Fe quota responds, indicating a phased response in Chlamydomonas, involving both primary and secondary responses during acclimation to poor Fe nutrition.