Photosynthetic Research Articles

One-Off Irrigation Combined Subsoiling and Nitrogen Management Enhances Wheat Grain Yield by Optimizing Physiological Characteristics in Leaves in Dryland Regions

Irrigation practice, tillage method, and nitrogen (N) management are the three most important agronomic measures for wheat (Triticum aestivum L.) production, but the combined effects on grain yield and wheat physiological characteristics are still poorly understood. We conducted a three-year split–split field experiment at the junction of the Loess Plateau and Huang-Huai-Hai Plain in China. The two irrigation practices (I0: non-irrigation and I1: one-off irrigation), three tillage methods (RT: rotary tillage, PT: plowing, and ST: subsoiling), and four N managements (N0, N120, N180, and N240) were assigned to the main plots, subplots, and sub-subplots, respectively. Irrigation practice, tillage method, N management, and most of their two-factor and three-factor interactions could significantly affect grain yield and the physiological characteristics of the leaves of winter wheat. One-off irrigation increased the grain yield by 46.9% by optimizing the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), the contents of proline (Pro) and soluble sugar (SS), and the net photosynthesis rate (Pn) in leaves during most growth stages of wheat. The improvement of grain yield and physiological characteristics under one-off irrigation was considerably affected by the tillage method and N management, and the effectiveness of one-off irrigation was improved under subsoiling and N180 or N240. One-off irrigation combining subsoiling and N180 had no significant difference relative to one-off irrigation combining subsoiling and N240, while it significantly increased grain yield by 47.1% over the three years, as well as increasing the activities of SOD, POD, and CAT, and Pn in wheat leaves by 23.2%, 41.2%, 26.1%, and 53.0%, respectively, and decreasing the contents of malondialdehyde (MDA), Pro, and SS by 29.2%, 65.4%, and 18.2% compared to non-irrigation rotary tillage combined with N240 across the two years and three stages. The wheat grain yield was significantly associated with the physiological characteristics in flag leaves, and the coefficient was greatest for POD activity, followed by SOD activity and Pn. Therefore, one-off irrigation combining subsoiling and N180 is an optimal strategy for the high-yield production of wheat in dryland regions where the one-off irrigation is assured.

Photoredox catalysis of acridinium and quinolinium ion derivatives

AbstractPhotoredox catalysis has attracted increasing attention because of wide range of synthetic transformations and solar energy conversion applications. Reviews on photoredox catalysis have so far focused predominantly on the synthetic applications. This review highlights how organic photoredox catalysts were developed and how they function as efficient photocatalysts in mechanistic point of views. In particular, 9‐mesityl‐10‐methylactidinium (Acr+–Mes) has been highlighted as one of the best organic photoredox catalysts. Acr+–Mes was originally developed as a model compound of the photosynthetic reaction center to mimic the long lifetime of the charge‐separated state in which the energy is converted to chemical energy in photosynthesis. The reason why Acr+–Mes acts as one of the most efficient photoredox catalyst is clarified in terms of the one‐electron redox potentials and long lifetimes of the electron‐transfer state (Acr•–Mes•+) produced upon photoexcitation of Acr+–Mes in different solvents. The reason why the mesityl substituent at the 9‐position of the Acr+ moiety is essential for the efficient photoredox catalysis is discussed in comparison with acridinium ions with different substituents R (Acr+–R) including 10‐methylacridinium ion with no substituent (AcrH+). The mechanisms of photoredox catalysis of Acr+–Mes are discussed in various synthetic transformations and solar energy conversion reactions mimicking photosynthesis. Photoredox catalysis of quinolinium ion and its derivatives is also discussed in comparison with that of Acr+–Mes. Finally, immobilization of Acr+–Mes and quinolinium ions to form the composite catalysts with redox catalyst is discussed to improve the photoredox catalytic activity and stability.

Advances and new horizons in metabolic engineering of heterotrophic bacteria and cyanobacteria for enhanced lactic acid production.

Bacteria species such as E.Coli, Lactobacilli, and pediococci play an important role as starter strains in fermentation food or polysaccharides into lactic acid. These bacteria were metabolically engineered using multiple proven genome editing methods to enhance relevant phenotypes. The efficacy of these procedures varies depending on the editing tool used and researchers' ability to pick suitable recombinants, which significantly increased genome engineering throughput. Cyanobacteria produce oxygenic photosynthesis and play an important role in carbon dioxide fixing. The fixed carbon dioxide is then retained as polysaccharides in cells and metabolised into various low carbon molecules such as lactate, succinate, and ethanol. Lactate is used as a building ingredient in various bioplastics, food additives, and medicines. This review covers the recent advances in lactic acid production through metabolic and genetic engineering in bacteria and cyanobacteria.

ThyD Is a Thylakoid Membrane Protein Influencing Cell Division and Acclimation to High Light in the Multicellular Cyanobacterium Anabaena sp. Strain PCC 7120.

Cyanobacteria developed oxygenic photosynthesis and represent the phylogenetic ancestors of chloroplasts. The model strain Anabaena sp. strain PCC 7120 grows as filaments of communicating cells and can form heterocysts, cells specialized for N2 fixation. In the Anabaena genome, ORF all2390 is annotated as encoding a SulA homolog, but sequence similarity to SulA of model bacteria is insignificant. We generated strains that lacked or overexpressed all2390, both of which showed instances of increased cell size, and observed that purified All2390 protein interfered with the invitro polymerization of FtsZ. Heterocyst frequency diminished by all2390 inactivation and increased by all2390 overexpression. Overexpression retarded the dismantlement of Z-ring structures that determines commitment in the differentiating cells. Thus, All2390 can influence cell division affecting heterocyst differentiation. An All2390-GFP fusion protein localized to the thylakoid membranes including the honeycomb membranes, which harbor photosynthetic complexes, in the heterocyst polar regions. Notably, all2390 expression strongly increased under high light, conditions under which growth of the null mutant is compromised. Thus, All2390 appears essential for adaptation to high light conditions. We named All2390 ThyD to reflect its thylakoidal localization and its dual role in cell division dynamics and acclimation of thylakoid membranes to increased light intensity.

Physiological parameters dictate bearing pattern in different mango cultivars: Study from Sub-tropical India

The bearing habit of mango has long been a subject of interest for pomologists. The difference in bearing pattern among various mango cultivars is attributed to complex physiological interaction. Despite multiple studies on mango bearing, detailed investigations in this area remain limited. This study aims to explore the interrelationship between the bearing patterns and the associated physiological changes in different mango cultivars. The physiological parameters were examined at various growth stages in Baramasi (a perennial bearer), Amrapali (a regular bearer) and Langra and Alphonso (irregular bearer) of mango (Mangifera indica L.). Significant variations were observed in chlorophyll content, internal carbon dioxide concentration, photosynthetic rate and flowering intensity. An increase in internal carbon dioxide concentration led to reduced carbon dioxide uptake, which impacted net photosynthesis production. A direct correlation between flowering intensity and photosynthetic rate was identified, while a nonlinear relationship between photosynthetic rate and total carbohydrate content was also noted. The study suggests that variations in the photosynthetic rate and the subsequent source-sink relationship may contribute to the differences in bearing patterns across mango cultivars. While further studies are needed for more conclusive results, this research can be valuable for pomologists, physiologists and breeders working with mango.

Multivariate analysis for agronomic, physiological, macro, and micronutrient traits of exotic vegetable amaranth genotypes

The genus amaranth is comprised of 60–70 species. This climate hardy plant is grown as a vegetable as well as cereal crop in many areas of the world. Current study multivariate analysis was used to characterize the exotic vegetable amaranth genotypes. The experiment was conducted in the research area of Muhammad Nawaz Shareef University of Agriculture, Multan under RCBD design with three replications of 50 exotic amaranth genotype. 22 different variables were investigated for the principal component and cluster analysis using different software packages in R studio. According to the results of principal component analysis the first five PCs had eigenvalues greater than one and they explained the 84.59% diversity in exotic vegetable amaranth accessions. First two principal components explained 57.31% of variation. Traits that loaded highly for first PC include moisture (-0.892), carbohydrates (0.938), energy (0.920), stomatal conductance (0.803), net photosynthesis (0.795) and dry weight (0.770). The traits which impacted the second PC highly include protein (0.692), fat (-0.571), nitrogen (0.692), calcium (0.545), phosphorus (0.908), zinc (0.960), iron (0.826) and potassium (0.872). For future breeding program the selection based on these results will be effective for crop enhancement drive in exotic vegetable amaranth genotypes. Hierarchical clustering was done and dendrogram split the 50 genotypes into 5 groups using silhouette method. The pairwise clustering revealed that intra cluster distance is smaller than inter cluster distance. The maximum inter cluster distance was observed between cluster I and II (9.88); between cluster I and III (9.47); between cluster II and IV (9.27).Clinical trial number Clinical trial number not applicable.

Alteration of phycobilisome excitation energy transfer properties in response to attenuations in peripheral electron flow

In Synechocystis sp. PCC 6803 (S. 6803), two types of phycobilisome (PBS) complexes, CpcG-PBS and CpcL-PBS, function to harvest light energy for photosynthetic reaction centers (RCs), photosystem I (PSI) and photosystem II (PSII). The compositional differences between these two forms of PBS and their specificity for RCs have led to suggestions that they may differ in function. To address this question, we examined how PBS-RC interactions, and the transfer of excitation energy from PBS to RCs, might be adjusted under conditions where electron demand and photon availability are modulated. The CpcG-PBS, CpcL-PBS, and RC complexes were isolated from a S. 6803 strain defective in expression of flavodiiron 1 (oxygen reduction reaction 1, ORR1) grown under varied light regimes. The energy transfer preference from CpcL-PBS to either PSI or PSII was investigated by in vitro crosslinking and 77 K fluorescence emission spectroscopy to assess energy transfer efficiency under photoexcitation. While the results demonstrate that the transfer of excitation energy from CpcL-PBS favors PSI over PSII in WT strains as previously shown, the preference of CpcL-PBS switches from PSI to PSII in ORR1 strains. Surprisingly, this change in preference was reproduced when ORR1 CpcL-PBS was crosslinked with WT RCs, or when WT CpcL-PBS was cross-crosslinked with ORR1 RCs, indicating there are physical modifications to both PBS and RCs that mediate the preference switch. In contrast, the analysis with ORR1 CpcG-PBS shows similar preferences to WT. Additionally, PBS populations in ORR1 shifted to a greater proportion of CpcL-PBS relative to CpcG-PBS. These results demonstrate that under conditions where electron utilization changes, there is a tuning of the excitation energy allocation from CpcL-PBS to RCs to manage the energy distribution for photosynthesis under dynamic flux conditions.

Pyramiding Descriptors Contributing Drought Stress Tolerance to Six Polyembryonic Rootstocks of Mango (Mangifera indica L.)

A better understanding of the drought stress on mango varieties is essential in an effort to keep the production and the quality of mango to meet the growing demand globally. Since drought stress has been one of the major abiotic stress affecting both production and quality of mango, we studied to understanding the drought stress phenomenon in mango, especially to evaluate the descriptors for drought stress tolerance in mango rootstocks. Irrigation was withhold for fifteen days in six polyembryonic mango rootstocks namely ‘Goa’, ‘Vellaikulamban’, ‘Nekkare’, ‘Starch’, ‘Kitchner’ and ‘M 13-1’ and then rehydrated up to five days. Morphological parameters, membrane stability index (MSI), wax content, chlorophyll content, gas exchange attributes were recorded at 0, 15th and 5th day of rehydration. MSI, chlorophyll content and gas exchange parameters such as intercellular CO2, stomatal conductance, net photosynthesis, and transpiration rate were reduced while cuticular wax content increased in all the polyembryonic mango rootstocks under drought stress and after rehydration same were recovered back up to greater extent. Rootstock ‘M 13-1’ showed more capacity to recover under drought stress as compared to five others rootstocks of mango. Therefore, rootstock ‘M 13-1’ can be recommended for scion varieties for frequent drought prone areas for taking sustainable mango production.

Integrative Analysis of Metabolome and Transcriptome Profiles to Evaluate the Response Mechanisms of Carex adrienii to Shade Conditions

Carex is a type of herbaceous plant with high application value, playing an important role in the urban periphery. Due to its unique morphology and ecological characteristics, Carex is widely used in various fields, such as landscaping, ecological restoration and soil and water conservation, which help to maintain the balance of the ecosystem. In order to explore the potential molecular mechanisms of shade tolerance in Carex, transcriptome and metabolome sequencing were performed on the leaves of the shade = tolerant species Carex adrienii E. G. Camus. under 80% shade and no shade conditions. Compared to control group (CK), the total chlorophyll, chlorophyll a, chlorophyll b and total carotenoid content in the C. adrienii leaves of the shading treatment were significantly upregulated. The antioxidant enzyme activity of the leaves, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), were also remarkably upregulated in the shading treatment groups. In addition, the net photosynthesis rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of the leaves were reduced, and the intercellular CO2 concentration (Ci) of the leaves was increased under shade. The transcriptome identified 5056 differentially expressed genes (DEGs) and the metabolome identified 889 differential accumulated metabolites (DAMs) in three treated samples. The integrated transcriptomic and metabolomic analyses results showed that the DEGs and DAMs were enriched in photosynthesis, plant hormone signal transduction and flavonoid biosynthesis synthesis pathways. The ABA content of the C. adrienii leaves was significantly increased under shade. Therefore, the shading conditions led to changes in chlorophyll and abscisic acid (ABA), as well as the accumulation of flavonoids in C. adrienii, both of which were achieved by regulating genes involved in photosynthesis, plant hormone signal transduction and flavonoid biosynthesis molecular networks. Our results provide new knowledge for the molecular response and metabolic regulatory mechanisms of C. adrienii to shade stress, and valuable genetic resources for C. adrienii shade tolerance molecular breeding.

Evaluation of commercial rhizobacteria-based bio-inoculants for the control of the false root-knot nematode Nacobbus aberrans sensu lato and the promotion of pepper plants

ABSTRACT Nacobbus sp. is a phytoparasitic nematode that affects economically important crops. Due to the negative environmental and health impacts of chemical nematicides, sustainable alternatives, such as the use of biological control agents, are being developed. Rhizobacteria are microorganisms that can suppress nematode reproduction by producing different metabolites, induce systemic resistance in plants and stimulate plant growth. The aim of this study was to investigate whether the inoculation with commercial formulations of plant-growth promoting rhizobacteria (PGPR) can mitigate the deleterious effects of the nematode N. aberrans s.l. and promote the growth of pepper plants grown in greenhouses under biotic stress. Different bacteria were tested in vitro before being inoculated into pepper plants. Plants were inoculated with Bacillus subtilis, Bacillus thuringiensis and Azospirillim brasilense at transplant and then every 15 days, in the presence and absence of N. aberrans s.l.. The pathogen reproduction factor was 5.34; 2.09; 0.88 and 12.46 for A. brasilense B. subtilis, B. thuringiensis and control, respectively. In both nematode-parasitized and unparasitized plants, the rhizobacteria increased the soluble proteins (54%) and chlorophyll (18%) content and exerted a positive effect on net photosynthesis, transpiration, stomatal conductance and increased water use efficiency, height, stem diameter, fresh and dry weight. This beneficial effect was also verified by a lower accumulation of proline and sugars, metabolites used by plants as osmoregulators in stress situations. These results showed that B. thuringiensis and B. subtilis perform better in promoting pepper growth in the presence of the nematode and in the biocontrol of this pathogen.

Nutrient enrichment can increase the thermal performance of Galápagos seaweeds

Thermal sensitivity in ectothermic organisms is often contingent upon environmental factors. Nutrient availability in particular is believed to influence the physiological responses of primary producers to global warming and is thus relevant to consider when forecasting the structure and functioning of future marine ecosystems. This study measured the effect of nutrient enrichment on the thermal sensitivity of 4 genera of Galápagos seaweeds (Ulva, Caulerpa, Padina, and Ochtodes), estimated as the thermal optimum (Topt), performance maximum (Pmax), activation energy, and deactivation energy. These parameters were quantified by modeling thermal performance curves for net photosynthesis under ambient and nutrient-enriched conditions. Our findings revealed variation in Topt among genera, ranging from 27.6° to 36.0°C. Nutrient additions enhanced Topt by ~2°C for 2 (Padina and Caulerpa) of the 4 taxa and also significantly increased Pmax in Padina, suggesting the ability for warming-induced ocean stratification and associated effects (i.e. decreasing nutrient availability) to reduce the capacities of these populations to maintain and support new growth. No significant differences in Topt or Pmax were observed for either Ulva or Ochtodes with enrichment. Ambient net photosynthesis and respiration rates were also compared across genera; Pmax rates for net photosynthesis were consistently higher than those for respiration (i.e. until just beyond Topt); however, photosynthetic Topt values were lower. Thus, this study suggests that further warming could reduce overall net primary productivity, with potentially far-reaching implications for marine food webs.

Physiological and biochemical response of strawberry cv. diamond to nano zeolite soil application and cinnamic acid foliar application

The increasing global population and climate change are pressing challenges that necessitate innovative agricultural solutions to ensure food security. One promising approach is the use of nano fertilizers and foliar spraying techniques, which enhance nutrient delivery to plants. The purpose of this research was to examine how three different concentrations of nano zeolite (0, 30, and 60 mg L− 1) applied to the soil through irrigation and three different concentrations of cinnamic acid (0, 100, and 200 µM) applied topically affected the physiological and biochemical characteristics of strawberry (Fragaria × ananassa Duch.) cv. diamond, as well as the crop’s yield and quality of its fruits. A factorial system with three replications was used in the experiment, which was designed in a completely randomized design. According to the data, all features except stomatal conductivity were considerably impacted by soil application of nano zeolite and foliar spraying of cinnamic acid. Moreover, cinnamic acid (200 µM) spray combined with soil application nano zeolite (60 mg L− 1) decreased electrolyte leakage, transpiration rate, and malondialdehyde, while enhanced chlorophyll content, net photosynthesis rate, leaf dry matter, relative water content, fruit length and diameter, yield, and fruit quality parameters.

Cyclic and pseudo-cyclic electron pathways play antagonistic roles during nitrogen deficiency in Chlamydomonas reinhardtii.

Nitrogen (N) scarcity frequently constrains global biomass productivity. N deficiency halts cell division, downregulates photosynthetic electron transfer, and enhances carbon storage. However, the molecular mechanism downregulating photosynthesis during N deficiency and its relationship with carbon storage are not fully understood. Proton Gradient Regulator-like 1 (PGRL1) controlling cyclic electron flow (CEF) and Flavodiiron proteins (FLV) involved in pseudo-CEF (PCEF) are major players in the acclimation of photosynthesis. To determine the role of PGRL1 or FLV in photosynthesis under N deficiency, we measured photosynthetic electron transfer, oxygen gas exchange, and carbon storage in Chlamydomonas reinhardtii pgrl1 and flvB knockout mutants. Under N deficiency, pgrl1 maintained higher net photosynthesis and O2 photoreduction rates and higher levels of Cytochrome b6f and PSI compared to the control and flvB. The photosynthetic activity of flvB and pgrl1 flvB double mutants decreased in response to N deficiency, similar to the control strains. Furthermore, the preservation of photosynthetic activity in pgrl1 was accompanied by an increased accumulation of triacylglycerol in certain genetic backgrounds but not others, highlighting the importance of gene-environment interaction in determining traits such as oil content. Our results suggest that in the absence of PGRL1-controlled CEF, FLV-mediated PCEF maintains net photosynthesis at a high level and that CEF and PCEF play antagonistic roles during N deficiency. They further illustrate how a strain's nutrient status and genetic makeup can affect regulation of photosynthetic energy conversion in relation to carbon storage and provide additional strategies for improving lipid productivity in algae.

Durable Photosynthesis of Hydrogen Peroxide Using a Uranyl Coordination Polymer: Exciton Dissociation and Hydrogen Abstraction.

The photosynthesis of hydrogen peroxide (H2O2), involving water oxidation and oxygen reduction, is crucial for optimizing light utilization. Here, a previously synthesized one-dimensional chain-like semiconductive uranyl coordination polymer (NDC-UCP) was used for the efficient overall photosynthetic reaction of H2O2 and its photocatalytic mechanism was systematically investigated. The excellent stability of NDC-UCP enables continuous H2O2 production for up to 96 h. Its unique hydrogen extraction capability enhances the photocatalytic performance, achieving a H2O2 production rate of 283.80 μmol g-1 h-1. Two mechanisms for H2O2 generation were revealed: efficient electron-hole separation in NDC-UCP facilitates a two-step one-electron oxygen reduction and direct water oxidation, while hydrogen abstraction of UO22+ generates hydroxyl (·OH) and hydroperoxyl radicals (HO2·), enhancing H2O2 photosynthesis. This study highlights the potential of uranyl coordination polymers in H2O2 production and their synergistic exciton dissociation and hydrogen abstraction functionalities in photocatalytic redox reactions.

A Structural and Functional Mimic of P680+

AbstractOne or multiple chlorophyll a molecules are employed in the reaction center of photosystem II′s main electron donor (defined as P680). We have a poor understanding of how the reaction center facilitates water oxidation in photosystem II and the roles that mono‐ and/or multimeric chlorophyll groups play when P680 oxidizes a neighboring tyrosine in order to drive water oxidation at the oxygen evolving complex. We have prepared a dimeric MgII‐porphyrin complex [Mg2(BTPP)] (1, H4‐BTPP=1,2‐bis‐(10,15,20‐triphenylporphyrin‐5‐yl)‐benzene) as a structural and functional mimic of the dimeric core of P680. 1 was oxidized by one‐electron to the corresponding π‐cation radical complex 2. The radical cation was characterized by UV/Vis‐NIR, FT‐IR, and EPR spectroscopic techniques. 2 was shown to be reactive towards phenols to give the corresponding phenoxyl radicals, mimicking the reactivity of the P680 cation radical which oxidizes tyrosine to tyrosyl radical. Critically, the dimeric π‐cation radical showed markedly higher rates of proton coupled electron transfer oxidation (PCET) of phenols when compared to its monomeric counterpart [Mg(TPP)] (TPP=5,10,15,20‐tetraphenylporphyrin). Our findings demonstrate that MgII‐porphyrin complexes are reliable mimics of photosynthetic PCET processes and suggest that photosynthetic reaction centers with multiple π‐conjugated complexes likely lower the barrier to PCET oxidation by π‐cation radical species.

Comparison of the Photosynthesis, Hydraulic Properties, and Anatomy of Pteroceltis tatarinowii Leaves Between a Limestone and a Cultivated Forest.

Pteroceltis tatarinowii Maxim is a famous paper-making tree endemic to China with a wide distribution. Leaves of this tree growing in different habitats show a certain plasticity, which is important for their ecological adaption. Here, the photosynthesis ability, hydraulic properties, and anatomy of P. tatarinowii leaves from a limestone forest (Langya Mountain) and a cultivated forest (Xiaoling Village) in Anhui province were compared. The results showed that leaves from Xiaoling Village had higher net photosynthesis rate and hydraulic conductivity, which were closely related to their higher vein density, stomatal density and palisade tissue thickness than leaves from Langya Mountain. However, lower leaf water potentials at turgor loss point and at 50% loss of conductivity, as well as a higher leaf hardness, for Langya Mountain leaves indicated their higher hydraulic safety and drought resistance than those of leaves from Xiaoling Village. This study reveals a hydraulic trade-off between efficiency and safety for P. tatarinowii leaves growing in distinct habitats. Further studies should include more habitats and different vegetation communities to clarify the ecological adaption so as to provide a scientific basis for the protection of this species.

Cyanobacterial Cultures, Cell Extracts, and Individual Toxins Decrease Photosynthesis in the Terrestrial Plants Lactuca sativa and Zea mays.

Cyanobacterial harmful algal blooms (cHABs) are increasing due to eutrophication and climate change, as is irrigation of crops with freshwater contaminated with cHAB toxins. A few studies, mostly in aquatic protists and plants, have investigated the effects of cHAB toxins or cell extracts on various aspects of photosynthesis, with variable effects reported (negative to neutral to positive). We examined the effects of cyanobacterial live cultures and cell extracts (Microcystis aeruginosa or Anabaena flos-aquae) and individual cHAB toxins (anatoxin-a, ANA; beta-methyl-amino-L-alanine, BMAA; lipopolysaccharide, LPS; microcystin-LR, MC-LR) on photosynthesis in intact plants and leaf pieces in corn (Zea mays) and lettuce (Lactuca sativa). In intact plants grown in soil or hydroponically, overall net photosynthesis (Pn), but not Photosystem-II (PSII) electron-transport yield (ΦPSII), decreased when roots were exposed to cyanobacterial culture (whether with intact cells, cells removed, or cells lysed and removed) or individual toxins in solution (especially ANA, which also decreased rubisco activity); cyanobacterial culture also decreased leaf chlorophyll concentration. In contrast, ΦPSII decreased in leaf tissue vacuum-infiltrated with cyanobacterial culture or the individual toxins, LPS and MC-LR, though only in illuminated (vs. dark-adapted) leaves, and none of the toxins caused significant decreases in in vitro photosynthesis in thylakoids. Principal component analysis indicated unique overall effects of cyanobacterial culture and each toxin on photosynthesis. Hence, while cHAB toxins consistently impacted plant photosynthesis at ecologically relevant concentrations, the effects varied depending on the toxins and the mode of exposure.

In vivo detection of spectral reflectance changes associated with regulated heat dissipation mechanisms complements fluorescence quantum efficiency in early stress diagnosis.

Early stress detection of crops requires a thorough understanding of the signals showing the very first symptoms of the alterations in the photosynthetic light reactions. Detection of the activation of the regulated heat dissipation mechanism is crucial to complement passively induced fluorescence to resolve ambuiguities in energy partitioning. Using leaf spectroscopy, we evaluated the capability of pigment spectral unmixing to calculate the fluorescence quantum efficiency (FQE) and simultaneously retrieve fast absorption changes in a drought and nitrogen deficiency experiment with tomato. In addition, active fluorescence measurements and pigment analyses of xanthophylls, carotenes and chlorophylls were conducted. We observed notable responses in noninvasive proximal sensing-retrieved FQE values under stress, but as expected, these alone were not enough to identify the constraints in photosynthetic efficiency. Reflectance-based detection of the 535-nm peak absorption change was able to complement FQE and indicate the activation of regulated heat dissipation for both stress treatments under growing light conditions. However, further complexity in the light harvesting energy regulation needs to be accounted for when considering additional light stress. Our results underscore the potential of complementary in vivo quantitative spectroscopy-based products in the early and nondestructive stress diagnosis of plants, marking the path for further applications.

Living photosynthetic microneedle patches for in situ oxygenation and postsurgical melanoma therapy

Surgical excision remains the principal treatment for melanoma, while tumor recurrence and delayed wound healing often occur due to the residual tumor cells and hypoxic microenvironment in the postoperative skin wounds. Herein, we present a living photosynthetic microneedle (MN) patch (namely MA/CM@MN) loaded with microalgae (MA) and cuttlefish melanin (CM) for postsurgical melanoma therapy and skin wound healing. Benefiting from the oxygenic photosynthesis of the alive MA in the MN base, the MA/CM@MN can generate oxygen under light exposure, thus facilitating skin cell proliferation and protecting cells against hypoxia-induced cell death. In addition, with CM nanoparticles embedded in the MN tips, the MA/CM@MN can be effectively heated up under near-infrared (NIR) irradiation, contributing to a strong tumor killing efficacy on melanoma cells in vitro. Further experiments demonstrate that the NIR-irradiated MA/CM@MN effectively prevents local tumor recurrence and simultaneously promotes the healing of tumor-induced wounds after incomplete tumor resection in melanoma-bearing mice, probably because the MA/CM@MN can inhibit tumor cell proliferation, stimulate tumor cell apoptosis, and mitigate tissue hypoxia in light. These results indicate that the living photosynthetic MN patch offers an effective therapeutic strategy for postoperative cancer therapy and wound healing applications.Graphical

The ‘photosynthetic C1 pathway’ links carbon assimilation and growth in California poplar

Although primarily studied in relation to photorespiration, serine metabolism in chloroplasts may play a key role in plant CO2 fertilization responses by linking CO2 assimilation with growth. Here, we show that the phosphorylated serine pathway is part of a ‘photosynthetic C1 pathway’ and demonstrate its high activity in foliage of a C3 tree where it rapidly integrates photosynthesis and C1 metabolism contributing to new biomass via methyl transfer reactions, imparting a large natural 13C-depleted signature. Using 13CO2-labelling, we show that leaf serine, the S-methyl group of leaf methionine, pectin methyl esters, and the associated methanol released during cell wall expansion during growth, are directly produced from photosynthetically-linked C1 metabolism, within minutes of light exposure. We speculate that the photosynthetic C1 pathway is highly conserved across the photosynthetic tree of life, is responsible for synthesis of the greenhouse gas methane, and may have evolved with oxygenic photosynthesis by providing a mechanism of directly linking carbon and ammonia assimilation with growth. Although the rise in atmospheric CO2 inhibits major metabolic pathways like photorespiration, our results suggest that the photosynthetic C1 pathway may accelerate and represents a missing link between enhanced photosynthesis and plant growth rates during CO2 fertilization under a changing climate.