Higher Photosynthetic Efficiency Research Articles

Co-culture systems of microalgae and heterotrophic microorganisms: applications in bioproduction and wastewater treatment and elucidation of mutualistic interactions.

In recent years, reducing the concentration of carbon dioxide in the atmosphere has become an important issue. Microalgae have a higher photosynthetic efficiency and growth rate than higher plants; thus, biological carbon dioxide fixation using microalgae is attracting particular attention as an efficient carbon dioxide fixation method. However, under dilute atmospheric conditions, microalgae exhibit lower growth rates and reduced carbon dioxide fixation efficiency. In recent years, technology that can efficiently fix carbon dioxide, even in the atmosphere, using a microalgae co-culture system that co-cultivates microalgae and heterotrophic microorganisms has attracted attention. In such a co-culture system, it is believed that a mutualistic relationship is established between microorganisms through the exchange of various compounds. This review focuses on the application of a co-culture system of microalgae and heterotrophic microorganisms for bioproduction and wastewater treatment. In addition, research to elucidate the mutualistic relationships in microalgal co-culture systems using analytical methods that have been widely used in recent years, such as next-generation sequencing technology, is also discussed. In the future, it is expected that the use of microalgae co-culture systems will expand on an industrial scale through the development of key technologies, such as efficient genetic modification techniques for microalgae and their heterotrophic microorganism partners, large-scale cultivation facilities that can efficiently cultivate microalgae, and stable control techniques for co-culture systems using advanced technology.

Expanding the Triangle of U: Comparative analysis of the Hirschfeldia incana genome provides insights into chromosomal evolution, phylogenomics and high photosynthesis-related traits.

The Brassiceae tribe encompasses many economically important crops and exhibits high intraspecific and interspecific phenotypic variation. After a shared whole-genome triplication (WGT) event (Br-α, ~15.9 million years ago), differential lineage diversification and genomic changes contributed to an array of divergence in morphology, biochemistry, and physiology underlying photosynthesis-related traits. Here, the C3 species Hirschfeldia incana is studied as it displays high photosynthetic rates under high-light conditions. Our aim was to elucidate the evolution that gave rise to the genome of H. incana and its high-photosynthesis traits. We reconstructed a chromosome-level genome assembly for H. incana (Nijmegen, v2.0) using nanopore and chromosome conformation capture (Hi-C) technologies, with 409Mb in size and an N50 of 52Mb (a 10× improvement over the previously published scaffold-level v1.0 assembly). The updated assembly and annotation was subsequently employed to investigate the WGT history of H. incana in a comparative phylogenomic framework from the Brassiceae ancestral genomic blocks and related diploidized crops. Hirschfeldia incana (x=7) shares extensive genome collinearity with Raphanus sativus (x=9). These two species share some commonalities with Brassica rapa and B. oleracea (A genome, x=10 and C genome, x=9, respectively) and other similarities with B. nigra (B genome, x=8). Phylogenetic analysis revealed that H. incana and R. sativus form a monophyletic clade in between the Brassica A/C and B genomes. We postulate that H. incana and R. sativus genomes are results of hybridization or introgression of the Brassica A/C and B genome types. Our results might explain the discrepancy observed in published studies regarding phylogenetic placement of H. incana and R. sativus in relation to the "Triangle of U" species. Expression analysis of WGT retained gene copies revealed sub-genome expression divergence, likely due to neo- or sub-functionalization. Finally, we highlighted genes associated with physio-biochemical-anatomical adaptive changes observed in H. incana which likely facilitate its high-photosynthesis traits under high light. The improved H. incana genome assembly, annotation and results presented in this work will be a valuable resource for future research to unravel the genetic basis of its ability to maintain a high photosynthetic efficiency in high-light conditions and thereby improve photosynthesis for enhanced agricultural production.

Effects of foliar application of two forms of selenium on anatomic features of Thymus daenensis Celak

To investigate selenium effects on anatomic features of Thymus daenensis, three concentrations of bulk and nanoparticles of the element (2, 4 and 8 ppm) along with distilled water, as a control, were sprayed on foliar of young seedlings of the plant species for six times with 2 weeks intervals. Transverse sections of stems, roots and leaves of the treated plants were manually produced and stained by Carmine and Methylene blue. Average of 5 readings was recorded for each treatment on several anatomic traits. Statistical analysis of the data revealed that the effects of selenium treatments were significantly different, at 1% of probability, on all of the studied anatomic characters. The first level of nanoparticles showed the most positive effects on several root characteristics. The highest level of selenium nanoparticles (8 ppm) showed the most positive effects on stem diameter and stem vascular cylinder diameter. The last two levels of nanoparticles had similar and the largest effect on stem epidermis thickness. The lowest level of bulk selenium (2 ppm) showed the most increment on leaf characteristics. Application of a low concentration of selenium by foliar spraying on young plants of the species is suggested for more vegetative growth and higher photosynthetic efficiency

Identification of High-Photosynthetic-Efficiency Wheat Varieties Based on Multi-Source Remote Sensing from UAVs

Breeding high-photosynthetic-efficiency wheat varieties is a crucial link in safeguarding national food security. Traditional identification methods necessitate laborious on-site observation and measurement, consuming time and effort. Leveraging unmanned aerial vehicle (UAV) remote sensing technology to forecast photosynthetic indices opens up the potential for swiftly discerning high-photosynthetic-efficiency wheat varieties. The objective of this research is to develop a multi-stage predictive model encompassing nine photosynthetic indicators at the field scale for wheat breeding. These indices include soil and plant analyzer development (SPAD), leaf area index (LAI), net photosynthetic rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), stomatal conductance (Gsw), photochemical quantum efficiency (PhiPS2), PSII reaction center excitation energy capture efficiency (Fv’/Fm’), and photochemical quenching coefficient (qP). The ultimate goal is to differentiate high-photosynthetic-efficiency wheat varieties through model-based predictions. This research gathered red, green, and blue spectrum (RGB) and multispectral (MS) images of eleven wheat varieties at the stages of jointing, heading, flowering, and filling. Vegetation indices (VIs) and texture features (TFs) were extracted as input variables. Three machine learning regression models (Support Vector Machine Regression (SVR), Random Forest (RF), and BP Neural Network (BPNN)) were employed to construct predictive models for nine photosynthetic indices across multiple growth stages. Furthermore, the research conducted principal component analysis (PCA) and membership function analysis on the predicted values of the optimal models for each indicator, established a comprehensive evaluation index for high photosynthetic efficiency, and employed cluster analysis to screen the test materials. The cluster analysis categorized the eleven varieties into three groups, with SH06144 and Yannong 188 demonstrating higher photosynthetic efficiency. The moderately efficient group comprises Liangxing 19, SH05604, SH06085, Chaomai 777, SH05292, Jimai 22, and Guigu 820, totaling seven varieties. Xinmai 916 and Jinong 114 fall into the category of lower photosynthetic efficiency, aligning closely with the results of the clustering analysis based on actual measurements. The findings suggest that employing UAV-based multi-source remote sensing technology to identify wheat varieties with high photosynthetic efficiency is feasible. The study results provide a theoretical basis for winter wheat phenotypic monitoring at the breeding field scale using UAV-based multi-source remote sensing, offering valuable insights for the advancement of smart breeding practices for high-photosynthetic-efficiency wheat varieties.

Pearl millet for good health and nutrition – An overview

Abstract Previously food was taken to satiate hunger and survival, but now it is for better health and wellbeing. It is imperative to take a healthy diet that includes energy, carbohydrates, proteins, fiber, and all essential vitamins and nutrients in optimum proportions. Millets have been acknowledged as climate-resilient crops and smart foods. Pearl millet is a C 4 plant grown mostly under scarce input and water supply conditions. Owing to high photosynthetic efficiency, it produces more dry matter and gives better economic returns even under adverse agro-climatic conditions. Globally, pearl millet is grown on 31.0 million ha, mainly in Africa and Asia and is a staple food for 90 million poor people. Among food crops (cereals and pulses), pearl millet is the cheapest energy source (361 kcal/100g), minerals, namely, phosphorus (296–360 mg/100g), iron (8–11 mg/100g), zinc (3.1–6.6 mg/100g), calcium (40–42 mg/100 g), magnesium (97–137 mg/100g) and vitamins, namely, vitamin A, E, riboflavin, thiamine, vitamin K and niacin, etc. Besides, it also has significant amount of fiber, protein, antioxidants like phenolic acids, flavonoids and low fats. Because of its rich nutritional composition, Government of India has designated it as nutri-cereals (Gazette of India, No. 133 dated 13th April, 2018) for production, consumption and trade. Besides rich nutritional value, pearl millet improves our immunity through enormous health benefits like reducing the risk of chronic diseases such as obesity, diabetes, and cardiovascular diseases. It improves the digestibility and bioavailability of food nutrients by reducing anti-nutrients. Being non-acid forming, it is also helpful in gastrointestinal problems and is non-glutinous beneficial for people suffering from celiac diseases. With these properties, it is regarded as a significant grain worldwide, yet it is least exploited. However, because of numerous potential health benefits and contributions to national food security, millet grains are now getting the growing attention of food nutritionists, scientists, technologists and industrialists.

Exploring the constituents and thermal characteristics of miscanthus floridulus for biomass composites

Miscanthus floridulus (MF) possesses notable attributes including high photosynthetic efficiency, rapid growth, robust adaptability, and substantial biomass yield. It is widely researched in fields such as genetics, special materials, bioenergy, and ecological protection. However, the research on the addition of MF for biomass composites remains limited due to the absence of comprehensive analysis concerning the composition, internal molecular structure, and properties of MF. A thorough exploration of the fundamental properties of MF has the potential to broaden their advantages and facilitate the advancement of biomass. This investigation delves into the structural characterization and properties of MF, focusing on its stems, leaves, and tassels. Firstly, the primary constituents of MF comprise cellulose, hemicellulose, and lignin. Cellulose predominates in the stem, exhibiting the highest crystallinity, while lignin content peaks in the tassel with the lowest crystallinity. The leaf falls between these extremes in terms of crystallinity. Secondly, carbon and oxygen elements constitute over 95 % of MF's primary components, alongside trace elements like phosphorus and sulfur. Additionally, chemical structure of MF features abundant characteristic functional groups such as hydroxyl, carbonyl, and benzene rings. Studies indicate that samples with low hemicellulose and high lignin content demonstrate superior thermal stability. Consequently, the stem of MF exhibits optimal low-temperature thermal stability, while the tassel excels in high-temperature conditions. Finally, the data highlights a significant influence in the mechanical properties of polylactic acid materials upon the addition of MF. With a 5 % addition of MF, the tensile modulus and flexural strength of the PLA composite reached their optimal values of 933.91 MPa and 55.28±8.77 MPa, respectively. This research establishes a theoretical groundwork for integrating MF into biomass composite materials.

Increased sugar content impairs pollen fertility and reduces seed-setting in high-photosynthetic-efficiency rice

Crop yield depends on biomass, which is primarily associated with photosynthesis. We previously demonstrated that two photorespiratory bypasses, i.e., GOC (glycolate oxidase + oxalate oxidase + catalase) and GCGT (glycolate oxidase + catalase + glyoxylate carboligase + tartronic semialdehyde reductase), significantly increased photosynthesis, biomass, and grain yield, but decreased seed-setting rates in rice. This study explored the underlying mechanism of how elevated photosynthetic efficiency impacted the seed-setting. First, pollen germination assessed in vivo and in vitro, revealed a reduced germination rate in GCGT rice. Subsequent analysis found that photosynthates highly accumulated in the leaves and stems; sucrose and soluble sugar levels were increased but the starch level was reduced in the anthers. Uridine diphosphate glucose (UDP-Glc) was increased but uridine diphosphate galactose (UDP-Gal) was unaltered, thus causing an imbalance in the UDP-Glc/UDP-Gal ratio in GCGT anthers. Most anthers in GCGT plants had two locules in contrast to four in the wild-type (WT). Pollen tapetum was developmentally abnormal, and genes related to sucrose synthesis, transport, and tapetal programmed cell death (PCD) were upregulated, whereas those involved in starch synthesis and conversion were downregulated in GCGT anthers. Taken together, our results demonstrated that an increase in sugar content was the primary factor causing reduced seed-setting rates in high photosynthetic efficiency rice, during which metabolic disorder of sugars and UDP sugar imbalance in anthers lead to impaired pollen fertility.

Spirulina platensis components mitigate bone density loss induced by simulated microgravity: A mechanistic insight

In microgravity conditions, the consumption of Spirulina platensis (SP) as a renewable food source shows promise in mitigating osteoporosis due to its high nutritional content photosynthetic efficiency, environmental adaptability and positive effects on bone density, though the exact bioactive components and mechanisms remain unclear. Using a hindlimb suspension (HLS) model, this study investigated SP components: proteins (SPP), polysaccharides (SPS), lipids (SPL), and residue (SPR) on bone density and metabolism. Findings revealed that SPP and SPS significantly enhanced bone density and reduced oxidative stress. Activation of the FoxO3/Wnt/β-catenin pathway reduced FoxO3a expression and increased Wnt signaling molecules and β-catenin protein, boosting bone formation. Moreover, these components promoted beneficial gut bacteria like Turicibacter, reduced the Firmicutes-to-Bacteroidetes ratio, and enhanced SCFAs production, crucial for bone health. This study emphasized the potential of Spirulina nutrients in addressing space-induced osteoporosis and developing functional foods for long-term space missions.

Photomorphogenesis and Photosynthetic Trait Changes in Melon Seedlings Responding to Red and Blue Light

Red and blue light have significant effects on plant growth; however, most of the current studies have focused on common horticultural crops such as cucumber and tomato, and there are fewer studies on how red and blue light affect the growth of melon seedlings. Therefore, in this study, we used melon (Cucumis melo L.) as the experimental material to investigate the effects of red and blue light ratios on the photomorphogenesis and photosynthesis of melon seedlings. Five red and blue light ratios were set at a fixed light intensity 200 μmol·m−2·s−1, including R:B = 1:9, R:B = 3:7, R:B = 1:1, R:B = 7:3, and R:B = 9:1. The results showed that with the increase in red light ratios, melon seedling height, stem diameter, total leaf area and stomatal pore size of melon seedlings increased, while the upper epidermis, palisade tissue, spongy tissue, leaf thickness, and stomatal density showed a decreasing trend. Under the R:B = 7:3 treatment, melon seedlings were optimized in all morphological indexes and had higher photosynthetic efficiency; these results indicated that the growth of melon seedlings could be regulated by adjusting the ratio of red to blue light, thus promoting the morphogenesis of melon seedlings.

Salt tolerance in mungbean is associated with controlling Na and Cl transport across roots, regulating Na and Cl accumulation in chloroplasts and maintaining high K in root and leaf mesophyll cells.

Salinity tolerance requires coordinated responses encompassing salt exclusion in roots and tissue/cellular compartmentation of salt in leaves. We investigated the possible control points for salt ions transport in roots and tissue tolerance to Na+ and Cl- in leaves of two contrasting mungbean genotypes, salt-tolerant Jade AU and salt-sensitive BARI Mung-6, grown in nonsaline and saline (75 mM NaCl) soil. Cryo-SEM X-ray microanalysis was used to determine concentrations of Na, Cl, K, Ca, Mg, P, and S in various cell types in roots related to the development of apoplastic barriers, and in leaves related to photosynthetic performance. Jade AU exhibited superior salt exclusion by accumulating higher [Na] in the inner cortex, endodermis, and pericycle with reduced [Na] in xylem vessels and accumulating [Cl] in cortical cell vacuoles compared to BARI Mung-6. Jade AU maintained higher [K] in root cells than BARI Mung-6. In leaves, Jade AU maintained lower [Na] and [Cl] in chloroplasts and preferentially accumulated [K] in mesophyll cells than BARI Mung-6, resulting in higher photosynthetic efficiency. Salinity tolerance in Jade AU was associated with shoot Na and Cl exclusion, effective regulation of Na and Cl accumulation in chloroplasts, and maintenance of high K in root and leaf mesophyll cells.

Advancements in Synthetic Biology for Enhancing Cyanobacterial Capabilities in Sustainable Plastic Production: A Green Horizon Perspective

This comprehensive review investigates the potential of cyanobacteria, particularly nitrogen-fixing strains, in addressing global challenges pertaining to plastic pollution and carbon emissions. By analyzing the distinctive characteristics of cyanobacteria, including their minimal growth requirements, high photosynthetic efficiency, and rapid growth rates, this study elucidates their crucial role in transforming carbon sequestration, biofuel generation, and biodegradable plastic production. The investigation emphasizes cyanobacteria’s efficiency in photosynthesis, positioning them as optimal candidates for cost-effective bioplastic production with minimized land usage. Furthermore, the study explores their unconventional yet promising utilization in biodiesel production, mitigating environmental concerns such as sulfur emissions and the presence of aromatic hydrocarbons. The resulting biodiesel exhibits significant combustion potential, establishing cyanobacteria as a viable option for sustainable biofuel production. Through a comprehensive assessment of both achievements and challenges encountered during the commercialization process, this review offers valuable insights into the diverse contributions of cyanobacteria. Its objective is to provide guidance to researchers, policymakers, and industries interested in harnessing bio-inspired approaches for structural and sustainable applications, thereby advancing global efforts towards environmentally conscious plastic and biofuel production.

Cross-species transcriptomics reveals differential regulation of essential photosynthesis genes in Hirschfeldia incana.

Photosynthesis is the only yield-related trait not yet substantially improved by plant breeding. Previously, we have established H. incana as the model plant for high photosynthetic light-use efficiency (LUE). Now we aim to unravel the genetic basis of this trait in H. incana, potentially contributing to the improvement of photosynthetic LUE in other species. Here, we compare its transcriptomic response to high light with that of Arabidopsis thaliana, Brassica rapa, and Brassica nigra, 3 fellow Brassicaceae members with lower photosynthetic LUE. We built a high-light, high-uniformity growing environment, in which the plants developed normally without signs of stress. We compared gene expression in contrasting light conditions across species, utilizing a panproteome to identify orthologous proteins. In-depth analysis of 3 key photosynthetic pathways showed a general trend of lower gene expression under high-light conditions for all 4 species. However, several photosynthesis-related genes in H. incana break this trend. We observed cases of constitutive higher expression (like antenna protein LHCB8), treatment-dependent differential expression (as for PSBE), and cumulative higher expression through simultaneous expression of multiple gene copies (like LHCA6). Thus, H. incana shows differential regulation of essential photosynthesis genes, with the light-harvesting complex as the first point of deviation. The effect of these expression differences on protein abundance and turnover, and ultimately the high photosynthetic LUE phenotype is relevant for further investigation. Furthermore, this transcriptomic resource of plants fully grown under, rather than briefly exposed to, a very high irradiance, will support the development of highly efficient photosynthesis in crops.

Growing in phosphorus-impoverished habitats in south-western Australia: How general are phosphorus-acquisition and -allocation strategies among Proteaceae, Fabaceae and Myrtaceae species?

Numerous phosphorus (P)-acquisition and -utilisation strategies have evolved in plants growing in severely P-impoverished environments. Although these strategies have been well characterised for certain taxa, like Proteaceae, P-poor habitats are characterised by a high biodiversity, and we know little about how species in other families cope with P scarcity. We compared the P-acquisition and leaf P-allocation strategies of Fabaceae and Myrtaceae with those of Proteaceae growing in the same severely P-impoverished habitat. Myrtaceae and Fabaceae exhibited multiple P-acquisition strategies: P-mining by carboxylates or phosphatases, P uptake facilitated by carboxylate-releasing neighbours, and dependence on the elevated soil P availability after fire. Surprisingly, not all species showed high photosynthetic P-use efficiency (PPUE). Highly P-efficient species showed positive correlations between PPUE and the proportion of metabolite P (enzyme substrates), and negative correlations between PPUE and phospholipids (cellular membranes) and nucleic acid P (mostly ribosomal RNA), while we found no correlations in less P-efficient species. Overall, we found that Myrtaceae and Fabaceae used a wider range of strategies than Proteaceae to cope with P scarcity, at both the rhizosphere and leaf level. This knowledge is pivotal to better understand the mechanisms underlying plant survival in severely nutrient-impoverished biodiverse ecosystems.

Salinity Stress Acclimation Strategies in Chlamydomonas sp. Revealed by Physiological, Morphological and Transcriptomic Approaches.

Climate changes may include variations in salinity concentrations at sea by changing ocean dynamics. These variations may be especially challenging for marine photosynthetic organisms, affecting their growth and distribution. Chlamydomonas spp. are ubiquitous and are often found in extreme salinity conditions. For this reason, they are considered good model species to study salinity adaptation strategies. In the current study, we used an integrated approach to study the Chlamydomonas sp. CCMP225 response to salinities of 20‱ and 70‱, by combining physiological, morphological, and transcriptomic analyses, and comparing differentially expressed genes in the exponential and stationary growth phases under the two salinity conditions. The results showed that the strain is able to grow under all tested salinity conditions and maintains a surprisingly high photosynthetic efficiency even under high salinities. However, at the highest salinity condition, the cells lose their flagella. The transcriptomic analysis highlighted the up- or down-regulation of specific gene categories, helping to identify key genes responding to salinity stress. Overall, the findings may be of interest to the marine biology, ecology, and biotechnology communities, to better understand species adaptation mechanisms under possible global change scenarios and the potential activation of enzymes involved in the synthesis of bioactive molecules.

Waterlogging‐Induced Changes in ABA, Carbohydrates and CBF6 Modify Freezing Tolerance in Prehardened Festuca pratensis

ABSTRACTChanges in precipitation and snow melt during warmer winters can increase low‐temperature waterlogging. Such conditions may bring about different effects when compared with a single stress trigger, such as low‐temperature or water excess. The effects of waterlogging are clearly related to water temperature, and the consequences of water excess might be less severe, as more oxygen is dissolved in colder water. The effect of waterlogging during cold acclimation (CA) is poorly understood; most experiments concerning water excess are performed at relatively high‐temperatures. In this study, we examined the effect of 3 weeks of waterlogging (approx. 2 cm above the soil level) on CA in Festuca pratensis Huds. (Fp), a cool‐season grass. Measurements were taken before CA (after prehardening, before flooding) and after 3 weeks of CA in waterlogged (treated) and non‐waterlogged (control) plants. The work included: (i) freezing tolerance test (regrowth after freezing), (ii) analysis of abscisic acid (ABA) content in the leaf, (iii) leaf stomatal conductance, (iv) leaf water content, (v) carbohydrates analysis, including fructans, and (vi) transcript levels of selected genes involved in freezing tolerance, ABA signalling and fructan biosynthesis. The aim of the study was to test a hypothesis that low‐temperature waterlogging in Fp enhances freezing tolerance (plant regrowth after freezing) related to increased ABA accumulation, increased C‐repeat‐binding transcription factor expression and/or increased carbohydrate accumulation, including fructans. Two out of four genotypes exhibited enhanced regrowth following freezing due to waterlogging relative to control. Principal component analysis (PCA) revealed a positive correlation between ABA levels and freezing tolerance in both treatments, with a more pronounced effect observed in the waterlogged plants. However, the phytohormone played different roles in these two treatments. In the context of low‐temperature waterlogging, ABA may be involved in the dehydration tolerance response in genotypes suffering from physiological drought, as well as the induction of C‐repeat‐binding transcription factors (CBFs) and sucrose, which may improve freezing tolerance. The increased fructan amount and polymerisation degree due to waterlogging may provide a carbohydrate sink to maintain a high photosynthetic efficiency, but are not directly responsible for freezing tolerance changes. The study indicates that tolerance mechanisms of Fp exposed to low‐temperature waterlogging involve maintaining a high photosynthetic rate, as well as oxidative and dehydration stress tolerance.

A complete reference genome of broomcorn millet

Broomcorn millet (Panicum miliaceum L.), known for its traits of drought resistance, adaptability to poor soil, short growth period, and high photosynthetic efficiency as a C4 plant, represents one of the earliest domesticated crops globally. This study reports the telomere-to-telomere (T2T) gap-free reference genome for broomcorn millet (AJ8) using PacBio high-fidelity (HiFi) long reads, Oxford Nanopore long-read technologies and high-throughput chromosome conformation capture (Hi-C) sequencing data. The size of AJ8 genome was approximately 834.7 Mb, anchored onto 18 pseudo-chromosomes. Notably, 18 centromeres and 36 telomeres were obtained. The assembled genome showed high quality in terms of completeness (BUSCO score: 99.6%, QV: 61.7, LAI value: 20.4). In addition, 63,678 protein-coding genes and 433.8 Mb (~52.0%) repetitive sequences were identified. The complete reference genome for broomcorn millet provides a valuable resource for genetic studies and breeding of this important cereal crop.

Effect of Salt-Induced Stress on the Calorific Value of Two Miscanthus sacchariflorus (Amur Silvergrass) Varieties

This study was designed to investigate the relationship between the caloric value and salt tolerance of two varieties of Miscanthus sacchariflorus (Amur silvergrass: M127 and M022). The salt tolerance capacity, photosynthetic characteristics, Na+ and K+ uptake by the roots and aboveground parts, and caloric value of different parts of the aboveground parts were obtained under hydroponic conditions. The results showed that M022 was more tolerant to salt stress than M127 and the former had a higher photosynthetic efficiency as well as a lower aboveground Na+ accumulation, K+ efflux, and larger K+/Na+ ratio. The calorific values of stems, spear leaves, aging leaves, and functional leaves of the two varieties showed a decreasing trend with increasing NaCl concentration. At 270 mM NaCl, the calorific values of the stems, aging leaves, functional leaves, and spear leaves was reduced by 18.10%, 46.73%, 26.11%, and 18.35% for M022 and 41.99%, 39.41%, 34.82%, and 45.09% for M127 compared to the controls, respectively. We observed that the aging leaves of M022 had a faster decline rate in calorific value than those of M127, indicating that the aging leaves of M022 preferentially isolated the harmful Na+ ion, reduced its accumulation in other parts, and increased the K+/Na+ ratio in the corresponding parts, thus inhibiting the decrease in calorific value. Following this result, it can be inferred that M022 inhibited the decline in calorific values during stress by efficiently compartmentalizing the distribution of Na+ and K+. Our results provide a theoretical basis and technical support for the efficient cultivation of salt-tolerant energy plants in saline–alkaline soil.

Overexpression of cassava melatonin receptor PMTR1 plays dual roles in development under light and dark conditions in Arabidopsis.

MePMTR1 is involved in plant development and production as well as photosynthesis in plant. Melatonin is widely involved in plant growth and development as well as stress responses. Compared with the extending studies of melatonin in stress responses, the direct link between melatonin and plant development in the whole stages remains unclear. With the identification of phytomelatonin receptor PMTR1 in plants, melatonin signalling is becoming much clearer. However, the function of MePMTR1 in tropical crop cassava remains elusive. In this study, we found that overexpression of MePMTR1 showed larger biomass than wild type (WT), including higher number and area of leaves, weight, and accompanying with higher photosynthetic efficiency. Consistently, exogenous melatonin accelerated photosynthetic rate in Arabidopsis. In addition, MePMTR1-overexpressed plants exhibited more resistance to dark-induced senescence compared with WT, demonstrated by higher chlorophyll, lower hydrogen peroxide and superoxide content. In summary, this study illustrated that melatonin and its receptor regulate growth, development and senescence in plants, highlighting the potential application of melatonin and its receptor in improving crop yield and photosynthesis.

The long and tortuous path towards improving photosynthesis by engineering elevated mesophyll conductance.

The growing demand for global food production is likely to be a defining issue facing humanity over the next 50 years. To tackle this challenge, there is a desire to bioengineer crops with higher photosynthetic efficiencies, to increase yields. Recently, there has been a growing interest in engineering leaves with higher mesophyll conductance (gm), which would allow CO2 to move more efficiently from the substomatal cavities to the chloroplast stroma. However, if crop yield gains are to be realised through this approach, it is essential that the methodological limitations associated with estimating gm are fully appreciated. In this review, we summarise these limitations, and outline the uncertainties and assumptions that can affect the final estimation of gm. Furthermore, we critically assess the predicted quantitative effect that elevating gm will have on assimilation rates in crop species. We highlight the need for more theoretical modelling to determine whether altering gm is truly a viable route to improve crop performance. Finally, we offer suggestions to guide future research on gm, which will help mitigate the uncertainty inherently associated with estimating this parameter.

Individual architecture and photosynthetic performance of the submerged form of Drosera intermedia Hayne

Drosera intermedia grows in acidic bogs in parts of valleys that are flooded in winter, and that often dry out in summer. It is also described as the sundew of the most heavily hydrated habitats in peatlands, and it is often found in water and even underwater. This sundew is the only one that can tolerate long periods of submersion, and more importantly produces a typical submerged form that can live in such conditions for many years. Submerged habitats are occupied by D. intermedia relatively frequently. The aim of the study was to determine the environmental conditions and architecture of individuals in the submerged form of D. intermedia. The features of the morphological and anatomical structure and chlorophyll a fluorescence of this form that were measured were compared with analogous ones in individuals that occurred in emerged and peatland habitats. The submerged form occurred to a depth of 20 cm. Compared to the other forms, its habitat had the highest pH (4.71–4.92; Me = 4.71), the highest temperature and substrate hydration, and above all, the lowest photosynthetically active radiation (PAR; 20.4–59.4%). This form differed from the other forms in almost all of the features of the plant’s architecture. It is particularly noteworthy that it had the largest main axis height among all of the forms, which exceeded 18 cm. The number of living leaves in a rosette was notable (18.1 ± 8.1), while the number of dead leaves was very low (6.9 ± 3.8). The most significant differences were in the shape of its submerged leaves, in which the length of the leaf blade was the lowest of all of the forms (0.493 ± 0.15 mm; p < 0.001) and usually the widest. The stem cross-sectional area was noticeably smaller in the submerged form than in the other forms, the xylem was less developed and collaterally closed vascular bundles occurred. Our analysis of the parameters of chlorophyll fluorescence in vivo revealed that the maximum quantum yield of the primary photochemistry of photosystem II is the highest for the submerged form (Me = 0.681), the same as the maximum quantum yield of the electron transport (Me φE0 = 0.183). The efficiency of energy use per one active reaction center of photosystem II (RC) was the lowest in the submerged form (Me = 2.978), same as the fraction of energy trapped by one active RC (Me = 1.976) and the non-photochemical energy dissipation (DI0/RC; Me = 0.916). The ET0/RC parameter, associated with the efficiency of the energy utilization for electron transport by one RC, in the submerged plant reached the highest value (Me = 0.489). The submerged form of D. intermedia clearly differed from the emerged and peatland forms in its plant architecture. The submerged plants had a thinner leaf blade and less developed xylem than the other forms, however, their stems were much longer. The relatively high photosynthetic efficiency of the submerged forms suggests that most of the trapped energy is utilized to drive photosynthesis with a minimum energy loss, which may be a mechanism to compensate for the relatively small size of the leaf blade.