Photosynthesis Research最新文献

The amount of absorbed light is one of the main factors governing plant photosynthesis, and ultimately, the gross primary production (GPP) of vegetation. Since canopy chlorophyll (Chl) content defines the amount of light that can be absorbed (thus the amount of energy available for photosynthesis), it is representative of the status of the photosynthetic apparatus and directly relates with vegetation productivity. The non-invasive assessment of these traits is the foundation of proximal and remote sensing and of high-throughput phenotyping of plants. The goal of this study is to explore: (i) the response of GPP to the absorption coefficient of Chl derived from canopy reflectance (i.e., assessed in situ) across the PAR and red-edge spectral regions in two plant species with contrasting biochemistry, structural properties, and photosynthetic pathway; (ii) the efficiency of contrasting plants in absorbing radiation and converting it into photosynthetic carbon uptake. The spectral composition of light absorbed by vegetation and the contribution of each spectral range to GPP were quantified. The highest responses of GPP to the Chl absorption coefficient occurred in the red-edge and green spectral regions. More notably, in contrasting plant species the GPP responses in the visible and red-edge spectral regions were almost identical and close to the quantum yield of CO₂ fixation. This potentially opens a novel avenue for the remote assessment of the quantum yield of photosynthesis. The uncertainty of the relationship between GPP and Chl absorption coefficient and its impact on the estimation of photosynthetic rates was also quantified.

Quantifying the effect of factors controlling CO₂ assimilation is crucial for understanding plant functions and developing strategies to improve productivity. Methods exist in numerous variants and produce various indicators, such as limitations, contributions, and sensitivity, often causing confusion. Simplifications and common mistakes lead to overrating the importance of diffusion-whether across stomata or the mesophyll. This work develops a consistent set of definitions that integrates all previous methods, offering a generalised framework for quantifying restrictions. Ten worked examples are provided in a free downloadable spreadsheet, demonstrating the simplicity and applicability to a wide range of questions.

This is a tribute to a truly inspirational plant biologist, Prof. John A. Raven, FRS, FRSE (25th June 1941- 23rd May 2024), who died at the age of 82. He was a leader in the field of evolution and physiology of algae and land plants. His research touched on many areas including photosynthesis, ion transport, carbon utilisation, mineral use, such as silicon, iron and molybdenum, the evolution of phytoplankton, the evolution of root systems, the impact of global change, especially on the acidification of the oceans, carbon gain and water use in early land plants, and ways of detecting extraterrestrial photosynthesis. Beginning his research career in the Botany School, University of Cambridge, John studied ion uptake in a giant algal cell. This was at the time of great strides brought about by Peter Mitchell (1920-1992) in elucidating the role of energy generation in mitochondria and chloroplasts and the coupling of ion transport systems to energy generation. With Enid MacRobbie and Andrew Smith, John pioneered early work on the involvement of ion transport in the growth and metabolism of plant cells.On leaving Cambridge John took up a lectureship at the University of Dundee in 1971, where he was still attached upon his death. His primary focus over the years, with one of us (Paul Falkowski), was on phytoplankton, the photosynthetic microalgae of the oceans. Still, his publication list of 5 books and over 600 scientific papers spans a very broad range. The many highly cited papers (see Table 1) attest to an outstanding innovator, who influenced a multitude of students and coworkers and a very wide readership worldwide. At the personal level, John Raven was a wonderful human being; he had an extraordinary memory, dredging up facts and little-known scientific papers, like a scientific magician, but at the same time making humorous jokes and involving his colleagues in fun and sympathetic appreciation. Table 1 Ten best cited articles (from google scholar) Citations Date Aquatic Photosynthesis, 3rd Edition P.G. Falkowski & J.A. Raven Princeton University Press, 2013 3854 2013 The evolution of modern eukaryotic phytoplankton P.G. Falkowski, M.E. Katz, A.H. Knoll, A. Quigg, J.A. Raven, et al Science 305, 354-360 1790 2004 CO₂ concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution M. Giordano, J. Beardall & J.A. Raven Annu. Rev. Plant Biol. 56 (1), 99-131 1648 2005 Algae as nutritional food sources: revisiting our understanding M.L. Wells, P. Potin, J.S. Craigie, J.A. Raven, S.S. Merchant, et al Journal of applied phycology 29, 949-982 1527 2017 Plant Nutrient acquisition strategies change with soil age H. Lambers, J.A. Raven, G.R. Shaver & S.E. Smith Trends in ecology & evolution 23, 95-103 1488 2008 Ocean acidification due to increasing atmospheric carbon dioxide J. Raven, K. Caldeira, H. Elderfield, O. Hoegh-Guldberg, P. Liss, et al The Royal Society, Policy Document, June 2005 1470 2005 Phytoplankton in

This study investigates extraction and quantification techniques for chlorophylls (Chl) in melanic lichens, with an emphasis on distinguishing between Chl and melanin absorbance during spectrophotometric assessments. We compared various extraction protocols, involving solvents such as dimethyl sulfoxide (DMSO) and acetone, and methods including intact thalli extraction, mortar grinding, and ball mill pulverizing. Three correction methods for melanic absorbance were also compared. Our findings indicated that DMSO was superior for Chl extraction compared to acetone, and differences in efficiency among the DMSO methods were minor. Correction for co-extracted melanin was deemed vital for accurate Chl quantification. The use of a C18 minicolumn was found to be effective for separating Chl and melanic pigments, providing reliable measurements of total Chl and Chl a/b-ratios. This method offers a simple cost-effective approach for Chl quantification in extracts containing a mix of Chl and other red light-absorbing pigments.

Timelapse microscopy has recently been employed to study the metabolism and physiology of cyanobacteria at the single-cell level. However, the identification of individual cells in brightfield images remains a significant challenge. Traditional intensity-based segmentation algorithms perform poorly when identifying individual cells in dense colonies due to a lack of contrast between neighboring cells. Here, we describe a newly developed software package called Cypose which uses machine learning (ML) models to solve two specific tasks: segmentation of individual cyanobacterial cells, and classification of cellular phenotypes. The segmentation models are based on the Cellpose framework, while classification is performed using a convolutional neural network named Cyclass. To our knowledge, these are the first developed ML-based models for cyanobacteria segmentation and classification. When compared to other methods, our segmentation models showed improved performance and were able to segment cells with varied morphological phenotypes, as well as differentiate between live and lysed cells. We also found that our models were robust to imaging artifacts, such as dust and cell debris. Additionally, the classification model was able to identify different cellular phenotypes using only images as input. Together, these models improve cell segmentation accuracy and enable high-throughput analysis of dense cyanobacterial colonies and filamentous cyanobacteria.

Myriophyllum spicatum, a semi-aquatic plant, can develop heterophylly by forming both submerged and aerial leaves to adapt to water level variations in its habitat. The aerial leaves exhibit shorter and fewer lobes, but thicker cuticle and developed stomata than submerged leaves. The heterophylly exhibited by M. spicatum could be controlled by hormones including abscisic acid, indole-3-acetic acid, and Jasmonic acid, as their levels were consistently higher in aerial leaves than in submerged leaves. Genes responsible for the formation of cuticle and stomata exhibited elevated expression in the aerial leaves, offering a molecular explanation for their structural adaptations to terrestrial environment. Moreover, aerial leaves exhibited greater resistance to intense light, while submerged leaves demonstrated a pronounced capacity of utilizing HCO₃^- for photosynthesis. Differential gene expression patterns pertaining to photosynthesis, carotenoid production, and HCO₃^- utilization elucidated the molecular mechanisms driving M. spicatum's photosynthetic adaptations to aquatic and terrestrial environment. In conclusion, the ability of M. spicatum to withstand changing water levels can be linked to its adaptable phenotype and the genetic characteristics inherited from its terrestrial ancestors, both of which are governed by hormonal regulation. These features may allow M. spicatum to outcompete other macrophytes that are more sensitive to water level fluctuations in their growing surroundings.

Evergreen conifers thrive in challenging environments by maintaining multiple sets of needles, optimizing photosynthesis even under harsh conditions. This study aimed to investigate the relationships between needle structure, photosynthetic parameters, and age along the light gradient in the crowns of Abies alba, Taxus baccata, and Picea abies. We hypothesized that: (1) Needle structure, photochemical parameters, and photosynthetic pigment content correlate with needle age and light levels in tree crowns. (2) The photosynthetic capacity of ageing needles would decline and adjust to the increasing self-shading of branches. Our results revealed a non-linear increase in the leaf mass-to-area ratio. The maximum quantum yield of photosystem II photochemistry decreased linearly with needle age without reaching levels indicative of photoinhibition. Decreased maximum electron transport rates (ETR_max) were linked to declining values of saturating photosynthetic photon flux density and increasing non-photochemical quenching of fluorescence (NPQ), indicating energy losses as heat. The chlorophyll a to chlorophyll b ratio linearly decreased, suggesting older needles sustain high light capture efficiency. These findings offer new insights into the combined effects of needle ageing and self-shading on photochemistry and pigment content. This functional needle balance highlights the trade-off between the costs of long-term needle retention and the benefits of efficient resource utilization. In environments where air temperature is less of a constraint on photosynthesis due to climate warming, evergreen coniferous trees could sustain or enhance their photosynthetic capacity. They can achieve this by shortening needle lifespan and retaining fewer cohorts of needles with higher ETR_max and lower NPQ compared to older needles.

The initial electron transfer (ET) processes in reaction centers (RCs) of Chloroflexus (Cfl.) aurantiacus were studied at 295 K using femtosecond transient absorption (TA) difference spectroscopy. Particular attention was paid to the decay kinetics of the primary electron donor excited state (P^*) and the formation/decay of the absorption band of the monomeric bacteriochlorophyll a anion (B_A^-) at ~ 1035 nm, which reflects the dynamics of the charge-separated state P⁺B_A^-. It was found that in Q_A-depleted RCs containing native bacteriopheophytin a (BPheo) molecules at the H_A and H_B binding sites, the decay of P^* to form the P⁺H_A^- state contains a fast (4 ps; relative amplitude 70%) and a slow (13 ps; relative amplitude 30%) kinetic components. The B_A^- absorption band at ~ 1035 nm was detected only for the fast component. Based on global analysis of the TA data, the results are discussed in terms of the presence of two P^* populations: in one, P^* decays in 4 ps via a dominant two-step activationless P^* → P⁺B_A^- → P⁺H_A^- ET with a contribution of 70% to the overall primary charge separation process, and in the other, P^* decays in 13 ps via a one-step superexchange P^* → P⁺H_A^- ET (contribution of 30%). Similar femtosecond TA measurements on Q_A-depleted-Pheo_A-modified RCs, in which the charge separation energetics was changed by replacing BPheo H_A with plant pheophytin a, suggest the presence of a P^* population where P⁺H_A^- formation can occur via a thermally activated two-step ET process.

Excitation energy transfer between the photochemically active protein complexes is key for photosynthetic processes. Phototrophic organisms like cyanobacteria experience subtle changes in irradiance under natural conditions. Such changes need adjustments to the excitation energy transfer between the photosystems for sustainable growth. Spectroscopic assessments on purified photosystems usually fail to capture these subtle changes. In this study, we examined whole cells from two model cyanobacteria, Synechocystis sp. PCC 6803 and Synechococcus elongatus UTEX 2973, grown under high and low light conditions to decode the high light tolerance of the latter. This allowed us to study photosynthetic machinery in the native state and in this work we particularly focused on the excitation energy transfer within PSII and PSI manifold. Understanding the high-light tolerance mechanism is imperative as it can help design strategies for increasing the light tolerance of cyanobacteria used for carbon neutral bioproduction. Our observations suggest that Synechococcus 2973 employs an uncommon photoprotection strategy, and the absence of hydroxy-echinenone pigment in this strain opens the possibility of an orange carotenoid protein homolog utilizing zeaxanthin as a scavenger of reactive oxygen species to provide photoprotection. Furthermore, the adjustments to the high-light adaptation mechanism involve downregulating the phycobilisome antenna in Synechococcus 2973, but not in Synechocystis 6803. Additionally, the stoichiometric changes to PSII/PSI are more tightly regulated in Synechococcus 2973.

The femtosecond dynamics of energy transfer from light-excited spirilloxanthin (Spx) to bacteriochlorophyll (BChl) a in the reaction centers (RCs) of purple photosynthetic bacteria Rhodospirillum rubrum was studied. According to crio-electron microscopy data, Spx is located near accessory BChl a in the B-branch of cofactors. Spx was excited by 25 fs laser pulses at 490 nm, and difference absorption spectra were recorded in the range 500-700 nm. To reveal the dynamics of individual states, we applied global analysis using different kinetic schemes. We found that the energy transfer Spx → BChl a occurs during 0.22 ps with a low efficiency of ~ 31%. The monomeric BChl a acts as the primary energy acceptor, presumably in the B-branch of cofactors. Then the energy is transferred to the BChl a dimer within 0.25 ps and subsequently used for charge separation. As a result of internal conversion in Spx, the majority (~ 69%) of the excitation energy transfers in 0.2 ps from the singlet-excited state S₂ to the states S₁ and S*, which, in turn, relax to the ground state in 1.5 and 9 ps, ​​respectively. We showed that the S₁ and S* states in Spx are not involved in energy transfer to BChl a. The found parameters of energy transfer Spx→BChl a turned out to be close to those in the light-harvesting complexes LH1 of Rhodospirillum rubrum. The sequence of events in Spx after its excitation is discussed.