Showing papers in "Photosynthetica in 2023"

On the evolution of the concept of two light reactions and two photosystems for oxygenic photosynthesis: A personal perspective

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Protection of nitrogenase from photosynthetic O2 evolution in Trichodesmium: methodological pitfalls and advances over 30 years of research

Abstract: The Trichodesmium genus comprises some of the most abundant N2-fixing organisms in oligotrophic marine ecosystems. Since nitrogenase, the key enzyme for N2 fixation, is irreversibly inhibited upon O2 exposure, these organisms have to coordinate their N2-fixing ability with simultaneous photosynthetic O2 production. Although being the principal object of many laboratory and field studies, the overall process of how Trichodesmium reconciles these two mutually exclusive processes remains unresolved. This is in part due to contradictory results that fuel the Trichodesmium enigma. In this review, we sift through methodological details that could potentially explain the discrepancy between findings related to Trichodesmium's physiology. In doing so, we exhaustively contrast studies concerning both spatial and temporal nitrogenase protective strategies, with particular attention to more recent insights. Finally, we suggest new experimental approaches for solving the complex orchestration of N2 fixation and photosynthesis in Trichodesmium.

The life story of Albert W. Frenkel (1919-2015): a pioneer in photosynthesis research

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Impact of additional green light and deficit in cryptochrome 1 on photosynthetic activity and pro-/antioxidant balance in Arabidopsis thaliana

Abstract: The light spectral composition acting through a set of photoreceptors, such as cryptochromes and phytochromes, plays an important role in maintaining sustainable photosynthesis. An impact of cryptochrome 1 deficiency and additions of green light (GL) against the background of red (RL) and blue (BL) (different ratios of RL:BL:GL) on the activity of the photosynthetic apparatus, the content of photosynthetic pigments, pro-/antioxidant balance, and expression of some genes in the leaves of 23-d-old Arabidopsis thaliana hy4 mutant plants was studied. The deficiency of cryptochrome 1 at RL/BL ratio of 4:1 led to a decrease in the rate of photosynthesis, photosystem II activity, and activity of ascorbate peroxidase and total peroxidase but to an increase in the content of products reacting with thiobarbituric acid. However, in the presence of additional GL, this difference for photosynthetic parameters either decreased or was absent, likely due to a GL-induced decrease in the content of active cryptochrome.

Photosynthetic machinery under salinity stress: Trepidations and adaptive mechanisms

Abstract: Chloroplasts and photosynthesis are the physiologically fateful arenas of salinity stress. Morphological and anatomical alterations in the leaf tissue, ultrastructural changes in the chloroplast, compromise in the integrity of the three-layered chloroplast membrane system, and defects in the light and dark reactions during the osmotic, ionic, and oxidative phases of salt stress are conversed in detail to bring the salinity-mediated physiological alterations in the chloroplast on to a single platform. Chloroplasts of salt-tolerant plants have evolved highly regulated salt-responsive pathways. Thylakoid membrane remodeling, ion homeostasis, osmoprotection, upregulation of chloroplast membrane and stromal proteins, chloroplast ROS scavenging, efficient retrograde signalling, and differential gene and metabolite abundance are the key attributes of optimal photosynthesis in tolerant species. This review throws light into the comparative mechanism of chloroplast and photosynthetic response to salinity in sensitive and tolerant plant species.

Photosystems under high light stress: throwing light on mechanism and adaptation

Abstract: High light stress decreases the photosynthetic rate in plants due to photooxidative damage to photosynthetic apparatus, photoinhibition of PSII, and/or damage to PSI. The dissipation of excess energy by nonphotochemical quenching and degradation of the D1 protein of PSII and its repair cycle help against photooxidative damage. Light stress also activates stress-responsive nuclear genes through the accumulation of phosphonucleotide-3'-phosphoadenosine- 5'-phosphate, methylerythritol cyclodiphosphate, and reactive oxygen species which comprise the chloroplast retrograde signaling pathway. Additionally, hormones, such as abscisic acid, cytokinin, brassinosteroids, and gibberellins, play a role in acclimation to light fluctuations. Several alternate electron flow mechanisms, which offset the excess of electrons, include activation of plastid or plastoquinol terminal oxidase, cytochrome b6/f complex, cyclic electron flow through PSI, Mehler ascorbate peroxidase pathway or water-water cycle, mitochondrial alternative oxidase pathway, and photorespiration. In this review, we provided insights into high light stress-mediated damage to photosynthetic apparatus and strategies to mitigate the damage by decreasing antennae size, enhancing NPQ through the introduction of mutants, expression of algal proteins to improve photosynthetic rates and engineering ATP synthase.

Variation in leaf mesophyll anatomy of fern species imposes significant effects on leaf gas exchange, light capture, and leaf hydraulic conductance

Abstract: The mesophyll anatomical traits are essential factors for efficient light capture, CO2 diffusion, and hydraulics in leaves. At the same time, leaf hydraulics are governed by the xylem anatomical traits. Thus, simultaneous analyses of the mesophyll and xylem anatomy will clarify the links among light capture, CO2 capture, and water use. However, such simultaneous analyses have been scarcely performed, particularly on non-seed plants. Using seven fern species, we first showed that fern species with a large mesophyll thickness had a high photosynthetic rate related to high light capture, high drought tolerance, and low leaf hydraulic conductance. The chloroplast surface area (Sc) per mesophyll thickness significantly decreased with an increase in mesophyll thickness, which may increase light diffusion and absorption efficiency in each chloroplast. The photosynthetic rate per Sc was almost constant with mesophyll thickness, which suggests that ferns enhance their light capture ability via the regulation of chloroplast density.

Effect of UV exclusion and AMF inoculation on photosynthetic parameters of Glycine max

Abstract: The study aims to understand the effect of UV exclusion and arbuscular mycorrhizal fungi (AMF) inoculation on the photosynthetic parameters of soybean. The study was conducted in nursery bags and plants were grown under iron mesh covered with UV cut-off filters. The plants grown under the exclusion of UV with AMF inoculation (I) showed higher photosynthetic pigments, carbonic anhydrase activity, reduced internal CO2 concentration, enhanced transpiration rate, and stomatal conductance as well as improved photosynthetic rate over uninoculated plants. Moreover, -UVB+I and -UVAB+I plants exhibited an increased performance index, the activity of the water-splitting complex on the donor side of PSII, and the concentration of active PSII reaction centers per excited cross-section. Overall, UV-excluded and AMF-inoculated plants showed the highest quantum yield of PSII and rate of photosynthesis. Our study will pave the way for future investigation to identify the possible role of UV exclusion and AMF in improving the photosynthetic performance for better yield of soybean.

Diurnal changes in the stomatal, mesophyll, and biochemical limitations of photosynthesis in well-watered greenhouse-grown strawberries

Abstract: The diurnal variations in the factors of photosynthesis reduction under well-watered greenhouse conditions remain poorly understood. We conducted diurnal measurements of gas exchange and chlorophyll fluorescence in strawberries (Fragaria × ananassa Duch.) for three sunny days. Quantitative limitation analysis was also conducted to investigate the diurnal variations of photosynthetic limitations [stomatal (SL), mesophyll (MCL), and biochemical limitation (BL)]. Under well-watered greenhouse conditions, a photosynthesis reduction was observed, and the respective limitations exhibited different diurnal changes based on the environmental stress severity. The main limitation was SL, varying between 11.3 and 27.1% around midday, whereas MCL and BL were in 4.3-14.2% and 1.7-8.5%, respectively, under relatively moderate conditions. However, both SL (11.2-34.2%) and MCL (4.8-26.4%) predominantly limited photosynthesis under relatively severe conditions, suggesting that stomatal closure was the main limitation and that the decline in mesophyll conductance was not negligible under strong environmental stress, even under well-watered greenhouse conditions.

Photosynthetic performance of walnut leaves during the occurrence of leaf scorch

Abstract: To clarify the effect of leaf scorch on walnut leaf photosynthesis, photosynthetic parameters were measured in Juglans regia 'Wen185' and 'Xinxin2' symptom trees (WS, XS) and symptomless trees (WH, XH). At the early stage of infection and under the low-grade leaf scorch, WS showed significantly lower net photosynthetic rate (PN), stomatal limitation (Ls), and higher intercellular CO2 concentration (Ci) than those of WH. However, at the mid to late stage of infection and under the high-grade leaf scorch, WS showed significantly lower PN, Ci, the maximal quantum yield of PSII photochemistry and higher Ls, minimal fluorescence yield of the dark-adapted state, nonphotochemical quenching than those of WH, which would occur once Juglans regia 'Xinxin2' was infected. The above results indicated the effect of leaf scorch on walnut leaf photosynthesis was related to the walnut varieties and the duration and severity of the disease. Under the influence of leaf scorch, the decline in photosynthesis of Juglans regia 'Wen185' leaves changed from stomatal to nonstomatal restriction, while Juglans regia 'Xinxin2' leaves showed always nonstomatal restriction.

Evaluation of the relationship between color-tuning of photosynthetic excitons and thermodynamic stability of light-harvesting chromoproteins

Abstract: Color-tuning is a critical survival mechanism for photosynthetic organisms. Calcium ions are believed to enhance both spectral tuning and thermostability in obligatory calcium-containing sulfur purple bacteria. This study examined the thermo- and piezo stability of the LH1-RC complexes from two calcium-containing sulfur purple bacteria notable for their extreme red-shifted spectra. The results generally show limited reversibility of both temperature and pressure effects related to the malleability of calcium-binding sites. While the pressure-induced decomposition product closely resembles the calcium-depleted form of the chromoproteins, the thermally induced products reveal monomeric B777 and dimeric B820 forms of bacteriochlorophyll a, similar to those seen in non-sulfur purple bacteria treated with detergent. The study further found nearly unison melting of the protein tertiary and secondary structures. Overall, our findings do not support a direct link between color adjustment and thermodynamic stability in light-harvesting chromoproteins.

Strong increase of photosynthetic pigments and leaf size in a pruned Ginkgo biloba tree

Abstract: A 50-year-old solitary, sun-exposed ginkgo tree had strongly been pruned in the fall of 2021. Very few buds for the formation of new leaves, twigs, and branches were left over. In spring 2022, these few remaining buds responded with the formation of a different leaf type. These leaves were 2.7 times larger and also thicker than in the years before. In addition, the mean content of total chlorophylls [Chl (a+b)] per leaf area unit of dark-green leaves was 1.45, those of green leaves two times higher as compared to the years leaves as compared to 435 to 770 mg m^-2 in leaves of other trees. The higher values for Chl (a+b) and total carotenoid content showed up also on a fresh and dry mass basis. Thus, with the formation of a new, larger leaf type by changes in morphology (leaf size and thickness) and the increase of photosynthetic pigments, the pruned ginkgo tree was able to compensate for the much lower number of leaves and photosynthetic units.

Excess energy and photosynthesis: responses to seasonal water limitations in co-occurring woody encroachers of the semi-arid Southern Great Plains

Abstract: Woody plant areal encroachment is pervasive throughout the Southern Great Plains, USA. The ability of woody plants to dissipate excess solar radiation - dynamically over the day and sustained periods without recovery overnight -is key for maintaining photosynthetic performance during dry stretches, but our understanding of these processes remains incomplete. Photosynthetic performance and energy dissipation were assessed for co-occurring encroachers on the karst Edwards Plateau (Juniperus ashei, Prosopis glandulosa, and Quercus fusiformis) under seasonal changes in water status. Only J. ashei experienced mild photoinhibition from sustained energy dissipation overnight while experiencing the lowest photochemical yields, minimal photosynthetic rates, and the highest dynamic energy dissipation rates at midday during the dry period - indicating susceptibility to photosynthetic downregulation and increased dissipation under future drought regimes. Neither other encroacher experienced sustained energy dissipation in the dry period, though P. glandulosa did experience marked reductions in photosynthesis, photochemical yields, and increased regulatory dynamic energy dissipation.

Downregulated expression of TaDeg7 inhibits photosynthetic activity in bread wheat (Triticum aestivum L.)

Abstract: Deg proteases play critical roles in photoprotection and PSII-repair circle, which remains elusive in cereal crops including wheat. Here, a Deg7-encoding gene TaDeg7 was silenced in wheat via a Barley stripe mosaic virus-induced gene-silencing system (BSMV-VIGS). When the expression level of TaDeg7 was downregulated, the photosynthetic activity including CO2 assimilation rate, actual photochemical efficiency of PSII, and electron transport rate declined while the nonphotochemical quenching increased significantly. When grown in high light, the BSMV:TaDeg7 plants accumulated more soluble sugar, malondialdehyde, and superoxide anion but had lower superoxide dismutase activity and less ascorbic acid. Additionally, the expression levels of TaPsbA and TarbcS were repressed in the BSMV:TaDeg7 plants in high light. The BSMV:TaDeg7 plants also were more sensitive to high-light stress. Collectively, it appeared that TaDeg7 may be a potential target for wheat radiation-use efficiency improvement against high light stress.

Changes of dorsoventral asymmetry and anoxygenic photosynthesis in response of Chelidonium majus leaves to the SiO2 nanoparticle treatment

Abstract: Natural SiO₂ nanoparticles (SiO₂-NPs) are widely distributed in the environment, and at the same time, synthetic SiO₂-NP may be applied in agriculture. Evaluations of physiological responses to SiO₂-NPs treatment of plants are controversial. They are often performed at adaxial leaf sides whereas NPs permeate leaf tissues through stomata located at the abaxial leaf side in the majority of bifacial plants. We measured coefficients of the functional dorsoventral asymmetry of NPs-stressed Chelidonium majus leaves, S, by values of the CO₂ assimilation rate (SP_N), dark respiration (SR), maximal and operating quantum yields of photosystem II (SF_v/F_m, SF_v'/F_m'; using PAM-fluorometry), and oxygen coefficients of photosynthesis (SΨ_O2; using photoacoustics). The results indicated that SP_N and SΨ_O2 were significantly influenced by SiO₂-NPs treatment, since P_N and Ψ_O2 were declining more markedly when the light was directed to the abaxial side of leaves compared to the adaxial side. Overall, SiO₂-NPs-induced stress increased 'anoxygenity' of photosynthesis.

The photosynthetic function analysis for leaf photooxidation in rice

Abstract: Photooxidative damage causes early leaf senescence and plant cell death. In this study, a light-sensitive rice cultivar, 812HS, and a non-light-sensitive cultivar, 812S, were used to investigate early leaf photooxidation. Leaf tips of 812HS exhibited yellowing under a light intensity of 720 µmol(photon) m-2 s-1, accompanied by a decrease in chlorophyll and carotenoids, but 812S was unaffected. The photosynthetic performance of 812HS was also poorer than that of 812S. The H2O2, O2*-, and malondialdehyde content increased sharply in 812HS, and associated antioxidant enzymes were inhibited. The degradation of core proteins in both PSI and PSII, as well as other photosynthesis-related proteins, was accelerated in 812HS. When shaded [180 µmol(photon) m-2 s-1], 812HS recovered to normal. Therefore, our findings suggested excess light disturbed the balance of ROS metabolism, leading to the destruction of the antioxidant system and photosynthetic organs, and thus triggering the senescence of rice leaves.

Morphological and physiological responses of two Osmanthus fragrans cultivars to salt stress

Abstract: We examined the morphological and physiological responses of Osmanthus fragrans 'Yingui' (Yin) and O. fragrans 'Jingui' (Jin) to different NaCl concentrations. NaCl concentrations significantly affected plant height and leaf mass per area. Total biomass decreased by 22.8-41.8% under moderate and high NaCl which inhibited O. fragrans growth. The ratio of root to shoot biomass in Yin was 44.3% higher than that in Jin at high NaCl concentrations which suggested that Yin possesses conservative resource acquisition strategies to resist salt stress. Compared to Yin, Jin showed higher net photosynthesis, stomatal conductance, and intercellular CO₂ concentration under high NaCl treatment. Jin exhibited also relatively higher proline, soluble sugar, K⁺ content, and K⁺/Na⁺ under the treatments implying that acquisitive resource acquisition may be the main strategy for salt resistance in Jin. Our results demonstrated that Yin and Jin could be cultivated in saline land in a short time and the two cultivars respond to salinity by different morphological and physiological mechanisms.

The basalt dust deposition on leaves does not influence the measurement of ecophysiological traits in grapevine

Abstract: In many crops, including grapevine, the distribution of reflecting dust on foliage is a practice potentially leading to the mitigation of environmental stresses such as excessive light and limited water supply. This study aimed to evaluate whether the presence of dust on the leaves may affect PSII photochemical efficiency and gas-exchange measurements, thus leading to biased results. The study was conducted in a winery located at Benevento (Italy) on Vitis vinifera L. subsp. vinifera 'Falanghina' where the application of basalt dust was tested on the canopy to alleviate the effects of water stress. The results showed that there is no difference in PSII photochemistry or gas-exchange parameters measured in the presence of dust or after cleaning the leaves. Therefore, we conclude there is no need to remove dust from leaves before performing the ecophysiological investigations, thus fastening and simplifying the data collection.

Influence of nitrogen and phosphorus additions on parameters of photosynthesis and chlorophyll fluorescence in Cyclocarya paliurus seedlings

Abstract: Cyclocarya paliurus has been traditionally used as a functional food in China. A hydroponic experiment was conducted to determine the effects of N and P additions on photosynthesis and chlorophyll fluorescence (ChlF) of C. paliurus seedlings. N and P additions significantly altered photosynthesis and ChlF in the seedlings, but responses of these parameters to the N and P concentrations varied at different developmental stages. The greatest net photosynthetic rate (P_N) and actual photochemical efficiency of PSII (Ф_PSII) occurred in the treatment of 150.0 mg(N) L^-1 and 25.0 mg(P) L^-1 addition, whereas the highest maximum quantum yield of PSII (F_v/F_m) and water-use efficiency (WUE) were recorded with 150.0 mg(N) L^-1 and 15.0 mg(P) L^-1 on the 60^th day after treatment. Significantly positive correlations of P_N with leaf relative chlorophyll content, transpiration rate, WUE, F_v/F_m, and Φ_PSII, as well as the Ф_PSII with the F_v/F_m, were found. Our results indicated that an optimal addition of N and P nutrients depends on their coupling effects on the photosynthetic capacity and PSII photochemistry.

Professor Charles Percival Whittingham (1922-2011)

Abstract: Professor Charles Percival Whittingham (1922–2011)  lived a full life as a botanist and a plant physiologist par excellence. Whittingham is respected not only for his research on plants but for educating students, internationally, through his excellent books on the chemistry of plant processes, photosynthesis, and the mechanism of photosynthesis.Â

The physiological responses of critically endangered species Ardisia gigantifolia Stapf (Primulaceae) to different light intensities

Abstract: To investigate the light intensity suitable for the growth of Ardisia gigantifolia Stapf, morphology, photosynthetic parameters, and indicators of oxidative stress were analyzed under different light intensities. Compared to high-irradiance treatment, medium and low-irradiance treatments promoted plant growth and restricted transpiration. Compared to medium irradiance, plants under high and low irradiance exhibited significantly lower maximal photochemical efficiency, potential photochemical efficiency, and electron transport rate, but significantly higher malondialdehyde content. This indicated that both excessive light and severe shading inhibited photosynthetic activity and induced oxidative stress, which resulted in a significant decrease in net photosynthetic rate. A. gigantifolia can adapt to different light intensities, improving light harvesting and utilizing capacity under low irradiance by increasing Chl (a+b) content and reducing Chl a/b ratio, and adapting to high irradiance by enhancing heat dissipation and activity of peroxidase. A. gigantifolia showed the best performance in growth and photosynthesis under medium irradiance treatment.

Improving salt tolerance of bean (Phaseolus vulgaris L.) with hydrogen sulfide

Abstract: The current study examined the H2S applications on growth, biochemical and physiological parameters of bean seedlings under saline conditions. The findings of the study indicated that salt stress decreased plant growth and development, photosynthetic activity, and mineral and hormone content [excluding abscisic acid (ABA)] in bean seedlings. Plant and root fresh mass and dry mass with H2S applications increased as compared to the control treatment at the same salinity level. Both salinity and H2S treatments significantly affected the net assimilation rate, stomatal conductance, transpiration rate, and intercellular CO2 content of bean seedlings. Significant increases occurred in H2O2, malondialdehyde (MDA), proline, sucrose content, enzyme activity, and ABA content with salt stress. However, H2S applications inhibited the effects of salinity on plant growth, photosynthetic activity, and mineral content in beans. H2S applications reduced H2O2, MDA, proline, sucrose content, enzyme activity, and ABA content in beans. As a result, exogenous H2S applications could mitigate the negative impacts of salinity in beans.