Quantum Yield Of PSII Research Articles

Inter-specific variability in photophysiological responses of epipelic diatoms to the actin inhibitor Latrunculin B

This study investigates whether the actin inhibitor Latrunculin B (Lat B) can be used to study the interplay between cellular motility and photosynthetic activity of pennate diatoms, by inhibiting their motility while not affecting their photosynthetic performance. The effects of increasing concentrations of Lat B (2.5, 5, and 10 µM) on cellular motility (% motile cells) was measured on several species of pennate diatoms and on natural microphytobenthic assemblages. The species Entomoneis paludosa, Nitzschia longissima, Craspedostauros britannicus, and Pleurosigma strigosum were used for testing the existence of species-specific effects. The results showed that all tested concentrations of Lat B inhibited diatom motility in all studied species, with no decrease in efficacy over at least 5 hours. The effect of Lat B on photosynthetic activity (PSII electron transport rate and non-photochemical quenching) was tested at 2.5 µM. Parameters extracted from light-response curves of relative electron transport rates of PSII (rETR vs E) and from light-induced photoprotection through thermal dissipation of energy (NPQ vs E) did not show common differences between treated and untreated cells. However, some species-specific effects were observed, underscoring the need for careful consideration when using chemicals, based on the specific model under study. Furthermore, treatment with Lat B did not affect the impact of high light exposure on PSII quantum yield. Nevertheless, Lat B appeared to partially reduce the ability of the cells to recover from high light stress, suggesting a potential involvement of actin filaments in photoinhibitory processes.

24‐Epibrassinolide Improves Potato (Solanum tuberosum L.) Tolerance to Alkaline Salt Stress by Regulating Antioxidant Defence and Photosynthetic Properties

ABSTRACTAlkaline salt stress, as a more diverse stress, severely affects the growth and development of potato (Solanum tuberosum L.) and leads to yield reduction. Brassinosteroids have been shown to regulate plant growth and play an essential role under environmental stress. However, the physiological responses by which brassinosteroids confer alkaline salt stress tolerance in potato remain unclear. We used potato ‘Atlantic’ as experimental material. The effects of 0.01, 0.1, 1 and 10 μmol·L−1 of 24‐epibrassinolide (EBR) on the physiological and photosynthetic characteristics of potato under alkaline salt stress (300 mmol·L−1 NaHCO3) were studied. The results showed that exogenous EBR increased the antioxidant enzyme activities, increased the content of osmoregulatory substances and decreased the production of peroxidation products in potato leaves under alkaline salt stress. EBR treatment improved the photosynthetic characteristics by accumulating more photosynthetic pigments. This was manifested by an increase in net photosynthetic rate, transpiration rate and stomatal conductance, and a decrease in intercellular carbon dioxide concentration. In addition, exogenous EBR increased the maximal quantum yield of photosystem II photochemistry and the effective PSII quantum yield of potato PSII under alkaline salt stress and ultimately increased yield. Potato tuber yield was significantly increased by 27.31% and 29.17% in T4 treatment compared to T1 in 2022 and 2023, respectively. Cluster and correlation analyses further demonstrated the beneficial effects of exogenous EBR on physiology, photosynthetic characteristics and potato yield under alkaline salt stress. In conclusion, exogenous EBR can enhance the tolerance of potato to alkaline salt stress by improving the antioxidant system and photosynthesis.

Effects of Water and Nitrogen on Eco-physiological Characteristics of Two Dominant Grassland Species on the Semiarid Loess Plateau

To investigate the eco-physiologcial traits in response to water and nitrogen supplying conditions of native species is of importance for understanding their eco-adaptation to the local environment, and also finding rational agronomy measures for using them in artificial grassland construction. In this study, using Bothriochloa ischaemum (C4 grass) and Lespedeza davurica (C3 legume) as research materials, a pot experiment was conducted to compare the leaf photosynthetic traits, leaf fluorescence parameter characteristics and leaf relative water content of the two dominant native species under three different soil moisture conditions (80%FC, 60%FC and 40%FC) and two nitrogen supplying (0 g N kg-1 and 0.025 g N kg-1) conditions when sown individually or in mixture. Results showed that as soil water content decreased from 80% FC (field capacity) to 40% FC, leaf net photosynthetic rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), and stomatal conductance (Gs) of monocultured plants showed an increasing trend, while the photosynthetic parameters of mixculture plants generally exhibited a decreasing trend. The Pn values of L. davurica were significantly higher than those of B. ishchaemum (P<0.05), and the maximum value was 12.50 mmol m-2 s-1. As soil water content decreased, the initial fluorescence values (Fo), maximum potential quantum yield of PSII (Fv/Fo), and maximum photochemical efficiency (Fv/Fm) values under no nitrogen treatment showed no significant change (P>0.05). Overall, the data indicated that when B. ischaemum and L. davurica were mixcultured, there existed a significant mutualistic effect under low soil water situation, indicating mixculture of B. ischaemum and L. davurica was beneficial for coping with drought in the semiarid region.

Evaluation of Tomato Landraces for Tolerance to Drought Stress Using Morphological and Physiological Traits

Drought is among the stress factors that, on a global scale, have direct negative effects on plant growth, yield, and quality. Great efforts are directed towards water shortage adaptation. Exploring the genetic diversity of landraces often tolerant to locally occurring stress can represent a valuable source for the development of cultivars with yield stability and improved quality under stress conditions. This study aimed to identify drought-tolerant tomato landraces based on an integrated approach involving morphological traits and physiological parameters. To investigate the effects of water deficit, five landraces and two controls were tested under optimum and 50% reduced irrigation. Yield and yield-related traits, color, firmness, and chlorophyll fluorescence measurements were evaluated. The summarized results indicated that the tomato landraces differed in their responses to water deficit. Water deficit decreased the yield by 44% and the average fruit weight by 29%. Physiological parameters were also significantly affected by water scarcity, with a decrease in the ratios Fv/Fm (the maximum quantum yield of PSII) and Fv/Fo (the maximum primary yield of photochemistry) of 8.2% and 35.5%, respectively, at 14 days’ exposure to stress. Landrace 1352, characterized by indeterminate growth habit and large, rounded, and red-colored fruits, showed a significantly lower reduction in yield and physiological parameters under reduced irrigation and could be used in breeding programs to develop new tomato lines combining resistance with quality.

Comparative Salt-Stress Responses in Salt-Tolerant (Vikinga) and Salt-Sensitive (Regalona) Quinoa Varieties. Physiological, Anatomical and Biochemical Perspectives

Soil salinization is an important stress factor that limits plant growth and yield. Increased salinization is projected to affect more than 50% of all arable land by 2050. In addition, the growing demand for food, together with the increase in the world population, forces the need to seek salt-tolerant crops. Quinoa (Chenopodium quinoa Willd.) is an Andean crop of high importance, due to its nutritional characteristics and high tolerance to different abiotic stresses. The aim of this work is to determine the physiological, anatomical, and biochemical salt-tolerance mechanisms of a salt-tolerant (Vikinga) and a salt-sensitive (Regalona) quinoa variety. Plants were subjected to salinity stress for 15 days, starting at 100 mM NaCl until progressively reaching 400 mM NaCl. Physiological, anatomical, and biochemical parameters including growth, chlorophyll content, quantum yield of PSII (ϕPSII), gas exchange, stomatal density, size, and lipid peroxidation (via malondialdehyde, MDA) were measured. Results show that chlorophyll content, ϕPSII, and MDA were not significantly reduced under saline stress in both varieties. The most stress-affected process was the CO2 net assimilation, with an up to 60% reduction in both varieties, yet Vikinga produced higher dry weight than Regalona due to the number of leaves. The stomatal densities increased under salinity for both varieties, with Regalona the one showing higher values. The averaged stomatal size was also reduced under salinity in both varieties. The capacity of Vikinga to generate higher dry weight is a function of the capacity to generate greater amounts of leaves and roots in any condition. The stomatal control is a key mechanism in quinoa’s salinity tolerance, acquiring higher densities with smaller sizes for efficient management of water loss and carbon assimilation. These findings highlight the potential of Vikinga for cultivation in temperate salinized environments during winter, such as Deltas and lowlands where rice is grown during summer.

A small-scale spatial heterogeneity in photochemical reflectance index and intensity of reflected light at 530 nm in pea (Pisum sativum) leaves is sensitive to action of salinization.

Remote sensing of stressor action on plants is an important step of their protection. Measurement of photochemical reflectance index (PRI) can be used to detect action of stressors including salinization; potentially, a small-scale spatial heterogeneity of PRI (within leaf or its part) can be an indicator of this action. The current work was devoted to analysis of sensitivity of the small-scale heterogeneity in PRI and in the reflected light intensity at 530nm (approximately corresponding to the measuring wavelength for PRI) in leaves of pea (Pisum sativum ) plants to action of salinization. Plants were cultivated under controlled conditions of a vegetation room and under open-air conditions. It was shown that both the standard deviation of PRI and coefficient of variation of the reflected light intensity at 530nm were sensitive to action of salinization on plants. Moreover, this variation coefficient was negatively corelated to the potential quantum yield of PSII; i.e. increasing the coefficient could be used to estimate decreasing this yield caused by photodamage of PSII under salinization. Our results show that the small-scale spatial heterogeneity in PRI and the reflected light intensity at 530nm can be used as additional tools of the remote sensing of plant responses under action of salinization.

Effects of Far-Red Light and Ultraviolet Light-A on Growth, Photosynthesis, Transcriptome, and Metabolome of Mint (Mentha haplocalyx Briq.).

To investigate the effects of different light qualities on the growth, photosynthesis, transcriptome, and metabolome of mint, three treatments were designed: (1) 7R3B (70% red light and 30% blue light, CK); (2) 7R3B+ far-red light (FR); (3) 7R3B+ ultraviolet light A (UVA). The results showed that supplemental FR significantly promoted the growth and photosynthesis of mint, as evidenced by the increase in plant height, plant width, biomass, effective quantum yield of PSII photochemistry (Fv'/Fm'), maximal quantum yield of PSII (Fv/Fm), and performance index (PI). UVA and CK exhibited minimal differences. Transcriptomic and metabolomic analysis indicated that a total of 788 differentially expressed genes (DEGs) and 2291 differential accumulated metabolites (DAMs) were identified under FR treatment, mainly related to plant hormone signal transduction, phenylpropanoid biosynthesis, and flavonoid biosynthesis. FR also promoted the accumulation of phenylalanine, sinapyl alcohol, methylchavicol, and anethole in the phenylpropanoid biosynthesis pathway, and increased the levels of luteolin and leucocyanidin in the flavonoid biosynthesis pathway, which may perhaps be applied in practical production to promote the natural antibacterial and antioxidant properties of mint. An appropriate increase in FR radiation might alter transcript reprogramming and redirect metabolic flux in mint, subsequently regulating its growth and secondary metabolism. Our study uncovered the regulation of FR and UVA treatments on mint in terms of growth, physiology, transcriptome, and metabolome, providing reference for the cultivation of mint and other horticultural plants.

Integration of Copper Toxicity Mechanisms in Raphidocelis subcapitata: Advancing Insights at Environmentally Relevant Concentrations.

This work aimed to characterize the impact of copper (Cu), at environmentally relevant concentrations, using the freshwater microalga Raphidocelis subcapitata. Algae were incubated with 33 or 53 µg/L Cu, in OECD medium, and toxic impacts were evaluated over 72 h, using different cellular and biochemical biomarkers. The exposure to 33 µg/L Cu had an algistatic effect: slowing growth and reducing algal population (53%, at 72 h) without compromising the cell membrane. This Cu concentration promoted a transient reduction in chlorophyll a (chla) content and typical markers of oxidative stress: increased levels of reactive oxygen species (ROS), augmented catalase (CAT) activity, and lipid peroxidation (malondialdehyde, MDA). Algae exposed to 53 µg/L Cu, suffered a severe effect with a 93% reduction in the number of cells, 50% decrease in chla content, and diminished (17%) maximum photochemical quantum yield of PSII (Fv/Fm). This population also presented increased levels of ROS and MDA, 33 and 20 times higher than the control, respectively, at 72 h, augmented CAT activity, and permeabilized cell membrane (5%, at 72 h). These findings provide valuable insights into Cu toxicity in aquatic ecosystems, highlighting the biochemical and physiological impacts at environmentally relevant concentrations.

Genome-wide survey of chlorophyllase (CLH) gene family in seven Rosaceae and functional characterization of MdCLH1 in apple (Malus domestica) leaf photosynthesis

Chlorophyll, a crucial pigment in plant photosynthesis, undergoes dynamic synthesis and degradation processes throughout the growth cycle of plants. Chlorophyllase (CLH) plays a crucial role in the degradation of chlorophyll by removing the phytol group from chlorophyll A to produce chlorophyllide A. However, Rosaceae species remain underexplored in terms of understanding the functional divergences among CLH gene family members (CLHs) involved in chlorophyll catabolism and photosynthesis. The apple (Malus domestica) CLHs also requires further systematic characterization and identification. In this study, 20 CLHs (MdCLH1-4, FvCLH1-2, PpCLH1-2, PcCLH1-3, PaCLH1-2, RrCLH1-4, RcCLH1-3) were identified from seven species belonging to the Rosaceae family. The chromosomal distribution of these gene family members is mostly separate across all species, except in Rosa rugosa. The number of amino acids encoded by these genes ranges from 171 aa to 391 aa, possessing a theoretical isoelectric point (PI) of 5.46-9.59, and a relative molecular weight of 18313.07D to 42413.21D. Secondary structure predictions highlight α-helix and random coil conformations as the dominant structural elements of CLH proteins present in Rosaceae species. Subcellular localization predictions indicate that all CLH proteins are expressed in chloroplasts, while MdCLH4 is uniquely localized to the nucleus. Phylogenetic analysis reveals high homology and close evolutionary relationships among the genes in three subfamilies. All these 20 CLHs contain elements responsive to phytohormones, environmental stress, and light. Furthermore, transcriptomic profiling using geneChip expression array coupled with qRT-PCR analyses revealed a heightened transcriptional activity of MdCLHs in leaf tissues and protective tissue of annual shoots as compared to other plant components. Additional experimental evidence specifically indicates MdCLH1 is located in the chloroplasts of tobacco leaves. Notably, MdCLH1 transient expression in apple leaves decreased chlorophyll a, carotenoids, total chlorophyll content, non - photochemical quenching coefficient (NPQ), and intercellular CO₂ concentration (Ci), while increasing chlorophyll b content, effective PSII quantum yield [Y(II)], net photosynthetic rate (Pn), stomatal conductance (Gs), and electron transport rate (ETR). These suggest MdCLH1 enhances light energy conversion in PSII by modulating chlorophyll degradation, potentially improving photosynthetic efficiency and reducing the potential for photoinhibition. This study lays a solid foundation for further exploration into the functional roles of CLHs in the Rosaceae family.

Glowing Graphene Quantum Dots Enhancing Photoelectric Transportation in Photosynthesis Carbon Trapping of Pteridophyta Fern

Pteridophyta fern plays an important role in photosynthesis to trap carbon in earth. The application of graphene also enhanced the quality of lettuce, resulting in reduced heavy accumulation in both leaves and roots and increasing in the levels of soluble sugar, protein, and vitamin C content. graphene was augmented the total size, surface area, average diameter, and the number of roots in lettuce roots. In this study, we investigated the response of plant growth by implanted different concentration of glowing graphene quantum dots in pteridophyta fern. Quantum yield and efficiency of chlorophyll fluorescence and were used to demonstrate photosynthesis function. Furthermore, CO2 exchange rate is determined to qualify the increasing carbon sink in plants. We found efficiency of donation electron to PSI (Fv/Fo), maximum quantum yield of PSII (Fv/Fm), performance index on absorption basis (PIABS) energy fluxes absorbed (ABS/RC) and trapped (TRo/RC) per reaction center (RC), primary photochemistry (ψo), electron transport rate (ETo/RC) and non-photochemical quenching for energy dissipation (DIo/RC) of Pteridophyta fern are enhanced after graphene is implanted in vein. Carbon trapping of pteridophyta fern is determined by Fv/Fm, PIABS, ABS/RC, TRo/RC, ψo, ETo/RC, and DIo/RC.

Ethyl methanesulfonate (EMS) mediated dwarfing mutation provides a basis for CaCO3 accumulation by enhancing photosynthetic performance in Ceratostigma willmottianum Stapf.

Ceratostigma willmottianum Stapf is a unique chalk gland (salt-excreting) plant from China, with a salt gland structure that excretes white crystals of calcium carbonate (CaCO3), which has potential biomineralization and carbon sequestration functions. Due to the narrow distribution of wild germplasm resources, there is a lack of diversity of new varieties to satisfy commercial development and scientific exploration. Therefore, we used ethyl methanesulfonate (EMS) mutagenesis to obtain new dwarf mutant germplasm, and analysed it in terms of morphology, growth, photosynthesis, salt glands, and excretion traits. All four dwarfing mutant strains (DM1, DM2, DM3, and DM4) exhibited extreme dwarfing (62.28%, 62.28%, 74.55% and 61.68% reduction in plant height, respectively), faster growth, increased belowground root biomass, and earlier bud differentiation and flowering. Photosynthetic capacity was enhanced: chlorophyll content, maximum quantum yield of PSII (Fv/Fm), effective quantum yield of PSII (ΦPSII), photochemical quenching coefficient (qP), electron transfer rate (ETR), net photosynthesis (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs), and transpiration (Tr), were significantly higher in leaves of DM mutants. The density of salt glands per unit leaf area and average Ca2+ excretion rate of individual salt glands increased significantly (especially in DM2), and CaCO3 accumulation per unit leaf area was 28.57% higher than that of the wild type. Pearson correlation analysis showed that photosynthetic capacity was significantly and positively correlated with CaCO3 excretion. The above study not only provided enriched new germplasm of C. willmottianum, but also important research material for studying the mechanism of CaCO3 excretion by salt glands and carbon sequestration capacity of biomineralization.

Effects of tillage methods on photosynthetic performance of different functional leaf groups of summer maize in coastal saline-alkali farmland.

This study aims to determine the changes in the photosynthetic performance of leaves at different leaf positions and their correlation and to screen out the basic tillage methods suitable for improving the yield. The decrease in soil salt content significantly improved the PSII performance index and quantum yield for electron transport of the bottom leaf group, synergistically enhanced the photosynthetic performance of summer maize leaves (especially the bottom leaf group), and enhanced the correlation between the bottom, middle (including the ear leaf), and upper leaf groups. Under subsoiling tillage conditions, the bottom leaves could produce more carbohydrates to meet the normal growth of the root system, promote the photosynthesis of the middle leaf group at the ear position, and increase the nutrient output of the upper leaf group to the female ear in the middle and later stages of maize aging.

Comparative Analysis of Pretreatment Methods for Fruit Waste Valorization in Euglena gracilis Cultivation: Impacts on Biomass, β-1,3-Glucan Production, and Photosynthetic Efficiency.

This study explored the sustainable valorization of fruit waste extracts from sugarcane bagasse (SB), banana peel (BP), and watermelon rind (WR) for Euglena gracilis biomass and β-1,3-glucan production. The extracts were prepared using water extraction (WE), high-temperature and pressure treatment (HTP), and dilute sulfuric acid treatment (DSA). The DSA-treated extracts consistently yielded the best results. E. gracilis cultured in SB-DSA showed the highest cell density with a 2.08-fold increase compared to the commercial HUT medium, followed by BP-DSA (1.35-fold) and WR-DSA (1.70-fold). Photosynthetic pigment production increased significantly, with chlorophyll a yield being highest in SB-DSA (1.90-fold increase). The chlorophyll a/b ratio and total carotenoid content also improved, indicating enhanced light-harvesting capacity and photoprotection. Photosynthetic efficiency, measured by chlorophyll fluorescence, notably improved. The maximum quantum yield of PSII (Fv/Fm) increased by up to 25.88% in SB-DSA, suggesting reduced stress and improved overall photosynthetic health. The potential photochemical efficiency (Fv/F0) showed even greater improvements: up to 40.53% in SB-DSA. Cell morphology analysis revealed larger cell aspect ratios, implying a more active cellular physiological state. β-1,3-glucan yield also increased by 23.99%, 12.92%, and 23.38% in SB-DSA, BP-DSA, and WR-DSA, respectively. This study demonstrates the potential of pretreated fruit waste as a cost-effective and sustainable medium for E. gracilis cultivation, offering the dual benefits of waste valorization and high-value compound production. These findings contribute to the development of more efficient biorefinery processes and align with the circular economy principles in food biotechnology.

Exogenous hydrogen sulfide increased Nicotiana tabacum L. resistance against drought by the improved photosynthesis and antioxidant system

Drought stress is an abiotic stressor that impacts photosynthesis, plant growth, and development, leading to decreased crop yields. Sodium hydrosulfide (NaHS), an exogenous additive, has demonstrated potential regulatory effects on plant responses to polyethylene glycol-induced drought stress in tobacco seedlings. Compared to the control, drought stress induced by 15 g/L PEG-6000 significantly reduced several parameters in tobacco seedlings: shoot dry weight (22.83%), net photosynthesis (37.55%), stomatal conductance (33.56%), maximum quantum yield of PSII (Fv/Fm) (11.31%), photochemical quantum yield of PSII (ΦPSII) (25.51%), and photochemical quenching (qP) (18.17%). However, applying NaHS, an H2S donor, mitigated these effects, ultimately enhancing photosynthetic performance in tobacco seedlings. Furthermore, optimal NaHS concentration (0.4 mM) effectively increased leaf stomatal aperture, relative water content (RWC) and root activity, as well as facilitated the absorption of N, K, Mg and S. It also enhanced the accumulation of soluble sugar and proline content to maintain osmotic pressure balance under drought stress. Compared to drought alone, pretreatment with NaHS also bolstered the antioxidant defense system in leaves, leading to 22.93% decrease in hydrogen peroxide (H2O2) content, a 22.19% decrease in malondialdehyde (MDA) content and increased activities of ascorbate peroxidase (APX) by 28.13%, superoxide dismutase (SOD) by 17.07%, peroxidase (POD) by 46.99%, and catalase (CAT) by 65.27%. Consequently, NaHS protected chloroplast structure and attenuated chlorophyll degradation, thus mitigating severe oxidative damage. Moreover, NaHS elevated endogenous H2S levels, influencing abscisic acid (ABA) synthesis and the expression of receptor-related genes, collaboratively participating in the response to drought stress. Overall, our findings provide valuable insights into exogenous NaHS’s role in enhancing tobacco drought tolerance. These results lay the foundation for further research utilizing H2S-based treatments to improve crop resilience to water deficit conditions.

Sufficient Light Intensity Is Required for the Drought Responses in Sweet Basil (Ocimum basilicum L.)

Various environmental factors not only affect plant growth and physiological responses individually but also interact with each other. To examine the impact of light intensity on the drought responses of sweet basil, plants were subjected to maintenance of two substrate volumetric water contents (VWC) using a sensor-based automated irrigation system under two distinct light intensities. The VWC threshold was set to either a dry (0.2 m3·m−3) or sufficiently wet condition (0.6 m3·m−3) under low (170 μmol·m−2·s−1) or high light intensities (500 μmol·m−2·s−1). The growth and physiological responses of sweet basil (Ocimum basilicum L.) were observed over 21 days in the four treatment groups, where the combination of two environmental factors was analyzed. Under high light intensity, sweet basil showed lower Fv/Fm and quantum yield of PSII, compared to that under low light intensity, regardless of drought treatment. Fourteen days after drought treatment under high light intensity, stomatal conductance and the photosynthetic rate significantly reduced. Whereas plants under low light intensity showed similar stomatal conductance and photosynthetic rates regardless of drought treatment. Assessment of shoot and root dry weights revealed that plant growth decline caused by drought was more pronounced under high light intensity than under low light intensity. Thus, sweet basil showed significant declines in growth and physiological responses owing to drought only under high light intensity; no significant changes were observed under low light intensity.

Photosynthetic Performance and Heterogeneous Anatomical Structure in Prunus humilis under Saline–Alkaline Stress

Prunus (P.) humilis is a small woody shrub that has been widely planted in northern China due to its high nutritional value and resistance to environmental abiotic stress. However, little information about the responses of photosynthetic performance and the anatomical structure of P. humilis to saline–alkaline stress (SAS) under field conditions is available. Here, we investigated the behavior of the photosynthetic apparatus of P. humilis by measuring the chlorophyll fluorescence parameters under moderate (MS) and severe (SS) saline–alkaline stress and analyzing their relationship to leaf anatomical traits. The results showed that SAS significantly decreased the net photosynthetic rate (An) but increased the substomatal CO2 concentration (Ci). The maximum photochemical quantum yield of PSII (Fv/Fm) and the efficient quantum yield of PSII [Y(II)] decreased under MS and SS conditions, and this decrease was greater in the distal (tip) than in the proximal (base) leaf. Compared to the leaf tip, the base of P. humilis leaves seemed to have a stronger ability to cope with MS, as was made evident by the increased quantum yield of regulated energy dissipation in PSII [Y(NPQ)] and decreased excitation pressure (1-qP). Under MS and SS conditions, the shapes of the chlorophyll a fluorescence transient (OJIP) changed markedly, accompanied by decreased PSII acceptor-side and donor-side activities. The palisade–spongy tissue ratio (PT/ST) increased significantly with increasing stress and showed a significant correlation with the chlorophyll fluorescence parameters in the leaf base. These results suggested that the activity of PSII electron transfer in the upper leaf position tended to be more sensitive to saline–alkaline stress, and a chlorophyll fluorescence analysis proved to be a good technique to monitor impacts of saline–alkaline stress on photosynthetic function, which may reflect the non-uniformity of leaf anatomy. In addition, among the anatomical structure parameters, the palisade–spongy tissue ratio (PT/ST) can be used as a sensitive indicator to reflect the non-uniform of photosynthetic function and leaf anatomy under stress.

Chloroplast ATP synthase restricts photosynthesis under fluctuating light in tomato but not in maize

Photosynthesis in fluctuating light requires coordinated adjustments of diffusion conductance and biochemical capacity, but the role of chloroplast ATP synthase activity (gH+) in dynamic photosynthesis is not well understood. In this study, we measured gas exchange, chlorophyll fluorescence and electrochromic shift signals in fluctuating light for leaves of tomato (Solanum lycopersicum) and maize (Zea mays). During the transition from sun to shade, simultaneous increases in gH+, effective quantum yield of PSII, and net CO2 assimilation rate (AN) occurred in tomato but uncoupled in maize, indicating that gH + limited AN during the sun-to-shade transition in tomato but not in maize. During the shade-to-sun transition, gH + increased simultaneously with stomatal conductance, mesophyll conductance and Rubisco carboxylation capacity in tomato, suggesting that gH+ is an overlooked factor affecting light induction of AN in tomato. By comparison, gH + maintained at high levels in maize and its AN was mainly restricted by stomatal conductance. Our results reveal that the kinetics of gH+ in fluctuating light differs between species, and chloroplast ATP synthase may be a potential target for improving dynamic photosynthesis in crops such as tomato.

Species-specific functional trait responses in two species coexisting along a shore-to-inland dune gradient.

Coastal dunes are characterised by strong gradients of abiotic stress, typically increasing in severity from inland areas towards the shoreline. Thus, dune gradients represent unique opportunities to study intraspecific responses to environmental changes and to investigate which factors drive community change. This study aims to examine functional trait variation in two coexisting species in response to environmental changes along a dune gradient in NW Spain. Trait convergence was also investigated and compared between both ends of the gradient. We measured functional leaf traits related to plant efficiency in the use of light, water and nutrients, also possible stressors (salt content and pH) and availability of limiting resources (water and nutrients) in the soil. Most soil variables showed changes following a non-directional gradient. Differences in soil variables were site specific and depended on growth of the study species. Structural and functional traits depended on species and/or plant position on the gradient, except for effective quantum yield of PSII and leaf δ15N. The pattern of variation was mostly directional for reflectance indices related to leaf physiology. Multivariate analyses showed significant interspecific differences in the set of traits they exhibited along positions in the gradient. Species also differed in the combination of traits selected under given environmental conditions. Coexisting species display a specific set of traits that reflects different strategies to environmental stress. Our study highlights the overly simplistic nature of some previous studies that assume dune gradients are monotonically directional, without considering that these gradients may be differentially modified by species activity.

Identification of genes involved in the tomato root response to Globodera rostochiensis parasitism under varied light conditions

Understanding the intricate interplay between abiotic and biotic stresses is crucial for deciphering plant responses and developing resilient cultivars. Here, we investigate the combined effects of elevated light intensity and nematode infection on tomato seedlings. Chlorophyll fluorescence analysis revealed significant enhancements in PSII quantum yield and photochemical fluorescence quenching under high light conditions. qRT-PCR analysis of stress-related marker genes exhibited differential expression patterns in leaves and roots, indicating robust defense and antioxidant responses. Despite root protection from light, roots showed significant molecular changes, including downregulation of genes associated with oxidative stress and upregulation of genes involved in signaling pathways. Transcriptome analysis uncovered extensive gene expression alterations, with light exerting a dominant influence. Notably, light and nematode response synergistically induced more differentially expressed genes than individual stimuli. Functional categorization of differentially expressed genes upon double stimuli highlighted enrichment in metabolic pathways, biosynthesis of secondary metabolites, and amino acid metabolism, whereas the importance of specific pathogenesis-related pathways decreased. Overall, our study elucidates complex plant responses to combined stresses, emphasizing the importance of integrated approaches for developing stress-resilient crops in the face of changing environmental conditions.

The Influence of Varying Wavelengths of LED Light on the Development, Physiology Response, and Metabolism Activities of Micropropagated Dendrobium Hybrid ‘Shuijing’ Plantlets

Dendrobium hybrids have a significant role in the present floral sector. The aim of this research was to evaluate how various light qualities affect the physiological and biochemical traits of Dendrobium ‘Shuijing’. In order to determine the optimal light quality for in vitro cultivation of Dendrobium plantlets, we examined the correlations between growth, antioxidant capacity, and nutrient and chlorophyll levels, as well as chlorophyll fluorescence. The growth rate was compared by using different light qualities emitted by the LED light source. These included red light (R), blue light (B), and three ratios: 8R:2B, 7R:3B, and equal proportions of both colors, known as white, fluorescent light (CK). The combination of 7R:3B resulted in noticeable enhancements in leaf count, root length, root activity, fresh and dry weight measurements, antioxidant capability, as well as chlorophyll content and fluorescence. Specifically, the mixture of red and blue LED lights at a ratio of 7R:3B led to increased leaf number, root length, root activity, fresh and dry weight measurements, antioxidant ability, and chlorophyll content with improved fluorescence. In order to explore the effect of light quality on the growth and development of Dendrobium, the chlorophyll content and chlorophyll fluorescence parameters of plants under all light quality conditions were analyzed by using a linear regression model with other physiological and biochemical indexes. A significant correlation between non-photochemical quenching (NPQ) and leaf length was also observed. The content of chlorophyll b showed significant correlations with both root number and leaf number. Furthermore, chlorophyll a, along with its ratio to chlorophyll b, significantly correlated with root length. Chlorophyll b and the relative electron transport rate of PSII (ETRII) significantly correlated with root activity and the free proline content (FPC) and catalase (CAT) activity. The photochemical quenching coefficient (qP) significantly correlated with total soluble sugars content (SSC) and peroxidase (POD) activity. The correlation between the quantum yield of PSII (Fv/Fm ratio) and superoxide dismutase (SOD) activity was found to be significant. Similarly, the effective quantum yield of PSII photochemistry (ΦPSII) showed significant correlations with fresh weight, dry weight, soluble protein content (SPC), and ascorbate peroxidase (APX) activity. Through a principal component analysis (PCA), it was observed that plants cultivated under the 7R:3B light treatment achieved significantly better comprehensive scores compared to those grown under different light treatments. In conclusion, growth achieved under an LED emitting a ratio of 7R:3B light yielded the most robust Dendrobium hybrid plantlets within a controlled environment.