Maximum Quantum Yield Of Photochemistry Research Articles

Alleviative Effect of Exogenous Application of Fulvic Acid on Nitrate Stress in Spinach (Spinacia oleracea L.)

Salt stress could be a significant factor limiting the growth and development of vegetables. In this study, Fulvic Acid (FA) (0.05%, 0.1%, 0.15%, 0.2%, and 0.25%) was applied under nitrate stress (150 mM), with normal Hoagland nutrient solution as a control to investigate the influence of foliar spray FA on spinach growth, photosynthesis, and oxidative stress under nitrate stress. The results showed that nitrate stress significantly inhibited spinach growth, while ROS (reactive oxygen species) accumulation caused photosystem damage, which reduced photosynthetic capacity. Different concentrations of FA alleviated the damage caused by nitrate stress in spinach to varying degrees in a concentration-dependent manner. The F3 treatment (0.15% FA + 150 mM NO3−) exhibited the most significant mitigating effect. FA application promoted the accumulation of biomass in spinach under nitrate stress and increased chlorophyll content, the net photosynthetic rate, the maximum photochemical quantum yield of PSII (Photosystem II) (Fv/Fm), the quantum efficiency of PSII photochemistry [Y(II)], the electron transport rate, and the overall functional activity index of the electron transport chain between the PSII and PSI systems (PItotal); moreover, FA decreased PSII excitation pressure (1 − qP), quantum yields of regulated energy dissipation of PSII [Y(NPQ)], and the relative variable initial slope of fluorescence. FA application increased superoxide dismutase, peroxidase, and catalase activities and decreased malondialdehyde, H2O2, and O2− levels in spinach under nitrate stress. FA can enhance plant resistance to nitrate by accelerating the utilization of light energy in spinach to mitigate excess light energy and ROS-induced photosystem damage and increase photosynthetic efficiency.

Phytoplankton Diversity, Spatial Patterns, and Photosynthetic Characteristics Under Environmental Gradients and Anthropogenic Influence in the Pearl River Estuary.

The Pearl River Estuary (PRE) is one of the world's most urbanized subtropical coastal systems. It presents a typical environmental gradient suitable for studying estuarine phytoplankton communities' dynamics and photosynthetic physiology. In September 2018, the maximum photochemical quantum yield (Fv/Fm) of phytoplankton in different salinity habitats of PRE (oceanic, estuarine, and freshwater zones) was studied, revealing a complex correlation with the environment. Fv/Fm of phytoplankton ranged from 0.16 to 0.45, with taxa in the upper Lingdingyang found to be more stressed. Community composition and structure were analyzed using 18S rRNA, accompanied by a pigment analysis utilized as a supplementary method. Nonmetric multidimensional scaling analysis indicated differences in the phytoplankton spatial distribution along the estuarine gradients. Specificity-occupancy plots identified different specialist taxa for each salinity habitat. Dinophyta and Haptophyta were the predominant taxa in oceanic areas, while Chlorophyta and Cryptophyta dominated freshwater. Bacillariophyta prevailed across all salinity gradients. Canonical correlation analysis and Mantel tests revealed that temperature, salinity, and elevated nutrient levels (i.e., NO3--N, PO43--P, and SiO32--Si) associated with anthropogenic activities significantly influenced the heterogeneity of community structure. The spatial distribution of phytoplankton, along with in situ photosynthetic characteristics, serves as a foundational basis to access estuarine primary productivity, as well as community function and ecosystem health.

Dieback of royal poinciana (Delonix regia) trees induced by Alternaria tenuissima and its impact on photochemical efficiency of photosystem II

In Saudi Arabia, poinciana (Delonix regia) trees are afflicted by dieback disease, manifesting symptoms that can lead to complete defoliation and, ultimately, the demise of trees in advanced stages. To investigate the dieback symptoms, samples were collected from branches at the transition zone. Identification of fungal isolates involved the assessment of colony and spore morphology, as well as PCR amplification and sequencing of the internal transcribed spacer (ITS) gene regions. The predominant fungus isolated was Alternaria tenuissima. Chlorophyll a fluorescence quenching and polyphasic fluorescence induction kinetics were conducted to assess the photochemical and nonphotochemical processes of Photosystem II (PSII) in stem barks affected by dieback. The dieback disease significantly reduced chlorophyll content, potentially hindering PSII performance in terms of maximum photochemical efficiency, quantum yield, electron flux, and photoprotection. These findings suggest that compromised photochemistry and photoprotection render poinciana trees inoculated by dieback less efficient in utilizing light energy and more susceptible to photoinhibition. Additionally, this study implies the use of non-invasive chlorophyll fluorescence techniques as a phenotyping tool for assessing photoprotective and photoinhibitory responses of stems to dieback stress.

Diverse nitrogen enrichments enhance photosynthetic resistance of Sargassum horneri to ultraviolet radiation

In recent years, golden tides caused by floating Sargassum have induced severe ecological disasters globally. Eutrophication is a significant factor contributing to the massive spread of Sargassum golden tides. Furthermore, the thalli of Sargassum that float on the ocean surface are subjected to more ultraviolet radiation (UVR). The coupled impact of eutrophication and UVR on the photosynthetic physiology of golden tide species remains unclear. In this study, the thalli of Sargassum horneri, known to cause golden tide, were cultured and acclimated to three distinct nitrogen (N) conditions (natural seawater, NSW; NH4+-N enrichment; and NO3–N enrichment) for 6 days. Subsequently, the thalli were exposed to two different radiation treatments (photosynthetically active radiation (150 W m-2), PAR, 400–700 nm; PAR (150 W m-2) + UVR (28 W m-2), 280–700 nm) for 120 min, to investigate the photosynthetic effects of UVR and N on this alga. The findings demonstrated that exposure to UVR impeded the photosynthetic capacity of S. horneri, as evidenced by a decrease in the maximum photochemical quantum yield (Fv/Fm), photosynthetic efficiency (α) and chlorophyll content. Under diverse N-enrichment conditions, the alga tended to adopt various strategies to mitigate the adverse effects of UVR. NH4+-enrichment dissipated excess UVR energy through a greater increase in non-photochemical quenching (NPQ). While NO3–enrichment protected alga by enhancing N assimilation (higher nitrate reductase activity (NRA) and soluble protein content), and maintained a stable energy captured per unit reaction center for electron transfer (ET0/RC) and a higher net photosynthetic rate. Although different N enrichments could not completely offset the damage caused by UV radiation, they secured the photoprotective ability of S. horneri in several ways.

Impact of exogenous melatonin foliar application on physiology and fruit quality of wine grapes (Vitis vinifera) under salt stress.

Soil salinisation is an important abiotic stress faced in grape cultivating, leading to weakened plant vigour and reduced fruit quality. Melatonin as a novel hormone has shown positive exogenous application value. Therefore, this study used wine grape (Vitis vinifera ) 'Pinot Noir' as a test material to investigate the changes of foliar spraying with different concentrations of melatonin on the physiology and fruit quality of wine grapes in a field under simulated salt stress (200mmolL-1 NaCl). The results showed that foliar spraying of melatonin significantly increased the intercellular CO2 concentration, maximum photochemical quantum yield of PSII, relative chlorophyll and ascorbic acid content of the leaves, as well as the single spike weight, 100-grain weight, transverse and longitudinal diameters, malic acid, α-amino nitrogen and ammonia content of fruits, and decreased the initial fluorescence value of leaves, ascorbate peroxidase activity, glutathione content, fruit transverse to longitudinal ratio and tartaric acid content of plants under salt stress. Results of the comprehensive evaluation of the affiliation function indicated that 100μmolL-1 melatonin treatment had the best effect on reducing salt stress in grapes. In summary, melatonin application could enhance the salt tolerance of grapes by improving the photosynthetic capacity of grape plants under salt stress and promoting fruit development and quality formation, and these results provide new insights into the involvement of melatonin in the improvement of salt tolerance in crop, as well as some theoretical basis for the development and industrialisation of stress-resistant cultivation techniques for wine grapes.

Comprehensive evaluation and screening identification indexes of heat‐resistance indices in cotton (Gossypium hirsutum L.)

AbstractCotton (Gossypium hirsutum L.) cultivars exhibit varying responses to heat stress. To investigate the heat resistance of various cotton and establish an index system for evaluating their heat resistance, 21 cotton cultivars were selected and subjected to two temperature regimes (CK, average temperature 28°C, 32/24°C; HT, average temperature 38°C, 42/34°C). The results showed that under high temperatures, different changes occurred in individual indexes of cotton, reflecting the differences in heat resistance in cotton cultivars. A total of 21 cotton cultivars could be classified into four types: heat‐tolerant, moderate heat‐tolerant, moderate heat‐sensitive and heat‐sensitive cultivars by multivariate statistical analysis. Moreover, the indexes of net photosynthetic rate (Pn), leaf superoxide dismutase activity (LSOD), the maximum photochemical quantum yield (Fv/Fm), the actual photochemical quantum yield (ΦPSII), leaf malondialdehyde content (LMDA), leaf catalase activity (LCAT), dry matter weight of shoot (SDW) and root malondialdehyde content (RMDA) were determined to be useful for evaluating the cotton heat tolerance by stepwise regression analysis. The pot experiment showed that the reduction of boll number, boll weight and seed cotton yield was more remarkable under HT in the heat‐sensitive cultivar CCRI‐92 than in the heat‐resistant cultivar CCRI‐69, which further verified the screening results. In conclusion, the heat‐sensitive cultivars CCRI‐92 and heat‐resistant cultivar CCRI‐69 which are identified by seedling experiment could serve as ideal experimental materials for studying heat resistance in cotton. The physiological indices such as Pn, LSOD, Fv/Fm, ΦPSII, LMDA, LCAT, SDW and RMDA be employed for assessing the heat tolerance in cotton.

Improved chlorophyll fluorescence, photosynthetic rate, and plant growth of Brassica napus L. after co‐application of biochar and phosphorus fertilizer in acidic soil

AbstractAimsBiochar has been used as an amendment to improve soil fertility and increase crop yield. A pot trial and incubation experiment were conducted to evaluate the effects of combined biochar and phosphate fertilizer applications on changes in soil physiochemical properties, photosynthetic parameters, and plant growth of Brassica napus L. in acidic soil.MethodsBiochar (B) was applied at rates (B0: 0%, B1: 2%, and B2: 4% w/w) to the soil, while phosphorus (P) as KH2PO4 was added at P0: 0 mg kg–1 soil, P1: 100 mg kg–1 soil, and P2: 150 mg kg–1 soil. Non‐amended soil served as the control (Ck).ResultsThe study found that the maximum photochemical quantum yield of photosystem II (Fv/Fm) and non‐photochemical quenching were affected by biochar and P fertilizer treatments. The Fv/Fm was significantly lower in the Ck while the highest in B2P1. Compared to the Ck treatment, the electron transport rate and photosynthetic rate were significantly increased under the application of biochar with P fertilizer. Additionally, malondialdehyde content declined by 68.9% when biochar was added with P fertilizer treatments. Furthermore, the plant P content and plant growth parameters were significantly increased. Biochar with and without P fertilizer treatments increased soil pH significantly, compared to the application of P fertilizer alone. Water‐soluble P decreased with incubation time, while Al‐P decreased significantly by 69.9% and 76.4% under B1 and B2 treatments, respectively, compared to CK.ConclusionThe findings revealed a positive effect of the combined application of biochar with phosphate fertilizer on the growth of oilseed rape in acidic soil.

Physiological and Photosynthetic Characteristics of Pumpkin Seedlings Cultivated Under Low-Light Stress

Low-light stress is known to have a significant impact on pumpkin yield in greenhouse conditions, it is crucial to understand the characteristics of low-light tolerance and identify resistant germplasm resources. In this study, four pumpkins (Cucurbita moschata) varieties were used, including three inbred lines (10–32, NY-1, and JB-1) and one hybrid line (NY-1×JB-1). Various low-light treatments (T0, no shade; T40, 40% shading; T80, 80% shading) were set, to explore their effects on morphology, photosynthetic characteristics, osmotic regulation substance content, and antioxidant enzyme activity in pumpkin seedling leaves. In the results, seedlings of inbred lines 10–32 and JB-1, as well as hybrid NY-1×JB-1, exhibited low-light resistance with shading rate increases. The maximum photochemical quantum yield of photosystem II (Fv/Fm) of all varieties decreased under low-light stress. Catalase (CAT) activity initially increased and then decreased, while superoxide dismutase (SOD) activity showed the opposite trend. Peroxidase (POD) activity gradually increased in 10–32, JB-1, and NY-1×JB-1, with JB-1 showing a significant increase at T80, and NY-1 displaying an initial decrease followed by an increase. Noteablely, the soluble proline (Pro) content decreased in 10–32, NY-1, and NY-1×JB-1. Significant differences in malondialdehyde (MDA) content were observed among the seedlings of four varieties. The MDA contents increased in 10–32 and JB-1 under T0 and T40, while showed no significant change in NY-1. The MDA content at T80 significantly decreased in NY-1, and first decreased and then significantly increased in NY-1×B-1. The soluble sugar content in 10–32 remained unchanged between T0 and T40, but significantly increased at T80. While in JB-1 and NY-1, it initially increased then decreased with increasing shading rate. The trend in NY-1×JB-1 was opposite to that of JB-1 and NY-1, with initially decreased followed by a significant increase. In conclusion, morphological characteristics associated with low-light tolerance can serve as reference indices for breeding low-light tolerance pumpkins. These parameters can be used as reference indices to assess pumpkin resistance to low-light stress.

Nitrogen enrichment ameliorates the stimulatory effects of reduced salinity on photosynthesis and growth of phytoplankton assemblages in the northern South China sea

Anthropogenic activities and climate change are exacerbating the occurrence of extreme rainfall that normally brings large amounts of nutrient-rich freshwater from the land to the sea, resulting in acute salinity decrease and nutrient increase. To evaluate the effects of such changes in salinity and nutrients, we tracked the changes in photosynthetic efficiency and growth of phytoplankton assemblages from the northern South China Sea at 5 salinity levels and at an intermediate salinity level with 3 or 4 nitrogen concentrations. The results showed that the reduction of salinity reduced the maximum photochemical quantum yield (FV/FM) of photosystem II of phytoplankton within a short-term cultivation (i.e. 24-72 h), followed by a stimulatory effect. The reducing effect of reduced salinity lasted longer in the nearshore area than in the offshore area, so the stimulatory effect occurred later in the former area. Nitrogen enrichment mitigated the negative effect of reduced salinity in short-term cultivation and showed a positive effect on FV/FM in long-term cultivation. Moreover, both reduced salinity and enriched nitrogen stimulated phytoplankton growth after an acclimation period. Our results suggest that the reduced salinity stresses phytoplankton in the short term, which is mitigated by nitrogen enrichment, but benefits them in the long term. This sheds light on how phytoplankton thrive and even flourish in coastal or estuarine environments where salinity and nutrients typically covary strongly after extreme rainfall.

Effects of UV radiation on photosynthesis of Sargassum muticum

As an invasive species of macroalgae, Sargassum muticum (Yendo) Fensholt has invaded European shores and the Mediterranean, and even drifting individuals have been observed in sea area near the Canary Islands, becoming a potential species responsible for the “Sargassum golden tide”. When drifting on the sea surface, algae receive more ultraviolet radiation (UVR). However, photosynthetic responses and adaptation mechanism of S. muticum to UVR remain unclear. In this study, thalli of S. muticum were respectively exposed under two radiation treatments of 200 W m−2 PAR (photosynthetically active radiation, 400–700 nm), and 200 W m−2 PAR + 38 W m−2 UVR (280–700 nm) for 120 mins, and then recovered at a low light (PAR) of 10 μmol photons m−2 s−1 for 240 mins. During this treatment, the photosynthetic properties of algae were measured, to investigate the responses and protection mechanism of S. muticum to UVR. The results showed that photosynthesis of thalli was significantly inhibited by UVR, reflected by decreased maximum photochemical quantum yield (Fv/Fm) and chlorophyll content, and changes of parameters of rapid light response curve and chlorophyll fluorescence induction curve in PAR and PAR + UVR treatments. Meanwhile, algae actively adopted several strategies to alleviate the inhibition caused by UVR, including photoprotection characterized by increased contents of UV-absorbing compounds (UVACs) and carotenoids (Car), excess light energy dissipation by elevated non-photochemical quenching (NPQ) coupled to the xanthophyll cycle, and photorepair manifested as an accelerated synthesis of D1 protein and enhanced antioxidant for scavenging ROS. Benefiting from the effects of the above several pathways, after 240 mins of low light recovery, photosynthesis was greatly restored in these two radiation treatments, with the restoration of Fv/Fm and parameters of rapid light response curve and chlorophyll fluorescence induction curve. Based on these results, we conservatively speculate that the photosynthesis of drifting S. muticum individuals may be restored in the evening with low light levels after being damaged by UVR on the surface of sea at midday, resulting in maintaining rapid growth and forming a golden tide.

Exposure to pentachlorophenol destructs the symbiotic relationship between zooxanthellae and host and induces pathema in coral Porites lutea

Stress from chemical pollutants is among the key issues that have adverse impacts on coral reefs. As a persistent organic pollutant, pentachlorophenol (PCP) has been detected in the seawater of Weizhou Island and was proved to have significant adverse effects on aquatic animals. However, little is known about its effects on scleractinian coral. Therefore, we investigated the response of the coral Porites lutea to PCP stress. Coral bleaching, photosynthesis parameters and antioxidant enzyme activities of P. lutea under PCP exposure were documented. After 96 h of exposure, significant tissue loss and bleaching occurred when the PCP concentration exceeded 100 μg/L. The density of symbiotic zooxanthellae decreased from 2.06 × 106 cells/cm2 to 0.93 × 106 cells/cm2 when the PCP concentration increased from 1 μg/L- 1000 μg/L. Long-term exposure of 120 days to PCP at 0.1 μg/L also led to coral bleaching, the maximum photochemical quantum yield of PSII in P. lutea nubbins significantly decreased to 0.482. The analysis of microbial community distribution indicated that the increase of the pathogenic bacterium Citrobacter may be one of the inducers of coral bleaching. Conjoint analysis of transcriptomics and proteomics showed that the metabolism of amino acids and carbohydrates in zooxanthellae was abnormal, leading to the destruction of its symbiotic relationship with the host. The immune system of the host was disrupted, which could be linked to the prevalence of coral pathema. The toxic responses of PCP on both zooxanthellae and its host were further confirmed by the upregulation of the differential metabolites including 1-naphthylamine and phosphatidylcholine, etc.

Assessment of the Drought-Tolerance Criteria for Screening Peach Cultivars

The article presents an analysis of the artificial dehydration effect of peach leaf tissues, simulating natural drought, on various physiological, morphological, and anatomical parameters described in the literature, associated with the trait of drought resistance. An investigation aimed to identify the most informative criteria for peach drought resistance which correlate with water loss during dehydration. The results present an assessment of the amount of water loss in 60 peach cultivars selected from different geographical areas and having different genetic origins. Four contrasting genotypes were identified, based on the results of the cluster analysis performed on the cultivar’s water regime. The influence of water regime parameters (leaf water content, water saturation deficit, dynamic of water loss), the morphological and anatomical structure of the leaf, the content of photosynthetic pigments, and the activity of the photosynthetic apparatus on drought resistance were investigated for selected peach cultivars. It was revealed that the most informative criteria for assessing drought resistance were dry and fresh leaf weight, leaf blade length, leaf width, and area (among morphometric parameters); stomatal pore length, stomata density, adaxial and abaxial epidermis thickness, and adaxial cuticle thickness (among anatomical parameters); and Fv/Fm—maximum photochemical quantum yield of PSII, Y(NO)—quantum yield of unregulated non-photochemical light energy dissipation in PS II and Y(NPQ)—controlled quantum losses (among indicators of photosynthetic activity).

Sustained xanthophyll pigments-related photoprotective NPQ is involved in photoinhibition in the haptophyte Tisochrysis lutea

Dynamic xanthophyll cycle (XC) related non-photochemical quenching (NPQd, also called qE) is present in most phototrophs. It allows dissipating excess light energy under adverse growing conditions. Generally, NPQd rapidly reverses for photosynthesis to resume when light intensity decreases back toward optimal intensity. Under certain environmental conditions and/or in some species, NPQ can be strongly sustained (NPQs showing hours-to-days relaxation kinetics). Tisochrysis lutea is a South Pacific haptophyte phytoplankton with a strong potential for aquaculture and biotechnology applications. It was previously reported to show a surprisingly low NPQd capacity while synthesizing large amounts of diatoxanthin (Dt), a pigment involved in the XC. In order to better understand this paradox, we investigated the characteristics of NPQ in T. lutea under various growth conditions of light and nutrient availability (different photoperiods, low and high light, nutrient starvations). We found a strong NPQs, unmeasurable with usual fluorometry protocols. Along with confirming the involvement of Dt in both NPQd and NPQs (by using the dithiothreitol inhibitor), we highlighted a strong relationship between Dt and the maximum quantum yield of photochemistry (Fv/Fm) across growing conditions and during relaxation experiments in darkness. It suggests that changes in Fv/Fm, usually attributed to the ‘photoinhibitory’ quenching (qI), are simultaneously largely impacted by photoprotective NPQ. The overlap of xanthophyll pigments-related photoprotective NPQ with several other mechanisms involved in the cell response (Photosystem II photoinactivation, changes in pigments composition, and detoxification by antioxidants) to energy unbalance is further discussed. Our findings question both how widespread NPQs is in the global ocean, particularly in nutrient starved environments (oligotrophic waters) and situations (post-bloom), and the use of adapted active fluorescence protocols (i.e. with extended NPQ relaxation period prior to measurement).

The Effect of Different Sludge Pretreatment Methods on Microalgae Performance and the Release of Pollutants in Hydrolysis Acidification Solutions

Waste-activated sludge disposal has now become a serious global problem. After pretreatment, sludge was hydrolyzed and acidified to release nutrients. The effects of different sludge pretreatments on microalgal growth and contaminants in a hydrolysis acidification solution were compared. Alkalinization (NaOH), ultrasound (US), and combined pretreatment techniques (US-NaOH) all promoted contaminants’ release from the sludge by triggering microbial cell wall rupture and extracellular polymer dissolution. The organics released from the pretreated sludge were more readily and rapidly consumed due the presence of abundant microorganisms. The US group was more capable of releasing contaminants than the NaOH group, while the US-NaOH group overrode both. The growth characteristics, photosynthetic performance, and effluent treatment properties of Chlorella were observed in all group. In the untreated group, Chlorella exhibited higher algal density, maximum photochemical quantum yield, and effluent treatment capacity. The results demonstrated that sludge pretreatment could facilitate the release and rapid consumption of pollutants. Additionally, the NaOH pretreatment could remove the refractory organics to a higher degree, and could also accumulate more photosynthetic pigments. This study demonstrated the feasibility of Chlorella being used in practical scenarios such as hydrolytic acidification solutions for different sludge treatment methods, providing data for wastewater treatment and resource utilization.

New foundations for the physical mechanism of variable chlorophyll a fluorescence. Quantum efficiency versus the light-adapted state of photosystem II.

Photosystem II (PSII) uses solar energy to oxidize water and delivers electrons to fix CO2. Although the structure at atomic resolution and the basic photophysical and photochemical functions of PSII are well understood, many important questions remain. The activity of PSII in vitro and in vivo is routinely monitored by recording the induction kinetics of chlorophyll a fluorescence (ChlF). According to the 'mainstream' model, the rise from the minimum level (Fo) to the maximum (Fm) of ChlF of dark-adapted PSII reflects the closure of all functionally active reaction centers, and the Fv/Fm ratio is equated with the maximum photochemical quantum yield of PSII (where Fv=Fm-Fo). However, this model has never been free of controversies. Recent experimental data from a number of studies have confirmed that the first single-turnover saturating flash (STSF), which generates the closed state (PSIIC), produces F1<Fm, and have uncovered rate-limiting steps (Δτ1/2 half-waiting times) in the multi-STSF-induced F1-to-Fm increments that originate from the gradual formation of light-adapted charge-separated states (PSIIL) with significantly increased stability of charges compared to the PSIIC state that is elicited by a single STSF. All the data show that the interpretation of ChlF must be laid on new foundations. Here, we discuss the underlying physical mechanisms and the significance of structural/functional dynamics of PSII as reflected by ChlF and variations in the novel parameter Δτ1/2.

Quantitative Representation of Water Quality Biotoxicity by Algal Photosynthetic Inhibition.

The method based on the photosynthetic inhibition effect of algae offers the advantages of swift response and straightforward measurement. Nonetheless, this effect is influenced by both the environment and the state of the algae themselves. Additionally, a single parameter is vulnerable to uncertainties, rendering the measurement accuracy and stability inadequate. This paper employed currently utilized photosynthetic fluorescence parameters, including Fv/Fm(maximum photochemical quantum yield), Performance Indicator (PIabs), Comprehensive Parameter Index (CPI) and Performance Index of Comprehensive Toxicity Effect (PIcte), as quantitative toxicity characteristic parameters. The paper compared the univariate curve fitting results with the multivariate data-driven model results and investigated the effectiveness of Back Propagation(BP) Neural Network and Support Vector Machine for Regression (SVR) models to enhance the accuracy and stability of toxicity detection. Using Dichlorophenyl Dimethylurea (DCMU) samples as an example, the mean Relative Root Mean Square Error (RRMSE) corresponding to the optimal parameter PIcte for the dose-effect curve fitting was 1.246 in the concentration range of 1.25-200 µg/L. On the other hand, the mean RRMSEs corresponding to the results of the BP neural network and SVR models were 0.506 and 0.474, respectively. Notably, BP neural network exhibited excellent prediction accuracy in the medium-high concentration range of 7.5-200 µg/L, with a mean RRSME of only 0.056. Regarding the stability of the results, the mean Relative Standard Deviation (RSD) of the univariate dose-effect curve results was 15.1% within the concentration range of 50-200 µg/L. In contrast, the mean RSDs for both BP neural network and SVR results were less than 5%. In the concentration range of 1.25-200 µg/L, the mean RSDs were 6.1% and 16.5%, with the BP neural network performing well. The experimental results of Atrazine were analyzed to further validate the effectiveness of the BP neural network in improving the accuracy and stability of results. These findings provided valuable insights for the development of biotoxicity detection by using the algae photosynthetic inhibition method.

Physiological Variables Influenced by 'Candidatus Liberibacter asiaticus' Infection in Two Citrus Species.

'Candidatus Liberibacter asiaticus' is the bacterium associated with the citrus disease known as huanglongbing (HLB). This study evaluated the influence of 'Ca. L. asiaticus' infection on a number of key plant physiological variables concerning photosynthesis, cell integrity, reactive oxygen species scavengers' activity, and osmoregulation of two different species of citrus-the pomelo Citrus maxima and the mandarin C. reticulata 'Tankan'-relative to their measured 'Ca. L. asiaticus' infection load. Results indicated that all measured physiological variables except soluble sugar were affected by increased 'Ca. L. asiaticus' infection titers, wherein the variety C. maxima proved overall more resistant than C. reticulata. 'Ca. L. asiaticus' infection was linked in both plants to decrease in chlorophyll concentration, cell membrane permeability, and malondialdehyde, as well as increased free proline and starch contents. Chlorophyll fluorescence measurements taken 9 months after grafting the mandarin C. reticulata with 'Ca. L. asiaticus' scions revealed a significant decrease in the photosynthesis variables maximum photochemical quantum yield of photosystem II (PSII), effective photochemical quantum yield of PSII, and coefficient of photochemical fluorescence quenching assuming interconnected PSII antennae, whereas nonphotochemical fluorescence quenching increased significantly; C. maxima plants, on the other hand, did not show significant differences until the 12th month from infection exposure. The variables superoxide dismutase, catalase, peroxidase, and soluble protein initially increased and later decreased. In addition, progression of 'Ca. L. asiaticus' replication in both citrus species was accompanied by rapid changes in three reactive oxygen species scavenging enzymes in C. maxima, while the pattern was different in C. reticulata. We hypothesize that the observed interspecific differences in physiological change are related to their relative resistance against 'Ca. L. asiaticus' infection. These results provide a scaffold for better describing the pathogenesis, selecting the most resistant breeds, or even validating pertaining omics research; ultimately, these detailed observations can facilitate the diagnosis of 'Ca. L. asiaticus' infection.

A Sensitive Response Index Selection for Rapid Assessment of Heavy Metals Toxicity to the Photosynthesis of Chlorella pyrenoidosa Based on Rapid Chlorophyll Fluorescence Induction Kinetics.

Heavy metals as toxic pollutants have important impacts on the photosynthesis of microalgae, thus seriously threatening the normal material circulation and energy flow of the aquatic ecosystem. In order to rapidly and sensitively detect the toxicity of heavy metals to microalgal photosynthesis, in this study, the effects of four typical toxic heavy metals, chromium (Cr(VI)), cadmium (Cd), mercury (Hg), and copper (Cu), on nine photosynthetic fluorescence parameters (φPo, ΨEo, φEo, δRo, ΨRo, φRo, FV/FO, PIABS, and Sm) derived from the chlorophyll fluorescence rise kinetics (OJIP) curve of microalga Chlorella pyrenoidosa, were investigated based on the chlorophyll fluorescence induction kinetics technique. By analyzing the change trends of each parameter with the concentrations of the four heavy metals, we found that compared with other parameters, φPo (maximum photochemical quantum yield of photosystem II), FV/FO (photochemical parameter of photosystem II), PIABS (photosynthetic performance index), and Sm (normalized area of the OJIP curve) demonstrated the same monotonic change characteristics with an increase in concentration of each heavy metal, indicating that these four parameters could be used as response indexes to quantitatively detect the toxicity of heavy metals. By further comparing the response performances of φPo, FV/FO, PIABS, and Sm to Cr(VI), Cd, Hg, and Cu, the results indicated that whether it was analyzed from the lowest observed effect concentration (LOEC), the influence degree by equal concentration of heavy metal, the 10% effective concentration (EC10), or the median effective concentration (EC50), the response sensitivities of PIABS to each heavy metal were all significantly superior to those of φRo, FV/FO, and Sm. Thus, PIABS was the most suitable response index for sensitive detection of heavy metals toxicity. Using PIABS as a response index to compare the toxicity of Cr(VI), Cd, Hg, and Cu to C. pyrenoidosa photosynthesis within 4 h by EC50 values, the results indicated that Hg was the most toxic, while Cr(VI) toxicity was the lowest. This study provides a sensitive response index for rapidly detecting the toxicity of heavy metals to microalgae based on the chlorophyll fluorescence induction kinetics technique.

Allelopathic Inhibition and Mechanism of Quercetin on Microcystis aeruginosa.

The utilization of allelochemicals to inhibit algal overgrowth is a promising approach for controlling harmful algal blooms (HABs). Quercetin has been found to have an allelopathic effect on algae. However, its responsive mechanism needs to be better understood. In the present study, the inhibitory effects of different quercetin concentrations on M. aeruginosa were evaluated, and the inhibition mechanisms were explored. The results demonstrated that quercetin significantly inhibited M. aeruginosa growth, and the inhibitory effect was concentration-dependent. The inhibition rate of 40 mg L-1 quercetin on algal density reached 90.79% after 96 h treatment. The concentration of chlorophyll-a (chl-a) in treatment groups with quercetin concentrations of 10, 20, and 40 mg L-1 decreased by 59.74%, 74.77%, and 80.66% at 96 h, respectively. Furthermore, quercetin affects photosynthesis and damages the cell membrane, respiratory system, and enzyme system. All photosynthetic fluorescence parameters, including the maximum photochemical quantum yield (Fv/Fm), the actual photochemical quantum yield (YII), the maximum relative electron transfer rate (rETRmax), and light use efficiency (α), exhibited a downtrend after exposure. After treatment with 20 mg L-1 quercetin, the nucleic acid and protein content in the algal solution increased, and the respiration rate of algae decreased significantly. Additionally, superoxide dismutase (SOD) activities significantly increased as a response to oxidative stress. In comparison, the activities of ribulose 1,5-biphosphate carboxylase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) decreased significantly. These results revealed that quercetin could inhibit M. aeruginosa by affecting its photosynthesis, respiration, cell membrane, and enzymic system. These results are promising for controlling M. aeruginosa effectively.

Characterization of Chlorophyll Fluorescence and Antioxidant Defense Parameters of Two Gracilariopsis lemaneiformis Strains under Different Temperatures.

In this study, two Gracilariopsis lemaneiformis strains-the wild type and a green-pigmented mutant-were cultured at three temperatures (8, 20, and 30 °C) for 7 days to explore their temperature tolerance using photosynthetic performance and antioxidant defense parameters. When the two strains of G. lemaneiformis were separately cultured at 30 °C, the fast chlorophyll fluorescence intensity of the wild type decreased, whereas the green mutant showed no significant change. The decrease in the performance index on absorption basis value under heat stress was lower in the green mutant than in the wild type. In addition, the green mutant had stronger antioxidant activity at 30 °C. Furthermore, a greater decrease in the values of maximum photochemical quantum yield and performance index on an absorption basis in the green mutant indicated that it had a greater degree of inhibition of photosynthetic performance under low temperatures. However, the green mutant produced less reactive oxygen species under low temperatures, suggesting that the antioxidant potential of the green mutant might be higher. In conclusion, the green mutant exhibited heat tolerance and could recover from low-temperature damage; therefore, it has the potential for large-scale cultivation.