Synthesis Of Photosynthetic Pigments Research Articles

Preparation of slow-release fertilizers by electrolytic manganese residue and alkali-activated laterite-based geopolymers: Mn release effects on Guizhou white tea seedlings growth

Electrolytic manganese residues (EMR) and alkali-activated laterite-based geopolymers were used to prepare slow-release fertilizers (SRFs) and the physicochemical properties and Mn release behavior of EMR-laterite-based SRFs (SRFs-LA) were studied. MnSO4·H2O in EMR transforms into CaMnSi2O6, MnO2 and (NH4)2Mn(SO4)2·6H2O after SRFs-LA synthesis. Geopolymers can slow Mn release through ion exchange and can physically encapsulate Mn-containing minerals. Mn release from the SRFs-LA system was primarily influenced by a combination of non-Fick diffusion and skeleton erosion. A comparative pot experiment was also conducted between SRFs-LA and SRFs prepared using alkali/acid-activated geopolymers with EMR (SRFs-alGo/SRFs-acGo) to examine the fertilization efficiency of Guizhou white tea seedlings. Compared with Mg(II), Mn(II) not only played a dominant role in the competitive root absorption process from the soil to the interior of seedlings, but also impeded Fe transportation by regulating the expression of citrate transporters. The slow release of Mn from SRFs-alGo and SRFs-LA could benefit tea seedling growth and protein and photosynthetic pigment synthesis, whereas EMR treatments with Mn burst release damaged the antioxidant system owing to the excessive accumulation of reactive oxygen species in leaves. The Mn released from SRFs-acGo may approach the tolerance limit of tea seedlings growth. The order of fertilizer efficiency for young Guizhou white tea seedlings was as follows: SRFs-LA > SRFs-alGo > SRFs-acGo. Moreover, the cost of SRFs-LA prepared using laterite instead of metakaolin as an active silicon–aluminum source could be reduced by approximately $18.7/t.

The Effects of Irrigation Water Salinity on the Synthesis of Photosynthetic Pigments, Gas Exchange, and Photochemical Efficiency of Sour Passion Fruit Genotypes.

The objective of this study was to evaluate the synthesis of photosynthetic pigments, gas exchange, and photochemical efficiency of sour passion fruit genotypes irrigated with saline water under the conditions of the semi-arid region of Paraíba state, Brazil. The experiment was conducted at the experimental farm in São Domingos, PB. A randomized block design was adopted, in a 5 × 3 factorial scheme, with five levels of electrical conductivity of irrigation water-ECw (0.3, 1.1, 1.9, 2.7, and 3.5 dS m-1)-and three genotypes of sour passion fruit (Gigante Amarelo-'BRS GA1'; Sol do Cerrado-'BRS SC1'; and Catarina-'SCS 437'. The increase in the electrical conductivity of irrigation water negatively affected most of the physiological characteristics of the sour passion fruit at 154 days after transplanting. Significant differences were observed between sour passion fruit genotypes when its tolerance was subjected to the salinity of irrigation water. There was an increase in the percentage of damage to the cell membrane with the increase in the electrical conductivity of irrigation water, with maximum values of 70.63, 60.86, and 80.35% for the genotypes 'BRS GA1', 'BRS SC1', and SCS 437', respectively, when irrigated with water of 3.5 dS m-1. The genotype 'BRS Sol do Cerrado' showed an increase in the synthesis of photosynthetic pigments when irrigated with water of 3.5 dS m-1, with maximum values estimated at 1439.23 μg mL-1 (Chl a); 290.96 μg mL-1 (Chl b); 1730.19 μg mL-1 (Chl t); and 365.84 μg mL-1 (carotenoids). An increase in photosynthetic efficiency parameters (F0, Fm, and Fv) of the genotype 'BRS Gigante Amarelo' was observed when cultivated with water with high electrical conductivity (3.5 dS m-1).

Inhibition mechanism and biological recycling utilization of microalgae culture aging solution

During the process of recovering microalgae culture media, the culture media will age and inhibit the growth of microalgae. When the culture media was reused for the third time, the maximum biomass of Spirulina platensis FACHB-439 was only 56.13% of the fresh culture media. But the inhibitors in the aging solution are not known. In this study, the growth inhibition mechanism of Spirulina platensis aging solution was clarified through the identification of target organic matter by cyclic culture experiment and ion chromatography. The results showed that the growth inhibitors in the aging solution were polysaccharides, mainly including fucose and rhamnose. Further reverse addition experiments confirmed that polysaccharide inhibitors would increase with the increase of repeated use of the culture media. By inhibiting the synthesis of photosynthetic pigments in microalgae, they could cause oxidative damage and membrane peroxidation of microalgae cells, resulting in stress on the growth of microalgae. At the same time, this study established a purification method for reusing aging solution of heterologous microalgae (Chlorella sp. L166) to obtain high lipid and high carbohydrate biomass energy. The results showed that the biomass of Chlorella sp. L166 in the first circulating aging solution of S.platensis FACHB-439 increased by 25%, the carbon utilization rate reached 21.36%, the lipid content per cell increased by 1.61 times, and the carbohydrate content increased by 86.71%. This work is helpful to solve the problem that aging of culture media inhibits carbon sequestration efficiency and biomass yield of microalgae in large-scale production of microalgae. And the results of this study have achieved high utilization rate of water resource for large-scale cultivation of microalgae, which is conducive to realize the scale development of microalgae biotechnology.

Chlorophyll biosynthesis under the control of arginine metabolism

In natural environments, photosynthetic organisms adjust their metabolism to cope with the fluctuating availability of combined nitrogen sources, a growth-limiting factor. For acclimation, the dynamic degradation/synthesisof tetrapyrrolic pigments, as well as of the amino acid arginine, is pivotal; however, there has been no evidence that these processes could be functionally coupled. Using co-immunopurification and spectral shift assays, we found that in the cyanobacterium Synechocystis sp. PCC 6803, the arginine metabolism-related ArgD and CphB enzymes form protein complexes with Gun4, an essential protein for chlorophyll biosynthesis. Gun4 binds ArgD with high affinity, and the Gun4-ArgD complex accumulates in cells supplementedwith ornithine, a key intermediate of the arginine pathway. Elevated ornithine levels restricted de novo synthesis of tetrapyrroles, which arrested the recovery from nitrogen deficiency. Our data reveal a direct crosstalk between tetrapyrrole biosynthesis and arginine metabolism that highlights the importance of balancing photosynthetic pigment synthesis with nitrogen homeostasis.

Phytotoxicity of nitrobenzene bioaccumulation in rice seedlings: Nitrobenzene inhibits growth, induces oxidative stress, and reduces photosynthetic pigment synthesis

Nitrobenzene (NB) has been used in numerous industrial and agricultural fields as an organic compound intermediate. NB has mutagenicity and acute toxicity, and is typically a toxic pollutant in industrial wastewater worldwide. To evaluate its phytotoxicity, we treated rice (Oryza sativa) with different concentrations of NB (0, 5, 25, 50, 75, and 100 mg L−1). NB inhibited growth indices of rice (shoot and root length, fresh shoot and root weight, and dry shoot and root weight) as NB treatment concentrations increased. High concentrations (>25 mg L−1) of NB significantly inhibited rice root and shoot growth; root growth was more susceptible to NB. NB treatment could damage the structure and reduce the activity of rice seedling roots. The result of high performance liquid chromatography (HPLC) indicated that the bioaccumulation of NB in rice seedlings had a dose-dependent effect on the growth inhibition. NB reduced the photosynthetic pigment content and the expression levels of chlorophyll synthesis genes. NB treatment increased active oxygen radicals, electrical conductivity, malondialdehyde (MDA), proline, and soluble sugar contents. The expressions of antioxidant enzyme genes were induced by NB stress, and exhibited a phenomenon of initial increase followed by decrease. When the NB concentration was higher than 50 mg L−1, the gene expression levels decreased rapidly. This study provides insight into the association between exposure to NB and its phytotoxic effects on rice seedlings, and assesses the potential risk of NB bioaccumulation for crops that require a large amount of irrigation water.

Trocas gasosas, pigmentos fotossintéticos e crescimento de quiabeiro hidropônico sob estresse salino e ácido salicílico

ABSTRACT The high concentrations of salts present in the water sources of the Brazilian Northeastern semi-arid region stand out as one of the limiting factors for agricultural production, contributing to soil salinization and/or sodification. Thus, it is extremely important to identify strategies to mitigate the effects of salt stress on plants, such as the foliar application of salicylic acid. In this context, the objective of the present study was to evaluate the effect of foliar application of salicylic acid as an attenuator of salt stress on leaf gas exchange, water relations, photosynthetic pigments, and growth of okra cv. Canindé grown in a hydroponic system. The experiment was conducted in a greenhouse, in Pombal, PB, Brazil. The treatments consisted of four levels of electrical conductivity of the nutrient solution - ECns (3.0, 5.0, 7.0, and 9.0 dS m-1) and four concentrations of salicylic acid - SA (0, 1.2, 2.4, and 3.6 mM) distributed in a completely randomized design in a split-plot scheme, considering the ECns levels as the plots and SA concentrations as the subplots, with four replicates and two plants per plot. ECns from 3.0 dS m-1 inhibited the synthesis of photosynthetic pigments, leaf gas exchange, and growth of okra cv. Canindé. Foliar application of salicylic acid at concentrations of up to 3.6 mM does not alleviate the effects of salt stress on water relations, gas exchange and growth of okra. Salicylic acid at a concentration of 1.8 mM stimulates chlorophyll a and b biosynthesis in okra under ECns of 3.0 and 4.0 dS m-1, respectively.

Translocation of TiO2 nanoparticles enhances phosphorus uptake by wetland plants: Evidence from Pistia stratiotes and Alisma plantago-aquatica

Titanium dioxide nanoparticles (nTiO2) and phosphorus (P) are widely present in sewages. To verify the hypothesis and the associated mechanisms that root-to-shoot translocation of nTiO2 can enhance plant P uptake thus P removal during sewage treatment, two wetland plants (Pistia stratiotes and Alisma plantago-aquatica) with different lateral root structures were used to examine the effect of nTiO2 (89.7% anatase and 10.3% rutile) on plant growth and P uptake in a hydroponic system. Inductively coupled plasma-optical emission spectroscopy and transmission electron microscopy-energy dispersive spectroscopy showed that P. stratiotes with well-developed lateral roots translocated 1.4–16 fold higher nTiO2 than A. plantago-aquatica with poorly developed roots, indicating P. stratiotes is efficient in nTiO2 uptake. In addition, nTiO2 root-to-shoot translocation in P. stratiotes increased with increasing nTiO2 concentration, while the opposite occurred in A. plantago-aquatica. Corresponding to the stronger nTiO2 translocation in P. stratiotes, its P uptake efficiency (Imax) and P accumulation were greater than that in A. plantago-aquatica, with Imax being increased by 35.8% and −16.4% and shoot P concentrations being increased by 16.2–64.6% and 11.4%, respectively. The strong positive correlation between Ti and P concentrations in plant tissues (r = 0.72–0.89, P < 0.01) indicated that nTiO2 translocation enhanced P uptake. Moreover, nTiO2-enhanced P uptake promoted plant growth and photosynthetic pigment synthesis. Therefore, wetland plants with well-developed lateral roots like P. stratiotes have potential to be used in P removal from nTiO2-enriched sewages.

Drought stress alleviation through nutrient management in Cyamopsis tetrogonoloba L.

Drought is one of the most serious issues since it reduces plant development and, as a result, yield significantly. This research is an attempt to provide an organic solution to combat the global issue of plant stress due to drought. To reduce the impact of drought on Cyamopsis tetragonoloba, the traditional preparation Panchagavya was used, and its effects on growth, photosynthetic and non-photosynthetic pigment synthesis, thylakoid protein composition, antioxidant activity, anatomy, and yield were investigated. Initially, drought had a negative effect on plant growth and other activities; however, as the duration of the treatment increased, the effect of drought decreased significantly. The plants that were under drought stress and were provided with nutrients, showed more plant growth and yield. Flavonoid and anthocyanin production was 50% higher in the plants under drought stress with nutrient supplementation than in the plants under drought stress and the control plants. The accumulation of 55, 47, 33, 27, and 20 kDa polypeptides of thylakoid protein also increased under nutrient conditions. Drought stress reduced overall fruit output by 10% relative to the control group (well irrigate plants). Nutrition management increased plant performance under stress conditions. Fresh & dry pod weights of control, drought stress, and drought with nutrients were recorded at 3.2 g & 0.6 g, 3 g & 0.52 g, and 4.5 g & 1.2 g, respectively. Under drought stress with nutrients, plants had more stomata per unit than control plants. This is the first study in which Panchagavya was used to alleviate drought. With the addition of beneficial nutrients, water use efficiency can be improved, and drought's negative impacts can be mitigated tangentially by activating plant physiological, biochemical, and metabolic processes. This study will add the crucial information required to determine the response of plants under drought stress conditions as well as how to alleviate its effects in a traditional organic way.

Salicylic Acid as a Salt Stress Mitigator on Chlorophyll Fluorescence, Photosynthetic Pigments, and Growth of Precocious-Dwarf Cashew in the Post-Grafting Phase.

Salicylic acid is a phytohormone that has been used to mitigate the effects of saline stress on plants. In this context, the objective was to evaluate the effect of salicylic acid as a salt stress attenuator on the physiology and growth of precocious-dwarf cashew plants in the post-grafting phase. The study was carried out in a plant nursery using a randomized block design in a 5 × 4 factorial arrangement corresponding to five electrical conductivity levels of irrigation water (0.4, 1.2, 2.0, 2.8, and 3.6 dS m-1) and four salicylic acid concentrations (0, 1.0, 2.0, and 3.0 mM), with three replications. Irrigation water with electrical conductivity levels above 0.4 dS m-1 negatively affected the relative water content in the leaf blade, photosynthetic pigments, the fluorescence of chlorophyll a, and plant growth and increased electrolyte leakage in the leaf blade of precocious-dwarf cashew plants in the absence of salicylic acid. It was verified through the regression analysis that salicylic acid at a concentration of 1.1 mM attenuated the effects of salt stress on the relative water content and electrolyte leakage in the leaf blade, while the concentration of 1.7 mM increased the synthesis of photosynthetic pigments in precocious-dwarf cashew plants.

Moringa Leaf Extract Mitigates the Adverse Impacts of Drought and Improves the Yield and Grain Quality of Rice through Enhanced Physiological, Biochemical, and Antioxidant Activities.

Agriculture, around the globe, is facing great challenges including the need to increase the production of nutrient-dense food and to withstand climate change's impact on water and soil conservation. Among these challenges, drought stress is considered the most overwhelming danger for the agriculture sector. Organic plant growth ingredients are frequently used to enhance the growth and production of field crops cultivated in normal and unfavorable conditions. The present study was designed to explore whether leaves extracted from various landraces of Moringa could play a defensive role against drought stress in rice. Seedlings were grown under three water conditions, i.e., normal conditions (control; 100% field capacity), moderate (75%), and severe drought (50%). Leaf extracts obtained from four Moringa landraces were used as foliar spray at the tillering, panicle initiation, and grain filling stages of cultivating rice plants. The levels of water stress negatively influenced photosynthetic pigment synthesis, gas exchange traits, antioxidant activities, and yield and grain quality parameters. Leaf extracts, at the rate of 3%, from all the landraces significantly enhanced the biochemical, physiological, and yield-related attributes of rice plants under normal and unfavorable growth conditions. Particularly, leaf extract from the Faisalabad landrace was the most effective biostimulant to increase photosynthetic (8.2%) and transpiration (13.3%) rates, stomatal conductance (8.3%), chlorophyll a (15.9%) and b (9.7%) contents, and carotenoids (10.4%) as compared to water spray. The maximum photosynthesis rate was observed at 14.27 µmol CO2 m-2 s-1 via application of leaf extract from the Faisalabad landrace followed by the DG Khan (13.92 µmol CO2 m-2 s-1) and Multan (13.9 µmol CO2 m-2 s-1) landraces, respectively. Improved grain yield (25.4%) and grain quality (an increase of 10.1% in amylose with a decrease of 2.8% in amylopectin) in rice plants along with enzymatic activities such as catalase (21.2%), superoxide dismutase (38.6%), and ascorbate peroxidase (24.3%) were observed at the peak after application of leaf extract from the Faisalabad landrace. The maximum grain yield of 53.59 g per plant was recorded when using Faisalabad landrace leaf extract and the minimum (40 g) using water spray. It is concluded from the findings of the current experiment that leaf extract from the Faisalabad landrace possesses higher biostimulant potential than other landraces and can be applied to mitigate the adverse impacts of drought stress with higher productivity and improved grain quality of rice.

Phosphorus protects against cadmium-induced phytotoxicity by stimulating plasma membrane H+-ATPase activity

Proper plant nutrition can be an effective strategy to alleviate the phytotoxicity and damaging effects of Cd stress on plants and to avoid its entry into the food chain. This study aimed to investigate effects of phosphorus concentrations, and pH levels in the nutrient solution on Cd uptake, growth, photosynthetic characters, total phytochelatins (PCs), and plasma membrane ATPase activity of sugar beet (Beta vulgaris L.) plants grown in sand culture. Two successive experimental studies were carried out under controlled conditions. In the first study, 10-day-old sugar beet seedlings were irrigated with a half-strength Hoagland and Arnon nutrient solution, adjusted to different pH (3.5, 5.0, 6.0, 7.0, or 8.0), and containing 0, 0.15, or 0.30 mg Cd L−1 as CdCl2. In the second study, 10-day-old sugar beet seedlings were irrigated with the same nutrient solution (pH 6), but combined with different phosphorus concentrations (0, 10, 25 and 50 µg P ml−1 as KH2PO4) and Cd levels (0, 0.15, and 0.30 mg Cd L−1 as CdCl2). The first study revealed that pH had a strong influence on Cd uptake by sugar beet roots. Cd stress significantly decreased sugar beet growth and Mg2+-ATPase activity, whereas it increased total phytochelatins (PCs). Second study indicated an antagonistic effect between P and Cd. Furthermore, phosphorus had the potential to stimulate Mg2+-ATPase activity and synthesis of photosynthetic pigments and to promote growth of sugar beet seedlings. Cadmium induced phytotoxicity in sugar beet seedlings can be alleviated by a proper pH and phosphorus nutrition.

The ecotoxicity of single-layer molybdenum disulfide nanosheets on freshwater microalgae Selenastrum capricornutum

Molybdenum disulfide (MoS2) nanomaterials have attracted considerable attention due to their unique physicochemical properties and promising applications, and subsequent risks to the environment and human health. However, the toxicological investigations of MoS2 nanosheets in aquatic environments are still limited. Herein, their aquatic toxic effects and involved mechanisms were explored using a freshwater green microalgae model, Selenastrum capricornutum. Several endpoints, including algal growth, photosynthetic pigment and macromolecular substances synthesis, were investigated after exposure to 0.02–50.0 mg/L MoS2 nanosheets. Furthermore, oxidative stress, membrane damage, lipid oxidation, and secretion of extracellular polymeric substances were elucidated as well. The results showed that single-layer MoS2 (SLMoS2) nanosheets at low concentrations (≤ 1.0 mg/L) stimulated the synthesis of chlorophyll and primary macromolecules, and they slightly promoted the growth of S. capricornutum. In contrast, higher concentrations of SLMoS2 (> 1.0 mg/L) inhibited algae growth through ROS-mediated membrane destruction and oxidative damage. Surprisingly, SLMoS2 accelerated extracellular polymeric substances (EPS) secretion and changed their fluorescent components, thus influencing algal growth. Taken together, MoS2 nanomaterials exerted bidirectional effects on S. capricornutum at the cellular, histological and organismal levels. These results provide considerable support regarding the adverse effects of MoS2 nanomaterials on freshwater microalgae.

Foliar Applications of Salicylic Acid on Boosting Salt Stress Tolerance in Sour Passion Fruit in Two Cropping Cycles.

Brazil stands out as the largest producer of sour passion fruit; however, the water available for irrigation is mostly saline, which can limit its cultivation. This study was carried out with the objective of evaluating the effects of salicylic acid in the induction of tolerance in sour passion fruit to salt stress. The assay was conducted in a protected environment, using a completely randomized design in a split-plot scheme, with the levels of electrical conductivity of the irrigation water (0.8, 1.6, 2.4, 3.2, and 4.0 dS m-1) considering the plots and concentrations of salicylic acid (0, 1.2, 2.4, and 3.6 mM) the subplots, with three replications. The physiological indices, production components, and postharvest quality of sour passion fruit were negatively affected by the increase in the electrical conductivity of irrigation water, and the effects of salt stress were intensified in the second cycle. In the first cycle, the foliar application of salicylic acid at concentrations between 1.0 and 1.4 mM partially reduced the harmful effects of salt stress on the relative water content of leaves, electrolyte leakage, gas exchange, and synthesis of photosynthetic pigments, in addition to promoting an increase in the yield and quality parameters of sour passion fruit.

Interaction of NaCl salinity and light intensity affect growth, physiological traits and essential oil constituents in Artemisia dracunculus L. (tarragon)

Soil salinity is one of the major limiting factors of medicinal plant performance and may affect their properties and chemical constituents. Although various reports have suggested the light quality-mediated modulation of growth and metabolism, little is known about physiological and phytochemicals aspects of light intensity on medicinal plants. In the present study, a factorial experiment as a randomized complete block design with three replicates was conducted to investigate the effects of salinity stress and light intensity on tarragon plants grown in pots at outdoor conditions. The experimental treatments consisted of NaCl salt stress at three levels (0, 60, and 120 mM) and different light intensities (full light, 75% of sunlight, and 50% of sunlight). According to the results, salinity led to a reduction in plant height, shoot dry weight, relative water content (RWC), and chlorophyll content compared to control conditions. While low light intensity improved the above mentioned characteristics. However, the interaction effect of salinity (60 mM) and low light intensity significantly increased anthocyanin and chlorophyll contents, and dry weight. Overall, tarragon yield can be improved at 75% of light intensity and moderate salinity by increasing the synthesis of photosynthetic pigments and phenolic compounds as protective substances. Essential oils examined here were particularly rich in methyl chavicol (68.39–79.02%), camphene (0.26–6.28%), β-pinene (0.24–5.21%), and trans-β-o-cymene (1.49–4.53%).

Effects of the Structure and Molecular Weight of Alkali-Oxygen Lignin Isolated from Rice Straw on the Growth of Maize Seedlings.

The abundant and low-cost features of lignin in combination with its natural activities make it a fascinating biopolymer for valorization, especially, in agriculture as an active plant growth regulator. However, the structure-activity relationship of lignin in regulating plant growth and metabolism remains unclear. In this work, rice-straw-based low-molecular-weight (LWM, 1860 Da) and high-molecular-weight (HMW, 6840 Da) alkali-oxygen lignins are structurally and comparatively investigated to understand their effects on the growth and metabolism of maize seedlings. The results indicate that LMW lignin at 150 mg·L-1 displays early growth stimulation in maize. Under the optimal concentration of LMW lignin (25 mg·L-1), the growth of maize shoot is ∼83% higher than that of the control one. Furthermore, LMW lignin also has a positive effect on the upregulation of photosynthetic pigment, carbohydrate, and protein synthesis. In contrast, HMW lignin shows an overall inhibitory effect on the above-mentioned biochemical parameters. Based on the structural characterization, LMW lignin contains a higher syringyl/guaiacyl ratio (0.78) and carboxyl content (1.64 mmol·g-1) than HMW lignin (0.43 and 1.27 mmol·g-1, respectively), which demonstrates that methoxyl and carboxyl content of lignin may play a decisive role in seedling growth.

Integrated transcriptomic and metabolomic analysis of Microcystis aeruginosa exposed to artemisinin sustained-release microspheres.

Artemisinin sustained-release microspheres (ASMs) have been shown to inhibit Microcystis aeruginosa (M. aeruginosa) blooms. Previous studies have focused on inhibitory mechanism of ASMs on the physiological level of M. aeruginosa, but the algal inhibitory mechanism of ASMs has not been comprehensively and profoundly revealed. The study proposed to reveal the toxicity mechanism of ASMs on M. aeruginosa based on transcriptomics and metabolomics. After exposure to 0.2g·L-1 ASMs for 7 days, M. aeruginosa biomass was significantly inhibited, with an inhibition rate (IR) of 47% on day 7. Transcriptomic and metabolomic results showed that: (1) 478 differentially expressed genes (DEGs) and 251 differential metabolites (DMs) were obtained; (2) ASMs inhibited photosynthesis by blocking photosynthetic pigment synthesis, destroying photoreaction centers and photosynthetic carbon reactions; (3) ASMs reduced L-glutamic acid content and blocked glutathione (GSH) synthesis, leading to an imbalance in the antioxidant system; (4) ASM disrupted nitrogen metabolism and the hindered synthesis of various amino acids; (5) ASMs inhibited glyoxylate cycle and TCA cycle. This study provides an important prerequisite for the practical application of ASMs and a new perspective for the management of harmful algal blooms (HABs).

Comparative studies of transformation behaviors and mechanisms of halophenols in multiple chemical oxidative systems

Due to wide applications, halophenols (HPs), especially bromophenols, chlorophenols, and fluorophenols, are commonly detected but resistant to biological removal in wastewater treatment plants (WWTPs). This study investigated the overall transformation behaviors of three representative HPs (2,4-dichlorophenol: 24-DCP, 2,4-dibromophenol: 24-DBP, 2,4-difluorophenol: 24-DFP) in six chemical oxidative systems (KMnO4, K2FeO4, NaClO, O3, UV, and persulfate (PS)). The results revealed fast removal of selected HPs by O3, PS and K2FeO4, while a large discrepancy in their removal efficiencies occurred under UV irradiation, KMnO4 oxidation and particularly chlorination. Based on the analysis of the identified intermediates and products, coupling among the five routes was the general route, and dimers were the main intermediates for HP oxidation. The effect of the halogen atom on the transformation pathways of HPs was highly reaction type dependent. Among the six chemical treatments, PS could induce HPs to yield relatively low-molecular-weight polymers and obtain the highest coupling degree. Transition state (TS) calculations showed that the H atom linked to the phenoxy group of HPs was the most easily abstracted by hydroxyl radicals to form the coupling precursor, i.e., phenoxy radicals. This high coupling behavior further resulted in the increased toxicity to green algae. Characterization revealed that HP reaction solutions treated with PS had a severely negative effect on algae growth, photosynthetic pigment synthesis, and the antioxidant enzyme system. These findings can shed light on the reaction mechanisms of advanced oxidation technologies and some risk management and control of PS technique may be considered when treating phenolic pollutants.

Sodium Bicarbonate (NaHCO3) Increases Growth, Protein and Photosynthetic Pigments Production and Alters Carbohydrate Production of Spirulina platensis.

Improving the biochemical status of Spirulina platensis will enhance the functional properties of this microalgae. The present study investigated the effects of adding NaHCO3 to the culture medium on the growth rate and biochemical composition, particularly the coproduction of proteins, carbohydrates, and photosynthetic pigments of S. platensis. Spirulina platensis was grown in different NaHCO3 concentrations (0-16g L-1). NaHCO3 positively affected the biomass production. The growth of S. platensis and biochemical compound content increased with an increase in the NaHCO3 concentration. The microalgae biomass grown on NaHCO3 also contained higher amounts of protein (64.20 ± 4.18% w w-1) and photosynthetic pigments (phycocyanin and chlorophyll a, b, and total). Protein productivity was especially enhanced by approximately 6-25% (from 0.006 ± 0.0030 to 0.025 ± 0.0031mg L-1day-1) with the addition of NaHCO3 compared to the control. In contrast, the content of carbohydrates and antioxidant compounds (phenolic, polyphenol oxidase, and peroxidase activities) decreased with culture age and an increase in the NaHCO3 concentration. These results suggest that S. platensis uses NaHCO3 as a carbon source for photosynthesis, biomass production, and acts as a metabolic energy carrier toward the synthesis of proteins and photosynthetic pigments, which are more energy-consuming metabolites than carbohydrates. The addition of NaHCO3 to the culture media is a potentially useful strategy toward improving the protein and photosynthetic pigment productivity of S. platensis.

Ácido salicílico atenua os efeitos do estresse salino sobre a morfofisiologia do cajueiro anão precoce

ABSTRACT Brazil is one of the largest cashew producers in the world, and its Northeast region stands out. However, cashew growth and development are negatively affected by irrigation with brackish water in its production. In this context, strategies have been employed to alleviate salt stress effects on plants. Among the strategies, the exogenous application of elicitor substances, such as salicylic acid, has stood out. Given the above, the objective of the present study was to evaluate the effect of foliar application of salicylic acid as an attenuator of salt stress on the morphophysiology of early dwarf cashew. The study was carried out in a greenhouse, in a randomized block design, in a 5 × 4 factorial arrangement, with five levels of electrical conductivity of the irrigation water - ECw (0.4, 1.2, 2.0, 2.8, and 3.6 dS m-1) and four concentrations of salicylic acid - SA (0, 1, 2, and 3 mM), with three replicates and one plant per plot. Irrigation with water of electrical conductivity above 0.4 dS m-1 negatively affected the leaf relative water content, gas exchange, photosynthetic pigments, and growth of plants. Salicylic acid at a concentration of 1 mM attenuated the effects of salt stress on electrolyte leakage, relative water content, gas exchange, synthesis of photosynthetic pigments, and growth of early dwarf cashew irrigated using water with ECw of up to 3.6 dS m-1, at 210 days after transplanting.

Irrigation with saline water in the cultivation of mini watermelon under phosphate fertilization.

The objective of this study was to evaluate the water status, photosynthetic pigments, and photochemical efficiency of mini watermelon plants under salt stress and phosphate fertilization. The experiment was conducted in pots under greenhouse conditions in Pombal, PB, Brazil. The experimental design used was randomized blocks in a 5 × 4 factorial scheme, with five levels of electrical conductivity of irrigation water - ECw (0.3, 1.3, 2.3, 3.3, and 4.3 dS m-1) and four doses of phosphorus (60, 80, 100, and 120% of the recommendation), with three replicates. The relative water content in the tissues decreased with the increase in ECw levels in all phosphorus doses, with decreases of 7.05, 7.81 and 8.83% per unit increase in ECw, in plants fertilized with 80, 100 and 120% P2O5. On the other hand, ECw levels increased electrolyte leakage, regardless of phosphorus doses of the recommendation. The synthesis of photosynthetic pigments and the quantum efficiency of photosystem II were inhibited by increasing water salinity from 0.3 dS m-1 in plants grown under phosphorus doses above 60% of the recommendation. Water salinity from 0.3 dS m-1 reduced chlorophyll b contents, initial, maximum, and variable fluorescence of mini watermelon plants, with a decrease of 11.86, 4.51, 4.53, and 4.54% per unit increment of ECw, respectively.