Chlorophyllase Activity Research Articles

Roles of Exogenous 5-Aminolevulinic Acid and Dihydroporphyrin Iron in Chlorophyll Precursor Synthesis and Chlorophyll-Related Enzyme Activities in Wheat Under Different Light Intensities

Aminolevulinic acid (5-ALA) and dihydroporphyrin iron chelates (DHFe) play roles in plant growth regulation under normal and stressful conditions. However, definitive data on their roles in regulating chlorophyll synthesis in wheat are lacking. In this study, the optimal concentrations for foliar-spray application of 5-ALA and DHFe to promote wheat seedling growth and leaf chlorophyll content were assessed. The optimal concentrations of 5-ALA or DHFe (50 mg/L and 0.01 mg/L, respectively) were applied as foliar sprays to seedlings of wheat ‘Bainong 4199’ (high light efficient) and ‘Zhoumai No. 18’ (average light efficient) under different light intensities. Chlorophyll precursor contents and activities of three chlorophyll synthesis-related enzymes were altered, and the combined application of 5-ALA and DHFe more strongly increased the leaf chlorophyll content. 5-ALA significantly increased the contents of the chlorophyll precursors porphobilinogen, uroporphyrinogen III, protoporphyrin IX, and magnesium-protoporphyrin IX, and the activities of 5-amino-ketovalerate dehydratase and uroporphyrinogen III synthase. DHFe resulted in an increase in chlorophyll content but a significant decrease in chlorophyllase activity and protochlorophyllide content. 5-ALA promoted the synthesis of chlorophyll precursors by regulating the activities of 5-amino-ketovalerate dehydratase and uroporphyrinogen III synthase. DHFe decreased chlorophyllase activity, thereby slowing chlorophyll degradation and increasing the chlorophyll content.

Prolonged Post-Harvest Preservation in Lettuce (Lactuca sativa L.) by Reducing Water Loss Rate and Chlorophyll Degradation Regulated through Lighting Direction-Induced Morphophysiological Improvements.

To investigate the relationship between the lighting direction-induced morphophysiological traits and post-harvest storage of lettuce, the effects of different lighting directions (top, T; top + side, TS; top + bottom, TB; side + bottom, SB; and top + side + bottom, TSB; the light from different directions for a sum of light intensity of 600 μmol·m-2·s-1 photosynthetic photon flux density (PPFD)) on the growth morphology, root development, leaf thickness, stomatal density, chlorophyll concentration, photosynthesis, and chlorophyll fluorescence, as well as the content of nutrition such as carbohydrates and soluble proteins in lettuce were analyzed. Subsequently, the changes in water loss rate, membrane permeability (measured as relative conductivity and malondialdehyde (MDA) content), brittleness (assessed by both brittleness index and β-galactosidase (β-GAL) activity), and yellowing degree (evaluated based on chlorophyll content, and activities of chlorophyllase (CLH) and pheophytinase (PPH)) were investigated during the storage after harvest. The findings indicate that the TS treatment can effectively reduce shoot height, increase crown width, enhance leaves' length, width, number, and thickness, and improve chlorophyll fluorescence characteristics, photosynthetic capacity, and nutrient content in lettuce before harvest. Specifically, lettuce's leaf thickness and stomatal density showed a significant increase. Reasonable regulation of water loss in post-harvested lettuce is essential for delaying chlorophyll degradation. It was utilized to mitigate the increase in conductivity and hinder the accumulation of MDA in lettuce. The softening speed of leafy vegetables was delayed by effectively regulating the activity of the β-GAL. Chlorophyll degradation was alleviated by affecting CLH and PPH activities. This provides a theoretical basis for investigating the relationship between creating a favorable light environment and enhancing the post-harvest preservation of leafy vegetables, thus prolonging their post-harvest storage period through optimization of their morphophysiological phenotypes.

Involvement of BcNAC083 in 1-MCP-induced delayed yellowing of pak choi (Brassica rapa subsp. Chinensis) through the regulation of reactive oxygen species metabolism and inhibition of major chlorophyll catabolic genes

Leaf yellowing is a typical senescence feature in postharvest pak choi. Plant-specific NAC transcription factors (TFs) are crucial regulators of plant senescence. In this study, a senescence-related NAC TF, BcNAC083, was investigated to identify its transcriptional regulation effects on the yellowing of pak choi by treatment with 1-methylcyclopropene (1-MCP). Applying 5.0 µL L–1 1-MCP alleviated yellowing and maintained a low respiration rate, high chlorophyll content, and relatively complete chloroplast structure in pak choi during storage. However, 10 μL L–1 ethylene accelerated yellowing, as demonstrated by the higher respiration rate, lower chloroplast structural integrity and chlorophyll content. In contrast to ethylene treatment, 1-MCP suppressed the activity of the reactive oxygen species (ROS) metabolism-related enzymes superoxide dismutase (SOD), catalase (CAT), ascorbic peroxidase (APX), and lipoxygenase (LOX), and correspondingly reduced superoxide anion (O2·–), hydrogen peroxide (H2O2), and malondialdehyde (MDA) accumulation. 1-MCP treatment also suppressed the transcript levels of ROS metabolic genes, including BcRBOHC, BcRBOHD, BcSOD, BcCAT, BcAPX, and BcLOX, and inhibited the activity of the chlorophyll catabolic enzymes chlorophyllase (CLH), Mg-de-chelatase, and pheophytin pheophorbide hydrolase (PPH) and transcript levels of associated genes, including BcCLH1/2, BcPPH1/2, BcPAO, BcNYC1, BcSGR1/2, BcHCAR, BcRCCR, and BcCAO. The expression of BcNAC083 was probably induced by ROS and was downregulated by 1-MCP and upregulated by ethylene. Molecular biology experiments determined that BcNAC083 bound directly to and activated the promoters of the chlorophyll metabolism-related genes BcCLH1, BcPPH1, BcNYC1, and BcHCAR. Importantly, transient overexpression of BcNAC083 stimulated the endogenous genes (NbCLH1, NbPPH1, NbNYC1, and NbHCAR) expression in tobacco leaves, resulting in rapid chlorophyll breakdown and leaf degreening. Treatment with 1-MCP may alleviated the yellowing of pak choi by inhibiting ROS accumulation and the transcriptional regulation of BcNAC083, which had positive regulatory effects on major chlorophyll metabolic genes.

Changes in Metabolism and Content of Chlorophyll in Common Duckweed (Lemna minor L.) Caused by Environmental Contamination with Fluorides.

The impact of fluorine on plants remains poorly understood. We examined duckweed growth in extracts of soil contaminated with fluorine leached from chicken manure. Additionally, fluorine levels were analyzed in fresh manure, outdoor-stored manure, and soil samples at varying distances from the manure pile. Fresh manure contained 37-48 mg F- × kg-1, while soil extracts contained 2.1 to 4.9 mg F- × kg-1. We evaluated the physiological effects of fluorine on duckweed cultured on soil extracts or in 50% Murashige-Skoog (MS) medium supplemented with fluorine concentrations matching those in soil samples (2.1 to 4.9 mg F- × L-1), as well as at 0, 4, and 210 mg × L-1. Duckweed exposed to fluorine displayed similar toxicity symptoms whether in soil extracts or supplemented medium. Fluoride at concentrations of 2.1 to 4.9 mg F- × L-1 reduced the intact chlorophyll content, binding the porphyrin ring at position 32 without affecting Mg2+. This reaction resulted in chlorophyll a absorption peak shifted towards shorter wavelengths and formation of a new band of the F--chlorophyll a complex at λ = 421 nm. Moreover, plants exposed to low concentrations of fluorine exhibited increased activities of aminolevulinic acid dehydratase and chlorophyllase, whereas the activities of both enzymes sharply declined when the fluoride concentration exceeded 4.9 mg × L-1. Consequently, fluorine damages chlorophyll a, disrupts the activity of chlorophyll-metabolizing enzymes, and diminishes the plant growth rate, even when the effects of these disruptions are too subtle to be discerned by the naked human eye.

Synergistic effects of planting density and nitrogen fertilization on chlorophyll degradation and leaf senescence after silking in maize

Regulating planting density and nitrogen (N) fertilization could delay chlorophyll (Chl) degradation and leaf senescence in maize cultivars. This study measured changes in ear leaf green area (GLAear), Chl content, the activities of Chl a-degrading enzymes after silking, and the post-silking dry matter accumulation and grain yield under multiple planting densities and N fertilization rates. The dynamic change of GLAear after silking fitted to the logistic model, and the GLAear duration and the GLAear at 42 d after silking were affected mainly by the duration of the initial senescence period (T1) which was a key factor of the leaf senescence. The average chlorophyllase (CLH) activity was 8.3 times higher than pheophytinase activity and contributed most to the Chl content, indicating that CLH is a key enzyme for degrading Chl a in maize. Increasing density increased the CLH activity and decreased the Chl content, T1, GLAear, and GLAear duration. Under high density, appropriate N application reduced CLH activity, increased Chl content, prolonged T1, alleviated high-density-induced leaf senescence, and increased post-silking dry matter accumulation and grain yield.

Potassium and jasmonic acid —Induced nitrogen and sulfur metabolisms improve resilience against arsenate toxicity in tomato seedlings

Despite the well-known individual roles of potassium (K+) and jasmonic acid (JA) in plant responses to various stresses, their combined effects on improving tolerance to metalloid arsenate (AsV) toxicity and their influence on physiological and biochemical mechanisms remain largely unexplored. Therefore, the present study was conducted to explore the concomitant role of K+ and JA in nitrogen (N) and sulfur (S) metabolisms and regulation of antioxidant system in tomato seedlings under AsV toxicity conditions. The obtained data reveal that K+ and/or JA boosted the tolerance of tomato (Solanum lycopersicum L.) seedlings to AsV toxicity. However, the effect of a combined dose of K+ and JA was found to be more efficient as compared to the alone application. Seedlings subjected to AsV exhibited suppressed morphological attributes (shoot and root length, shoot and root fresh weight, and shoot and root dry weight), and physio-biochemical characteristics. Also, AsV-treated tomato seedlings showed enhanced reactive oxygen species (ROS) and increased the activity of ROS-producing enzymes (O2•— -generating NADPH oxidase activity and H2O2-generating glycolate oxidase] and also a chlorophyll (Chl) degrading enzyme [chlorophyllase (Chlase) activity]. However, the exogenous supply of K+ and JA synergistically inhibited Chl degradation and overproduction of ROS by suppressing their responsible enzymes activity. Moreover, it induced gas exchange parameters and activity of enzymes responsible for the photosynthesis process (carbonic anhydrase and Rubisco), Chl biosynthesis (δ-aminolevulinic acid dehydratase), and suppressed Chlase activity, and overproduction of ROS and their producing enzymes activity. Most interestingly, the combined application of K+ and JA substantially increased N and S content and their assimilation by upregulating the activity of enzymes involved in these key pathways (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, ATP sulfurylase, adenosine 5-phosphosulfate reductase, O-acetylserine (thiol) lyase and sulfide reductase). The obtained results strongly reveal that the combined application of K+ and JA improved tolerance of tomato seedlings to AsV toxicity by enhancing N and S assimilation pathways and antioxidant system.

S-nitrosoglutathione-facilitated activation of ATP synthase involves hydrogen sulfide during the response of plants to cadmium toxicity

The contamination of soils with cadmium (Cd) threatens agricultural productivity worldwide. The ability of plants to withstand challenging circumstances is primarily contingent upon their inherent capacity for tolerance and defense. The purpose of the current work is to gain a better understanding of how the mitochondrial ATP synthase enzyme, the antioxidant defense system, redox homeostasis, and chlorophyll metabolism in tomato seedlings are regulated by nitric oxide and hydrogen sulfide under Cd stress. The results demonstrate that exposure of tomato seedlings to Cd stress resulted in a substantial decrease in the activity of ATP synthase. The plants exposed to Cd stress, exhibited an increase in chlorophyllase activity and a substantial decrease in the activity of δ-aminolevulinic acid dehydratase, which resulted in a substantial loss of chlorophyll content. Elevation in the antioxidant defense system under Cd stress could not bring a significant positive change in the plants’ defense system that resulted in lipid peroxidation and leakage of electrolytes. Incubation of Cd-stressed seedlings with nitric oxide donor S-nitrosoglutathione (GSNO) proved remarkable in improving the performance of the plants. The results exhibit that GSNO application improved the activity of ATP synthase, superoxide dismutase, peroxidase, and catalase and the performance of the ascorbate-glutathione system, which efficiently scavenged excess reactive oxygen species. The positive effect of GSNO application was also shown by decreased lipid peroxidation and electrolyte leakage. However, application of DL-propargylglycine (a biosynthesis inhibitor of hydrogen sulfide) to the stressed-seedlings reversed the effect of GSNO, which resulted in the weak performance of the defense system and the commencement of oxidative stress. The results of the study substantiate that nitric oxide, in association with endogenous hydrogen sulfide, was remarkable in providing protection to the plants against Cd toxicity.

Adaptive reactions of wheat plants to drought conditions under the influence of salicylic acid

Background. Drought is one of the most important factors affecting plant growth and productivity. The study addressed the perspectives of usage of salicylic acid, a stress protective compound, to increase the adaptive potential of Triticum aestivum L. plants under drought conditions. The effect of salicylic acid on the photosynthetic apparatus of wheat plants under the conditions of drought with a subsequent gradual resumption of watering was investigated. Materials and methods. Plants of the Podolyanka variety of wheat (Triticum aestivum L.) were the objects of our study. Seeds were pre-soaked in a solution of salicylic acid (50 mM) for 3 h. First seeds germinated in an incubator, and on the 3rd day of growth were transplanted into plastic pots (d = 14 cm). Plants were grown on soil substrate, whose humidity was maintained at 60 % of full moisture capacity – the optimal water supply. The model of drought was created by the simultaneous cessation of irrigation (30 % of soil moisture capacity) for 12 days. Upon termination of the drought, soil moisture in the pots was adjusted to 60 % of its full capacity. The control plants were grown from the seeds not treated with salicylic acid under conditions of optimal water supply (60 %). Study samples were taken from the shoots of wheat on the 7th, 9th and 12th days of the drought period and on the first day after the resumption of irrigation (14 days). The concentrations of TBA-active products, chlorophyll, carotenoids, glucose, sucrose and chlorophyllase activity were determined. Results. The influence of salicylic acid on the content of chlorophyll, carotenoids and TBA-active products along with chlorophyllase activity in shoots of wheat under the drought conditions on the early stages of ontogenesis was determined. It was found that both drought and salicylic acid modify the content of chlorophyll and carotenoids in the shoots of Triticum aestivum L., apparently by altering their metabolism. Chlorophyllase plays an important role in the adaptation of photosynthetic apparatus to the drought conditions. Our results suggest that salicylic acid causes an increase in the content of photosynthetic pigments and a decrease in chlorophyllase activity in drought conditions. In addition, salicylate causes the accumulation of glucose and sucrose in the shoot tissues of wheat plants under stressful conditions. Conclusions. Our research suggests participation of salicylic acid in the plants’ adaptation processes under the conditions of moisture deficiency. It was also found that under the effect of salicylic acid the content of TBA-active products decreases in the plant shoots under the conditions of drought. Considering the fact that the content of TBA-active products is an important indicator of lipid peroxidation intensity, the decrease of this index reveals the reduced activity of free radical processes in plant tissues under the effect of salicylic acid. Thus, it can be assumed that SA has a positive effect on plant metabolism under drought conditions.

Effect of coating using beeswax and sodium nitroprusside on chlorophyll stability and quality factors of lime during cold storage.

Lime (Citrus floridana) is a quickly perishable fruit, limiting its shelf life because of reduced chlorophyll content and post-harvest quality under different storage conditions. To increase chlorophyll stability as well as other quality factors of limes, they were coated with beeswax in 0.1 wt.% and sodium nitroprusside in three various concentrations (0.1, 0.2, and 0.4 mM) at 25 °C for 3 min and then stored at 8 °C for 60 days. In this research, changes in weight loss, juice content, firmness (F), chlorophyll, chlorophyllase activity, polyphenol oxidase activity, color, total acidity (titratable acidity), ascorbic acid (ASA) and sensory evaluation were studied. During storage at low temperatures, BW surface coating (0.1%) alone, sodium nitroprusside alone, and also in combination with each other and a double layer were effective in maintaining chlorophyll and the qualitative characteristics of limes. In our observations, the best treatment was the treatment where the limes were coated by beeswax enriched by sodium nitroprusside coating. This treatment contained the highest content of lime juice and the highest chlorophyll plus the lowest activity of chlorophyllase and polyphenol oxidase, while the amount of green color was maintained to a large extent. As a result, it is possible to use beeswax enriched by sodium nitroprusside coating method to maintain the quality and chlorophyll of cold-stored lime fruits.

Effect of sodium hydrosulfide on physicochemical characteristics and melatonin mediated stress mitigation in bitter gourd (Momordica charantia L.) grown under lead stress

Lead (Pb) is a toxic heavy metal that contaminates soil and water resources after its discharge from different industries. This research study was held to check the consequence of Pb stress and NaHS growth regulator on physicochemical features of Mamodica charantia. A pot experiment was conducted to determine the effect of NaHS (1 Mm and 1.5 Mm) for the screening of M. charantia exposed to severe Pb (500 ppm,1000 ppm and 2000 ppm) stress. Our results depicted that maximum growth of plants was recorded at 1.5 mM concentration, while inhibition was observed in the plants of M. charantia at highest concentration of lead chloride (2000 ppm). Significant positive change in agronomical structures of bitter melon like leaf, root, shoot, branches, root length and shoot length recorded at high concentration of NaHS growth regulator (1.5 mM). In case of lead stress study, plants show reduction in growth and development due to production of ROS species. ROS species reduced the concentration of divalent cations such Zn2+, Mn2+, Mg2+, Ca2+, and Fe2+ by restricting the flow of water. Leaves of M. charantia had lessen carotenoid and chlorophylls and enhanced activity of chlorophyllase in leaves. Biological content of antioxidants (CAT and POD), Protein and Proline were found maximum in NaHS treated plants while minimum in stressed plants. Nutrient content of root and shoot (K, Na and Ca) and morphological characteristics also behaved differently on different concentration of NaHS and Pb stress. Here, we concluded that the application of NaHS under the exposure to Pb stress significantly improved physiological and biochemical structures of M. charantia.

Evaluation of light irradiation on anthocyanins and energy metabolism of grape (Vitis vinifera L.) during storage

Grape is the world’s economic horticultural crop; it is perishable due to various pathogens and abiotic stress attributed to water loss-induced issues. To address these postharvest problems, this research investigates the effects of light irradiation on anthocyanins synthesis and energy metabolism in stored grapes to enhance their postharvest quality. The activities of chlorophyllase (1.17 U gk−1), Mg-dechelatase (351.69 U gk−1), chlorophyll-degraded peroxidase (3.49 U gk−1), and pheophytinase (0.85 U gk−1) were significantly higher in the control fruit than in the treated fruit at the end of storage. The red-light treatment showed higher levels of anthocyanins biosynthesis-related enzymes than green, blue-light, and control treatments. Additionally, light irradiation resulted in a decrease in adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, and energy charge. This was attributed to decreased activity of energy metabolism enzymes, reduced nicotinamide adenine dinucleotide phosphate content, and increased nicotinamide adenine dinucleotide content. These findings offer a theoretical foundation for optimizing grape coloration and energy metabolism during storage, thus prolonging the shelf-life of grapes by improving quality attributes. This research highlights the potential of light irradiation as a technique for enhancing the postharvest quality of agricultural products.

Effects of Mg on chlorophyll degradation and leaf chroma during the airing of cigar tobacco leaves

Magnesium (Mg) is the central atom of the chlorophyll porphyrin ring and plays an important role in the degradation of chlorophyll. In this study, the Mg contents in cigar tobacco leaves (Folium cigarum) under different fertilization (no (CK), NPK (NPK), and NPK+MgO (NKP+Mg)) were investigated by a field experiment, and the effects of Mg in cigar tobacco leaves on the chlorophyll degradation and leaf chroma during airing period were analyzed. The results showed that the application of Mg fertilization significantly increased Mg contents in cigar tobacco leaves. The chromaticity values (luminance value L*, red-green value a*, yellow-blue value b*, and total color difference value ΔE) of cigar tobacco leaves in NPK+Mg treatment were lower than other treatments during the airing. The contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll (TC) were decreased rapidly in the first eight airing days, and the decreasing trend of total chlorophyll/carotenoid (TC/Car) was more smoothly in NPK+Mg treatment than other treatments. The chromaticity values (L*, a*, b*, ΔE) were extremely significantly negatively correlated with pigment contents (Chl a, Chl b, TC, Car), which indicated that the leaf color was determined by the pigment contents. The activities of pheophytin pheophorbide hydrolase (PPH) in NPK+Mg treatment were the highest, while the activities of chlorophyllase (CLH) had no significant difference among the three treatments. The PPH activities were extremely significantly positively correlated with pigment contents (Chl a, Chl b, TC, Car), and significantly negatively correlated with ΔE values, but the CLH activities were not correlated with pigment contents and ΔE. Therefore, the application of Mg fertilizer was beneficial to chlorophyll degradation by increasing the PPH activities of cigar tobacco leaves, and then it regulated the formation of leaf color.

A structure-function analysis of chlorophyllase reveals a mechanism for activity regulation dependent on disulfide bonds

Chlorophyll pigments are used by photosynthetic organisms to facilitate light capture and mediate the conversion of sunlight into chemical energy. Due to the indispensable nature of this pigment and its propensity to form reactive oxygen species, organisms heavily invest in its biosynthesis, recycling, and degradation. One key enzyme implicated in these processes is chlorophyllase, an α/β hydrolase that hydrolyzes the phytol tail of chlorophyll pigments to produce chlorophyllide molecules. This enzyme was discovered a century ago, but despite its importance to diverse photosynthetic organisms, there are still many missing biochemical details regarding how chlorophyllase functions. Here, we present the 4.46-Å resolution crystal structure of chlorophyllase from Triticum aestivum. This structure reveals the dimeric architecture of chlorophyllase, the arrangement of catalytic residues, an unexpected divalent metal ion-binding site, and a substrate-binding site that can accommodate a diverse range of pigments. Further, this structure exhibits the existence of both intermolecular and intramolecular disulfide bonds. We investigated the importance of these architectural features using enzyme kinetics, mass spectrometry, and thermal shift assays. Through this work, we demonstrated that the oxidation state of the Cys residues is imperative to the activity and stability of chlorophyllase, illuminating a biochemical trigger for responding to environmental stress. Additional bioinformatics analysis of the chlorophyllase enzyme family reveals widespread conservation of key catalytic residues and the identified "redox switch" among other plant chlorophyllase homologs, thus revealing key details regarding the structure-function relationships in chlorophyllase.

Effet combiné du Triton X-100 et du chlorure de calcium sur le processus de murissement de la banane et quelques composants physiologiques impliqués

Fruits are products of high economic value with a very important nutritional contribution due to their richness in vitamins, minerals, fibers and bioactive compounds. However, their consumption remains insufficient because of high post-harvest losses. This is why this study was conducted with the aim of reducing post-harvest losses of bananas. Fruit treatment consisted of soaking in Triton X-100 for 10 min, then in calcium chloride solutions at different concentrations for 30 min. The effects of treatments on shelf life and ripening parameters (ripening rate and index, firmness, pH, titratable acidity, pigment and ascorbic acid contents, and activity of chlorophyllase and pectin-methylesterase) were determined. The results show that the longest storage times (25 to 27 days) were recorded in bananas treated with Triton X-100 at 2 or 4% CaCl2. The 6 % and 8% CaCl2 treatments as well as the control bananas showed the lowest storage time. The low index and slow ripening kinetics were found in bananas treated with 2 and 4% calcium chloride. The chlorophyll content gradually decreased during the storage and this in a similar way for all the treatments. No significant variation in carotenoid content was observed over time. Firmness and pH decreased significantly, while titratable acidity and ascorbic acid content increased over time. The activity of chlorophyllase and that of pectin-methylesterase increased over time. From all the above, it appears that the combined treatments with Triton X-100 and 2 or 4% calcium chloride solution significantly extended the green life duration of the bananas and slowed the physiological processes associated to ripening.

Стрес-індуковані реакції мохів на періодичне короткочасне і тривале висушування залежно від водного режиму їхніх місцевиростань

Bryophytes are poikilohydric higher plants and their water content as well as metabolic activity depend on the water regime of the environment. The aim of the study was to establish the features of stress-induced reactions of mosses under controlled conditions of short-term and long-term drying depending on the water regime of their habitats. A culture of shoots of the same age from agar mediums the same level of relative humidity was used to study the effect of periodic drying. Dehydration was carried out within 24 hours, removing the polyethylene cover from the pots with moss culture. Plant watering was carried out twice a week in the variant of the experiment with short-term drying: immediately after dehydration and on the third day after drying. In the variant with long-term drying plants were watered once a week – on the third day after 24-hour dehydration. Control plants were sprayed twice a week. A significant decrease in the size of shoots, leaves and an increase in the density of moss turf under the influence of short-term and long-term drying have been established, based on the analysis of morphometric parameters of Barbula unguiculata Hedw. and Physcomitrella patens (Hedw.) Bruch & Schimp. In the moss Weissia longifolia Mitt. long-term drying caused a slight increase in leaf size and elongation of shoots, comparing with control and short-term drying, and at the same time activated the formation of chloronеmal dendroids, which proved its greatest adaptability and ability to adapt to perio­dic changes in humidity. A higher sensitivity of the pigment system of B. unguiculata and P. patens to drying compared to W. longifolia was established. It was found that in the pigment system of the hygromesophytic moss P. patens the significant role belongs to chlorophyll b and pheophytin b, functioning of the assimilation complex of the xeromesophytic moss Barbula unguiculata depends on chlorophyll a and pheophytin a, in xerophytic moss W. longifolia – due to the stability of chlorophyll a and the strength of the bound of carotenoids with protein complexes of the pigment system. The dependence of the component composition of the pigment apparatus, the strength of the bond of pigment-protein complexes (PPC), the activity of chlorophyllase, and the total carbohydrate content of the studied mosses on the duration of drying and their species characteristics was determined.

Physiological and Metabolic Responses of Gac Leaf (Momordica cochinchinensis (Lour.) Spreng.) to Salinity Stress.

Gac is a carotenoid-rich, healthful tropical fruit; however, its productivity is limited by soil salinity, a growing environmental stress. This study aimed to evaluate the effects of salinity stress on key physiological traits and metabolites in 30-day-old gac seedling leaves, treated with 0, 25-, 50-, 100-, and 150-mM sodium chloride (NaCl) for four weeks to identify potential alarm, acclimatory, and exhaustion responses. Electrolyte leakage increased with increasing NaCl concentrations (p < 0.05) indicating loss of membrane permeability and conditions that lead to reactive oxygen species production. At 25 and 50 mM NaCl, superoxide dismutase (SOD) activity, starch content, and total soluble sugar increased. Chlorophyll a, and total chlorophyll increased at 25 mM NaCl but decreased at higher NaCl concentrations indicating salinity-induced thylakoid membrane degradation and chlorophyllase activity. Catalase (CAT) activity decreased (p < 0.05) at all NaCl treatments, while ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) activities were highest at 150 mM NaCl. GC-MS-metabolite profiling showed that 150 mM NaCl induced the largest changes in metabolites and was thus distinct. Thirteen pathways and 7.73% of metabolites differed between the control and all the salt-treated seedlings. Salinity decreased TCA cycle intermediates, and there were less sugars for growth but more for osmoprotection, with the latter augmented by increased amino acids. Although 150 mM NaCl level decreased SOD activity, the APX and GPX enzymes were still active, and some carbohydrates and metabolites also accumulated to promote salinity resistance via multiple mechanisms.

Acetylsalicylic acid and salicylic acid alleviate postharvest leaf senescence in Chinese flowering cabbage (Brassica rapa var. parachinensis)

The leaves of ‘Ningxia Chinese flowering cabbage’ readily become yellow and senesce after harvest. To test the effects of acetylsalicylic acid (ASA) and salicylic acid (SA) on postharvest leafy vegetables, Chinese flowering cabbages were sprayed with 2 mmol L−1 ASA and 1.5 mmol L−1 SA, and stored at 15 °C. Compared with the controls, during storage, ASA- and SA-treated cabbages retained higher levels of total chlorophyll (Chl), Chl a, and Chl b, and lower activities of chlorophyllase, Mg dechelatase, pheophytinase, and Chl-degrading peroxidase, and had more intact chloroplasts. Furthermore, ASA and SA repressed respiration intensity, ethylene rate, the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase, and ACC content, decreased reactive oxygen species (ROS) levels, and increased the activities of superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, phenylalanine ammonia lyase, cinnamate 4-hydroxylase, 4-coumarate-CoA ligase, chalcone synthase, chalcone isomerase, and cinnamyl alcohol dehydrogenase, promoting the accumulation of phenolics and flavonoids. Using principal component and hierarchical clustering analyses, leaf senescence was attributed to higher respiration, ethylene synthesis, and ROS levels, while the delay of senescence in treated cabbages resulted from the cooperation of ROS metabolism and the phenylpropanoid pathway. ASA and SA slowed leaf degreening and senescence. Between the two treatments, 2 mmol L−1 ASA was the most effective.

Calcium and jasmonic acid exhibit synergistic effects in mitigating arsenic stress in tomato seedlings accompanied by antioxidative defense, increased nutrient accumulation and upregulation of glyoxalase system

No substantial information is available to explain the associative roles of calcium (Ca2+) and jasmonic acid (JA) in enhancing tolerance of plants to abiotic stresses. It is therefore, imperative to investigate the interaction of these biomolecules in plants subjected to heavy metal stress. The concomitant effects of Ca2+ and/or JA on the physiological mechanism associated with metalloid stress tolerance are still not substantially explored in tomato seedlings. Present study unveils the synergistic role of Ca2+ and JA in mitigation of arsenic toxicity (As) in tomato seedlings. Present evidence reveals that plant grown in As toxicity conditions exhibited a decrease in growth attributes (shoot length, shoot fresh weight and shoot dry weight) and supressed the biosynthesis mechanism of chlorophyll (Chl), nutrients homeostasis [Ca2+, nitrogen (N), phosphorus (P), and potassium (K)] and glyoxalase system. Exogenous As induced the over production of reactive oxygen species (ROS) and methylglyoxal (MG), and enhanced Chl degrading enzyme [chlorophyllase (Chlase) activity in tomato seedlings. However, exogenous application of Ca2+ and/or JA supressed the adverse effect of As. Moreover, combined application of Ca2+ and JA was found to be more effective than their individual effects to the seedlings. Application of Ca2+ and JA together significantly enhanced the biosynthesis of Chl by supressing Chlase activity and enhancing the δ-aminolevulinic acid dehydratase (δ-ALAD) activity (a Chl synthesising enzyme) and also improved activity of glyoxalase I (Gly I) and Gly II activity (responsible for the detoxification of MG ). Exogenous supply of Ca2+ and JA maintained the balance supply of nutrients and glycine betaine in tomato seedlings under As toxicity conditions. Combined application of Ca2+ and JA supressed the overproduction of ROS by modulating activity of antioxidant enzymes, such as superoxide dismutase, ascorbate peroxidase and glutathione reductase. When Ca2+ and JA were supplied with the Ca2+-chelator EGTA (ethylene glycol-bis(b-aminoethylether)-N,N,N',N'-tetraacetic acid), the efficacy of Ca2+ was eliminated, confirming the participation of Ca2+ and JA in mitigation of As toxicity. Thus, it is evident that Ca2+ and JA together mediated As tolerance of tomato seedlings t by improving physiological defence mechanisms.

Taxifolin delays the degradation of chlorophyll in pakchoi (Brassica rapa L subsp. chinensis) by regulating the ascorbate-glutathione cycle

The effects of taxifolin (TF) treatment on chlorophyll (Chl) degradation and the ascorbate-glutathione (AsA-GSH) cycle were evaluated in pakchoi. Compared with a control and other treatment concentrations, 1000 mg L−1 TF treatment had the greatest green retention effect on pakchoi. This treatment delayed the degradation of Chl and its derivatives and inhibited the activities of chlorophyllase, Mg-dechelatase, pheophytinase, and pheophorbide a oxygenase. The expression of Chl degradation (BrNYC1, BrNOL, BrCLH, BrSGR1, BrSGR2, BrPPH, BrPAO, and BrRCCR) and senescence (BrSAG12) related-genes was also suppressed, leading to better quality pakchoi. In addition, TF treatment alleviated decreases in total ascorbic acid, reduced ascorbic acid, dehydroascorbic acid, total glutathione, reduced glutathione, and oxidized glutathione, while enhancing the activities of ascorbic acid peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase. This contributed to maintained high free radical scavenging ability and lower membrane lipid peroxidation. These results demonstrate that TF can regulate the AsA-GSH cycle and maintain the activity to scavenge reactive oxygen species, thus reducing membrane lipid oxidation and ultimately reducing nutrient loss and Chl degradation in pakchoi.

Carboxymethyl cellulose coating regulates cell wall polysaccharides disassembly and delays ripening of harvested banana fruit

Banana is a perishable fruit that ripens and deteriorates quickly after harvest. In this work, we investigated the impact of a dip in carboxymethyl cellulose (CMC) at concentrations of 0.5%, 1.0% and 1.5% on the quality of harvested bananas during storage at ambient conditions of 20 ± 1 ºC for a 15-d period. It was noted that 1.5% CMC markedly delayed the occurrence of decay incidence (9%) and suppressed physiological weight loss (6%). The 1.5% CMC treatment suppressed the activities of chlorophyllase, pheophytinase, Mg-dechelatase and chlorophyll (Chl)-degrading peroxidase (POD), which ultimately delayed banana peel color changes by conserving higher total Chl contents and reducing the accumulation of carotenoids. This subsequently resulted in higher L* and a* along with a lower increase in b* values as compared with control. Banana fruit coated with 1.5% CMC exhibited delayed ethylene and respiration peaks in comparison with control. In the same way, 1.5% coating maintained higher firmness and showed higher contents of protopectin, chelate-soluble pectin, sodium carbonate soluble pectin, cellulose and hemicellulose along with lower water-soluble pectin due to reduced activities of cellulase, pectin methylesterase, polygalacturonase and β-glucosidase. In the same way, postharvest application of 1.5% CMC coating suppressed the increase in total soluble solids (TSS) and showed higher titratable acidity (TA) along with a lower ripening index (TSS/TA ratio) in flesh of banana fruit compared with control. In conclusion, 1.5% CMC application could be an appropriate coating concentration to delay the ripening and rapid softening of harvested bananas stored in ambient conditions.