Active Oxygen Scavenging Enzymes Research Articles

Study on the control effect and physiological mechanism of Wickerhamomyces anomalus on primary postharvest diseases of peach fruit

Brown rot, aspergillosis and soft rot are the primary diseases of postharvest peach fruit. Our study aimed to investigate the biocontrol effect of Wickerhamomyces anomalus on the primary postharvest diseases of peach fruit and to explore its underlying physiological mechanism. The findings demonstrated that W. anomalus had an obvious inhibitory effect on Monilinia fructicola, Aspergillus niger and Rhizopus stolonifer. At the same time, W. anomalus can grow stably on the wound and surface of peach fruit at 25 °C and 4 °C and can form biofilm. W. anomalus increased the activity of resistance-related enzymes such as PPO, POD, GLU and the content of secondary metabolites such as total phenols, flavonoids and lignin in peach. Furthermore, the application of W. anomalus led to a reduced MDA level in peach fruit and increased activity of the active oxygen-scavenging enzyme system. This increase involved various antioxidant defense enzymes such as SOD and CAT, as well as ascorbic acid-glutathione (AsA-GSH) enzymes, including APX, GPX, GR, DHAR, and MDHAR. Our findings demonstrate that W. anomalus exerts its biocontrol effect by growing rapidly, competing with pathogens for nutrition and space, and enhancing the disease resistance and antioxidative capabilities of the peach fruit.

Hydrogen-Rich Water Treatment of Fresh-Cut Kiwifruit with Slightly Acidic Electrolytic Water: Influence on Antioxidant Metabolism and Cell Wall Stability.

The synergistic impact of hydrogen-rich water (HRW, 394 ppb) and slightly acidic electrolyzed water (SAEW, pH of 6.25 ± 0.19) on the antioxidant metabolism of fresh-cut kiwifruit during storage was investigated (temperature: (3 ± 1) °C, humidity: 80%-85%). Compared with control group, H+S treatment increased the contents of active oxygen-scavenging enzymes (SOD, CAT, POD, and APX) and inhibited the increase of O2•- and H2O2 contents during the storage of fresh-cut kiwifruit. Meanwhile, H+S treatment could reduce the activities of the cell wall-degrading enzymes PG, PME, PL, Cx, and β-Gal, inhibit the formation of soluble pectin, delay the degradation rate of propectin, cellulose, and pseudocellulose, and maintain higher fruit hardness and chewability. The results showed that H+S treatment could enhance free radical scavenging ability and reduce the cell wall metabolism of fresh-cut kiwifruit, maintaining the good texture found in fresh-cut fruit.

RNA sequencing and weighted gene co-expression network analysis uncover the hub genes controlling cold tolerance in Helictotrichon virescens seedlings.

Helictotrichon virescens is a perennial herbaceous plant with a life expectancy of about 10 years. It has high cold and heat resistance and can successfully survive over winter in the habitats with a temperature range of −25 to 25°C. Therefore, this study aimed to identify the key genes regulating low-temperature stress responses in H. virescens and analyze cold tolerant at molecular level. This study used RNA sequencing (RNA-Seq) and weighted gene co-expression network analysis (WGCNA) to identify the hub genes associated with cold tolerance in H. virescens. RT-PCR was conducted, homologous genes were identified, and related bioinformatics were analyzed to verify the identified hub genes. Moreover, WGCNA analysis showed that only the brown module had the highest correlation with the active-oxygen scavenging enzymes [peroxide (POD), superoxide dismutase (SOD), and catalase (CAT)]. The expression levels of three hub genes in the brown module (Cluster-37118.47362, cluster-37118.47713, and cluster-37118.66740) were significantly higher under low-temperature stress than those under control conditions. Furthermore, gene ontology (GO) and KEGG annotations showed that the three hub genes were mainly enriched in the metabolism pathways of sphingolipids, selenocompounds, glyoxylate, and dicarboxylate, carotenoids biosynthesis, and other biological pathways. The results of this study also showed that the subcellular localization prediction results showed that the cold tolerance hub genes were all localized to the plasma membrane. By constructing a protein interaction network, it was found that the hub gene Cluster-37118.66740 interacted with Sb09g003460.1 and Sb04g020180.1 proteins in Sorghum bicolor. By constructing phylogenetic trees of the four species of H. virescens, Sorghum bicolo, Oryza sativa Japonica, and Arabidopsis thaliana, the results showed that, the hub gene Cluster 37118.66740 (of H. virescens) and Os03g0340500 (of Oryza sativa Japonica) belonged to the same ancestral branch and were in the same subfamily. Thus, this study provides methodology and guidance to identify the cold tolerance genes for other herbage and their cold tolerant molecular mechanisms at molecular level.

Bacillus-Secreted Oxalic Acid Induces Tomato Resistance Against Gray Mold Disease Caused by Botrytis cinerea by Activating the JA/ET Pathway.

Bacillus spp. are known for their ability to control plant diseases; however, the mechanism of disease control by Bacillus spp. is still unclear. Previously, bacterial organic acids have been implicated in the process of disease suppression. We extracted the total organic acid from Bacillus cereus AR156 culture filtrate and identified oxalic acid (OA) as the programmed cell death-inducing factor. OA strongly suppressed the lesion caused by Botrytis cinerea without significant antagonism against the fungus. Low concentration of OA produced by Bacillus spp. inhibited cell death caused by high concentrations of OA in a concentration- and time-dependent manner. Pretreatment with a low concentration of OA led to higher accumulation of active oxygen-scavenging enzymes in tomato leaves and provoked the expression of defense-related genes. The activation of gene expression relied on the jasmonic acid (JA) signaling pathway but not the salicylic acid (SA) pathway. The disease suppression capacity of OA was confirmed on wild-type tomato and its SA accumulation-deficient line, while the control effect was diminished in JA synthesis-deficient mutant, suggesting that the OA-triggered resistance relied on JA and ethylene (ET) signaling transduction. OA secretion ability was widely distributed among the tested Bacillus strains and the final environmental OA concentration was under strict regulation by a pH-sensitive degradation mechanism. This study provides the first systematic analysis on the role of low-concentration OA secreted and maintained by Bacillus spp. in suppression of gray mold disease and determines the dependence of OA-mediated resistance on the JA/ET signaling pathway. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2022.

Changes in Ultrastructure and Oxidation Resistance of Peel of Pear Cultivars during Shelf Life

Postharvest period is a process of natural maturation and senescence. The peel structure and antioxidant capacity of pears are the most important factors that affect its postharvest quality. However, the changes in pear peel properties are still unclear during shelf life. In this study, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to investigate the ultrastructural characteristics of pear peel during shelf life, and to determine the changes in peel antioxidants, active oxygen scavenging enzymes, and antioxidant capacity. The results showed that after a 30-day shelf life, the peel cuticles of all tested varieties had varying degrees of color loss and withering, and the integrity of the cells of peel was also damaged, but the surface layer cells of Xuehuali (XH), Huangguan (HG), and Yali (YL) were smoother than Wonhwang (WH) and Housui (HS), and the integrity of the peel cells was also better. In this experiment, there were significant differences in the contents of total polyphenol and total flavonoids among different varieties, and also significant differences in the variation range and variation trends in the activities of peroxidase and catalase (p < 0.05). The total antioxidant capacity of YL pear peel was the highest (68.76 Ug−1), while that of WH pear peel was the lowest (26.37 Ug−1). In conclusion, YL and XH, the representative varieties of White Pear, have better skin structure stability and antioxidant capacity than Sand Pear varieties HS and WH. The overall results provide a theoretical basis for further structure and function investigation of pear peel.

Heat shock treatment maintains the quality attributes of postharvest jujube fruits and delays their senescence process during cold storage.

The effects of heat shock (HT), 1-methylcyclopropene (1-MCP), or their combination (HT+1-MCP) on the quality of fresh jujube fruits during cold storage were studied. Among them, HT showed the best preservation effect on jujube fruits, which was more effective than others in inhibiting the increase of red index, decay incidence, and weight loss and delaying the decrease of firmness, soluble solids content (SSC), titratable acidity (TA), and ascorbic acid (AsA) content. Besides, it could delay the degradation rate of the cell wall to maintain the integrity of cell membrane, and keep the high activity of active oxygen scavenging enzymes. During cold storage, malondialdehyde (MDA) content and relative electrolyte leakage (REL) of the HT group were significantly lower than those of the control group, 1-MCP, and HT+1-MCP group (p<.05), while superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were significantly higher than those of other groups (p<.05). It was concluded that the postharvest HT treatment could effectively delay the senescence and decay of jujube fruits. PRACTICAL APPLICATIONS: Jujube fruits have high nutritional value used for food and medicine. However, they are not tolerant to storage after harvest, resulting in high economic losses. Therefore, it is of great significance to find a suitable method to maintain the quality of jujube fruits. Our results revealed the effect of HT, 1-MCP, and their combination on the quality maintenance of jujube fruits, and found that HT could effectively maintain the quality of them, which could be used as an effective method for keeping jujube fruits fresh.

ITRAQ-Based Proteomics Investigation of Critical Response Proteins in Embryo and Coleoptile During Rice Anaerobic Germination

Direct-seeding of rice has become popular in recent years due to its low cost and convenience, however, hypoxic condition limits seedling establishment. In this study, weedy rice WR04-6 with high germination ability under anaerobic conditions was used as a gene donor, and we successfully improved the seedling establishment rate of rice cultivar Qishanzhan (QSZ) based on selection of a new rice line R42 from the recombinant inbred line population. R42 inherited high anaerobic germination (AG) ability, and was used for isobaric tags for relative and absolute quantitation (iTRAQ)-based comparative proteomic studies with QSZ to further explore the molecular mechanism of AG. A total of 719 differentially abundant proteins (DAPs) were shared by R42 and QSZ responded to AG, and thus defined as common response DAPs. A total of 300 DAPs that responded to AG were only identified from R42, which were defined as tolerance-specific DAPs. The common response and tolerance-specific DAPs had similar biochemical reaction processes and metabolic pathways in response to anoxic stress, however, they involved different proteins. The tolerance-specific DAPs were involved in amino acid metabolism, starch and sucrose metabolism, tricarboxylic acid cycle pathway, ethylene synthesis pathway, cell wall-associated proteins and activity of active oxygen scavenging enzyme. The in silico protein-protein interactions for the top 60 DAPs indicated that tolerance-specific DAPs had relatively independent protein interaction networks in response to an anoxic environment compared with common response DAPs. The results of physiological indicators showed that α-amylase and superoxide dismutase activities of R42 were significantly increased under anoxic conditions compared with aerobic conditions. Multiple lines of evidence from western blot, physiological analysis and quantitative real-time PCR jointly supported the reliability of proteomics data. In summary, our findings deepened the understanding of the molecular mechanism for the rice response to AG.

A Susceptible Scion Reduces Rootstock Tolerance to Ralstonia solanacearum in Grafted Eggplant

The bacterial wilt pathogen (Ralstonia solanacearum) is a highly pathogenic soil-borne bacterium that invades the vascular system of a host plant leading to plant wilting and death. In agricultural systems, tolerant rootstocks are usually used to enhance disease resistance and tolerance in crop plants to soil-borne pathogens. Here, two distinct eggplant cultivars with different tolerances to R. solanacearum infection, the disease-tolerant cultivar ‘S21′ and the disease-susceptible cultivar ‘Rf’, were used to investigate if scion tolerance level can affect tolerance of rootstock upon an infection of the same pathogen. Three scion/rootstock grafted combinations were considered: Rf/S21, S21/S21, and Rf/Rf. Plants that resulted from the combination Rf/S21, composed of the susceptible scion grafts, showed weak tolerance to R. solanacearum infection, and exhibited the poorest growth compared to the tolerant scion grafts (S21/S21). As expected, the combination Rf/Rf showed the lowest level of disease tolerance. Furthermore, a high level of exopolysaccharides (EPSs) and cell wall degrading enzymes (CWDEs) were detected in susceptible scion grafts. These factors are involved in plant growth inhibition due to blocking transport between scion and rootstock and damage of vascular tissues in the plant. A high level of reactive oxygen species (ROS) and active oxygen scavenging enzymes were also detected in susceptible scion grafts. Excess accumulation of these substances harms the dynamic balance in plant vascular systems. These results indicated that the use of a susceptible scion in scion/rootstock eggplant grafts contributed to a reduction in rootstock tolerance to Ralstonia solanacearum.

Selection of rootstocks for better morphological characters and resistance to low-temperature stress in the sweet pepper cultivar ‘Hongxing No. 2’

To promote the stress resilience of sweet pepper crops (Capsicum annuum L.) and phase out the use of pesticides and other environmentally harmful materials, grafting has been used to integrate biotic or abiotic stress-resistance characteristics with sustainable crop production. This study aimed to determine the changes in the morphological characteristics, physiological features and low-temperature resistance of the sweet pepper cultivar ‘Hongxing No. 2’ grafted onto five rootstocks (‘No. 14’, ‘No. 15’, ‘No. 16’, ‘Jiaozhen108’, and ‘J4-908’) and itself. The morphological features of the aerial organs and roots of the different graft combinations were monitored, as were the activities of active oxygen-scavenging enzymes. Most morphological and physiological characteristics were significantly improved in the graft combination No. 2/Jiaozhen108, which indicated that Jiaozhen108 had a higher graft affinity with Hongxing No. 2 than the other rootstocks. No. 2/Jiaozhen108 also had a higher resistance to low temperatures. Therefore, the Jiaozhen108 rootstock is considered a quality candidate for grafting with the sweet pepper cultivar Hongxing No. 2, providing a theoretical basis for the screening and greenhouse production of low-temperature resistant stocks.

English

Angelica sinensis (Oliv.) Diels (family Apiaceae) is a perennial herb that has been widely used in Traditional Chinese Medicine. The soil sickness has become one of the major constrains in A. sinensis cultivation. A pot experiment was done to evaluate the role of biological nature in A. sinensis soil sickness. The pot experiment include three treatments (i) contol, which represent as the soil in pot taken from spring wheat stands, (ii) AA, which represent as the soil in pot taken from A. sinensis stands, (iii) S-AA, which represent as the soil in pot was sterilized by steam at 121°C for 4 h taken from A. sinensis stands. Results showed that the plant height, dry weight of aboveground part and roots, root yield and quality, and the activities of SOD and POD in leaves were significantly higher in sterilized replant soil than in non-sterilized replant soil treatment, while the activity of CAT and content of MDA in leaves were declined, which indicated that soil sterilization improved plant haleness and increased the activities of active oxygen scavenging enzymes. The results also demonstrated that soil sterilization can change the number of culturable microbial populations and the species diversity of bacterial functional group. Higher Shannon-Wiener index was found in rhizosphere soils under sterilized soil cropping than that under non-sterilized soil cropping. This suggests that the biological factor played a causal role in the development of A. sinensis soil sickness and sterilization of continuous cropping soil could change the composition and structure of soil microbial community, which further promote plant growth and alleviate A. sinensis soil sickness. © 2016 Friends Science Publishers

Effects of squalene/squalane on dopamine levels, antioxidant enzyme activity, and fatty acid composition in the striatum of Parkinson^|^rsquo;s disease mouse model

Active oxygen has been implicated in the pathogenesis of Parkinson's disease (PD); therefore, antioxidants have attracted attention as a potential way to prevent this disease. Squalene, a natural triterpene and an intermediate in the biosynthesis of cholesterol, is known to have active oxygen scavenging activities. Squalane, synthesized by complete hydrogenation of squalene, does not have active oxygen scavenging activities. We examined the effects of oral administration of squalene or squalane on a PD mouse model, which was developed by intracerebroventricular injection of 6-hydroxydopamine (6-OHDA). Squalene administration 7 days before and 7 days after one 6-OHDA injection prevented a reduction in striatal dopamine (DA) levels, while the same administration of squalane enhanced the levels. Neither squalene nor squalane administration for 7 days changed the levels of catalase, glutathione peroxidase, or superoxide dismutase activities in the striatum. Squalane increased thiobarbituric acid reactive substances, a marker of lipid peroxidation, in the striatum. Both squalane and squalene increased the ratio of linoleic acid/linolenic acid in the striatum. These results suggest that the administration of squalene or squalane induces similar changes in the composition of fatty acids and has no effect on the activities of active oxygen scavenging enzymes in the striatum. However, squalane increases oxidative damage in the striatum and exacerbates the toxicity of 6-OHDA, while squalene prevents it. The effects of squalene or squalane treatment in this model suggest their possible uses and risks in the treatment of PD.

Effects of Pb2+ on the active oxygen-scavenging enzyme activities and ultrastructure in Potamogeton crispus leaves

The effects of various concentrations of Pb2+ on the antioxidant enzyme activities and the ultrastructure in Potamogeton crispus leaves were studied. Peroxidase (POD) activity and malondialdehyde (MDA) content peaks were observed with an increase in Pb2+ concentration, whereas superoxide dismutase (SOD) and catalase (CAT) activities decreased firstly and then rose. Meantime, the chlorophyll content declined with increasing Pb2+ concentration. Simultaneously, high concentrations of Pb2+ aggravated ultrastructural damage to the leaf cells including swelling of chloroplasts, disruption and disappearance of chloroplast envelopes; swelling of mitochondrial cristae, deformation and vacuolation of mitochondria; condensation of chromatin, dispersion of nucleoli, and disruption of nuclear membrane. Changes in antioxidant enzyme activities and damage to fine structure are the results of lead-induced ROS accumulation. The estimated lethal concentration to P. crispus ranged from 10 to 15 mg/l lead.

Nitric oxide protects against oxidative stress under heat stress in the calluses from two ecotypes of reed

Calluses from two ecotypes of reed (Phragmites communis Trin.) plant (dune reed [DR] and swamp reed [SR]), which show different sensitivity to heat stress, were used to study plant acclimations to heat stress. SR callus suffered more oxidative damage than DR callus, and DR callus maintained higher relative growth rate and cell viability and lower ion leakage than SR callus under heat stress. Application of two nitric oxide donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP), dramatically alleviated heat stress induced ion leakage increase, growth suppression and cell viability decrease in both calluses under heat stress. H2O2 and MDA contents were decreased and the activities of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase increased in both calluses in the presence of NO donors under heat stress. The potassium salt of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger, arrested NO donors mediated protective effects. Moreover, measurement of the rate of NO release showed that NO production increased significantly in DR callus while kept stable in SR callus under heat stress. Pretreatment with cPTIO had no effect on SR callus under heat stress while it significantly enhanced oxidative stress in DR callus compared with that of heat stress alone. These results suggest that NO can effectively protect both calluses from oxidative stress induced by heat stress and that NO might act as a signal in activating active oxygen scavenging enzymes under heat stress and thus confer DR callus thermotolerance.

Effects of La3+ on the Active Oxygen-Scavenging Enzyme Activities in Cucumber Seedling Leaves

The effects of La3+ on the antioxidant enzyme activities and the relative indices of cellular damage in cucumber seedling leaves were studied. When cucumber seedlings were treated with low concentrations of LaCl3 (0.002 and 0.02 mM), peroxidase (PO) activity increased, and catalase (CAT) activity was similar to that of control leaves at 0.002 mM La3+ and increased at 0.02 mM La3+, whereas superoxide dismutase (SOD) activity did not change significantly. The increase in the contents of chlorophyll (including chlorophylls a and b), carotenoids in parallel with the decrease in the level of malondialdehyde (MDA) suggested that low concentration of La3+ promoted plant growth. However, except the increase in SOD activity at 2 mM La3+, CAT and PO activities and the contents of pigments decreased at high concentrations of La3+ (0.2 and 2 mM), leading to the increase of MDA content and the inhibition of plant growth. It is suggested that lanthanum ion is involved in the regulation of active oxygen-scavenging enzyme activities during plant growth.

Effects of hydrogen peroxide and nitric oxide on both salt and heat stress tolerance in rice

Higher plants growing in natural environments experience various abiotic stresses. H 2O 2 and nitric oxide (NO) free radicals are produced and cause oxidative damage to plants under various abiotic stress conditions. However, in the present study, we found that pretreating rice seedlings with low levels (<10 μM) of H 2O 2 or NO permitted the survival of more green leaf tissue, and of higher quantum yield for photosystem II, than in non-treated controls, under salt and heat stresses. It was also shown that the pretreatment induces not only active oxygen scavenging enzymes activities, but also expression of transcripts for stress-related genes encoding sucrose-phosphate synthase, Δ′-pyrroline-5-carboxylate synthase, and small heat shock protein 26, These results suggest that H 2O 2 and NO can increase both salt and heat tolerance in rice seedlings by acting as signal molecules for the response.

Relationship between photosystem stoichiometries and changes in active oxygen scavenging enzymes in natural grown rice seedlings

The relationship between antioxidative enzymes and photosystemstoichiometries was examined in rice leaves. The photosystem (PS) II/PS Ireaction centre ratio decreased from the top to the bottom leaves, suggestinganimbalance of light absorption and electron flow as well as a probableover-reduction between the two photosystems. We used rice leaves from juvenileseedlings and obtained the following results: (1) Photosynthetic capacitymeasured from the pulse-amplitude modulation (PAM) fluorometer showed the PS IIphotochemistry to have a reduced capacity, but the excitation-energy trappingcapacity at PS II gradually increased from the top to the bottom leaves. (2)Thelevels of Chl, soluble protein, and ascorbate decreased, but those ofH2O2 increased slightly in the bottom leaves. (3) Whendetermined on the basis of leaf area, glycolate oxidase, catalase, ascorbateperoxidase and glutathione reductase degraded in the bottom leaves. (4) On thebasis of unit of Chl, the levels of superoxide dismutase (SOD) and guaiacolperoxidase (GPX) increased dramatically. Based on the above results, we discussthe relationship between the two photosystem stoichiometries and changes in theantioxidative enzymes.

Effect of 5-Aminolevulinic acid (ALA) on Photosynthetic Rate, Hydrogen Peroxide Content, Antioxidant Level and Active Oxygen-Scavenging Enzymes in Spinach (Spinacia oleracea L.)

The effects of 5-aminolevulinic acid (ALA), a key precursor in the biosynthesis of porphyrins, in a low level (0, 0.18, 0.60 or 1.80mM) on the photosynthetic rate, hydrogen peroxide contents, antioxidant substrates, and active oxygen-scavenging enzymes were investigated in the 3rd leaves of spinach (Spinacia oleracea). 1. Photosynthetic rates of leaves that were treated with different concentrations of ALA, increased significantly in day 3, and remained so for 6 days. 2. Hydrogen peroxide (H2O2) contents in leaves increased from day 6 to 9. The increase seems to be correlated with the promotion of the photosynthetic rate. 3. Oxidized ascorbate (DHA)/reduced ascorbate (ASC) ratio in treated leaves tended to remain constant, whereas reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio increased. 4. Catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities increased by day 3 after the ALA treatment. Superoxide dismutase (SOD) activity did not vary after ALA treatment.

Oxidative cell damage in Kat-sod assay of oxyhalides as inorganic disinfection by-products and their occurrence by ozonation.

Nine oxyhalides as possible inorganic disinfection by-products were tested for oxidative cell damage by Kat-sod assay with E. coli mutant strains deficient in the active oxygen-scavenging enzymes. Chlorine dioxide, chlorite, and iodate were highly cytotoxic, whereas in the presence of cysteine, bromate (BrO3-) and metaperiodate (IO4-) showed more growth inhibition toward the superoxide dismutase-deficient strains than the wild strain. BrO3- also showed oxidative mutagenicity with cysteine or glutathione ethyl ester in S. typhimurium TA 100. To identify oxyhalides formed by ozonation of raw water containing sea water, the occurrence of ozonation by-products of bromide and iodide was investigated. The results indicate that BrO3- is toxicologically one of the most remarkable oxyhalides detectable in drinking water because IO4- was not detected in the ozonated solution of iodide, and the ozonation condition to lower BrO3- is to keep it neutral in the presence of ammonium ion.

Cold Acclimation and Photoinhibition of Photosynthesis Accompanied by Needle Color Changes in Cryptomeria japonica during the Winter

This study focused on the physiological changes in Cryptomeria japonica accompanied by needle color changes during the winter. The physiological measurements include gas exchange, chlorophyll fluorescence, pigments, active oxygen scavenging enzymes, and several proteins in the photosynthetic apparatus. The light-saturated photosynthesis decreased during the winter. Total chlorophyll content and chlorophyll a/b ratio decreased; meanwhile xanthophyll cycle pigments and lutein contents increased significantly. These results indicate that cold acclimation had occurred. Photoinhibition was also observed in C. japonica which can be determined from the decreases in photochemical efficiency of PS II and the partial closure of PS II reaction centers. Small and large subunits of Rubisco and LHC II in the needles of C. japonica showed only a slight decrease during the winter, indicating that photoinhibition in C. japonica probably reflects a protective process to prevent more severe damage to the photosynthetic apparatus during low-temperature stress.

Active oxygen-scavenging enzymes activities in developing apple flowers and fruits

The activities of active oxygen-scavenging enzymes, superoxide dismutase, catalase and peroxidase were evaluated during apple ( Malus domestica Borkh cv. Red Spur Delicious) flower bud and fruit development. In dormant buds, superoxide dismutase, peroxidase and catalase activities were initially low, then increased sharply (2- to 5-fold) during bud swelling. With onset of bud break and during fruit development, superoxide dismutase and peroxidase activities decreased by 5- to 8-fold, while catalase activity remained relatively high throughout flower bud development and during early stages of fruit growth, before declining at full fruit development. A second increase in peroxidase activity occurred at full fruit development. In immature and mature fruits, superoxide dismutase activity was detected only in the peel, but not in cortex (flesh) or in seed tissue. Peroxidase activity was highest in peel, low in cortex and absent in seed tissue. Catalase activity was highest in seed, followed by peel, and cortex. Soluble protein levels in the seed were 7- and 12-fold higher than in the peel and cortex, respectively. Changes in the activities of these enzymes were related to growth and development of apple flower and fruit.