PAL), Polyphenoloxidase Research Articles

Antioxidant Benefits and Potential Mechanisms of Slightly Acidic Electrolyzed Water Germination in Sesame.

Slightly acidic electrolytic water (SAEW) treatment for seed germination is a promising technique for sustainable agriculture. This study investigated the antioxidant activity of germinated sesame seeds treated with SAEW for the first time. Specifically, the impact and correlation of SAEW on the activities of total phenols, total flavonoids, and antioxidant oxidase in sesame seeds were examined. The results showed that SAEW with low ACC inhibited sesame germination, SAEW with high ACC promoted sesame germination, and sesame buds treated with SAEW with 30 mg/L and 50 mg/L ACC showed lower antioxidant activity and total phenolic and flavone content compared to tap water. In contrast, SAEW with 30 mg/L ACC had no significant effect on sesame growth but positively influenced the antioxidant activity of sesame seed germination by promoting phenolic compound synthesis through increased phenylalanine ammonia-lyase (PAL) activity and enhancing antioxidant activity by boosting PAL, polyphenol oxidase (PPO), and peroxidase (POD) activities. Generally, antioxidant ability was the most prominent in SAEW with 30 mg/L ACC, and positive correlations between antioxidation and total phenols and flavonoids content were found in sesame. These findings provide valuable insights into the mechanisms underlying the enhanced antioxidant capacity observed in germinated sesame seeds under SAEW stress.

Control of dry rot and resistance induction in potato tubers against Fusarium sambucinum using red onion peel extract

The efficacy of red onion peel methanol extract to prevent dry rot in potato tubers caused by Fusarium sambucinum was investigated. At 20 mg mL−1, the methanol extract caused a great decrease in the fungal growth and spore germination by 86.3 %, and 91.2 %, respectively. Also, the dry rot control efficacy in potato slices inoculated with F. sambucinum reached 91.8 % at the same concentration. The treatment with methanol extract significantly increased the total phenolics to 0.31 g kg−1 compared with the control (0.19 g kg−1) in potato slices on the fourth day of the storage period as well as the increase in the level of total flavonoids. The relative leakage rate was 46.3 % in treated potato tuber slices compared to the control by 76.5 % and MDA content was much lower in slices treated compared with control slices during four days of storage. The methanol extract enhanced the activity of phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO), catalase (CAT), and peroxidase (POD) in potato slices throughout the experiment. The major compounds in the methanol extract were the flavonoids rutin, quercetin triglucoside, ferulic acid, quercetin diglucoside, quercetin monoglucoside, isorhamnetin glucoside, quercetin, kaempferol, and isorhamnetin using HPLC-UV/DAD, QTOF, and NMR spectra (1H NMR, APT, HSQC, COSY, HMBC, and NOESY).

Volatile Dimethyl Disulfide from Guava Plants Regulate Developmental Performance of Asian Citrus Psyllid through Activation of Defense Responses in Neighboring Orange Plants.

Intercropping with guava (Psidium guajava L.) can assist with the management of Asian citrus psyllid (ACP, Diaphorina citri Kuwayama), the insect vector of the huanglongbing pathogen, in citrus orchards. Sulfur volatiles have a repellent activity and physiological effects, as well as being important components of guava volatiles. In this study, we tested whether the sulfur volatiles emitted by guava plants play a role in plant–plant communications and trigger anti-herbivore activities against ACP in sweet orange plants (Citrus sinensis L. Osbeck). Real-time determination using a proton-transfer-reaction mass spectrometer (PTR-MS) showed that guava plants continuously release methanethiol, dimethyl sulfide (DMS), and dimethyl disulfide (DMDS), and the contents increased rapidly after mechanical damage. The exposure of orange plants to DMDS resulted in the suppression of the developmental performance of ACP. The differential elevation of salicylic acid (SA) levels; the expression of phenylalanine ammonia lyase (PAL), salicylate-O-methyl transferase (SMT), and pathogenesis-related (PR1) genes; the activities of defense-related enzymes PAL, polyphenol oxidase (PPO), and peroxidase (POD); and the total polyphenol content were observed in DMDS-exposed orange plants. The emission of volatiles including myrcene, nonanal, decanal, and methyl salicylate (MeSA) was increased. In addition, phenylpropanoid and flavonoid biosynthesis, and aromatic amino acid (such as phenylalanine, tyrosine, and tryptophan) metabolic pathways were induced. Altogether, our results indicated that DMDS from guava plants can activate defense responses in eavesdropping orange plants and boost their herbivore resistance to ACP, which suggests the possibility of using DMDS as a novel approach for the management of ACP in citrus orchards.

Exogenous salicylic acid improves resistance of aphid-susceptible wheat to the grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae).

Salicylic acid (SA), a phytohormone, has been considered to be a key regulator mediating plant defence against pathogens. It is still vague how SA activates plant defence against herbivores such as chewing and sucking pests. Here, we used an aphid-susceptible wheat variety to investigate Sitobion avenae response to SA-induced wheat plants, and the effects of exogenous SA on some defence enzymes and phenolics in the plant immune system. In SA-treated wheat seedlings, intrinsic rate of natural increase (rm), fecundity and apterous rate of S. avenae were 0.25, 31.4 nymphs/female and 64.4%, respectively, and significantly lower than that in the controls (P < 0.05). Moreover, the increased activities of phenylalanine-ammonia-lyase, polyphenol oxidase (PPO) and peroxidase in the SA-induced seedlings obviously depended on the sampling time, whereas activities of catalase and 4-coumarate:CoA ligase were suppressed significantly at 24, 48 and 72 h in comparison with the control. Dynamic levels of p-coumaric acid at 96 h, caffeic acid at 24 and 72 h and chlorogenic acid at 24, 48 and 96 h in wheat plants were significantly upregulated by exogenous SA application. Nevertheless, only caffeic acid content was positively correlated with PPO activity in SA-treated wheat seedlings (P = 0.031). These findings indicate that exogenous SA significantly enhanced the defence of aphid-susceptible wheat variety against aphids by regulating the plant immune system, and may prove a potential application of SA in aphid control.

Nitric oxide maintains postharvest quality of navel orange fruit by reducing postharvest rotting during cold storage and enhancing antioxidant activity

Current study aimed to evaluate the effects of fumigation with 15 μl L−1 nitric oxide (NO) on the quality of ‘Newhall’ navel orange fruit during storage at 5 °C. Fruits quality parameters, decay rate, antioxidant capacity, antioxidant enzymes activities and disease resistance related enzymes activities were evaluated. NO treatment significantly inhibited the increasing weight loss, maintained soluble solid content (SSC), titratable acid (TA) and vitamin C (VC) contents (P<0.05). Furthermore, NO treatment significantly decreased the respiration rate, suppressed superoxide anion (O2−·) and hydrogen peroxide (H2O2) generation (P<0.05). Antioxidant capacity, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities in NO-treated navel oranges were significantly higher than controls (P<0.05). Moreover, exogenous NO significantly enhanced the activities of phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO), β-1,3-glucanase (GLU) and chitinase (CHT) (P<0.05). Application of NO would be a promising method in maintaining the quality of postharvest navel orange in the future.

Physiological and biochemical insights into the basal level of resistance of two maize hybrids in response to Fusarium verticillioides infection

Fusarium stalk rot (FSR), caused by Fusarium verticillioides, is one of the most destructive diseases impacting maize yield worldwide. In this study, net carbon assimilation rate (A), stomatal conductance to water vapor (gs), transpiration rate (E), and internal CO2 concentration (Ci) were evaluated on leaves and the activities of enzymes (chitinase (CHI), β-1-3-glucanase (GLU), phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POX)) as well the concentrations of total soluble phenolics (TSP), lignin-thioglycolic acid (LTGA) derivatives, and malondialdehyde (MDA) were evaluated in the internodes and nodes of plants from maize hybrids moderately resistant (BRS 1035) and susceptible (30F35Y) to FSR. The upward relative lesion length (URLL) and radial fungal colonization (RFC) were 46 and 29% lower for the BRS 1035 hybrid in comparison to 30F35Y hybrid, respectively, at 30 after inoculation (dai). For both hybrids, A, gs, and E values significantly decreased while the Ci values increased on infected leaves compared to noninoculated plants. Inoculated plants from BRS 1035 hybrid showed an increase in A compared to inoculated plants from 30F35Y hybrid, and the increase in Ci values was greater for plants from 30F35Y hybrid at 30 dai compared to plants from BRS 1035 hybrid. The CHI, GLU, PPO, CAT, APX, and POX activities increased for inoculated plants from both hybrids compared to the noninoculated plants. In the internodes region, the increase in the activities of CHI (during the infection process of F. verticillioides) and GLU (at earlier stages of F. verticillioides infection) was more pronounced for plants from BRS 1035 hybrid than for plants from 30F35Y hybrid. In the region of the nodes, activities of CHI (during the infection process of F. verticillioides), PAL (at 20 dai), PPO (at 30 dai), and CAT and POX (both at three dai) were more pronounced for plants from BRS 1035 hybrid than for plants from 30F35Y hybrid. In the internodes region, the lower TSP concentration at 30 dai was linked to a high concentration of LTGA derivatives for inoculated plants from BRS 1035 hybrid compared to inoculated plants from 30F35Y hybrid. Taking together, the results of the present study allowed to conclude that the infection by F. verticillioides triggered physiological and biochemical changes on the stalk of maize plants influencing photosynthesis on leaves. A more robust antioxidative metabolism for reactive oxygen species removal in association with an efficient and strong activity of defense enzymes helped to minimize the cellular damage caused by F. verticillioides infection resulting, therefore, in an increase in maize resistance to FSR.

Activity of Purpureocillium lilacinum filtrates on biochemical characteristics of Sclerotinia sclerotiorum and induction of defense responses in common bean

White mold of common bean caused by Sclerotinia sclerotiorum is a serious disease in temperate and subtropical regions. The present study evaluated the effects of culture filtrates of Purpureocillium lilacinum on S. sclerotiorum under in vitro and in vivo conditions at the concentration of 75% of culture filtrates. The mycelial growth, sclerotia formation, myceliogenic and carpogenic germination of S. sclerotiorum were prevented by 100, 100, 93.5 and 90%, respectively. Lipid peroxidation and cell membrane permeability of S. sclerotiorum mycelia were increased, while oxalic acid content was decreased compared to the control at 75% of the filtrates. Application of the culture filtrates at 75% significantly reduced the disease severity by 83.3% under greenhouse conditions. Besides, the filtrate enhanced the activities of phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO) and peroxidase (POD) in common bean plants. The nuclear magnetic resonance (NMR) measurements of the filtrate revealed that its major compounds are the peptides leucinostatins H and K.

Over-expression of the Pseudomonas syringae harpin-encoding gene hrpZm confers enhanced tolerance to Phytophthora root and stem rot in transgenic soybean.

Phytophthora root and stem rot (PRR) caused by Phytophthora sojae is one of the most devastating diseasesreducing soybean (Glycine max) production all over the world. Harpin proteins in many plant pathogenic bacteria were confirmed to enhance disease and insect resistance in crop plants. Here, a harpin protein-encoding gene hrpZpsta from the P. syringae pv. tabaci strain Psta218 was codon-optimized (renamed hrpZm) and introduced into soybean cultivars Williams 82 and Shennong 9 by Agrobacterium-mediated transformation. Three independent transgenic lines over-expressing hrpZm were obtained and exhibited stable and enhanced tolerance to P. sojae infection in T2-T4 generations compared to the non-transformed (NT) and empty vector (EV)-transformed plants. Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of salicylic acid-dependent genes PR1, PR12, and PAL, jasmonic acid-dependent gene PPO, and hypersensitive response (HR)-related genes GmNPR1 and RAR was significantly up-regulated after P. sojae inoculation. Moreover, the activities of defense-related enzymes such as phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), peroxidase, and superoxide dismutase also increased significantly in the transgenic lines compared to the NT and EV-transformed plants after inoculation. Our results suggest that over-expression of the hrpZm gene significantly enhances PRR tolerance in soybean by eliciting resistance responses mediated by multiple defense signaling pathways, thus providing an alternative approach for development of soybean varieties with improved tolerance against the soil-borne pathogen PRR.

The Effect and Action Mechanisms of Oligochitosan on Control of Stem Dry Rot of Zanthoxylum bungeanum.

In this report, the effects of two oligochitosans, i.e., oligochitosan A (OCHA) and oligochitosan B (OCHB), on control of dry rot of Zanthoxylum bungeanum (Z. bungeanum) caused by Fusarium sambucinum (F. sambucinum) were evaluated. First, both oligochitosans show desirable ability to decrease the infection of F. sambucinum. Second, the oligochitosans strongly inhibit the radial colony and submerged biomass growth of F. sambucinum. Lastly, these oligochitosans are capable of increasing the activities of phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO) and peroxidase (POD) significantly, as well as enhancing the content of total phenolics in Z. bungeanum stems. These findings indicate that the protective effects of OCHA and OCHB on Z. bungeanum stems against dry rot may be associated with the direct fungitoxic function against pathogen and the elicitation of biochemical defensive responses in Z. bungeanum stems. The outcome of this report suggests that oligochitosans may serve as a promising natural fungicide to substitute, at least partially, for synthetic fungicides in the disease management of Z. bungeanum.

Effects of Ethephon on Fresh In‐Husk Walnut Preservation and its Possible Relationship with Phenol Metabolism

Fresh walnuts (Juglans regia L.) are in demand due to their high nutrition value and unique flavor of the kernel. In this study the effects of ethephon on decay control and kernel quality of fresh walnuts and its possible relationship with phenolic metabolism were investigated. Fresh in-husk walnuts treated with 0, 10, 500, and 800 mg/L ethephon were stored at 0 ± 0.5°C for 42 d. Decay incidence, total phenolic (TP) compounds, phenylalanine ammonialyase (PAL), polyphenol-oxidase (PPO), and peroxidase (POD) activities of green husks, and acid values (AV) and peroxide values (PV) of kernels were assessed at 6-d intervals. The respiration rate of the whole walnut was assessed at 3-d intervals. Treatment with 500 mg/L ethephon enhanced respiration, reduced the decay index, and inhibited PPO and POD activity and browning of green husks, and also promoted PAL activity and TP content of green husks. This treatment also reduced the PV and AV of kernels. A concentration of 10 mg/L ethephonhad similar, but weaker, effects on walnuts. Treatment with 8000 mg/L ethephon, however, had opposite effects. These data indicate ethephon treatment at a proper concentration can extend storage life and maintain kernel quality of fresh in-husk walnuts through the manipulation of phenolic metabolism.

Effects of chitosan/nano-silica on postharvest quality and antioxidant capacity of loquat fruit during cold storage

Loquat (Eriobotrya japonica Lindl.) fruit has a very short shelf-life during ambient temperature storage, and is susceptible to cold storage appearing chilling injury symptoms. The effect of chitosan/nano-silica coating on chilling tolerance in white-flesh loquat fruit (cv Baiyu) stored at 5°C for 40d was investigated. In comparison with control fruit, internal browning and weight loss in chitosan/nano-silica treated fruit were significantly delayed. Likewise, the decrease of total soluble solids (TSS) and titratable acidity (TA) was also inhibited. Glucose and fructose contents increased from 11.31 to 12.76gkg−1 and from 33.20 to 44.37gkg−1, respectively. The increase of reducing sugars contributed to the improvement of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities, reaching the peaks of 623510.12, 462371.21 and 41114.35Ukg−1, respectively. Enhanced activities of antioxidant enzymes markedly alleviated the generation of superoxide anion (O2−) and hydrogen peroxide (H2O2). Low levels of malondialdehyde (MDA) and membrane permeability in chitosan/nano-silica treated fruit were also detected, ranged from 4.35 to 8.31mmolkg−1 and from 24.32 to 43.45%, respectively. Moreover, activities of phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO) and lipoxidase (LOX) were also much lower than those in treatment alone and control fruit. Our results indicated that the use of chitosan/nano-silica coating was effective in enhancing chilling tolerance and providing a longer storage life with acceptable external and internal quality in loquat fruit.

Active Changes in Lignification Related Enzymes in Cluster bean after the attack ofMacrophomina phaseolina

The natural resistance of plants to disease is based not only on preformed mechanisms, but also on induced mechanisms. The defense mechanisms present in resistant plants may also be found in susceptible ones. In this study, the activities of polyphenol, phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), and peroxidase (POD) were assayed in cluster bean seedlings (Cyamopsis tetragonoloba L.) at 0, 24, 48, 72, 96, 120, 144 and 168 h after they were infested by Macrophomina phaseolina using spectrophotometric analysis. The results indicated that pathogen infestation increased the activities of polyphenols, PAL, PPO, and POD. The polyphenols and enzymes showed different activity levels at different times after the infestation. The polyphenol content reached the highest peak at 120 h by 39% in comparison to control. The PAL activity reached the first high peak by 32% at 48 h and the highest peak by 37% at 96 h compared to the control. The PPO activity reached the first high peak by 42% at 48 h and the highest peak by 80% at 120 h, and the POD activity reached the highest peak by 39% at 48 h and another higher peak value by 67% at 120 h. The results suggest that the enhanced activities of the polyphenols and enzymes may contribute to bioprotection of cluster bean plants against M. phaseolina infestation.

Biological control mechanisms of D-pinitol against powdery mildew in cucumber

D-pinitol is an effective agent for controlling powdery mildew (Podosphaera xanthii) in cucumber. In this study, we determined the mechanisms of D-pinitol in controlling powdery mildew in cucumber plants. We compared P. xanthii development on cucumber leaf surface treated with D-pinitol or water (2 mg ml−1) at different time points after inoculation. The germinating conidia, hyphae, and conidiophores of the pathogen were severely damaged by D-pinitol at any time of application tested. The highest level of suppression of fungal development was obtained at 3 days after inoculation. The contents of chlorophyll, total phenolics, flavonoid, and gallic acid and its derivatives (GAD); the activities of phenylalanine ammonialyase (PAL), polyphenoloxidase (PPO), peroxidase (POX), and superoxide dismutase (SOD); and the expression of the genes encoding for PR-1, peroxidase (POX), lipoxygenase (LOX1), chitinase (Chit1) were higher in the cucumber leaves treated with D-pinitol and inoculated than in the leaves either treated with D-pinitol or inoculated with the pathogen. These results suggest that D-pinitol triggers several plant defense responses in cucumber leading to pathogen suppression and resistance to powdery mildew.

Effects of oligosaccharides from endophytic Fusarium oxysporum Dzf17 on activities of defense-related enzymes in Dioscorea zingiberensis suspension cell and seedling cultures

article i nfo Background: Three oligosaccharides (EOS, WOS and SOS) were respectively prepared from the corresponding polysaccharides, namely exopolysaccharide (EPS), water-extracted mycelial polysaccharide (WPS) and sodium hydroxide-extracted mycelial polysaccharides (SPS) from the endophytic fungus Fusarium oxysporum Dzf17. In this study, the effects of EOS, WOS and SOS on the activities of the defense-related enzymes, namely phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO) and peroxidase (POD) in its host plant Dioscorea zingiberensis cultures were investigated. Results: For the suspension cell cultures of D. zingiberensis, the highest PAL activity was induced by 0.5 mg/mL of WOS at 48 h after treatment, which was 4.55-fold as that of control. Both PPO and POD activities were increased to the maximum values by 0.25 mg/mL of WOS at 48 h after treatment, which were respectively 3.74 and 3.45-fold as those of control. For the seedling cultures, the highest PAL activity was elicited by 2.5 mg/mL of EOS at 48 h after treatment, which was 3.62-fold as that of control. Bot hP PO and POD reached their maximum values treated with 2.5 mg/mL of WOS at 48 ha fter treatment, which were 4.61 and 4.19-fold as those of control, separately. Conclusions: Both EOSand WOSsignificantly increased the activities of PAL, PPO and POD in the suspension cell and seedling cultures of D. zingiberensis. The results suggested that the oligosaccharides from the endophytic fungus F. oxysporum Dzf17 may be related to the activation and enhancement of the defensive mechanisms of D. zingiberensis suspension cell and seedling cultures.

Changes in defence-related enzymes in rice responding to challenges by Rhizoctonia solani

Sheath blight disease caused by Rhizoctonia solani Kuhn is becoming a major constraint to rice production, especially in the intensified cultivation system. To know the in rice, it is important to get the knowledge of the activity of defence-related enzymes due to the fungal infection. The pathogen induced superoxide dismutase (SOD) and chitinase activities in rice plants, while suppressing peroxidase (POD) and phenylalanine ammonia-lyase (PAL) activities at 36 and 24 h after inoculation, respectively. Induction of two POD isozymes, POD-3 and -4, up to 48 h after inoculation and disappearance of the said isomers at 72 h onwards in rice–Rhizoctonia interaction implicated the role of these isomers in susceptible host–pathogen interaction. Apart from POD and SOD, the activities of other stress-related enzymes, viz. PAL, polyphenol oxidase (PPO) and β-1,3-glucanase were also studied. From this study, it was found that these defence-related enzymes are most significantly related to host–pathogenic interaction.

Use of thiamine for controlling Alternaria alternata postharvest rot in Asian pear (Pyrus bretschneideri Rehd. cv. Zaosu)

SummaryThe effects of thiamine (vitamin B1) against Alternaria rot caused by Alternaria alternata and its possible mechanism in harvested Asian pear fruit were investigated. Thiamine strongly inhibited spore germination and mycelial growth of A. alternata in vitro. Thiamine at a concentration of 100 mm effectively inhibited the development of Alternaria rot, enhanced the activities of defence‐related enzymes, such as phenylalanine ammonia‐lyase (PAL), polyphenoloxidase (PPO) and peroxidase (POD), and increased the content of flavonoids, phenolics and lignin. Thiamine also affected reactive oxygen metabolism of the pear fruit by increasing its production and H2O2 content, and enhancing the activities of major detoxifying enzymes, such as superoxide dismutase (SOD). These findings suggest that the effects of thiamine on Alternaria rot in pear fruit may be associated with its direct fungitoxic property against the pathogens, and the elicitation of biochemical defence responses in the fruit.

Effect of riboflavin on postharvest disease of Asia pear and the possible mechanisms involved

The effects of riboflavin (vitamin B2) against Alternaria rot caused by Alternaria alternata and its possible mechanism in harvested Zaosu pear fruit were investigated. Riboflavin at a concentration of 1.0 mM effectively inhibited development of Alternaria rot and enhanced the activities of defense-related enzymes, such as phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO) and peroxidase (POD), and increased accumulation of flavonoids, phenolics and lignin. Riboflavin also affected reactive oxygen metabolism of pear fruit by increasing O 2 – production and H2O2 content, and enhancing the activities of the main detoxifying enzymes, such as catalase (CAT) and superoxide dismutase (SOD). Spore germination and mycelial growth of A. alternata were inhibited by riboflavin and the inhibitory effect was highly correlated with the riboflavin concentration used in this study. It is suggested that the effects of riboflavin on Alternaria rot in pear fruit may be associated with its direct fungitoxic property against the pathogens, and the elicitation of biochemical defense responses in the fruit.

Analysis of defence enzymes induced by antagonistic bacteriumBacillus subtilis strain AR12 towardsRalstonia solanacearum in tomato

Bacterial wilt, caused byRalstonia solanacearum (Smith) Yabuuchiet al., is an economically important disease on tomato in many provinces of China. Antagonistic bacteriumBacillus subtilis strain AR12 was used to control bacteria wilt of tomato (Lycopersicon esculentum Miller) in the greenhouse. The biocontrol efficiency was as high as 90.18%. Superoxide anion and hydrogen peroxide generation rates and changes in phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities were studied in tomato plants. Antagonist AR12 advanced and increased significantly activities of PAL, PPO, POD and SOD. As comparison, the activities of these four enzymes increased less and later in tomato only treated withR. solanacearum TM15 (control 2), and kept lowest level with few change in tomato with sterilised water (control 1). The maximum activities of these four enzymes in tomato treated with AR12 occurred in different stages: activity of PAL, PPO, POD, and SOD increased to the top level at 48, 48, 12 and 12 h, respectively, after pathogen inoculation and kept high level for some time. H2O2 is associated with hypersensitive response (HR) during systemic acquired resistance. H2O2 content increased significantly in tomato treated with AR12, but HR response was not seen. CAT and APX are the key H2O2 detoxifying enzymes. Activities of APX in tomato treated with AR12 were increased significantly, while CAT was degraded until 80 h after pathogen inoculation. This work support the view that increased antioxidant enzyme activities could be involved at least in part, in the beneficial effects of plant growth-promoting rhizobacteria strains on the performance of vegetable grown under the pathogen infection conditions.

Effect of methyl jasmonate on the inhibition of Colletotrichum acutatum infection in loquat fruit and the possible mechanisms

The effect of methyl jasmonate (MeJA) on reducing anthracnose rot caused by Colletotrichum acutatum infection in postharvest loquat fruit ( Eriobotrya japonica L. cv. Jiefangzhong) and the possible mechanisms involved were investigated. Freshly harvested loquat fruit were treated with 10 μmol/L MeJA at 20 °C for 24 h. Both the treated and the untreated fruit were artificially wounded and inoculated with Colletotrichum acutatum spore suspension (1.0 × 10 5 spores/mL) 1 day after the treatment, and then incubated at 20 °C for 6 days. Treatment of loquat fruit with MeJA resulted in significantly lower disease incidence and smaller lesion diameters than in control fruit. MeJA treatment significantly inhibited activities of catalase (CAT) and ascorbate peroxidase (APX) while superoxide dismutase (SOD) activity was not significantly affected in early infection, thus resulting in a higher level of H 2O 2 in the earlier period of incubation. The enhanced H 2O 2 generation by MeJA treatment might serve as a signal to induce resistance against C. acutatum infection. However, MeJA treatment inhibited the increase in phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO) and peroxidase (POD) activities and lignin content, indicating that lignification is not the major defense mechanism against anthracnose rot in loquat fruit. The in vitro experiment showed that MeJA significantly inhibited spore germination, germ tube elongation and mycelial growth of C. acutatum. These results suggest that MeJA treatment can effectively inhibit anthracnose rot caused by C. acutatum in postharvest loquat fruit. It is postulated that the control of the disease is directly because of the inhibitory effect of MeJA on pathogen growth, and indirectly because of the induced disease resistance triggered by enhanced H 2O 2 levels.

Enhancement of Phenylalanine Ammonia Lyase, Polyphenoloxidase, and Peroxidase in Cucumber Seedlings by Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Infestation

In this study, the activities of phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), and peroxidase (POD) were assayed in cucumber seedlings ( Cucumis sativus L.) at 0, 6, 12, 24, 48, 72, and 96 h after they were infested by Bemisia tabaci (Gennadius) using spectrophotometric analysis. The results indicated that herbivore infestation increased the activities of PAL, PPO, and POD. The enzymes showed different activity levels at different times after the infestation. The PAL activity reached the first high peak by 23.1% at 6 h and the highest peak by 29.1% at 48 h compared to the control. The PPO activity reached the first high peak by 22.7% at 6 h and the highest peak by 52.6% at 24 h, and the POD activity reached the highest peak by 213.2% at 6 h and another higher peak value by 135.2% at 96 h. The results suggest that the enhanced activities of the enzymes may contribute to bioprotection of cucumber plants against B. tabaci infestation.