Biochemical alterations in leaves of resistant and susceptible cotton genotypes infected systemically by cotton leaf curl Burewala virus

Leaf curl disease caused by Cotton Leaf Curl Burewala virus (CLCuBuV) has been recognized as serious threat to cotton in Indian subcontinent. However, information about cotton–CLCuBuV interaction is still limited. In this study, the level of phenolic compounds, total soluble proteins, and malondialdehyde (MDA) and the activities of phenylalanine ammonia-lyase (PAL), peroxidase (POX), catalase (CAT), proteases, superoxide dismutase (SOD), and polyphenol oxidase (PPO) were studied in leaves of two susceptible (CIM-496 & NIAB-111) and two resistant (Ravi and Co Tiep Khac) cotton genotypes. Disease symptoms were mild in the resistant genotypes but were severe in highly susceptible genotypes. The results showed that phenolic compounds, proteins, PAL, POX, CAT, proteases, SOD, PPO, and MDA play an active role in disease resistance against CLCuBuV. The amount of total phenols, proteases, MDA, and PPO was significantly higher in leaves of CLCuBuV-inoculated plants of both resistant genotypes as in non-inoculated plants, and decreased in CLCuBuV-inoculated plants of both susceptible genotypes over their healthy plants. POX, protein content, SOD, and PAL activities showed lower values in resistant genotypes, while they decreased significantly in susceptible genotypes as compared to the noninoculated plants except PAL, which showed non-significant decrease. CAT was found to be increased in both susceptible and resistant genotypes with maximum percent increase in resistant genotype Ravi, as compared to non-inoculated plants. The results showed significantly higher concentrations of total phenols and higher activity of protease, MDA, SOD, and PPO in resistant genotype Ravi after infection with CLCuBuV, suggesting that there is a correlation between constitutive induced levels of these enzymes and plant resistance that could be considered as biochemical markers for studying plant-virus compatible and incompatible interactions.     

Salicylic Acid Enhances Resistance to Fusarium oxysporum f. sp. phaseoli in Common Beans (Phaseolus vulgaris L.)

Fusarium wilt caused by Fusarium oxysporum f. sp. phaseoli (Fop) is one of the most serious diseases of common bean (Phaseolus vulgaris L.) and is especially prevalent in China. In this study, we demonstrated that exogenous application of 2 mM salicylic acid (SA) by leaf spraying could induce resistance against Fop in common beans. Accumulation of free and conjugated SA in roots was detected by HPLC analysis and compared. After 168 h of daily SA treatment, the free SA level in roots was eight times higher than in control plants. However, the conjugated SA level reached a peak at 72 h of SA treatment, which was nine times higher than in control plants, and then sharply declined at 168 h. The activities of phenylalanine ammonia lyase (PAL, EC 4.3.1.5) and peroxidases (POX, EC 1.11.1.7) in roots were 9.4 and 6.3 times higher than in control plants after 168 h of SA treatment, respectively. H₂O₂ and O₂ ^? levels reached 2.6 and 13.6 times higher, respectively, than in the control plants at 168 h after SA treatment. Host reactions of SA-treated plant roots infected by Fop observed in microscopy included the deposition of electron-dense materials along the secondary walls. However, untreated inoculated plants showed marked cell wall degradation and total cytoplasm disorganization of root cells. These results indicated that SA applied to foliar tissue is capable of enhancing the systemic acquired resistance of common bean roots to infection by Fop.     

Effect of drought on biomass, protein content, lipid peroxidation and antioxidant enzymes in two sesame cultivars

The effects of drought on growth, protein content, lipid peroxidation, superoxide dismutase (SOD), peroxidase (POX), catalase (CAT) and polyphenol oxidase (PPO) were studied in leaves and roots of Sesamum indicum L. cvs. Darab 14 and Yekta. Four weeks after sowing, plants were grown under soil moisture corresponding to 100, 75, 50 and 25 % field capacity for next four weeks. Fresh and dry masses, and total protein content in leaves and roots decreased obviously under drought. However, several new proteins appeared and content of some proteins was affected. Measurement of malondialdehyde content in leaves and roots showed that lipid peroxidation was lower in Yekta than in Darab 14. Severe stress increased SOD, POX, CAT and PPO activities in leaves and roots, especially in Yekta. According to the present study Yekta is more resistant to drought than Darab 14.     

Antioxidative defense system in pigeonpea roots under waterlogging stress

Pigeonpea [Cajanus cajan (L.) Millsp.] is a waterlogging-sensitive legume crop. We studied the effect of waterlogging stress on hydrogen peroxide (H₂O₂) content, lipid peroxidation and antioxidant enzyme activities in two pigeonpea genotypes viz., ICPL-84023 (waterlogging resistant) and MAL-18 (waterlogging susceptible). In a pot experiment, waterlogging stress was imposed for 6 days at early vegetative stage (20 days after sowing). Waterlogging treatment significantly increased hydrogen peroxide accumulation and lipid peroxidation, which indicated the extent of oxidative injury posed by stress conditions. Enzyme activities of peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD) and polyphenol oxidase (PPO) increased in pigeonpea roots as a consequence of waterlogged conditions, and all the enzyme activities were significantly higher in waterlogged ICPL-84023 than in MAL-18. POX activity was the maximum immediately after imposing stress, therefore, it was suggested to be involved in early scavenging of H₂O₂, while rest of the enzymes (CAT, APX, SOD and PPO) were more important in late responses to waterlogging. Present study revealed that H₂O₂ content is directly related to lipid peroxidation leading to oxidative damage during waterlogging in pigeonpea. Higher antioxidant potential in ICPL-84023 as evidenced by enhanced POX, CAT, APX, SOD and PPO activities increased capacity for reactive oxygen species (ROS) scavenging and indicated relationship between waterlogging resistance and antioxidant defense system in pigeonpea.     

Polyamine metabolism and lipoxygenase activity during Fusarium oxysporum f. sp. ricini -Castor interaction

Polyamine oxidase and lipoxygenase enzymes are key players for hyper sensitive reaction (HR) during incompatible interaction of host-pathogen. Thus, the role of lipoxygenase and polyamines was studied in the wilt pathogen infected and non infected tissues of resistant and susceptible genotypes of castor at 0 days after infection (DAI), 5 DAI and 10 DAI (30 days after sowing). The lipoxygenase (LOX) and polyamine oxidase (PAO) activities were higher in the incompatible interaction at all the stages of analysis. The constitutive level of malondyaldehyde (MDA) content, a product of lipid peroxidation was higher in susceptible genotypes (VP-1 and VI-9), while induced level was higher in resistant genotypes (48–1 and SKP-84) at 5 DAI and 10 DAI . Polyamine profiling using HPTLC showed higher spermidine and spermine content in resistant genotypes at 10 DAI. Furthermore, spermidine was detected only in the roots of resistant genotypes at 10 DAI. These results suggest the role of high titers of polyamines, LOX and PAO in disease resistance possibly through HR induction.     

Variations of Phenoloxidase Activities as a Consequence of Stresses that Induce Resistance to Fusarium Wilt of Tomato

The variations over 7–8 day of peroxidase (PO) and polyphenoloxidase (PPO) activity have been investigated in tomato plants the roots of which had been subjected to stresses (heat, chloroform and a non-pathogenic form of Fusarium oxysporum) that induce resistance to Fusarium oxysporum f. sp. lycopersici. All treatments induced increase of PO and PPO activity that reached a maximum 3 days after the treatments in leaves, 4 days in stem and roots and were higher in leaves than in other parts. Activity decreased to levels for the control plants after 8 days. Inoculation with Fusarium oxysporum f. sp. lycopersici further stimulated PO and PPO activity in all treated plants over that caused by the treatments alone. Again, activity of treated plants was lower than in controls 7 days after inoculation. It is concluded that 1. increased PO and PPO activity in tomato is a systemic response to cellular injury caused in the root by heat, chloroform and non-pathogenic Fusarium oxysporum, 2. these treatments do no prevent the pathogen from interacting with the plants and inducing further enzyme increase, 3. treated plants react more strongly to the challenge inoculation than untreated plants.     

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.     

The effect of methyl jasmonate on enzyme activities in wheat genotypes infected by the crown and root rot pathogen <Emphasis Type="Italic">Fusarium culmorum</Emphasis>

The hemibiotrophic pathogen Fusarium culmorum (Fc) causes crown and root rot (CRR) in wheat. In this study, MeJA treatment was done 6 h after pathogen inoculation (hai) to focus the physiological and biochemical responses in root tissue of the susceptible wheat cv Falat, partially resistant cv Pishtaz and the tolerant cv Sumai3 at the beginning of the necrotrophic stage. The results indicate that treatment with MeJA at 6 hai significantly delayed the necrotic progress in cv Falat, whereas no significant difference was seen in other cultivars. The activities of pathogen responsive defense-related enzymes (SOD, CAT, POX, PPO, LOX and PAL), total phenols and callose contents were higher in Sumai3, while treatment with MeJA significantly increased these enzymes activities and total phenols content in Falat, signifying the most sensitive cultivar which had a weak reaction to the pathogen but a strong response to MeJA treatment. Additionally, MeJA treatment decreased the level of H₂O₂ and MDA contents particularly in cv Falat. This is the first work reporting the regulation of defense-related enzymes by MeJA treatment at particular time point of 6 hai suggests the possible role of JA in regulating basal resistance in CRR pathogen–wheat interaction. Taken together, our data add new insights into the mechanism of wheat defense including enzymatic events controlling wheat protection against Fc infection.     

Influence of salinity and <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> as the stress factors on morpho-physiological and yield attributes in onion

Occurrence of salt stress with the soil borne fungus Fusarium oxysporum f. sp. cepa (FOC) are potential threat to the crop yield. This investigation reports effect of the concurrent stresses (salinity and FOC) on morpho-physiological and yield attributes in onion. In vitro growth tests revealed proliferation of FOC biomass at different levels of salinity (2–8 dS m^?1). A greenhouse pot experiment with the proposed levels of salinity (2.5, 3.5 and 4.5 dS m^?1) in combination with FOC inoculation showed more drastic effect of combined stress on disease severity, plant growth and bulb as compared to the individual stress. In general, osmotic potential, total chlorophyll content, membrane stability index and total protein content of the leaf were decreased, while total phenolics were increased due to the given stress/s. Total sugar content decreased due to effect of the  individual stress of FOC, while it increased under the individual stress of salinity and in combination with FOC. FOC infection did not change activity of polyphenol oxidase (PPO), while it improved peroxidase (POX) and phenylalanine ammonia lyase (PAL) and decreased catalase (CAT) activity. Activities of POX and PPO increased, however PAL and CAT declined under individual as well as simultaneous stress of salinity ?and ?FOC. The research work concluded that FOC will be a more severe disease threat for onion cultivation in saline soils.     

The Effect of Pseudomonas fluorescens and Fusarium oxysporum f.sp. cubense on Induction of Defense Enzymes and Phenolics in Banana

The effect of Pseudomonas fluorescens treatment and Fusarium oxysporum f. sp. cubense inoculation on induction of phenylalanine ammonia-lyase (PAL), peroxidase (POX), chitinase, -1,3-glucanase and accumulation of phenolics in banana (Musa sp.) was studied. When banana roots were treated with P. fluorescens strain Pf10, a two-fold increase in phenolic content in leaf tissues was recorded 3 – 6 d after treatment. Challenge inoculation with F. oxysporum, the wilt pathogen, steeply increased the phenolic content in P. fluorescens-treated banana plants. Significant increase in POX activity was detected 6 – 9 d after P. fluorescens treatment. PAL, chitinase and -1,3-glucanase activities increased significantly from 3 d after P. fluorescens treatment and reached the maximum 6 d after treatment. Challenge inoculation with F. oxysporum further increased the enzyme activities. These results suggest that the enhanced activities of defense enzymes and elevated content of phenolics may contribute to bioprotection of banana plants against F. oxysporum.     

The effects of boron toxicity on root antioxidant systems of two chickpea (Cicer arietinum L.) cultivars

Significant differences in the antioxidant systems of the roots of two chickpea (Cicer arietinum L.) cultivars differing in tolerance to drought were observed in under toxic boron (B) conditions. Three-week-old chickpea seedlings were subjected to 0.05 mM (control), 1.6 mM or 6.4 mM B in the form of boric acid (H₃BO₃) for 7 days. At the end of the treatment period, root length, dry weight, boron concentration, malondialdehyde (MDA) content, and the activities of antioxidant enzymes—superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), ascorbate peroxidase (APOX) and glutathione reductase (GR)—were measured. Root length of the drought-tolerant Gökce cultivar did not change under 1.6 mM B but increased under 6.4 mM B. On the contrary, root length decreased in the drought-sensitive Küsmen cultivar under both B concentrations. While root dry weight was unaffected in Gökce, it decreased in Küsmen under both B concentrations. Boron concentration was significantly higher in Küsmen than in Gökce at both B levels. Significant increases in SOD and POX activities were observed in roots of both cultivars under 1.6 and 6.4 mM B. Root extracts exhibited three SOD and three POX activity bands in both cultivars under B stress when compared to control groups. Although CAT activity in Gökce was increased, it decreased in Küsmen at the highest B concentration as compared to control groups. Roots of both cultivars showed no significant change in APOX activity under B toxicity (except in 1.6 mM B treated roots of Küsmen) when compared to control groups. GR activity in the roots of Küsmen decreased significantly with increasing B concentration. However, a significant increase in GR activity was found in Gökce under 1.6 mM B stress. In addition, lipid peroxidation levels of drought-sensitive Küsmen increased, indicating more damage to membrane lipids due to B toxicity. Lipid peroxidation did not change in the drought-tolerant Gökce cultivar at either B concentration. These results suggest that roots of Gökce are better protected from B-stress-induced oxidative stress due to enhanced SOD, CAT and POX activities under high B levels.     

Alterations in photosynthetic pigments,protein, and carbohydrate metabolism in a wild plant <Emphasis Type="Italic">Coronopus didymus</Emphasis> L. (Brassicaceae) under lead stress

Coronopus didymus has been emerged as a promising wild, unpalatable plant species to alleviate lead (Pb) from the contaminated soils. This work investigated the hypothesis regarding various metabolic adaptations of C. didymus under lead (Pb) stress. In pot experiments, we assessed the effect of Pb at varied concentrations (500–2900 mg kg^?1) on growth, photosynthetic pigments, alteration of macromolecular (protein and carbohydrate) content, and activities of enzymes like protease, α-and β-amylase, peroxidase (POX), and polyphenol oxidase (PPO) in C. didymus for 6 weeks. Results revealed that Pb exposure enhanced the growth, protein, and carbohydrate level, but decreased the leaf pigment concentration and activities of hydrolytic enzymes. The activities of POX and PPO in roots increased progressively by ~337 and 675%, respectively, over the control, at 2900 mg kg^?1 Pb treatment. Likewise, contemporaneous findings were noticed in shoots of C. didymus, strongly indicating its inherent potential to cope Pb-induced stress. Furthermore, the altered plant biochemical status and upregulated metabolic activities of POX and PPO indulged in polyphenol peroxidation elucidate their role in allocating protection and conferring resistance against Pb instigated stress. The current work suggests that stress induced by Pb in C. didymus stimulated the POX and PPO activities which impart a decisive role in detoxification of peaked Pb levels, perhaps, by forming physical barrier or lignifications.     

Differential Expression of Antioxidant Enzymes During Degradation of Azo Dye Reactive black 8 in Hairy roots of Physalis minima L.

The enzymes involved in the protection of plant metabolism in presence of azo dye was characterized by studying activities of the role of antioxidant enzymes in the hairy roots (HRs) of Physalis minima L. during degradation of an azo dye, Reactive Black 8 (RB8). When the HRs were exposed to RB8 (30 mg L^?1), a nine fold increase in SOD activity was observed after 24 h, while 22 and 50 fold increase in activity was observed for POX and APX respectively after 72 h, whereas there was no significant change in activity of CAT. The activation of different antioxidant enzymes at different time intervals under dye stress suggests the synchronized functioning of antioxidant machinery to protect the HRs from oxidative damage. FTIR analysis confirmed the degradation of dye and the non-toxic nature of metabolites formed after dye degradation was confirmed by phytotoxicity study.     

Antioxidative enzymes and isozymes analysis of taro genotypes and their implications in <Emphasis Type="Italic">Phytophthora</Emphasis> blight disease resistance

Assessment of the differential expression of antioxidative enzymes and their isozymes, was done in 30 day-old ex vitro raised plants of three highly resistant (DP-25, Jhankri and Duradim) and one highly susceptible (N-118) genotypes of taro [Colocasia esculenta (L.) Schott]. Antioxidative enzymes were assayed in the ex vitro plants, 7 days after inoculation with the spores (15,000 spores ml⁻¹ water) of Phytophthora colocasiae Raciborski to induce taro leaf blight disease. Uninoculated ex vitro plants in each genotype were used as control. The activity of superoxide dismutase (SOD) and guaiacol peroxidase (GPX) increased under induced blight condition when compared with control. Increase in antioxidative enzymes was more (67–92%) in the resistant genotypes than that (21–29%) of the susceptible genotype. The zymograms of SOD and GPX in the resistant genotypes, with pathogenic infection, showed increased activity for anodal isoform of SOD and increased expression and/or induction of either POX 1 or POX 2 isoforms of GPX. In susceptible genotype, expression of the above isoforms was faint for SOD and nearly absent for GPX under both blight free and induced blight conditions. Induction and/or increased activity of particular isoform of SOD and GPX against infection of Phytophthora colocasiae in the resistant genotypes studied led to the apparent conclusion of linkage of isozyme expression with blight resistance in taro. This might be an important criterion in breeding of taro for Phytophthora leaf blight resistance.     

The apoplastic antioxidant system in Prunus: response to long-term plum pox virus infection

This work describes, for the first time, the changes taking place in the antioxidative system of the leaf apoplast in response to plum pox virus (PPV) in different Prunus species showing different susceptibilities to PPV. The presence of p-hydroxymercuribenzoic acid (pHMB)-sensitive ascorbate peroxidase (APX) (class I APX) and pHMB-insensitive APX (class III APX), superoxide dismutase (SOD), peroxidase (POX), NADH-POX, and polyphenoloxidase (PPO) was described in the apoplast from both peach and apricot leaves. PPV infection produced different changes in the antioxidant system of the leaf apoplast from the Prunus species, depending on their susceptibility to the virus. In leaves of the very susceptible peach cultivar GF305, PPV brought about an increase in class I APX, POX, NADH-POX, and PPO activities. In the susceptible apricot cultivar Real Fino, PPV infection produced a decrease in apoplastic POX and SOD activities, whereas a strong increase in PPO was observed. However, in the resistant apricot cultivar Stark Early Orange, a rise in class I APX as well as a strong increase in POX and SOD activities was noticed in the apoplastic compartment. Long-term PPV infection produced an oxidative stress in the apoplastic space from apricot and peach plants, as observed by the increase in H2O2 contents in this compartment. However, this increase was much higher in the PPV-susceptible plants than in the resistant apricot cultivar. Only in the PPV-susceptible apricot and peach plants was the increase in apoplastic H2O2 levels accompanied by an increase in electrolyte leakage. No changes in the electrolyte leakage were observed in the PPV-inoculated resistant apricot leaves, although a 42% increase in the apoplastic H2O2 levels was produced. Two-dimensional electrophoresis analyses revealed that the majority of the polypeptides in the apoplastic fluid had isoelectric points in the range of pI 4-6. The identification of proteins using MALDI-TOF (matrix-assisted laser desorption/ionization-time of flight) and peptide mass fingerprinting analyses showed the induction of a thaumatin-like protein as well as the decrease of mandelonitrile lyase in peach apoplast due to PPV infection. However, most of the selected polypeptides showed no homology with known proteins. This fact emphasizes that, at least in Prunus, most of the functions of the apoplastic space remain unknown. It is concluded that long-term PPV infection produced an oxidative stress in the leaf apoplast, contributing to the deleterious effects produced by PPV infection in leaves of inoculated, susceptible Prunus plants.     

Putrescine modulates antioxidant defense response in wheat under high temperature stress

Effects of putrescine (Put) on responses of wheat (Triticum aestivum) seedlings or detached tillers at mid-milky stage to high temperature (HT) stress were investigated. The heat tolerant cv. PBW 343 exhibited higher content of antioxidants and activities of antioxidative enzymes, while lower content of lipid peroxides as compared to the heat-sensitive cv. HD 2329. HT elevated peroxidase (POX) and superoxide dismutase (SOD) activities, while diamine oxidase (DAO) and polyamine oxidase (PAO) activities were reduced in roots, shoots and developing grains. Application of Put under HT further enhanced POX and SOD activities along with increased content of ascorbate and tocophereol in grains. Invariably POX and SOD revealed higher activities in roots while CAT, DAO and PAO activities were higher in shoots. The content of lipid peroxides was increased in roots and shoots of HT stressed seedlings but less in Put-treated cv. PBW 343.     

First record of Fusarium vascular wilt on grapevine in Egypt

During the summer season of 2003 and 2004, wilt syndromes of grapevine leaves (Cv. crimson) and vascular discolouration of roots have been observed in 2-year-old grapevine plants in the field at two sides in Gharbeia Governorate, Egypt. First, symptoms of wilt began on bottom leaves borderline as chlorosis and then these turned to necrotic spots and the leaves died. Wilt symptoms were spread to apical associated with vascular discolouration of roots and stem basal. Routine isolations of discoloured root tissue from diseased plant yielded eight isolates of Fusarium oxysporum Schlechtend only where no other fungi were developed. Microscopic examination revealed the presence of three shapes of microconidia, first is avoid shape non-septate measuring 2.5–3.0 μm × 6–10 μm, second is cylindrical with one septa measuring 2.6 μm × 17.0 μm and third shape also cylindrical with two septate measuring 3.0 μm × 20.0 μm. Macroconidia was rarely with three septate measuring 3.5– 4.0 μm × 35.0–38.0 μm, and chlamydospores were found singly or in pairs or chains. F. oxysporum isolates attacked grapevine plants (Cv. crimson) causing vascular wilt (66.7%) and root-rot syndrome (33.3%). In vitro isolates of F. oxysporum causing wilt of grapevine (Cv. crimson) varied for producing lytic enzymes, i.e. polygalacturonase (PG) and cellulase. The reactions of several grapevines (Cvs.) with a virulent isolate of F. oxysporum indicated the presence of two different symptoms, i.e. vascular wilt only on grapevine plants (Cv. crimson) and root-rot on the other grapevine (Cvs.), i.e. superior, Thompson, King robi and flame seedless. All F. oxysporum isolates caused vascular wilt of grapevine Cv. crimson, successfully reisolated from symptomatic vascular infected tissue and complete identification on the basis of colony, conidia morphology and host range at formae speciales level as F. oxysporum f. sp. herbemontis (Tochetto) Gordan. This is the first report of Fusarium wilt on grapevine in Egypt.     

Induction of total phenolics and defence-related enzymes during β-aminobutyric acid-induced resistance in Brassica carinata against Alternaria blight

Exogenous foliar application of β-aminobutyric acid (BABA) led to a significant reduction in disease severity in Brassica carinata caused by Alternaria brassicae. To get a better insight about changes in defence-related enzymes like phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO), isoform analysis of superoxide dismutase (SOD) and peroxidase (POX) were studied. BABA-treated plants showed a significant increase in PAL, PPO enzyme activities and total phenolic content in response to pathogen inoculation. However, isoform analysis of SOD and POX revealed no change in isoform number but a quantitative change in activity was observed in response to pathogen.