Effect of chilling on antioxidant enzymes and DPPH-radical scavenging activity of high- and low-vigour cucumber seedling radicles

The chilling tolerance of cucumber seedling radicles was influenced by their relative levels of vigour. Radicles of high‐vigour seedlings grew to 20 mm in length in 36 h at 25 °C, whereas it took 60 h for low‐vigour seedling radicles to reach that length. Chilling at 2·5 °C for 48 h inhibited the subsequent growth of high‐ and low‐vigour seedlings by 39 and 68%, respectively. The 2,3,5‐triphenyltetrazolium chloride (TTC) viability index, and α,α‐diphenyl‐β‐picrylhydrazyl (DPPH)‐radical scavenging activity were higher in high than low‐vigour radicles. Higher ascorbate peroxidase (APX) and catalase (CAT) enzyme activity, DPPH‐radical scavenging activity, and recovery of CAT activity after chilling in high‐vigour radicles corresponded with their higher level of chilling tolerance in comparison with low‐vigour radicles. In contrast, elevated levels of superoxide dismutase, glutathione reductase and guaiacol peroxidase appear to be correlated with chilling injury since they only showed substantial increases in activity in the more chilling‐­sensitive low‐vigour radicles after chilling. Manipulation of APX, CAT, and/or DPPH activity could produce plants with superior and persistent chilling tolerance.     

Activity of enzymatic antioxidant defense systems in chilled and heat shocked cucumber seedling radicles

Chilling whole cucumber seedlings that had 10‐mm long radicles for 4 days at 2.5°C significantly inhibited subsequent radicle growth both by increasing the time it took the seedlings to recover from chilling and attain a linear rate of radicle growth, and by decreasing the subsequent rate of linear growth. Exposing cucumber seedlings to 45°C for up to 20 min had no effect on subsequent radicle growth, while longer exposures produced reductions in growth. A heat shock at 45°C for 10 min induced the optimal protection to 4 days of chilling at 2.5°C by reducing chilling inhibition from 60 to 42%. Two hours after being chilled, heat shocked or heat shocked and then chilled, there was no difference in protein content of the apical 1 cm of the seedling radicle among these treatments and the non‐heat shocked, non‐chilled control. Two days after treatment, the protein content was still similar in tissue that had been heat shocked or heat shocked and chilled, while it was significantly reduced in tissue that had been chilled. In general, 2 h after treatment, the activity of the 5 antioxidant enzymes examined in this study [superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), guaiacol peroxidase (GPX; EC 1.11.1.7) and glutathione reductase (GR; EC 1.6.4.2)] were reduced by chilling and unaffected or increased by heat shock. When heat shock was followed by chilling, there was a consistent effect of the heat shock treatment on preventing the loss of enzyme activity following chilling. This protective effect of the heat shock treatment was even more pronounced after 2 days of recovery at 25°C for SOD, CAT and APX. In contrast, the activity of GR and GPX was substantially higher in chilled tissue than in tissue that had been heat shocked before being chilled. Elevated levels of GR and GPX therefore appear to be correlated with the development of chilling injury, while elevated levels of SOD, CAT and APX appear to be correlated with the development of heat shock‐induced chilling tolerance.     

Postharvest chilling induces oxidative stress response in the dwarf tomato cultivar Micro-Tom

Oxidative stress is involved in the response of Lycopersicon esculentum fruits (cultivar Micro-Tom) to chilling. Changes in activated oxygen scavenging enzymes, superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2) were examined during ripening after postharvest chilling. Also, lipid peroxidation, respiration, and pigment contents were determined. These parameters were affected by chilling, especially the lycopene content and the respiration rate that showed a high value when the fruits were transferred to higher temperatures. CAT activity increased the day after the fruits were re-warmed, while the activity of GR was higher in the chilled than in the non-chilled green fruits. Lipid peroxidation was more evident at the 'pre-chilled' yellow and red fruits. APX and SOD were not affected by previous chilling in ripening fruits. These results indicate that oxidative stress is generated by conservation at 4°C. The antioxidant response of tomato fruit could be mediated by CAT and GR but not by SOD or APX. Moreover, CAT seemed to respond to the increase in the respiration rate.     

Chilling tolerance of cucumber (Cucumis sativus) seedling radicles is affected by radicle length, seedling vigor, and induced osmotic- and heat-shock proteins

Cucumber seedling radicles decrease in chilling tolerance as they increase in length or decrease in vigor. The protein content of the apical 5 mm of the radicle decreased with decreases in chilling tolerance ( R ² = 0.92). This general reduction in protein content was reflected in a decrease of six dehydrin-like proteins with apparent molecular weights of 13.0, 15.0, 16.8, 23.0, 26.8, and 33.5 kDa. The disappearance of naturally occurring dehydrin-like proteins in cucumber seedling radicles as they elongate or lose vigor was correlated with a loss of chilling tolerance. Exposure to an osmotic (0.6 M mannitol) or heat (2 min at 45°C) stress enhanced chilling tolerance. The osmotic-shock treatment induced both chilling tolerance and the appearance or strengthening of dehydrin-like proteins previously present in radicles. The heat-shock treatment also induced high levels of chilling tolerance and protein(s) that reacted with a 23 and 70 kDa antibody. However, these heat-shock protein (HSPs) did not cross react with the probe for dehydrin-like proteins. When organized into high, medium, and low chilling tolerance groups, radicle that were chilling tolerant contained either the 13.0 and 16.8 kDa dehydrin-like proteins, or the 15.0 and 23.0 kDa dehydrin-like proteins, or the 23 or 70 kDa HSP.     

Differential chilling sensitivity in cucumber (Cucumis sativus) seedlings

Cucumber ( Cucumis sativus L. cv. Poinsett 76) seeds were chilled at 2.5°C in a study of the chilling sensitivity and recovery of radicle tissue. The effect of chilling on radicle growth and the production of carbon dioxide and ethylene was measured. Chilling sensitivity of radicles increased as they grew from 1 to 7 mm in length. The length, not the age of the radicles, determined the level of chilling sensitivity. Apical tissue was most sensitive to chilling and slowest to recover from chilling, followed by subapical and basal tissue. Our data demonstrate that the chilling sensitivity of young seedling radicles differs along their length and that the rapid chilling-induced inhibition of elongation is probably due to an inability of meristematic cells to remain viable and active when chilled.     

Effect of heat shock on the chilling sensitivity of trichomes and petioles of African violet (Saintpaulia ionantha)

Chilling at 6°C caused an immediate cessation of protoplasmic streaming in trichomes from African violets ( Saintpaulia ionantha ), and a slower aggregation of chloroplasts in the cells. Streaming slowly recovered upon warming to 20°C, reaching fairly stable rates after 4, 15, 25 and 35 min for tissue chilled for 2 min and for 2, 14 and 24 h, respectively. The rate of ion leakage from excised petioles into an isotonic 0.2  M mannitol solution increased after 12 h of chilling and reached a maximum after 3 days of chilling. A heat shock at 45°C for 6 min reduced chilling-induced rates of ion leakage from excised 1-cm petiole segments by over 50%, namely to levels near that from non-chilled control tissue. Heat-shock treatments themselves had no effect on the rate of ion leakage from non-chilled petiole segments. Protoplasmic streaming was stopped by 1 min of heat shock at 45°C, but slowly recovered to normal levels after about 30 min Chloroplasts aggregation was prevented by a 1 or 2 min 45°C heat-shock treatment administered 1.5 h before chilling, but heat-shock treatments up to 6 min only slightly delayed the reduction in protoplasmic streaming caused by chilling. Tradescantia virginiana did not exhibit symptoms associated with chilling injury in sensitive species (i.e. cessation of protoplasmic streaming in stamen hairs and increased ion leakage from leaf tissue).     

Combined action of antioxidant defense system and osmolytes in chilling shock-induced chilling tolerance in Jatropha curcas seedlings

Low non-freezing temperature is one of the major environmental factors affecting growth, development and geographical distribution of chilling-sensitive plants, Jatropha curcas is considered as a sustainable energy plants with great potential for biodiesel production. In this study, chilling shock at 5 °C followed by recovery at 26 °C for 4 h significantly improved survival percentage of J. curcas seedlings under chilling stress at 1 °C. In addition, chilling shock could obviously enhance the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR), and the levels of antioxidants ascorbic acid (AsA) and glutathione (GSH), as well as the contents of osmolytes proline and betaine in leaves of seedlings of J. curcas compared with the control without chilling shock. During the process of recovery, GR activity, AsA, GSH, proline and betaine contents sequentially increased, whereas SOD, APX and CAT activities gradually decreased, but they markedly maintained higher activities than those of control. Under chilling stress, activities of SOD, APX, CAT, GR and GPX, and contents of AsA, GSH, proline and betaine, as well as the ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)] in the shocked and non-shock seedlings all dropped, but shocked seedlings sustained significantly higher antioxidant enzyme activity, antioxidant and osmolyte contents, as well as ratio of reduced antioxidants to total antioxidants from beginning to end compared with control. These results indicated that the chilling shock followed by recovery could improve chilling tolerance of seedlings in J. curcas, and antioxidant enzymes and osmolytes play important role in the acquisition of chilling tolerance.     

植物谷胱甘肽过氧化物酶研究进展

氧化胁迫可诱导植物多种防御酶的产生, 其中包括超氧化物歧化酶(SOD, EC1.15.1.1)、抗坏血酸过氧化物酶(APX, EC1.11.1.11)、过氧化氢酶(CAT, E.C.1.11.1.6 )和谷胱甘肽过氧化物酶(GPXs,EC1.11.1.9)。它们在清除活性氧过程中起着不同的作用。GPXs是动物体内清除氧自由基的主要酶类,但它在植物中的功能报道甚少。最近几年研究表明, 植物体内也存在类似于哺乳动物的GPXs家族, 并对其功能研究已初见端倪。本文综述了有关GPXs的结构以及植物GPXs功能的研究进展。     

Abscisic acid-regulated responses of aba2-1 under osmotic stress: the abscisic acid-inducible antioxidant defence system and reactive oxygen species production

We investigated the interaction among abscisic acid (ABA), reactive oxygen species (ROS) and antioxidant defence system in the transduction of osmotic stress signalling using Arabidopsis thaliana WT (Columbia ecotype, WT) and an ABA-deficient mutant (aba2-1). For this, 50 μm ABA and osmotic stress, induced with 40% (w/v) polyethylene glycol (PEG8000; -0.7 MPa), were applied to WT and aba2-1 for 6, 12 or 24 h. Time course analysis was undertaken for determination of total/isoenzyme activity of the antioxidant enzymes, superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), NADPH oxidase (NOX; EC 1.6.3.1) activity; scavenging activity of the hydroxyl radical (OH˙), hydrogen peroxide (H(2) O(2) ); endogenous ABA and malondialdehyde (MDA). The highest H(2) O(2) and MDA content was found in PEG-treated groups of both genotypes, but with more in aba2-1. ABA treatment under stress reduced the accumulation of H(2) O(2) and MDA, while it promoted activity of SOD, CAT and APX. APX activity was higher than CAT activity in ABA-treated WT and aba2-1, indicating a protective role of APX rather than CAT during osmotic stress-induced oxidative damage. Treatment with ABA also significantly induced increased NOX activity. Oxidative damage was lower in ABA-treated seedlings of both genotypes, which was associated with greater activity of SOD (Mn-SOD1 and 2 and Fe-SOD isoenzymes), CAT and APX in these seedlings after 24 h of stress. These results suggest that osmotic stress effects were overcome by ABA treatment because of increased SOD, CAT, APX and NOX.     

Exogenous H<Subscript>2</Subscript>O<Subscript>2</Subscript> improves the chilling tolerance of manilagrass and mascarenegrass by activating the antioxidative system

The effect of foliar pretreatment by hydrogen peroxide (H₂O₂) at low concentrations of 0, 5, 10, and 15 mM on the chilling tolerance of two Zoysia cultivars, manilagrass (Zoysia matrella) and mascarenegrass (Zoysia tenuifolia), was studied. The optimal concentration for H₂O₂ pretreatment was 10 mM, as demonstrated by the lowest malondialdehyde (MDA) content and electrolyte leakage (EL) levels and higher protein content under chilling stress (7°C/2°C, day/night). Prior to initiation of chilling, exogenous 10 mM H₂O₂ significantly increased catalase (CAT), ascorbate peroxidase (APX), glutathione-dependent peroxidases (GPX), and glutathione-S-transferase (GST) activities in manilagrass, and guaiacol peroxidase (POD), APX, and glutathione reductase (GR) activities in mascarenegrass, suggesting that H₂O₂ may act as a signaling molecule, inducing protective metabolic responses against further oxidative damage due to chilling. Under further stress, optimal pretreatments alleviated the increase of H₂O₂ level and the decrease of turfgrass quality, and improved CAT, POD, APX, GR, and GPX activities, with especially significant enhancement of APX and GPX activities from the initiation to end of chilling. These antioxidative enzymes were likely the important factors for acquisition of tolerance to chilling stress in the two Zoysia cultivars. Our results showed that pretreatment with H₂O₂ at appropriate concentration may improve the tolerance of warm-season Zoysia grasses to chilling stress, and that manilagrass had better tolerance to chilling, as evaluated by lower MDA and EL, and better turfgrass quality, regardless of the pretreatment applied.     

Changes of polyamines and ethylene in cucumber seedlings in response to chilling stress

Cucumber ( Cucumis sativus L. cv. Victory) seedlings were exposed to chilling at 5°C and endogenous levels of polyamines and 1-aminocyclopropane-1-carboxylic acid (ACC) were measured after chilling and after warming at 20°C. The level of spermidine was higher in the chilled seedlings than in the non-chilled seedlings. Treatment with a plant bioregulator, (2RS,3RS)-1-(4-cholorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol), reduced the chilling injury and the levels of spermidine in the chilled seedlings. The levels of ACC and production of ethylene showed sharp increases after warming following exposure to chilling. These increases were suppressed by the application of aminooxyacetic acid (AOA). However, AOA treatment did not reduce chilling injury or affect the levels of polyamines in the tissue. These data indicate that the increase in ACC and ethylene is a response of the tissue to the chilling exposure and is not a cause of the injury. The data also suggest that the syntheses of polyamines and ethylene are not competitive with each other even under chilling stress conditions.     

植物谷胱甘肽过氧化物酶研究进展

氧化胁迫可诱导植物多种防御酶的产生,其中包括超氧化物歧化酶(SOD,EC1.15.L1)、抗坏血酸过氧化物酶(APX,EC1.11.1.11)、过氧化氢酶(CAT,E.C.1.11.1.6)和谷胱甘肽过氧化物酶(GPXs,EC1.11.1.9).它们在清除活性氧过程中起着不同的作用.GPXs是动物体内清除氧自由基的主要酶类,但它在植物中的功能报道甚少.最近几年研究表明,植物体内也存在类似于哺乳动物的GPXs家族,并对其功能研究已初见端倪.本文综述了有关GPXs的结构以及植物GPXs功能的研究进展.     

Spread of oxidative damage and antioxidative response through cell layers of tobacco callus after UV-C treatment.

Tobacco (Nicotiana tabacum L. cv. Petit Havana) callus cultures were exposed to UV-C high dose pulse-treatment (254 nm, 50 kJ m(-2), 1 h-treatment). After 6, 24 and 48 h from the end of the treatment, calli were cut transversally in two layers and oxidative damage (malondialdehyde [MDA] and hydrogen peroxide), non-enzymatic (radical scavenging antioxidants [RSA] and polyamines) and enzymatic antioxidants (ascorbate peroxidase [APX, EC 1.11.1.11], glutathione reductase [GR, EC 1.6.4.2], catalase [CAT, EC 1.11.1.6] and guaiacol peroxidase [GPX, EC 1.11.1.7]) were evaluated. At each time-point data referred to UV-C treated calli were compared to data of untreated ones (control). Despite of a strong increase of H2O2 content, a slight cellular damage was observed in both upper and lower layers 24 and 48 h after UV-C treatment. An activation first of non-enzymatic antioxidants and then of enzymatic antioxidants was detected in UV-C treated calli. In particular, RSA and putrescine (PUT) accumulated 6 h after UV-C treatment while APX, GR and GPX enzyme activities increased 24 h after UV-C irradiation. Catalase activity did not change. UV-C-induced oxidative stress and antioxidative response were observed also in cell layers not directly exposed to UV irradiation, indicating that a stress signal was transmitted to the whole mass of callus.     

Does grafting provide tomato plants an advantage against H2O2 production under conditions of thermal shock?

Non-grafted tomato plants ( Lycopersicon esculentum L. cv. Tmknvf₂) and grafted tomato plants ( L. esculentum L. cv. Tmknvf₂ ×  L. esculentum L. cv. RX-335) were grown for 30 days at three different temperatures (10°C, 25°C and 35°C). In the leaves of these plants, the enzymatic activities of SOD, GPX, CAT, APX, DHAR and GR were analysed, as were the concentrations of total H₂O₂, ascorbate and glutathione as well as foliar DW. Regardless of whether the plant was grafted or not, our results indicate that the thermal stress occurred mainly at 35°C, with the following effects: (1) high SOD activity; (2) H₂O₂ accumulation; (3) foliar-biomass reduction; (4) low GPX, CAT, APX, DHAR and GR activities; and (5) high concentrations of ascorbate and glutathione. In addition, our data show these effects to be much weaker in grafted than in non-grafted plants, directly reflected in greater biomass production. Therefore, the use of grafted plants under excessively high temperatures may offer an advantage over non-grafted plants in terms of resistance against thermal shock.     

The relations between antioxidant enzymes and chlorophyll fluorescence parameters in common bean cultivars differing in sensitivity to drought stress

Effects of the antioxidant system and chlorophyll fluorescence on drought tolerance of four common bean (Phaseolus vulgaris L.) cultivars were studied. The cultivars were positioned in the order of a decrease in their drought tolerance: Yakutiye, Pinto Villa, Ozayse, and Zulbiye on the basis of changes in the water potential, stomatal conductance, photosynthetic pigment content, and lipid peroxidation. Under drought conditions, the level of H₂O₂ was not changed in cv. Pinto Villa but decreased in other cultivars. Antioxidant enzymes (superothide dismutase (SOD), guaiacol peroxidase (GPX), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR)) were generally activated in all cultivars. Interestingly, CAT, APX, and GR activities were not changed in cv. Pinto Villa, APX activity decreased in cv. Yakutiye, and CAT activity was not changed in cv. Zulbiye. The increases in SOD and GPX activities in cv. Ozayse were higher than in other cultivars. Drought stress reduced the effective quantum yield of PS2 (Φ_PS2) and the photochemical quenching (q_p), while it increased nonphotochemical quenching (NPQ) in all cultivars. The reduction or increase was more pronounced in cv. Zulbiye. There were generally significant correlations between q_p, NPQ, and ROS scavenging by SOD and APX. Also, there were significant correlations between SOD and q_p in tolerant cultivars and APX and q_p in sensitive ones. The results indicate that activation of SOD and APX was closely related to the efficiency of PS2 in common bean cultivars. This interaction was essential for protection of photosystems and plant survival under drought.     

Chilling tolerance of maize,cucumber and rice seedling leaves and roots are differentially affected by salicylic acid

Salicylic acid (SA) is one component of a complex signalling pathway that is induced by a number of biotic and abiotic stresses. Exposing seedling radicles to aqueous solutions of 0.5 m M salicylic acid for 24 h before chilling at 2.5°C for 1–4 days reduced the chilling-induced increase in electrolyte leakage from maize and rice leaves, and cucumber hypocotyls, but not from their radicles. The SA treatments that induced chilling tolerance in the aerial portion of the seedlings did not induce chilling tolerance in the radicles, even though the SA treatments were applied to the radicles. A comparison of activity among five antioxidant enzymes showed that SA did not alter enzyme activities in the radicles, but that chilling tolerance induced by SA in the aerial portions of maize and cucumber plants was associated with an increase in the activity of glutathione reductase and guaiacol peroxidase.     

Effect of acetaldehyde, arsenite, ethanol, and heat shock on protein synthesis and chilling sensitivity of cucumber radicles

Exposure to a chilling temperature of 2.5°C for 96 h inhibited the subsequent growth of cucumber seedling radicles at 25°C by 92%. Exposing seedling with 5 ± 1 mm long radicles to acetaldehyde vapour (275 µl l⁻¹) or to an aqueous ethanol solution (0.6  M ) for 2 h, or to 45°C for 10 min before chilling, increased chilling tolerance so that the chilling treatment reduced growth by only 47, 39 or 36%, respectively. All of these effective treatments induced the synthesis of a number of proteins, and suppressed de novo protein synthesis (i.e. the incorporation of [³⁵S]-methionine) by about 70%. In contrast, treatment for 2 h with an aqueous arsenite solution (100 µ M ) had no effect on chilling sensitivity or the incorporation of [³⁵S]-methionine, yet it induced the synthesis of a complement of proteins that were similar to that induced by the effective heat-shock treatment. A unique protein or set of proteins may be responsible for heat-shock-induced chilling tolerance, but none was detected. The ability of various abiotic stresses to suppress protein synthesis may be more important in increasing tolerance to chilling injury than their ability to induce the synthesis of specific proteins.     

克隆整合提高淹水胁迫下狗牙根根部的活性氧清除能力

虽然国内外已开展大量关于克隆整合影响植物抗逆生理的研究,但迄今未见克隆整合是否会影响逆境下不同分株清除活性氧过程的报道。以河岸带适生克隆植物狗牙根(Cynodon dactylon)为例,研究克隆植物的抗氧化生理响应,检测了狗牙根在先端淹水/不淹水、先端与基端匍匐茎连接/切断两个因素的交互作用下的根部主要抗氧化酶:超氧化岐化酶(Superoxide dismutase, SOD)、抗坏血酸过氧化物酶(Ascorbate peroxidase, APX)、过氧化氢酶(Catalase, CAT)的活力以及生物量的变化。结果显示,淹水环境中狗牙根先端的生物量和根部SOD酶活力在匍匐茎连接处理下显著高于切断处理组,同一处理的生物量以及根部APX、CAT酶活力总体上表现出不同程度的提高趋势;与受淹先端连接的基端分株根部抗氧化酶活力均低于切断处理组,且SOD和CAT受连接处理影响显著;淹水和切断处理显著降低先端分株的生物量,但对基端和克隆片段影响不明显。这表明淹水胁迫下克隆整合提高了其根部活性氧清除能力,显著改善了先端分株的表现。     

Changes of antioxidants and GSH-associated enzymes in isoproturon-treated maize

The recommended field dose (RFD) of isoproturon induced significant accumulations of H₂O₂ in the leaves of 10-d-old maize seedlings throughout the following 20 d; the accumulation increased with time and also with herbicide dose. Meanwhile, low doses significantly increased ascorbic acid, glutathione and thiols while high doses caused diminutions. Superoxide dismutase (SOD; EC 1.15.1.1) activity was significantly enhanced up to the 12th d whereas ascorbate peroxidase (APX; EC 1.11.1.7) activity was significantly reduced after the fourth d onwards. Catalase (CAT; EC 1.11.1.6) and guaiacol peroxidase (GPX; EC 1.11.1.7) activities were similarly increased during the first 4 d but decreased from the 12th and the eighth d, respectively. Low doses increased SOD and GPX activities but high doses led to diminutions whereas CAT and APX were reduced by all doses. The activities of γ-glutamyl-cysteine synthethase (γ-GCS; EC 6.3.2.2) and glutathione synthethase (GSS; EC 6.3.2.3) were enhanced for 4 d; high doses caused general reductions. Isoproturon significantly reduced activities of glutathione S-transferase (GST; EC 2.5.1.18) isoforms [GST_(CDNB), GST_(ALA), or GST_(MET)] after the fourth d, however, it had no effect on GST_(ATR). Similar reductions in activities of glutathione peroxidase (GSPX; EC 1.15.1.1) and glutathione reductase (GR; EC 1.6.4.2) were detected up to the 16th and the 12th d, respectively. The activities of GST isoforms, GSPX and GR were reduced by high doses. These changes seemed to be related and might point to an oxidative stress state that exacerbated with prolonged time and/or increased isoproturon dose.     

2-Benzoxazolinone (BOA) induced oxidative stress, lipid peroxidation and changes in some antioxidant enzyme activities in mung bean (Phaseolus aureus)

2-Benzoxazolinone (BOA), a well-known allelochemical with strong phytotoxicity, is a potential herbicidal candidate. The aim of the present study was to determine whether phytotoxicity of BOA is due to induction of oxidative stress caused by generation of reactive oxygen species (ROS) and the changes in levels of antioxidant enzymes induced in response to BOA. Effect of BOA was studied on electrolyte leakage, lipid peroxidation (LP), hydrogen peroxide (H(2)O(2)) generation, proline (PRO) accumulation, and activities of antioxidant enzymes-superoxide dismutase (SOD, 1.15.1.1), ascorbate peroxidase (APX, 1.11.1.11), guaiacol peroxidase (GPX, 1.11.1.7), catalase (CAT, 1.11.1.6) and glutathione reductase (GR, 1.6.4.2) in Phaseolus aureus (mung bean). BOA significantly enhanced malondialdehyde (MDA) content, a product of LP, in both leaves and roots of mung bean. The amount of H(2)O(2), a product of oxidative stress, and endogenous PRO increased many-fold in response to BOA. Accumulation of PRO, MDA and H(2)O(2) indicates the cellular damage in the target tissue caused by ROS generated by BOA. In response to BOA, there was a significant increase in the activities of scavenging enzymes SOD, APX, GPX, CAT, and GR in root and leaf tissue of mung bean. At 5 mM BOA, GR activity in roots showed a nearly 22-fold increase over that in control. The present study concludes that BOA induces oxidative stress in mung bean through generation of ROS and upregulation of activities of various scavenging enzymes.