Stress stimulus induced resistance to Cladosporium cucumerinum in cucumber seeding

Up to date, the studies of plant induced resistance have become the focus in plant pathology and physiology. During the course of pathogens penetrating the plant cell, besides of chemical secretion, the pathogens may generate mechanical signal caused by the physical pressure on the plant cell. In the non-host resistance, both the chemical signal and the mechanical stress signal are considered to have contribution to the entire defense reaction acted by the plant. The penetration of pathogen Cladosporium cucumerinum to cucumber is thought to be one of the model in research of plant induced resistance. In the current study, as a mechanical signal elicitor, the appropriate stress stimulus was proved to effectually induce the resistance of cucumber seedling to C. cucumerinum. After the treatment of the stress stimulus on leaves, the activities of resistance-related enzymes were significantly increased, such as phenylanine ammonia lyase (PAL), peroxidase (POD). Also, we found that stress stimulation may cause synthesis of lignin, which acts as the physical barrier to defense the pathogens. The results suggest that stress stimulation may not only enhance ability of the plant cell resistance to pathogen penetration but also elicit the accumulation of pathogens suppression or antimicrobial chemical substance in the plant cell.     

Non-thermal Plasma Induced Expression of Heat Shock Factor A4A and Improved Wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) Growth and Resistance Against Salt Stress

There is a huge interest in making and applying innovating functional devices based on basic sciences (like physics) to improve plant growth and resistance against various stress conditions. This research was carried out in order to investigate effects of cold plasma on expressions of heat shock factor A4A (HSFA4A), plant growth and post reactions to salt stress. Wheat seedlings were treated with plasma (0.84 W/cm² surface power densities) at different exposure times. In both three and 6 h after plasma, inductions in expressions of HSFA4A were recorded in roots, compared to control. Six hours after treatments, plasma-induced the shoot expressions of HSFA4A in the treated seedlings, contrasted to 3 h. Plasma treatment caused not the only enhancement in shoot fresh and dry mass and total leaf area, but also alleviated adverse impacts of salinity. Destroying impacts of salinity on chlorophyll contents were mitigated by plasma. Peroxidase activity was decreased by 27% for salinity treatment alone over control, while it was increased by 15% for plasma and salinity-treated samples, compared to salinity control. The highest activities of phenylalanine ammonia lyase (PAL) were found in plasma treatment alone. PAL activity was found to be higher in plasma-pretreated seedlings counteracted to salt stress, relative to the salinity control. The plasma treatment may act as an effective elicitor to modify gene expression, thereby improving plant growth and resistance. Plasma technology should be considered as a new functional technology in plant sciences.     

过量Fe2+对水稻的毒害效应

通过5个Fe2 水平的营养液培养试验,研究过量Fe2 对水稻的毒害效应以及水稻抗铁毒机理。结果表明,过量Fe2 胁迫显著抑制水稻生长,低质量浓度Fe2 (50、150 mg/L)胁迫,地上部受害程度远高于根系;高质量浓度Fe2 胁迫(2503、50 mg/L),根系受害程度大于地上部;随Fe2 质量浓度增加,水稻根系和地上部的Fe含量显著升高,根系的增长幅度远高于地上部,表明根系的Fe吸收性强于地上部,能阻止过量Fe进一步向地上部迁移,为地上部Fe的过量吸收提供良好的屏障;系列Fe2 质量浓度处理后,水稻的POD活性呈先升后降的趋势,说明一定范围内的过量Fe2 会诱导保护酶活性,对水稻抗铁毒发挥一定的作用。     

Protective Effect of Hydroxytyrosol Against Oxidative Stress Mediated by Arsenic-Induced Neurotoxicity in Rats

The present study reports beneficial effect of hydroxytyrosol (HT) against arsenic (As)-induced oxidative stress in the rat brain. Rats were orally administered with sodium arsenite dissolved in distilled water (25 ppm, by oral gavage) for 8 weeks or HT (10 mg/kg b. wt.) in combination with As. Results showed increase in protein oxidation and lipid peroxidation, while catalase and superoxide dismutase (SOD) activities as well as GSH content were decreased after As exposure in rat brain. Fourier transform infrared analysis showed significant alteration in peak area values that also validated the oxidative damage to lipids and proteins. In addition, As exposure caused increase in protein expression of caspase-3 and Bax, while Bcl-2 expression was downregulated resulting in translocation of cytochrome c from mitochondria to cytosol. Treatment of HT with As reversed protein oxidation, lipid peroxidation, and increased GSH content as well as catalase and SOD activities. Administration of HT also prevented translocation of cytochrome c from mitochondria and increased mitochondria/cytosol ratio of cytochrome c. Hence, treatment of HT with As improved antioxidant system and efficiently lowered the generation of oxidative stress in rat brain.     

Production of Plant Beneficial and Antioxidants Metabolites by Klebsiella variicola under Salinity Stress

Bacteria that surround plant roots and exert beneficial effects on plant growth are known as plant growth-promoting rhizobacteria (PGPR). In addition to the plant growth-promotion, PGPR also imparts resistance against salinity and oxidative stress and needs to be studied. Such PGPR can function as dynamic bioinoculants under salinity conditions. The present study reports the isolation of phytase positive multifarious Klebsiella variicola SURYA6 isolated from wheat rhizosphere in Kolhapur, India. The isolate produced various plant growth-promoting (PGP), salinity ameliorating, and antioxidant traits. It produced organic acid, yielded a higher phosphorous solubilization index (9.3), maximum phytase activity (376.67 ± 2.77 U/mL), and copious amounts of siderophore (79.0%). The isolate also produced salt ameliorating traits such as indole acetic acid (78.45 ± 1.9 µg/mL), 1 aminocyclopropane-1-carboxylate deaminase (0.991 M/mg/h), and exopolysaccharides (32.2 ± 1.2 g/L). In addition to these, the isolate also produced higher activities of antioxidant enzymes like superoxide dismutase (13.86 IU/mg protein), catalase (0.053 IU/mg protein), and glutathione oxidase (22.12 µg/mg protein) at various salt levels. The isolate exhibited optimum growth and maximum secretion of these metabolites during the log-phase growth. It exhibited sensitivity to a wide range of antibiotics and did not produce hemolysis on blood agar, indicative of its non-pathogenic nature. The potential of K. variicola to produce copious amounts of various PGP, salt ameliorating, and antioxidant metabolites make it a potential bioinoculant for salinity stress management.     

Neuroprotective Effect of Dioscin against Parkinson’s Disease via Adjusting Dual-Specificity Phosphatase 6 (DUSP6)-Mediated Oxidative Stress

Exploration of lead compounds against Parkinson’s disease (PD), a neurodegenerative disease, is of great important. Dioscin, a bioactive natural product, shows various pharmacological effects. However, the activities and mechanisms of dioscin against PD have not been well investigated. In this study, the tests on 6-hydroxydopamine (6-OHDA)-induced PC12 cells and rats were carried out. The results showed that dioscin dramatically improved cell viability, decreased reactive oxygen species (ROS) levels, improved motor behavior and tyrosine hydroxylase(TH) levels and restored the levels of glutathione (GSH) and malondialdehyde (MDA) in rats. Mechanism investigation showed that dioscin not only markedly increased the expression level of dual- specificity phosphatase 6 (DUSP6) by 1.87-fold in cells and 2.56-fold in rats, and decreased phospho-extracellular regulated protein kinases (p-ERK) level by 2.12-fold in cells and 2.34-fold in rats, but also increased the levels of nuclear factor erythroid2-related factor 2 (Nrf2), hemeoxygenase-1 (HO-1), superoxide dismutase (SOD) and decreased the levels of kelch-1ike ECH-associated protein l (Keap1) in vitro and in vivo. Furthermore, DUSP6 siRNA transfection experiment in PC12 cells validated the protective effects of dioscin against PD via regulating DUSP6 to adjust the Keap1/Nrf2 pathway. Our data supported that dioscin has protection against PD in regulating oxidative stress via DUSP6 signal, which should be considered as an efficient candidate for the treatment of PD in the future.     

Metal-based anti-diabetic drugs: advances and challenges

The current status and likely future directions of complexes of V(V/IV), Cr(III), Mo(VI), W(VI), Zn(II), Cu(II), and Mn(III) as potential oral drugs against type 2 diabetes are reviewed. We propose a unified model of extra- and intracellular mechanisms of anti-diabetic efficacies of V(V/IV), Mo(VI), W(VI), and Cr(III), centred on high-oxidation-state oxido/peroxido species that inhibit protein tyrosine phosphatases (PTPs) involved in insulin signalling. The postulated oxidative mechanism of anti-diabetic activity of Cr(III) via carcinogenic Cr(VI/V) (which adds to safety concerns) is consistent with recent clinical trials on Cr(III) picolinate, where activity was apparent only in patients with poorly controlled diabetes (high oxidative stress), and the correlation between the anti-diabetic activities and ease of oxidation of Cr(III) supplements and their metabolites in vivo. Zn(II) and Cu(II) anti-diabetics act via different mechanisms and are unlikely to be used as specific anti-diabetics due to their diverse and unpredictable biological activities. Hence, future research directions are likely to centre on enhancing the bioavailability and selectivity of V(V/IV), Mo(VI), or W(VI) drugs. The strategy of potentiating circulating insulin with metal ions has distinct therapeutic advantages over interventions that stimulate the release of more insulin, or use insulin mimetics, because of many adverse side-effects of increased levels of insulin, including increased risks of cancer and cardiovascular diseases.     

Functional analysis of polyphenol oxidases by antisense/sense technology

Polyphenol oxidases (PPOs) catalyze the oxidation of phenolics to quinones, the secondary reactions of which lead to oxidative browning and postharvest losses of many fruits and vegetables. PPOs are ubiquitous in angiosperms, are inducible by both biotic and abiotic stresses, and have been implicated in several physiological processes including plant defense against pathogens and insects, the Mehler reaction, photoreduction of molecular oxygen by PSI, regulation of plastidic oxygen levels, aurone biosynthesis and the phenylpropanoid pathway. Here we review experiments in which the roles of PPO in disease and insect resistance as well as in the Mehler reaction were investigated using transgenic tomato (Lycopersicon esculentum) plants with modified PPO expression levels (suppressed PPO and overexpressing PPO). These transgenic plants showed normal growth, development and reproduction under laboratory, growth chamber and greenhouse conditions. Antisense PPO expression dramatically increased susceptibility while PPO overexpression increased resistance of tomato plants to Pseudomonas syringae. Similarly, PPO-overexpressing transgenic plants showed an increase in resistance to various insects, including common cutworm (Spodoptera litura (F.)), cotton bollworm (Helicoverpa armigera (Hübner)) and beet army worm (Spodoptera exigua (Hübner)), whereas larvae feeding on plants with suppressed PPO activity had higher larval growth rates and consumed more foliage. Similar increases in weight gain, foliage consumption, and survival were also observed with Colorado potato beetles (Leptinotarsa decemlineata (Say)) feeding on antisense PPO transgenic tomatoes. The putative defensive mechanisms conferred by PPO and its interaction with other defense proteins are discussed. In addition, transgenic plants with suppressed PPO exhibited more favorable water relations and decreased photoinhibition compared to nontransformed controls and transgenic plants overexpressing PPO, suggesting that PPO may have a role in the development of plant water stress and potential for photoinhibition and photooxidative damage that may be unrelated to any effects on the Mehler reaction. These results substantiate the defensive role of PPO and suggest that manipulation of PPO activity in specific tissues has the potential to provide broad-spectrum resistance simultaneously to both disease and insect pests, however, effects of PPO on postharvest quality as well as water stress physiology should also be considered. In addition to the functional analysis of tomato PPO, the application of antisense/sense technology to decipher the functions of PPO in other plant species as well as for commercial uses are discussed.     

Lipoic Acid Combined with Melatonin Mitigates Oxidative Stress and Promotes Root Formation and Growth in Salt-Stressed Canola Seedlings (Brassica napus L.)

Lipoic acid (LA) and melatonin (MT) are pleiotropic molecules participating in plant stress resistance by modulating cellular biochemical changes, ion homeostasis, and antioxidant enzyme activities. However, the combined role of these two molecules in counteracting the detrimental impacts of salinity stress is still unknown. In the present study, we determined the effects of exogenous LA (0.5 µM), MT (1 µM) and their combination (LA + MT) on growth performance and biomass accumulation, photosynthetic pigments, enzymatic and non-enzymatic antioxidant activities, and ions homeostatic in canola (Brassica napus L.) seedlings under salinity stress (0, 100 mM) for 40 days. The results indicate that exogenous application of LA + MT improved the phenotypic growth (by 25 to 45%), root thickness (by 68%), number of later lateral roots (by 52%), root viability (by 44%), and root length (by 50%) under salinity stress. Moreover, total soluble protein, chlorophyll pigments, the concentration of superoxide dismutase (SOD), catalase peroxidase (CAT), and ascorbic peroxidase (ASA) increased with the presence of salt concentration into the growth media and then decreased with the addition of LA + MT to saline solution. Leaf protein contents and the degradation of photosynthetic pigments were lower when LA + MT treatments were added into NaCl media. The proline and phenol contents decreased in the exogenous application of LA + MT treatments more than individual LA or MT treatments under the salinity stress. The incorporation of LA or MT or a combination of LA + MT to saline solution decreased salinity-induced malondialdehyde and electrolyte leakage. In conclusion, the alteration of metabolic pathways, redox modulation, and ions homeostasis in plant tissues by the combined LA and MT application are helpful towards the adaptation of Brassica napus L. seedlings in a saline environment. The results of this study provide, for the first time, conclusive evidence about the protective role of exogenous LA + MT in canola seedlings under salinity stress.     

Effects of Vitamin E on the Activities of Protective Enzymes and Membrane Lipid Peroxidation in Leymus Chinensis under Drought Stress

Leymus chinensis seedlings were treated with 0.05--10 mmol/L vitamin E under osmotic stress in the presence of polyethylene glycol（PEG） as the stress reagent. The effects of the different concentrations of exogenous vitamin E on the activities of SOD, POD and free proline, and the MDA contents under drought stress were examined so as to ascertain the mechanism of Leymus chinensis resistance to drought stress and explore the possible preventive measures. The results indicate that the activities of SOD and POD decreased but the free proline and MDA contents increased as drought stress was accentuated, showing an enhancement of oxidative stress that may cause a decline in membrane stabilization. However, the activities of SOD and POD and the free proline content increased, whereas the MDA content reduced in Leymus chinensis pretreated with vitamin E in comparison with that of the control. This indicates that exogenous vitamin E enhanced the antioxidation of Leymus chinensis seedlings. It suggests that cytomembrane can be protected from damage by increasing the free proline content and the activities of SOD and POD that result in enhancing the drought resistance of Leymus chinensis seedlings.     

ADRIAMYCIN RESISTANCE IN CHINESE HAMSTER FIBROBLASTS FOLLOWING OXIDATIVE STRESS INDUCED BY PHOTODYNAMIC THERAPY

Photodynamic therapy (PDT) generates reactive oxygen species that are responsible for the initial cytotoxic events produced by this treatment. An extended (16 h) porphyrin incubation prior to light irradiation increased expression of the 75, 78 and 94 kDa glucose-regulated stress proteins (GRP), as well as the cognate form of the 70 kDa heat shock protein. However, these stress proteins were not induced following isoeffective PDT doses using a short (1 h) porphyrin incubation protocol. In the current study, Chinese hamster fibroblasts were used to examine sensitivity to adjunctive PDT and adriamycin as previous reports indicate a correlation between stress protein synthesis and a decrease in adriamycin cytotoxicity. Treatments that either induced GRP ( i.e . PDT with an extended porphyrin incubation or exposure to the calcium ionophore A23187) or did not induce GRP ( i.e . PDT with a short porphyrin incubation or UV irradiation) were followed at increasing time intervals with a 1 h adriamycin incubation. A time-dependent decrease in adriamycin cytotoxicity was observed when cells were first exposed to either of the PDT protocols or to A23187. Alterations in intracellular drug levels did not account for the change in adriamycin sensitivity. Likewise, intracellular glutathione concentrations and antioxidant enzyme activities were not significantly altered following PDT or A23187. Parameters associated with altered adriamycin sensitivity included a decrease in the percentage of S phase cells following PDT and A23187 as well as a depletion of intracellular ATP after PDT using the extended porphyrin incubation. These results demonstrate that PDT can be added to the growing list of diverse stresses producing transient resistance to adriamycin and that stress protein induction is not universally associated with all oxidative treatments inducing this resistance.     

Effect of sound wave stress on antioxidant enzyme activities and lipid peroxidation of Dendrobium candidum

The effect of sound wave stress on important medicinal plant, Dendrobium candidum Wall. ex Lindl, was investigated, including the responses on malondialdehyde (MDA) content, the activities change of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX). Results were found that the activities of SOD, CAT, POD and APX enhanced totally in different organs of D. candidum, as leaves, stems and roots, in response to the stress. Furthermore there happened similar shift of antioxidant enzymes activities, which increased in the initial stimulation and decreased afterwards. Data showed SOD, CAT, POD and APX activities ascended to max at day 9, 6, 9 and 12 in leaves, at day 9, 6, 12 and 9 in stems, and at day 12, 6, 9 and 9 in roots, respectively. As a lipid peroxidation parameter, MDA content in different organs increased in the beginning, dropped afterward, and increased again in the late. Anyway the total trend was the rise of MDA level compared to the control. It was interesting that the MDA content appeared the lowest levels almost when the antioxidant enzymes activities were up to the highest. Our results demonstrated the different organs of D. candidum might produce accumulation of active oxygen species (AOS) under initial treatment of sound wave stress. Later AOS might start to reduce due to the enhancement of antioxidant enzymes activities treated by the stress. The data revealed that the antioxidant metabolism was to be important in determining the ability of plants to survive in sound stress, and the up regulation of these enzymes activities would help to reduce the build up of AOS, which could protect plant cells from oxidative damage. Moreover, different cell compartments might activate different defensive system to reduce excessive amount of AOS. Finally the mechanism of this action was also discussed simply.     

1H and 13C NMR spectral assignments of chalcones bearing pyrazoline–carbothioamide groups

Chalcones are known to act on various physiological targets. As a result, structural modifications of chalcones have been studied extensively. Benzochalcones, in which the A‐ring of chalcone is substituted with a naphthalene unit, inhibits breast cancer resistance protein. Chalcones in which the α,β‐unsaturated carbonyl group is switched with a pyrazoline moiety are potent cytotoxic agents against various cancer cell lines, and chalcones with a pyrazoline‐1‐carbothioamide group instead of an α,β‐unsaturated carbonyl group exhibit antimicrobial activities. The present report describes hybrid molecules designed from benzochalcone and pyrazoline–carbothioamide. Methoxylation of plant‐derived polyphenols alters their hydrophobicity, resulting in changes in biological function and intracellular compartmentation. In the current study, 22 novel methoxylated 3‐(naphthalen‐2‐yl)‐N,5‐diphenyl‐pyrazoline‐1‐carbothioamide derivatives were prepared. This report provides complete assignments of their ¹H and ¹³C NMR data, which can be used to subsequently identify chalcones bearing pyrazoline–carbothioamide groups. Copyright © 2013 John Wiley & Sons, Ltd.     

酸雨胁迫下小麦微弱延迟发光及其生理、生态变化相关性研究

以小麦幼苗为对象，研究了在酸雨胁迫下小麦叶片延迟发光强度变化与小麦叶 片内生理物质，包括叶绿素a，叶绿素b，类胡萝卜素，丙二醛，CAT，POD，SOD含 量变化及小麦生态变化的相关性．实验结果说明，在酸雨胁迫下延迟发光强度与小 麦抗逆过程中CAT，POD，SOD，类胡萝卜素和丙二醛含量变化，具有明显的一致性 ．CAT，POD，SOD指示着小麦组织内活性氧自由基和过氧化氢含量的变化，类胡萝 卜素和丙二醛也反映出小麦组织内氧化性物质含量的变化．说明延迟发光强度与植 物体内活性氧含量及还原性物质含量具有明确的相关性．由于上述各种生理变化与 植物抗病、抗逆机制密切相关，因此可以利用延迟发光结合生态变化作为综合性反 映植物抗逆过程的指标．     

Biophysical,Biochemical, and Molecular Docking Investigations of Anti-Glycating,Antioxidant, and Protein Structural Stability Potential of Garlic

Garlic has been reported to inhibit protein glycation, a process that underlies several disease processes, including chronic complications of diabetes mellitus. Biophysical, biochemical, and molecular docking investigations were conducted to assess anti-glycating, antioxidant, and protein structural protection activities of garlic. Results from spectral (UV and fluorescence) and circular dichroism (CD) analysis helped ascertain protein conformation and secondary structure protection against glycation to a significant extent. Further, garlic showed heat-induced protein denaturation inhibition activity (52.17%). It also inhibited glycation, advanced glycation end products (AGEs) formation as well as lent human serum albumin (HSA) protein structural stability, as revealed by reduction in browning intensity (65.23%), decrease in protein aggregation index (67.77%), and overall reduction in cross amyloid structure formation (33.26%) compared with positive controls (100%). The significant antioxidant nature of garlic was revealed by FRAP assay (58.23%) and DPPH assay (66.18%). Using molecular docking analysis, some of the important garlic metabolites were investigated for their interactions with the HSA molecule. Molecular docking analysis showed quercetin, a phenolic compound present in garlic, appears to be the most promising inhibitor of glucose interaction with the HSA molecule. Our findings show that garlic can prevent oxidative stress and glycation-induced biomolecular damage and that it can potentially be used in the treatment of several health conditions, including diabetes and other inflammatory diseases.     

Effects of CO2 laser pretreatment on drought stress resistance in wheat

In order to determine the role of laser in drought stress resistance of spring wheat (Triticum aestivum L.), seed embryos were exposed to CO2 laser radiation for 0min, 1min, 3min and 5min, respectively, and when the seedlings were 12 days old they were treated with 10% (w/v) PEG6000 solution for 10 days. Changes in the concentration of malondialdehyde (MDA), hydrogen peroxide (H2O2), glutathione (GSH), ascorbate (AsA), oxidized glutathione (GSSG), carotenoid, zeaxanthin, the production rate of superoxide radical (O2(-)), the activities of ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), glutathione peroxidase (GP), glutathione-S-transferase (GST) and the growth parameters of seedlings (plant height, leaf area and dry weight) were measured to test the effects of laser pretreatment. The results showed that suitable laser pretreatment of embryos enhanced drought stress resistance in wheat seedlings by decreasing the concentration of MDA and H2O2, GSSG, the production rate of O2(-), leaf area and increasing the activities of APX, GST, GP and POD and AsA, carotenoid and zeaxanthin concentration. It is suggested that those changes in MDA, O2(-) H2O2, anti-oxidative enzymes and anti-oxidative compounds were responsible for the increase in drought stress resistance observed in the experiments. The results also showed that the laser had a long-term positive physiological effect on the growth of drought stress seedlings. This is the first investigation reporting the use of CO2 laser pretreatment to enhance drought stress resistance of spring wheat.     

Bioactive Compounds Extracted from Ecklonia cava by Using Enzymatic Hydrolysis Protects High Glucose-Induced Damage in INS-1 Pancreatic β-Cells

Pancreatic ??-cells are very sensitive to oxidative stress and this might play an important role in ??-cell death in diabetes. In the present study, we investigated whether the brown alga Ecklonia cava has protective effects against high glucose-induced damage in INS-1 pancreatic ??-cells. For that purpose, we prepared an enzymatic hydrolysate from E. cava (EHE) by using the carbohydrase, Celluclast. High-glucose (30?mM) treatment induced glucotoxicity, whereas EHE prevented cells from high glucose-induced damage then restoring cell viability was significantly increased. Furthermore, lipid peroxidation, intracellular reactive oxygen species (ROS) and nitric oxide (NO) were overproduced as the result of the treatment by high glucose; however, these lipid peroxidation, ROS and NO generations were effectively inhibited by addition of EHE in a dose-dependent manner. Moreover, EHE treatment increased activities of antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-px) in high glucose pretreated INS-1 pancreatic ??-cells. EHE slightly reduced the expression of pro-apoptotic protein Bax induced by high glucose but increased the expression of Bcl-2, an anti-apoptotic protein. These findings indicate that EHE might be used as potential nutraceutical agent which will protect the glucotoxicity caused by hyperglycemia-induced oxidative stress associated with diabetes.     

Microwave treatment of eight seconds protects cells of Isatis indigotica from enhanced UV-B radiation lesions

To determine the role of microwaves in the stress resistance of plants to enhanced ultraviolet-B (UV-B) radiation, Isatis indigotica Fort. seeds were subjected to microwave radiation for 8 s (wavelength 125 mm, power density 1.26 mW mm(-2), 2450 MHz). Afterwards they were cultivated in plastic pots in an artificial-glass greenhouse maintained at 25 degrees C, 70% relative humidity, and 400 micromol mol(-1) CO2, under visible-light conditions of 1500 micromol m(-2) s(-1) for 8 h day(-1). When the seedlings were 10 days old, they were subjected to 10.08 kJ m(-2) UV-B (PAR: 220 micromol m(-2) s(-1)) radiation for 8 days. Changes in a number of physiological and biochemical characteristics and in the thermal decomposition enthalpy of biomass were measured and used as indicators of the protective capacity of microwave radiation in this experiment. Our results revealed that microwave pretreatment of seeds enhanced UV-B stress resistance in the seedlings by decreasing the concentration of malondialdehyde (MDA) and increasing the concentration of ascorbic acid (AsA) and UV-B-absorbing compounds, increasing the activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), and increasing the energy accumulation of photosynthesis. All these results suggest that microwave radiation enhances plant metabolism and results in increased UV-B stress resistance. This is the first investigation reporting the use of microwave pretreatment to protect the cells of Isatis indigotica from UV-B-induced lesions.     

Prospects for using proteinase inhibitors to protect transgenic plants against attack by herbivorous insects

Proteinase inhibitors which act on the digestive enzymes of insect herbivores are a basic mechanism of plant defence. Attempts to exploit this defence mechanism in plant genetic engineering have used over-expression of both endogenous and exogenous inhibitors. While significant protection against insect pests has been routinely achieved, the engineered plants do not show levels of resistance considered commercially viable. As a result of selective pressures, insect herbivores have developed multiple mechanisms of adaptation to overcome the defensive effects of plant proteinase inhibitors. Common polyphagous crop pests are well adapted to deal with a range of different inhibitors, which have only limited effects on fitness as a result. A range of strategies have been attempted to improve effectiveness of proteinase inhibitors as antimetabolites towards insects, including selection for inhibitory activity against insect digestive enzymes, mutagenesis for novel inhibitory activity, and engineering inhibitors with multiple functions. However, proteinase inhibitor genes have only been used in transgenic crops in combination with other insecticidal genes. In Chinese genetically engineered cotton varieties which express Bt toxins as an insecticidal protein against lepidopteran larvae, the CpTI (cowpea trypsin inhibitor) gene has been employed as a second transgene to improve protection. This gene combination represents the only commercial deployment of a proteinase inhibitor transgene to date, with Bt/CpTI cotton grown on over 0.5 million hectares in 2005. Future prospects for using proteinase inhibitor genes to enhance insect resistance in transgenic crops will require reassessment of their mechanisms of action, particularly in affecting processes other than digestion, as exemplified by effects on sap-feeding hemipteran pests.