硅对水稻几丁质酶和β-1,3-葡聚糖酶活性的影响及其与抗纹枯病的关系

在溶液培养条件下,以水稻抗病品种91SP和感病品种Lemont为材料,研究施硅和接种纹枯病菌对水稻纹枯病发生情况、外切几丁质酶、内切几丁质酶和β-1,3-葡聚糖酶活性的影响。结果表明,施硅能降低抗病品种91SP的纹枯病病级和病情指数,显著降低感病品种Lemont的病级和病情指数。在未接种纹枯病菌条件下,施硅增加了抗病品种几丁质酶活性,增加了感病品种的几丁质酶活性,但对β-1,3-葡聚糖酶活性影响不大。接种纹枯病菌后,水稻几丁质酶活性被迅速激活后又下降,施硅通过提高抗病品种91SP几丁质酶和β-1,3-葡聚糖酶活性,以及通过提高感病品种Lemont几丁质酶活性来增强对纹枯病的抗性,但感病品种Lemont施硅处理的几丁质酶活性降低幅度小于抗病品种91SP。     

Effect of Rice Blast and Sheath Blight on Physical Properties of Selected Rice Cultivars

Observations in 1997 indicated a significant reduction in kernel bulk density and head rice yield of rice cultivar LaGrue due to blast (Pyricularia grisea). A more detailed study on rice cultivar M202 in 1998 confirmed such observations but it also showed negative effects of blast on other physical properties of rice. Rough rice from blast‐infected panicles was drier by 7–10 percentage points and 10% thinner than rough rice from blast‐free panicles. Blast also caused incidences of chalky, unfilled, and fissured kernels that were 21, 30, and 7 percentage points higher, respectively. The effects of sheath blight (Rhizoctonia solani) on kernel thickness and moisture content of rice cultivars Cocodrie, Cypress, Drew, and LaGrue were similar to the effect of blast on M202. Sheath blight generally reduced kernel bulk density but did not significantly affect head rice yield of the cultivars in 1997 and 1998 (except in one sample of Drew). There was a general trend toward higher incidences of unfilled, chalky, and fissured kernels in sheath‐blight‐infected samples. The data indicated that blast could be a significant preharvest factor in causing high variability in physical properties as well as in reducing the milling quality of rice. Sheath blight is also a potentially significant preharvest factor in affecting these properties in situations where sheath blight pressure is high.     

硅对黄瓜白粉病抗性的影响及其生理机制

以黄瓜感病品种为材料,研究了施硅和诱导接种白粉菌对抗坏血酸过氧化物酶(AsA-POD)、脱氢抗坏血酸还原酶(DR)、苯丙氨酸解氨酶(PAL)、多酚氧化酶(PPO)活性与酚类物质含量变化的影响。结果表明:诱导接种后,营养液中加硅酸盐显著降低黄瓜白粉病病情指数,显著提高了黄瓜叶片中AsA-POD、PPO的活性,而DR、PAL活性低于不施硅处理,但差异不显著。施硅处理的酚类物质含量较高,并显著降低病情指数。     

硅对水稻防御性关键酶活性的影响及其与抗稻瘟病的关系

通过室内溶液培养试验,研究了硅酸盐对接种稻瘟病菌后水稻的病情指数、植株生物量、过氧化物酶（POD）、多酚氧化酶（PPO）和苯丙氨酸解氨酶（PAL）活性的影响。结果表明,施硅能显著降低水稻稻瘟病的发病率和病情指数,防治效果达60.59%;显著减轻稻瘟病对水稻地上部的危害,干物质量显著高于不施硅处理,但对地下部生长影响不明显;接种后水稻叶片POD活性均升高,在第5 d达到最大值,施硅处理显著低于不施硅处理,与稻瘟病抗性成负相关;水稻叶片PPO活性在接种后第5 d达到峰值,从第4 d开始施硅处理显著高于不施硅处理;接种后水稻叶片的PAL活性快速升高,在第24 h达到最大值,施硅处理显著高于不施硅处理,是其1.44倍。说明硅能提高防御性关键酶的活性,参与水稻本身防卫机制,通过一系列的生理生化作用来增强水稻的抗性。     

Silicon modulates the metabolism and utilization of phenolic compounds in cucumber (Cucumis sativus L.) grown at excess manganese

Cucumber plants (Cucumis sativus L. cv. Chinese long) were grown in nutrient solution with increasing manganese (Mn) concentrations (0.5, 50, and 100 µM) with (+Si) or without silicon (–Si) supplied as silicic acid at 1.5 mM. High external Mn supply induced both growth inhibition of the whole plant and the appearance of Mn‐toxicity symptoms in the leaves. The application of Si alleviated Mn toxicity by increasing the biomass production. Although the total Mn concentration in the leaves did not differ significantly between +Si and –Si plants, symptoms of Mn toxicity were not observed in Si‐treated plants. The concentrations of phenolic compounds, particularly in the leaf extracts of cucumber plants grown at high external Mn concentrations, differed from those of plants grown without Si. The increased tissue concentrations of phenols (e.g., coniferyl alcohol, coumaric and ferulic acids) were in agreement with enhanced enzymes activities, i.e., peroxidases (PODs) and polyphenol oxidases (PPO) in the tissues of –Si plants. The activities of both enzymes were kept at a lower level in the tissue extracts of +Si plants grown at high external Mn concentrations. These results suggest that Si nutrition modulates the metabolism and utilization of phenolic compounds mainly at the leaf level, most probably as a consequence of the formation of Si‐polyphenol complexes.     

Induction of systemic resistance in rice against sheath blight disease by Pseudomonas fluorescens

Two Pseudomonas fluorescens strains viz., PF1 and FP7 which inhibited the mycelial growth of sheath blight fungus Rhizoctonia solani and increased the seedling vigour of rice plants in vitro were selected for assessing induced systemic resistance (ISR) against R. solani in rice. The Pseudomonas application as a bacterial suspension or a talc-based formulation through seed, root, soil and foliar application either alone or in combination (seed+root+soil+foliar) effectively reduced sheath blight disease incidence, promoted plant growth and ultimately increased yields under glasshouse or field conditions. Efficacy of Pseudomonas strains against R. solani was comparable to that of the fungicide carbendazim, which is normally used in the field to manage the disease. Pseudomonas treatment of rice cv IR50 led to induction of systemic resistance against R. solani, as a result of increase in chitinase and peroxidase activity. However, the extent of increase varied between treatments, Pseudomonas strains used and their duration. Though two chitinase isoforms (35 and 28 kDa) and five peroxidase isozymes (PO1–PO5) were found to be associated with the ISR, 35 kDa chitinase and three peroxidase isozymes (PO3–PO5) were established as the major determinants of ISR. Although a single application of a Pseudomonas strain resulted in ISR, the combined application through all of the four (seed, root, soil and foliar) methods increased the durability of ISR in rice plants. In addition, the Pseudomonas strains produced chitinase in the culture medium. It is presumed that the induced chitinase, peroxidase and bacterial chitinase may be either directly or indirectly involved in the reduction of sheath blight disease development in rice.     

甘薯抗薯瘟病的苯丙烷类代谢研究

甘薯瘟病是甘薯的重要病害, 严重影响甘薯的品质和产量.本试验在甘薯苗期, 通过剪叶法接菌研究甘薯抗感病品种苯丙烷类代谢的变化规律.结果表明: 甘薯抗感病品种接菌后PAL、POD活性均有所提高, 且提高速度与品种抗性呈正相关; 抗病品种接菌后木质素和绿原酸含量显著增加, 感病品种接菌后绿原酸、总酚和类黄酮含量波动较大, 木质素含量降低.相关性分析表明, 接菌后木质素和绿原酸的积累与甘薯品种抗病性密切相关.接菌后PAL、POD活性迅速提高并积累木质素和绿原酸等抗病物质是甘薯抗薯瘟病的苯丙烷类代谢基础, 在抗病品种鉴定方面有一定的参考价值.     

硅对水稻叶片抗氧化酶活性的影响及其与白叶枯病抗性的关系

以感白叶枯病的水稻品种日本晴(Oryza sativa L. cv. Nipponbare)为材料,在溶液培养条件下,研究了硅对接种白叶枯病菌后的水稻病情指数、叶片丙二醛(MDA)和过氧化氢(H2O2)含量以及超氧化物岐化酶(SOD)、过氧化氢酶(CAT)、脂氧合酶(LOX)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX)活性的影响。结果表明,施硅能显著降低水稻白叶枯病的病情指数,防治效果达62.86%。接种白叶枯病菌后48 h内,施硅处理的水稻植株,叶片中丙二醛(MDA)和过氧化氢(H2O2)含量显著升高;显著提高感病植株叶片中脂氧合酶(LOX)和超氧化物歧化酶(SOD)活性;降低过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX)活性;促进过氧化氢(H2O2)在植物体内积累,加强膜脂过氧化作用。因此,硅可通过参与植株体内代谢,调节抗氧化系统酶活性,激发机体过敏反应(HR),增强植株对白叶枯病抗性。     

Effect of wash water temperature and chlorination on phenolic metabolism and browning of stored iceberg lettuce photosynthetic and vascular tissues

Cut tissues from distinct anatomical locations in iceberg lettuce (Lactuca sativa L.) were subjected to washing in cold (4 degrees C) and warm (47 degrees C) water with or without chlorine to assess their propensity to discoloration during storage. Total protein (Bradford method) and phenolic (TPH; Folin-Ciocalteu method) contents and polyphenol oxidase (PPO; spectrophotometric method using catechol as a substrate), peroxidase (POD; guaiacol substrate), and phenylalanine ammonia-lyase (PAL; phenylalanine substrate) activities were determined in photosynthetic and vascular tissue from outer and inner leaves. Unprocessed photosynthetic and inner leaf tissues had significantly higher (P < 0.05) levels of protein and TPH and PPO and POD activities than vascular and outer leaf tissues. PAL activities (on a fresh weight basis) were similar in all tissues. Changes in browning (light reflectance measurement) and phenolic metabolism in all four tissue types were observed during aerobic storage at 5 degrees C over 10 days. PAL activity increased in all tissues after 1-2 days of storage and then gradually decreased. POD activity also increased steadily for the storage duration. Protein content and PPO activity remained constant. Edge browning (measured with a Minolta Chroma Meter) and TPH increased in all tissues, especially in outer vascular tissue. Cut photosynthetic and vascular tissues washed at 4 and 47 degrees C with and without 100 microg mL(-1) chlorine for 3 min were analyzed during 7 days in storage at 5 degrees C. Enzyme activities and accumulation of phenolics in all tissues washed at 47 degrees C were significantly (P < 0.05) lower compared to controls or tissues washed at 4 degrees C. Chlorine had no additional effect at 47 degrees C but significantly (P < 0.05) reduced browning and accumulation of phenolics in lettuce washed at 4 degrees C. These results showed that inherent differences between tissues affect phenolic metabolism and browning in stored, fresh-cut lettuce.     

Phenolic compounds and related enzymes are not rate-limiting in browning development of fresh-cut potatoes

The effect of minimal processing on polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL), and phenolic compounds was studied in five potato cultivars (Agria, Cara, Liseta, Monalisa, and Spunta). Minimal processing caused an overall increase in PPO, POD, and PAL activities. The isoform pattern of PPO was the same for all of the cultivars before and after processing. No latent PPO was detected. The isoperoxidase pattern was approximately the same among cultivars. An increase in POD activity was related to the specific induction of an acidic isoperoxidase. PAL showed an induction pattern characterized by the presence of a maximum peak of activity after 4 days of processing for all of the cultivars. The sequence of browning susceptibility of potato cultivars was as follows: Monalisa > Spunta > Liseta > Cara > Agria. Browning development was only partially correlated to PAL activity (only during the first 4 days after wounding). However, this correlation could not explain the above sequence of browning susceptibility. Minimal processing caused an increase of chlorogenic acid, whereas tyrosine content remained unchanged. In summary, no significant correlation was found between either rate or degree of browning and any other biochemical and physiological attribute investigated (PPO, POD, hydrogen peroxide, ascorbic acid content, and initial phenolics content as well as total and individual phenolics accumulation).     

施硅提高玉米抗蚜性的组成型和诱导型生理代谢机制

  【目的】  禾谷缢管蚜 (Rhopalosiphum padi) 是危害玉米的主要害虫之一,其生长繁殖严重影响了玉米的产量和品质。分析施硅 (Si) 诱导玉米植株对蚜虫的抗性对玉米正常生长尤为重要。本研究从玉米抗氧化系统、次生代谢和信号传导途径3个方面,探究了施硅提高玉米抗蚜性的生理代谢机制。  【方法】  采用玉米水培试验方法,共设置4个处理:不施硅不接蚜虫 (–Si–A)、不施硅接蚜虫 (–Si+A)、施硅不接蚜虫 (+Si–A)、施硅接蚜虫 (+Si+A)。分别于蚜虫侵染后48、60、72、96、120 h,调查玉米植株蚜虫密度,并取样分析玉米植株抗氧化系统 (CAT、SOD、H₂O₂和MDA)、次生代谢 (PAL、PPO、LOX和木质素含量) 和信号传导物质 (JA、SA) 含量,以未接虫玉米3个系统中的相关成分含量为组成型抗性,以接虫前后各成分含量的差值为诱导型抗性,讨论了硅对玉米抗蚜组成型和诱导型抗性的影响。  【结果】  随着蚜虫侵染后时间的延长,蚜虫密度增加,与侵染后48 h相比,在–Si处理下,侵染后60～120 h时蚜虫数量显著增加了12.50%～40.18%;+Si处理下,侵染后60～120 h蚜虫数量显著增加了12.36%～49.44%;在侵染后48～120 h相同时间点下,与不施硅处理相比,施硅处理的蚜虫种群密度显著降低了15.29%～20.64%。整个培养时间内,与不施硅处理相比,施硅处理的玉米抗氧化系统中组成型CAT、SOD活性均显著提高,组成型H₂O₂、MDA含量分别降低了4.41%～15.35%、5.35%～17.95%,诱导型CAT活性显著增加 (除侵染后72 h外),诱导型SOD活性显著降低,诱导型H₂O₂含量先提高后降低;施硅处理显著提高了次生代谢中组成型PAL、LOX和PPO活性、木质素含量,降低了诱导型PPO活性、木质素含量,诱导型PAL活性表现为先提高后降低,诱导型LOX活性表现为先降低后升高随后又降低;施硅处理显著提高了信号传导中组成型JA、SA含量,增加了诱导型SA含量43.77%～117.48%,降低了诱导型JA含量。同一时间点,无论是否施硅,组成型CAT、SOD活性、H₂O₂和MDA含量、PAL、LOX和PPO活性、木质素、JA和SA含量均显著高于诱导型。PCA与相关性分析结果表明,组成型和诱导型CAT、SOD活性和诱导型H₂O₂、SA含量为体现玉米抗蚜虫的组成型和诱导型抗性的较优指标。  【结论】  施硅可显著降低蚜虫的密度,并显著提高玉米抗氧化系统、次生代谢和信号传导途径各物质的组成型与诱导型抗性,因此,施用硅肥为玉米田间蚜虫的生态调控提供了理论基础和科学依据。     

Contents of Antioxidant Compounds in Turkish Oats: Simple Phenolics and Avenanthramide Concentrations

Antioxidant products such as simple phenolic compounds and avenanthramides in oat (Avena sativa L.) may have health‐promoting effects on humans. Therefore, it is very important to determine simple phenolics and avenanthramide concentrations of different genotypes of oats from different regions of the world. The aim of this research was to determine the concentrations of simple phenolics and avenanthramides of Turkish oat genotypes. According to the results, Turkish oat genotypes were significantly different for three major avenanthramides (Bc, Bp, and Bf) and the simple phenolic, ferulic acid (FA), while not significantly different for p‐coumaric acid (PCA). Ferulic acid concentrations of Turkish oat genotypes were higher than a standard U.S. cultivar, Belle. However, the major avenanthramide concentrations of Turkish oat genotypes were significantly lower than Belle.     

硅调节植物抗病性的机理:进展与展望

【目的】硅素营养增强作物对病虫害的防御能力已得到充分证实,但其作用机理至今仍然没有明确。本文对国内外有关硅素营养与作物病害发展的相互关系及相关机理的最新研究进展进行了归纳总结,为通过植物营养调节技术来提高作物病害防御能力的研究提供理论支撑。【内容】土壤有效硅包括土壤溶液中的单硅酸和易转化为单硅酸的盐类,土壤中有效硅含量一般在50～260 mg/kg。硅虽然不是植物生长发育的必需矿质营养元素,但是硅在减轻植物多种生物和非生物胁迫以及提高植物对病菌的抵抗能力等方面起着重要作用。施硅可以显著地抑制水稻稻瘟病、 纹枯病、 白叶枯病、 胡麻叶斑病,小麦、黄瓜、番茄等植物白粉病等多种病害的发生。关于硅调节植物抗病性的机理,首先提出了机械或物理屏障假设,认为施硅促进了细胞硅化作用的增强,细胞壁角质-硅双层以及表皮细胞乳突的增强,对病菌的入侵起到了物理防御作用。但随着研究的深入,发现物理屏障并非唯一机制,而后提出硅积极参与了生物化学防御过程,发现硅可以诱导感病植物产生酚醛类、黄酮类等抗毒素物质,以及施硅可以提高植物中几丁质酶、过氧化物酶、多酚氧化酶的活性、苯丙氨酸解氨酶等感病植物中病程相关蛋白酶的活性,从而通过化学防御过程提高植物对病害的抵抗能力。随着现代分子技术的发展,从基因组、转录组水平对其防御机制进行了阐明。研究认为硅通过主动的上调感病植物防卫基因及病程相关蛋白基因的表达,以应对病菌侵染。硅诱导植物产生乙烯、茉莉酸、活性氧等系列信号,使植物处于预激活化状态,从而减轻生物胁迫,但是硅在调节植物胁迫信号转导方面的机制还需要深入的研究。【结论】在缺硅土壤中施用硅肥,可以增强作物对病害的抵抗能力,从而大量降低杀菌剂的使用。关于硅调节植物抗病性机理,不能单一归因于某一方面,物理屏障防御机制与生物化学防御过程兼在。硅可能与关键的植物胁迫信号系统相互作用,而最终诱导产生对病原菌的抵抗, 但是这方面的确切机制还不是很清楚,是今后的研究重点。     

Exploring genetic diversity and potential novel disease resistance genes in a collection of rice (<Emphasis Type="Italic">Oryza</Emphasis> spp.) wild relatives

Wild relatives of rice (Oryza spp.) are an important source of novel resistance (R-)genes for rice improvement. Rice sheath blight, caused by Rhizotonia solani, and leaf blast, caused by Magnaportha oryzae, are major fungal diseases of rice worldwide. To identify novel R-genes, a group of Oryza spp. accessions represented by O. alta, O. australiensis, O. barthii, O. glaberrima, O. glumaepatula, O. latifolia, O. meridionolis, O. nivara, O. officinalis, and O. rufipogon, were evaluated for their reaction to leaf blast and sheath blight disease, and genotyped with 176 microsatellite (SSR) markers. Selected rice (O. sativa) accessions were included as reference. Cluster analysis performed with PowerMarker software using Rogers genetic distance and UPGMA, revealed most Oryza spp. accessions clustered with the same species or a closely related Oryza spp. Only a few Oryza spp. accessions grouped with the O. sativa accessions included as a reference. Analysis of this genotypic data in the software Structure revealed that the Oryza spp. accessions were assigned into eight different subpopulations and fit well into eight different backgrounds. Marker-trait associations between the SSR markers and disease reactions to blast and sheath blight were ascertained using the software TASSEL. Associations with blast disease were identified in ten different chromosomal regions and five of the ten were not located near known blast R-genes. Three associations were discovered with sheath blight disease and one was not near previously reported sheath blight QTL. These newly identified regions may represent novel R-genes that will be the basis future fine mapping studies. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

兼具水稻纹枯病拮抗功能的生物水稻育苗基质效果研究

水稻纹枯病是水稻上常见的土传病害之一,为了研发出可防治水稻纹枯病兼具促生效果的功能型生物水稻育苗基质,本研究选用前期筛选出具有固氮解磷功能的根际促生菌:LY5枯草芽孢杆菌(Bacillus subtilis)、LY11解淀粉芽孢杆菌(Bacillus amyloliquefaciens)、X2摩拉维亚假单胞菌(Pseudomonas moraviensis)、X3沙芬西芽孢杆菌(Bacillus safensis)、X8绿针假单胞菌(Pseudomonas chlororaphis),首先探索该5株促生菌对水稻纹枯病病原菌的抑菌率,再将其与水稻纹枯病病原菌混合,在实验室已筛选出的最适配比基质基础上,研发功能型生物水稻育苗基质。在盆栽条件下,与市售水稻育苗基质对比,验证功能型生物水稻育苗基质对水稻纹枯病发病率、水稻幼苗生长和体内抗性相关酶类的影响。结果表明:(1)5株根际促生菌对水稻纹枯病病原菌均具有拮抗作用,抑菌率达到35.31%～40.20%。(2)5株拮抗促生菌能够降低水稻纹枯病的发病率,其中添加LY11菌株的处理较对照处理的每盘出苗数显著增加了110.41%,而发病率显著降低了...     

Phenylalanine Ammonia-Lyase and Phenolic Compounds in Chamomile Tolerance to Cadmium and Copper Excess

Phenylalanine ammonia-lyase activity (PAL, EC 4.3.1.5), total phenolics, soluble proteins, malondialdehyde and metals accumulation in four-week old chamomile (Matricaria chamomilla) plants cultivated in nutrient solution and exposed to low (3 μM) and high (60 and 120 μM) levels of cadmium (Cd) or copper (Cu) for 7 days were studied. High Cd concentrations had a stimulatory effect on PAL activity and soluble phenolics accumulation while high Cu doses decreased soluble proteins in the leaf rosettes. In the roots, extreme stimulatory effects of 60 and 120 μM Cu were observed on PAL activity, phenolics and malondialdehyde accumulation, while protein content was reduced by these Cu doses. Cd accumulation was higher in the leaf rosettes compared to copper, but the opposite was recorded in the roots. Taken together, the stimulatory effect of Cu on phenolic metabolism was recorded, even though high malondialdehyde accumulation may be an indication that phenolics was not sufficient to counteract reactive oxygen species formation thus leading to damage of membrane integrity. In comparison to Cd, Cu had more noticeable effect on the parameters studied to support its strong redox-active properties. These facts in correlation to antioxidative properties of phenolic metabolites are also discussed.     

硅对水稻病程相关蛋白活性和酚类物质含量的影响及其与诱导抗性的关系

为阐明硅提高水稻抗稻瘟病的生理机制,采用室内溶液培养试验,研究了硅对接种稻瘟病菌后水稻叶片的几丁质酶和β-1,3-葡聚糖酶活性以及总可溶性酚和木质素含量的影响。结果表明,接种稻瘟病菌能诱导几丁质酶活性的快速上升,不施硅处理的几丁质酶活性在第2 d达到第一个峰值后就开始下降,而施硅处理的几丁质酶活性则继续上升直到第4 d才开始下降,从第4～8 d显著高于不施硅处理。β-1,3-葡聚糖酶活性在接种后的第4 d之前均上升缓慢,处理间差异不显著;第4 d后开始上升,到第8 d达到最大值;不施硅处理上升更快,显著高于施硅处理。接种稻瘟病菌能诱导水稻叶片总可溶性酚含量快速上升,施硅处理和不施硅处理分别在接种后的第3和第4 d达到峰值,并开始快速下降;施硅能显著提高总可溶性酚含量。水稻叶片中的木质素含量在接种后的第1 d快速上升,并维持较高水平,施硅处理显著高于不施硅处理;但在感病后期（第6 d）,施硅处理开始显著低于不施硅处理。     

Preharvest L-arginine treatment induced postharvest disease resistance to Botrysis cinerea in tomato fruits

L-arginine is the precursor of nitric oxide (NO). In order to examine the influence of L-arginine on tomato fruit resistance, preharvest green mature tomato fruits (Solanum lycopersicum cv. No. 4 Zhongshu) were treated with 0.5, 1, and 5 mM L-arginine. The reduced lesion size (in diameter) on fruit caused by Botrytis cinerea, as well as activities of phenylalanine ammonia-lyase (PAL), Chitinase (CHI), β-1,3-glucanase (GLU), and polyphenoloxidase (PPO), was compared between L-arginine treated fruits and untreated fruits. We found that induced resistance increased and reached the highest level at 3-6 days after treatment. Endogenous NO concentrations were positively correlated with PAL, PPO, CHI, and GLU activities after treatment with Pearson coefficients of 0.71, 0.94, 0.97, and 0.87, respectively. These results indicate that arginine induces disease resistance via its effects on NO biosynthesis and defensive enzyme activity.     

Effect of wounding on phenolic enzymes in six minimally processed lettuce cultivars upon storage

The effect of wounding on polyphenol oxidase (PPO), peroxidase (POD), and phenylalanine ammonia-lyase (PAL) was studied in six minimally processed lettuce (Lactuca sativa L.) cultivars upon storage for 7 days at 5 degrees C (Iceberg Mikonos (IM), I. Green Queen (IGQ), I. Asdrúbal (IA), Little Gem Sandra (LGS), Romaine Cazorla (RC), and R. Modelo (RM)). Wounding of lettuce tissue midribs (because of minimal processing) caused an exponential increase in PPO activity due to the activation process from latent to fully active PPO by following first order kinetics in the time range from 3.7 days (LGS) to 6.3 days (RC). However, total PPO activity (active plus latent) remained constant. Isoform pattern of PPO changed upon storage probably because of posttranslational processes. POD activity linearly increased with induction of new POD isoenzymes. PAL activity presented a typical bell-shaped induction pattern in four cultivars. Only IM and IGQ showed a second induction response which has not been previously described in the literature. IM was the cultivar most susceptible to browning and RC was the cultivar least susceptible. However, no clear correlation was observed between browning and any of the biochemical and physiological attributes investigated (PPO, PAL, and POD activities, total and individual phenols accumulation, and ascorbic acid content).     

Comparison of content in phenolic compounds,polyphenol oxidase,and peroxidase in grains of fifty sorghum varieties from burkina faso

Analysis of fifty sorghum [Sorghum bicolor (L.) Moench] varieties used in Burkina Faso showed that they have different contents of phenolic compounds, peroxidase (POX), and polyphenol oxidase (PPO). Most of the varieties (82%) had a tannin content less than 0.25% (w/w). POX specific activity was higher than the monophenolase and o-diphenolase specific activities of PPO. For POX, there was a diversity of isoforms among varieties. No clear correlation could be made between the quantitative composition of the grain in phenolics, PPO, and POX, and resistance of plant to pathogens. In general, varieties good for a thick porridge preparation ("t?") had low phenolic compounds content and a medium POX activity. From the red varieties, those used for local beer ("dolo") had a high content in phenolic compounds and PPO, and a low POX activity. The variety considered good for couscous had a low POX content. The characteristics might be useful as selection markers for breeding for specific applications.