Glycosidases in pear pollen tube development

During the in vitro germination of pear pollen, several hydrolaseswere released into the medium. They were apparently eluted fromthe pollen grain, since the activity was the same when germinationwas inhibited. These enzymes, once released, had no role intube growth, since resuspension of pollen in fresh medium after1.5 hr of incubation did not result in a change of the subsequenttube growth. Homogenates of the pollen suspension at differentstages of development showed no significant changes in phosphatase,ß-glucosidase, or ß-galactosidase activity.However, patent ß-glucosidase activity measured directlyin suspensions of intact pollen did increase after germinationin proportion to tube wall development. Nojirimycin, a specificinhibitor of glucosidases, reduced this ß-glucosidaseactivity by 75% at 10^–5M and significantly reduced growthrate at 10^–4 M. (Received December 19, 1978; )     

葡糖基水杨酸: 一种可能参与植物诱导型耐热性形成的信号物质

该文旨在初步探讨水杨酸的主要结合态——葡糖基水杨酸(salicylic acid 2-O-β-D-glucose, SAG), 是否参与了高温诱导的植物耐热性信号传递过程。采用水杨酸(salicylic acid, SA)生物合成抑制剂——多效唑(paclobutrazol, PAC), 预处理豌豆(Pisum sativum)叶片, 再加以高温诱导, 结果发现与未经PAC处理的对照相比, 豌豆叶片受高温诱导的耐热性降低。同时, PAC预处理导致高温锻炼过程中SAG信号峰值消失。利用同位素标记和蛋白免疫印迹分析发现, PAC所导致的SAG信号减弱, 不仅是由于SA生物合成受到抑制, 而且还归因于水杨酸糖苷转移酶(salicylic acid glucosyltransferase, SAGT)蛋白合成和活性降低所引起的自由态SA向SAG转化的减缓。以上结果表明, SAG表现出了与自由态SA相似的信号功能, 并参与了高温锻炼诱导植物耐热性的信号传递过程。     

Changes in Cell Walls Associated with Cell Separation in Suspension Cultures of Paul's Scarlet Rose

Studies of the formation and separation of cellular aggregatesin Paul's Scarlet rose suspension cultures have been conductedin an attempt to resolve the basis for intercellular adherence.During the typical growth cycle, cellular aggregates begin tofragment spontaneously at about day 12 in culture. This fragmentationis accompanied by a sharp decrease in the galactose contentof wall polysaccharides. At approximately this same time, thereis an increase in ß-glucosidase and ß-galactosidaseactivity associated with the cell surface. The presence of aß-glucosidase inhibitor, nojirimycin, inhibits thesurface ß-glycosidase activity, reduces the extentto which cell wall galactose is decreased, and prevents theseparation of cells. No other cell wall component examined changesin a manner consistent with cell separation. The results suggestthat a galactose-containing wall polysaccharide may be involvedin the maintenance of intercellular coherency and that partialremoval of this component may be causally related to the spontaneousseparation of cells in culture.     

Interconversion of the salicylic acid signal and its glucoside in tobacco

Salicylic acid (SA) has been proposed to play a role in the induction of pathogenesis-related (PR) proteins and systemic acquired resistance (SAR) in tobacco. Since SA is rapidly converted to salicylic acid β-glucoside (SAG) in tobacco, we have attempted to assess the role of SAG in pathogenesis by application of chemically synthesized SAG to tobacco leaves. SAG was as active as SA in induction of PR-1 gene expression. This induction was preceded by a transient release of SA, which occurred in the extracellular spaces. The existence of a mechanism that releases SA from SAG suggests a possible role for SAG in SAR.     

Salicylic acid glucoside acts as a slow inducer of oxidative burst in tobacco suspension culture

Salicylic acid beta-glucoside (SAG) is a storage form of a defense signal against pathogens, releasing free salicylic acid (SA), to meet the requirements in plants. Since excess SA induces locally restricted cell death following oxidative burst and Ca2+ influx in plants, the effects of SAG on cell viability, Ca2+ influx, and generation of superoxide (O2*-) were examined in suspension-cultured tobacco BY-2 cells expressing aequorin. Among SA-related chemicals tested, only SAG induced the slow and long-lasting O2*- generation, although SAG was less active in acute O2*- generation, Ca2+ influx and induction of cell death. The prolonging action of SAG is likely due to gradual release of SA and the data suggested that a peroxidase-dependent reaction is involved. Notably, pretreatment with low-dose SA (50 micromu) enhanced the response to SAG by 2.5-fold. There are four possible secondary messengers in early SA signaling detectable in the BY-2 culture, namely O2*-, H2O2, Ca2+ and protein kinase (PK). If these messengers are involved in the low-dose SA-dependent priming for SAG response, they should be inducible by low-dose SA. Among the four SA-inducible signaling events, PK activation was excluded from the low-dose SA action since a much higher SA dose (> 0.4 mmu) was required for PK activation.     

Salicylic Acid Enhances Biocontrol Efficacy of the Antagonist Cryptococcus laurentii in Apple Fruit

Biological control and induced resistance are two of the promising approaches to the control of postharvest diseases. This study was conducted to evaluate the efficacy of salicylic acid (SA) alone or in combination with an antagonistic yeast, Cryptococcus laurentii, in controlling the blue mold disease caused by Penicillium expansum on apple fruit wounds. SA alone significantly inhibited the spore germination of P. expansum in vitro when its concentration was increased to 1000 μg ml⁻¹, but it was not effective in controlling the disease in vivo. Simultaneous application of SA and C. laurentii to the wounds on the apple fruit surface showed that SA could improve the efficacy of C. laurentii against P. expansum in a concentration-dependent manner, being most effective at 10 μg ml⁻¹ but less effective at a higher or lower concentrations. Besides reducing the blue mold incidence in the local wound sites, the combination of C. laurentii with SA at 10 μg ml⁻¹ also had a synergistic effect on the induction of fruit resistance to the disease, which might be associated with a rapid increase in peroxidase, phenylalanineamonialyase and lipoxygenase activities. In addition, SA at 100 μg ml⁻¹ or above showed an adverse effect on the growth of C. laurentii in vitro and in vivo, whereas it had no effect when its concentration was decreased to 10 μg ml⁻¹ or lower. This suggested that SA could enhance the biological activity of C. laurentii in apple fruit by inducing resistance to pathogens based on the antagonistic activity of C. laurentii.     

Salicylic acid and salicylic acid glucoside in xylem sap of <Emphasis Type="Italic">Brassica napus</Emphasis> infected with <Emphasis Type="Italic">Verticillium longisporum</Emphasis>

Salicylic acid (SA) and its glucoside (SAG) were detected in xylem sap of Brassica napus by HPLC–MS. Concentrations of SA and SAG in xylem sap from the root and hypocotyl of the plant, and in extracts of shoots above the hypocotyl, increased after infection with the vascular pathogen Verticillium longisporum. Both concentrations were correlated with disease severity assessed as the reduction in shoot length. Furthermore, SAG levels in shoot extracts were correlated with the amount of V. longisporum DNA in the hypocotyls. Although the concentration of SAG (but not SA) in xylem sap of infected plants gradually declined from 14 to 35 days post infection, SAG levels remained significantly higher than in uninfected plants during the whole experiment. Jasmonic acid (JA) and abscisic acid (ABA) levels in xylem sap were not affected by infection with V. longisporum. SA and SAG extend the list of phytohormones potentially transported from root to shoot with the transpiration stream. The physiological relevance of this transport and its contribution to the distribution of SA in plants remain to be elucidated.     

Thermotolerance and Related Antioxidant Enzyme Activities Induced by Heat Acclimation and Salicylic Acid in Grape (Vitis vinifera L.) Leaves

Thermotolerance and related antioxidant enzyme activities induced by both heat acclimation and exogenous salicylic acid (SA) application were studied in grapevine (Vitis vinifera L. cv. Jingxiu). Heat acclimation and exogenous SA application induced comparable changes in thermotolerance, ascorbic acid (AsA), glutathione (GSH), and hydrogen peroxide (H₂O₂) concentrations, and in activities of the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), glutathione reductase (GR), ascorbic peroxidase (APX) and catalase (CAT) in grape leaves. Within 1 h at 38 °C, free SA concentration in leaves rose from 3.1 μg g⁻¹ FW to 19.1 μg g⁻¹ FW, then sharply declined. SA application and heat acclimation induced thermotolerance were related to changes of antioxidant enzyme activities and antioxidant concentration, indicating a role for endogenous SA in heat acclimation in grape leaves.     

Differential Accumulation of Salicylic Acid and Salicylic Acid-Sensitive Catalase in Different Rice Tissues

We previously proposed that salicylic acid (SA)-sensitive catalases serve as biological targets of SA in plant defense responses. To further examine the role of SA-sensitive catalases, we have analyzed the relationship between SA levels and SA sensitivity of catalases in different rice (Oryza sativa) tissues. We show here that, whereas rice shoots contain extremely high levels of free SA, as previously reported (I. Raskin, H. Skubatz, W. Tang, B.J.D. Meeuse [1990] Ann Bot 66: 369-373; P. Silverman, M. Seskar, D. Kanter, P. Schweizer, J.-P. Metraux, I. Raskin [1995] Plant Physiol 108: 633-639), rice roots and cell-suspension cultures have very low SA levels. Catalases from different rice tissues also exhibit differences in sensitivity to SA. Catalase from rice shoots is insensitive to SA, but roots and cell-suspension cultures contain SA-sensitive catalase. The difference in SA sensitivity of catalases from these different tissues correlates with the tissue-specific expression of two catalase genes, CatA and CatB, which encode highly distinctive catalase proteins. CatA, which encodes a catalase with relatively low sequence homology to the tobacco SA-sensitive catalases, is expressed at high levels exclusively in the shoots. On the other hand, in roots and cell-suspension cultures, with northern analysis we detected expression of only the CatB gene, which encodes a catalase with higher sequence homology to tobacco catalases. The role of catalases in mediating some of the SA-induced responses is discussed in light of these results and the recently defined mechanisms of catalase inhibition by SA.     

Salicylic Acid and Disease Resistance in Plants

SA has been shown to play an important signaling role in the activation of various plant defense responses following pathogen attack. These responses include the induction of local and systemic disease resistance, the potentiation of host cell death, and the containment of pathogen spread. The mechanisms through which SA mediates these effects are varied and can involve alterations in the activity or synthesis of certain enzymes, increased defense gene expression, potentiation of several defense responses, and/or the generation of free radicals. Through the analysis of mutant plants exhibiting aberrant responses to pathogen infection, many genes encoding products involved in the SA-mediated defense pathway(s) have been isolated. In addition, mounting evidence suggests that certain defense responses can be activated via a SA-independent pathway(s). This review focuses primarily on recent discoveries pertaining to the SA signaling pathway(s) leading to disease resistance; however, a very brief discussion of the SA-independent pathway (s) and its ability to cross-talk with the SA pathway is also presented.     

Purification, cloning, and expression of a pathogen inducible UDP-glucose:Salicylic acid glucosyltransferase from tobacco

Salicylic acid (SA) plays an important role in plant disease resistance. Inoculation of tobacco leaves with incompatible pathogens triggers the biosynthesis of SA which accumulates primarily as the SA 2-O-beta-D-glucoside (SAG) and glucosyl salicylate (GS). The tobacco UDP-glucose:salicylic acid glucosyltransferase (SA GTase) capable of forming both SAG and GS was purified, characterized, and partially sequenced. It has an apparent molecular mass of 48 kDa, a pH optimum of 7.0, and an isoelectric point at pH 4.4. UDP-glucose was the sole sugar donor for the enzyme. However, SA and several phenolics served as glucose acceptors. The apparent K(m) values for UDP-glucose and SA were 0.27 and 1-2 mM, respectively. Zn(2+) and UDP inhibited its activity. The corresponding cDNA clone which encoded a protein of 459 amino acids was isolated from an SA-induced tobacco cDNA library and overexpressed in Escherichia coli. The recombinant protein catalyzed the formation of SAG and GS, and exhibited a broad specificity to simple phenolics, similar to that of the purified enzyme. Northern blot analysis showed that the SA GTase mRNA was induced both by SA and incompatible pathogens. The rapid induction timing of the mRNA by SA indicates that it belongs to the early SA response genes.     

Distribution of Glycosidases and Acid Invertase Activities in Relation to Elongation Growth in Pearl Millet Internode

The mean cell length along a differentiating internode and alliedchanges in the activities of ß-glucosidase, - andß-galactosidase. -mannosidase and acid invertase,together with the contents of reducing and non-reducing sugars,were examined in pearl millet (Pennisetum americanum L. Leekecv. BJ-104). The specific activities of cytoplasmic -mannosidase,wall ß-glucosidase, and cytoplasmic and wall acidinvertase showed close relationships with the rate of cell elongation.The linear regressions of the rate of cell elongation, and thespecific activities of wall ß-glucosidase and cytoplasmicand wall invertase showed significant positive correlations(P<0·05), whereas cytoplasmic -mannosidase was negativelycorrelated (P<0·01). The results are discussed in the light of cell wall looseningand the provision of carbon substrates for cell elongation. Key words: Glycosidases, acid invertase, sugars, cell elongation, Pennisetum americanum L., Leeke     

Salicylic Acid and Phenylalanine Ammonia-Lyase in Potato Plants Infected with the Causal Agent of Late Blight

In tuber tissues of potato (Solanum tuberosum L.) infected with an incompatible race of Phytophthora infestans (Mont.) de Bary, the activity of phenylalanine ammonia-lyase and the contents of free and bound salicylic acid (SA) considerably exceeded the corresponding indices in the tissues infected with a compatible race of the oomycete. The accumulation of the free form of SA apparently resulted from both enhanced SA biosynthesis and the liberation from the bound SA forms. SA accumulation in the incompatible host-pathogen combination presumes that SA participated in the local potato resistance to late blight.__________Translated from Fiziologiya Rastenii, Vol. 52, No. 4, 2005, pp. 573–577.Original Russian Text Copyright © 2005 by Panina, Gerasimova, Chalenko, Vasyukova, Ozeretskovskaya.     

Production and enzymatic decomposition of organic matter by microplankton in a eutrophic lake

This report presents studies on temporal variations of phytoplanktonand bacterioplankton production and the kinetics of bacterialenzyme activity (aminopeptidase, ß-glucosidase andlipase) in the littoral and pelagial sampling sites of a highlyeutrophic lake. Bacterial and algal production correlated wellin pelagic water, but in the littoral there was no significantcorrelation between these processes. The highest activity ofbacterial enzymes occurred during phytoplankton blooms (exceptß-glucosidase). The rates of enzymatic decompositionof organic matter in the littoral and pelagial sampling siteswere similar. Turnover time of enzymatic hydrolysis of the studiedbiopolymers in lake water was the shortest for proteins andlipids during phytoplankton blooms in both sampling sites. Themost dynamic changes in turnover time displayed were for thehydrolysis of polysaccharides by ß-glucosidase inthe littoral samples. The significance of organic matter forbacterial production and enzyme activity, and the role of enzymesin bacterial processing of biopolymers in a lake ecosystem arediscussed     

Enhanced Disease Susceptibility 1 and Salicylic Acid Act Redundantly to Regulate Resistance Gene-Mediated Signaling

Resistance (R) protein–associated pathways are well known to participate in defense against a variety of microbial pathogens. Salicylic acid (SA) and its associated proteinaceous signaling components, including enhanced disease susceptibility 1 (EDS1), non–race-specific disease resistance 1 (NDR1), phytoalexin deficient 4 (PAD4), senescence associated gene 101 (SAG101), and EDS5, have been identified as components of resistance derived from many R proteins. Here, we show that EDS1 and SA fulfill redundant functions in defense signaling mediated by R proteins, which were thought to function independent of EDS1 and/or SA. Simultaneous mutations in EDS1 and the SA–synthesizing enzyme SID2 compromised hypersensitive response and/or resistance mediated by R proteins that contain coiled coil domains at their N-terminal ends. Furthermore, the expression of R genes and the associated defense signaling induced in response to a reduction in the level of oleic acid were also suppressed by compromising SA biosynthesis in the eds1 mutant background. The functional redundancy with SA was specific to EDS1. Results presented here redefine our understanding of the roles of EDS1 and SA in plant defense.     

水杨酸调节决明根系铝诱导的氧化胁迫

水杨酸(Salicylicacid,SA)在调节生物和非生物胁迫,诱导植物氧化胁迫中起着重要的作用,但对铝诱导的氧化胁迫的调节作用尚不清楚。本文研究了SA对决明(CassiatoraL.)根系铝诱导的H2O2和O2-含量变化,包括抗氧化酶活性以及细胞质膜过氧化胁迫变化的影响。介质中20mmol/L铝处理增加质膜透性,导致MDA含量上升及根尖细胞Evansblue染色加重(测定细胞死亡),而外源供给5mmol/LSA能缓解铝诱导的氧化胁迫。SA处理能明显降低根尖H2O2和O2-的含量,但两者含量与CAT、APX和GR的活性变化没有相关性,而与POD活性增加有关。水杨酸诱导H2O2含量的下降与抑制O2-积累和SOD活性有关。结果表明,SA可能激活一条由H2O2介导的、依赖于POD的抗氧化机制来缓解脂质的过氧化作用。     

Salicylic Acid in Rice (Biosynthesis,Conjugation, and Possible Role)

Salicylic acid (SA) is a natural inducer of disease resistance in some dicotyledonous plants. Rice seedlings (Oryza sativa L.) had the highest levels of SA among all plants tested for SA content (between 0.01 and 37.19 [mu]g/g fresh weight). The second leaf of rice seedlings had slightly lower SA levels than any younger leaves. To investigate the role of SA in rice disease resistance, we examined the levels of SA in rice (cv M-201) after inoculation with bacterial and fungal pathogens. SA levels did not increase after inoculation with either the avirulent pathogen Pseudomonas syringae D20 or with the rice pathogens Magnaporthe grisea, the causal agent of rice blast, and Rhizoctonia solani, the causal agent of sheath blight. However, leaf SA levels in 28 rice varieties showed a correlation with generalized blast resistance, indicating that SA may play a role as a constitutive defense compound. Biosynthesis and metabolism of SA in rice was studied and compared to that of tobacco. Rice shoots converted [14C]cinnamic acid to SA and the lignin precursors p-coumaric and ferulic acids, whereas [14C]benzoic acid was readily converted to SA. The data suggest that in rice, as in tobacco, SA is synthesized from cinnamic acid via benzoic acid. In rice shoots, SA is largely present as a free acid; however, exogenously supplied SA was converted to [beta]-O-D-glucosylSA by an SA-inducible glucosyltransferase (SA-GTase). A 7-fold induction of SA-GTase activity was observed after 6 h of feeding 1 mM SA. Both rice roots and shoots showed similar patterns of SA-GTase induction by SA, with maximal induction after feeding with 1 mM SA.     

Salicylic Acid Induces Extracellular Superoxide Generation Followed by an Increase in Cytosolic Calcium Ion in Tobacco Suspension Culture: The Earliest Events in Salicylic Acid Signal Transduction

Addition of salicylic acid (SA) to tobacco (Nicotiana tabacum)suspension culture immediately induced a rapid and transientgeneration of superoxide anion (O^–₂), followed by a transientincrease in cytosolic free calcium ion concentration ([Ca²⁺]_c).The level of SA-induced O^–₂ was lowered by treatment withseveral scavengers of active oxygen species and a peroxidaseinhibitor, but not with an NADPH oxidase inhibitor. The SA-induced[Ca²⁺]_c elevation was also lowered by inhibitors which effectivelylowered the O^–₂ level. Inhibition of [Ca²⁺]_c elevationby Ca²⁺ channel blockers and a Ca²⁺ chelator indicated thatextracellular Ca²⁺ was responsible for the increased [Ca²⁺]_c.Among the several SA analogs, only compounds that actively inducedthe O^–₂ generation also elevated [Ca²⁺]_cIn addition, theinhibitory effects of SA analogs on catalase activity correlatedwell with their effects on the O^–₂ generation and the[Ca²⁺]_c elevation. SA-dependent O^–₂ generation was shownto occur extracellularly, requiring both H₂O₂ and at least oneproteinaceous factor excreted from the cells. This factor wasdetermined to be a salicylhydroxamic acid-sensitive extracellularguaiacol-utilizing peroxidase. ⁴Present address: Isehara Research Laboratory, Kanto ChemicalCo., Inc., Suzukawa, Isehara, 259-1146 Japan.     

Changes in Salicylic Acid and Antioxidants during Induced Thermotolerance in Mustard Seedlings

Heat-acclimation or salicylic acid (SA) treatments were previously shown to induce thermotolerance in mustard (Sinapis alba L.) seedlings from 1.5 to 4 h after treatment. In the present study we investigated changes in endogenous SA and antioxidants in relation to induced thermotolerance. Thirty minutes into a 1-h heat-acclimation treatment glucosylated SA had increased 5.5-fold and then declined during the next 6 h. Increases in free SA were smaller (2-fold) but significant. Changes in antioxidants showed the following similarities after either heat-acclimation or SA treatment. The reduced-to-oxidized ascorbate ratio was 5-fold lower than the controls 1 h after treatment but recovered by 2 h. The glutathione pool became slightly more oxidized from 2 h after treatment. Glutathione reductase activity was more than 50% higher during the first 2 h. Activities of dehydroascorbate reductase and monodehydroascorbate reductase decreased by at least 25% during the first 2 h but were 20% to 60% higher than the control levels after 3 to 6 h. One hour after heat acclimation ascorbate peroxidase activity was increased by 30%. Young leaves appeared to be better protected by antioxidant enzymes following heat acclimation than the cotyledons or stem. Changes in endogenous SA and antioxidants may be involved in heat acclimation.     

Studies on the {beta}-glucosidase System of Trifolium repens L.

Using DEAE-cellulose two distinct ß-glucosidase enzymeshave been identified in white clover; one form is primarilyassociated with the seed, the other with young leaves. Evidenceis presented for the separate nature of ß-glucosidaseand ß-galactosidase activity in dry seed flour andin young leaf tissue. These results are considered in relationto the function of the Li locus in white clover, which is shownto control both ß-glucosidase and ß-galactosidaseactivity in expanding leaves.