Expression of class I chitinase and

Postharvest Biology and Technology 41(2006)

9–15

Expression of class I chitinase and ?-1,3-glucanase genes and

postharvest fungal decay control of table grapes by

high CO 2pretreatment

Irene Romero 1,Mar′?a T.Sanchez-Ballesta 1,Roberto Maldonado,

Mar′?a I.Escribano,Carmen Merodio ?

Departamento de Ciencia y Tecnolog′?a de Productos Vegetales,Instituto del Fr′?o,IF-CSIC,Jos′e Antonio Novais 10,Ciudad Universitaria,E-28040Madrid,Spain

Received 8November 2005;accepted 2March 2006

Abstract

The effect of pretreatment with 20%CO 2plus 20%O 2for 3days was studied with regard to its effectiveness on natural postharvest

decay control and its possible induction of speci?c PR genes in table grapes.Full-length cDNAs encoding a class I chitinase (Vcchit1b )and ?-1,3-glucanase (Vcgns1)were isolated from table grapes (Vitis vinifera L.cv.‘Cardinal’).Our results indicate that this short-term high CO 2treatment had a residual effect and signi?cantly reduced decay incidence of table grapes during low temperature storage and upon transfer to 20?C.Our results indicate that during low temperature storage the expression pattern differed between the two tested PR genes.So,while the abundance of Vcgns1transcript increased sharply at the beginning of storage at 0?C,the increase in Vcchit1b mRNA levels was paralleled by the change in total decay.High CO 2pretreatment restrained the up-regulation of Vcgns1gene expression and delayed the accumulation of Vcchit1b transcript as compared with non-treated grapes.Upon transfer to 20?C after 33days of cold storage,when attainment of maximum total decay was observed,there was a sharp increase in the accumulation of Vcchit1b mRNA in both treated and non-treated grapes,which was higher in the non-treated ones.Our results point out that the expression of class I chitinase and ?-1,3-glucanase genes is not enhanced in CO 2-treated grapes which control total fungal decay.These results suggest,then,that the ef?cacy of high CO 2pretreatment in reducing total fungal decay is not mediated by induction of the above-mentioned PR genes.?2006Elsevier B.V .All rights reserved.

Keywords:Table grapes;Postharvest technology;Carbon dioxide;Botrytis cinerea ;Pathogenesis-related proteins;Gene expression

1.Introduction

Postharvest deterioration of table grapes normally results from fungal decay,largely caused by Botrytis cinerea ,and desiccation of stems and pedicels,which limits prolonged storage of grapes at low temperature.Control against Botrytis disease during storage and transportation of grapes is cur-rently achieved by application of fungicides (Luvisi et al.,1992).However,fungicides and chemical treatments may cause damage to grape berries if used excessively,and some

?Corresponding author.Tel.:+34915492300;fax:+34915493627.E-mail address:merodio@if.csic.es (C.Merodio).1

These authors contributed equally to this work.

consumers develop allergic reactions.Moreover,frequent prophylactic use of fungicides may lead to multiple resistance in the pathogen population (Raposo et al.,1996;Alfonso et al.,2000).Some alternative strategies have been tried in the place of fungicides (Yahia et al.,1983;Crisosto et al.,2002;Lydakis and Aked,2003;Retamales et al.,2003).However,to evaluate the ef?cacy of postharvest treatments for control of decay,we need to know whether these treatments have a direct effect on the fruit’s defense responses.

Plant resistance is correlated with the activation of several defense mechanisms including the transcriptional activation of numerous defense-related genes,deposition of mechani-cal barriers,accumulation of phytoalexins and synthesis of speci?c pathogenesis-related (PR)proteins.Among PR pro-

0925-5214/$–see front matter ?2006Elsevier B.V .All rights reserved.doi:10.1016/j.postharvbio.2006.03.001

10I.Romero et al./Postharvest Biology and Technology41(2006)9–15

teins,the most fully characterized enzymes are chitinases and?-1,3-glucanases which hydrolyze polymers of fungal cell walls,and it has therefore been suggested that both enzymes are involved in plant defense mechanisms against fungal infection(Boller,1985;Collinge et al.,1993).Chiti-nases and?-1,3-glucanases,generally encoded by multigenic families,have been classi?ed by sequence similarity into six and four families,respectively.Also,various studies have demonstrated that transgenic plants overexpressing chitinase and?-1,3-glucanase genes show enhanced resistance to fun-gal infection(Zhu et al.,1994;Grison et al.,1996).

Multiple isoforms of chitinase and?-1,3-glucanase have been reported in grapes(Busam et al.,1997;Robinson et al., 1997),but the available data concerning their expression in grape berries are limited.Increased levels of chitinases and glucanase mRNAs,or their activities,have been reported in grapevine leaves infected by Botrytis cinerea(Derckel et al., 1996;Renault et al.,1996).Busam et al.(1997)reported that the expression of a class III chitinase gene might serve as a marker for systemic acquired resistance in grapevine leaves. In stored tropical fruit,coordinate accumulation of PR pro-teins such as chitinase-like protein and?-1,3-glucanase has been reported in fruit able to withstand chilling temperature storage(Merodio et al.,1998).However,there are no studies showing changes in the transcript accumulation of defense-related genes in response to high CO2levels.

The purpose of this study was to investigate whether the effect of20%CO2on natural postharvest decay control of table grapes directly affects the expression of speci?c PR genes.The effect of pretreatment with20%CO2on chiti-nase activity and expression of cDNAs encoding a class I chitinase(Vcchit1b)and?-1,3-glucanase(Vcgns1)was ana-lyzed.Our results indicate that the tested PR genes are not induced in CO2-treated grapes that are able to control fungal attack.High CO2pretreatment may have an indirect effect on the expression of the class I chitinase gene,and it has a clear effect on avoiding class I?-1,3-glucanase gene induction.

2.Materials and methods

2.1.Plant material

Table grapes(Vitis vinifera L.cv.Cardinal)were harvested at random in Camas(Sevilla,Spain)in July.Early-harvest mature berries were used in this work(12.7%total soluble solids;0.81%tartaric acid).Immediately after harvesting,?eld-packaged bunches were transported to the laboratory, where fruit were forced-air-cooled for14h at?1?C.After cooling,bunches free from physical and pathological defects were randomly divided into two lots and stored at0±0.5?C and95%relative humidity(RH)in two sealed neoprene con-tainers of1m3capacity.Ten plastic boxes containing about 3kg of table grapes per box were stored in each container. One lot was stored under normal atmosphere for33days (non-treated fruit)and the other under a gas mixture con-taining20%CO2+20%O2+60%N2(CO2-treated fruit)for 3days.This CO2concentration was maintained during the pretreatment experiment and it was measured daily using an automated system gas chromatograph equipped with a ther-mal conductivity detector and Poraplot Q column(Varian Chrompack CP20033P).After3days,CO2-treated grapes were transferred to air under the same conditions as the non-treated fruit until the end of the storage period.After12and 33days CO2-treated and non-treated grapes were transferred to ventilated storage containers for2days at20?C and95% RH,to simulate shelf-life during marketing.Ten clusters were sampled periodically during low temperature storage and at the end of their shelf-life.Berries obtained from?ve clusters (approximately300g each cluster)were peeled and the skin was frozen in liquid nitrogen,ground to a?ne powder and stored at?80?C until analysis.

2.2.Evaluation of storage decay

Storage decay was evaluated on the basis of the total decay after removing and weighing the healthy berries.The weight of the decayed berry was calculated by subtracting healthy berries from the total cluster weight.Thus,total decay was expressed as a percentage of decayed berries with respect to the original cluster weight.

2.3.cDNA cloning

Total RNA was isolated from4g of frozen berry skin tis-sues according to Salzman et al.(1999).RT-PCR and5 -3 RACE were used in cloning the full-length cDNA clones of class I chitinase and?-1,3-glucanase.Partial cDNA clones of class I chitinase and?-1,3-glucanase were obtained by RT-PCR.cDNA synthesis was performed with10?g of total RNA from the skin tissues of non-treated and CO2-treated grapes stored at0?C.The reaction was carried out in the pres-ence of500ng of oligo-dT with100units of Reverse Tran-scriptase(Ecogen).Chitinase and?-1,3-glucanase gene DNA fragments were obtained by PCR ampli?cation using the cDNA as template and degenerate oligonucleotide primers complementary to conserved peptide regions of the class I chitinase and?-1,3-glucanase.A550-bp fragment of class

I chitinase was ampli?ed by combining the sense primer

5 -TGC/T TGC AGC AAG/A TTC/T GGC/T TG/TG/C TG-3 ,corresponding to the peptide motif CCS(K/Q)FG(F/W)C of the chitin-binding domain,and the antisense primer5 -A/C/T/GGA C/TTG A/C/T/GGG A/C/T/GGT CAT CCA GAA CCA-3 derived from the peptide WFWMT(A/P)QS. A850-bp fragment of class I?-1,3-glucanase was ampli-?ed using a sense primer5 -TA/C/T/GG GTG TA/C/T/GT GC/TT ATG GAA TGC T-3 derived from the conserved peptide VGVCYGML,and the antisense primer5 -CTC A/GTC AAA CAT G/AGC AAA A/T/C/GAG/T/A G/A-3 corresponding to the peptide(L/I)FAMFDE.Both PCR-fragments were cloned into pGEMT(Promega)and con-?rmed by sequencing.The sequences were used to select

I.Romero et al./Postharvest Biology and Technology41(2006)9–1511

oligonucleotide primers for performing both5 -and3 -rapid ampli?cation of cDNA ends(RACE)to obtain the full-length. The5 /3 RACE kit(Roche)was applied according to the manufacturer’s instructions using total RNA isolated to syn-thesize the cDNA mentioned above.The chitinase and?-1,3-glucanase5 and3 PCR-RACE products were subcloned and sequenced.The sequences of these PCR-RACE products and the chitinase550-bp and?-1,3-glucanase850-bp internal PCR products yielded overlapping PCR products extending to the5 and3 ends of the cDNA.

2.4.Northern-blot hybridization

Samples of denatured total RNA(10?g)from the skin were fractionated and blotted as described in Sanchez-Ballesta et al.(2000).Equal loading was con?rmed by ethid-ium bromide staining and by membrane staining with methy-lene blue.As probes we used the full-length cDNAs Vcchit1b and Vcgns1random-primer labeled with?32P-dCTP.Filters were prehybridized and hybridized at65?C in7%sodium dodecyl sulfate,0.33M phospate buffer,pH7.2and1mM EDTA,then washed twice in2×SSC,0.1%SDS at room temperature and twice in0.1×SSC,0.1%SDS at65?C and exposed to Kodak X-Omat SX?lm at?80?C.Autoradio-graphs were digitally scanned and band densities quanti?ed by20image densitometry using Scion Image Software(Scion Corporation,Frederick,MD).The100%was assigned to the maximum optical density value achieved in each northern and the rest of optical densities were normalized to the maximum value and expressed as percentage of relative accumulation (RA).

2.5.Chitinase extraction and activity

Protein was extracted by homogenizing ground frozen berry skin tissues(250mg fresh weight)at4?C in5mL of100mM sodium acetate buffer,pH5.0and2%(w/v) polyvinylpyrrolidone.The homogenate was centrifuged at 27,000×g for30min at4?C and the clari?ed supernatant was recovered.Chitinase activity was assayed using a com-mercial blue enzyme substrate,CM-chitin-RBV solution (Loewe),based on the precipitability of a non-degraded, highly polymerized substrate when acid is added.Chitinase activity was determined utilizing different dilutions from the crude extract until a linear range of activity versus substrate was established.Enzyme activity was assayed by incubating a standard reaction mixture containing70?L of diluted crude enzyme extract(14?L of original crude extract),200?L of aqueous CM-chitin-RBV(2mg mL?1)and100mM sodium acetate buffer,pH5.0to yield a?nal reaction volume of 0.8mL,for15min at37?C.The reaction was stopped by adding200?L of2N HCl and cooling on ice for10min. The mixture was then centrifuged at10,000×g for5min to precipitate the non-degraded substrate.The supernatant con-taining degraded polymers was diluted(1:1,v/v)with nanop-ure water and absorbance was measured at550nm against a blank reaction(incubation mixture with HCl-treated crude extract).Speci?c enzyme activity was de?ned as“absorbance at550nm h?1mg?1of protein”.Protein concentration was measured by the Bradford(1976)method using a protein-dye reagent(Bio-Rad)and BSA as a standard.

2.6.Statistical analyses

Data from at least three replicates per sample were sub-jected to analysis of variance(ANOV A)(Stargraphics Pro-gram,STSC,Rockville,MD).Multiple variance analysis was employed to determine the signi?cance of the data at P≤0.05.The results presented here are representative of data from two separate experiments performed in succession. 3.Results

3.1.Isolation and sequence analysis of Vcchit1b and Vvgns1genes

The full lengths of the Vcchit1b(GeneBank Acces-sion no.DQ267094)and Vcgns1(GeneBank Accession no.DQ267748)cDNAs were isolated using RT-PCR and 5 -3 RACE strategies.The Vcchit1b cDNA consisted of 1133bp with an open reading frame of942bp and encoded a polypeptide of314amino acids.The amino acid sequence of VcCHIT1b shared100%identity with the class I chitinases VCHIT1b(Busam et al.,1997)and VvCHIT1a(Robert et al.,2002),previously isolated from‘Ugni Blanc’and‘Pinot Noir’cultivars,respectively.In addition,sequence domains typical of class I chitinase,such as a putative signal pep-tide of20amino acids followed by a cysteine-rich chitin-binding domain,were found in the N-terminal sequence.A hinge domain of only three amino acid residues separated the cysteine-rich domain from the catalytic domain.Also, the VcCHIT1b protein contained a C-terminal extension of at least seven amino acids,suggesting a vacuolar localization. The mature protein of286amino acids presented a calculated p I of8.44and a calculated molecular mass of31.27kDa.

The full-length cDNA sequence of the Vcgns1consisted of1316bp and contained an open reading frame of1080bp encoding a protein of360amino acid residues.The amino acid sequence of VcGNS1shared69.1and74.5%identity with the basic class I?-1,3-glucanases of Hevea brasilien-sis and Nicotiana plumbaginifolia(gns1)(Chye and Cheung, 1995;Castresana et al.,1990),https://www.wendangku.net/doc/fa16942945.html,parison with other?-1,3-glucanases in the databases revealed similari-ties of only40–55%.The deduced amino acid sequence of VcGNS1contains both N-and C-terminal signal peptide sequences of22and21amino acids,respectively,present in the class I?-1,3-glucanase proteins and required for tar-geting the protein to the vacuole(Meins et al.,1992).It was assumed that N-and C-terminal processing occurs in a man-ner similar to that reported for class I?-1,3-glucanase from

12I.Romero et al./Postharvest Biology and Technology41(2006)9–15 tobacco(Shinshi et al.,1988),a mature protein of317amino

acids with a calculated p I of9.68and a molecular mass of

34.6kDa.

3.2.Effect of high CO2levels on total fungal decay

during postharvest storage at low temperature

In non-treated grapes,total decay increased progressively

during postharvest storage at0?C,reaching levels of about

25%after33days.The bene?cial effect of high CO2levels on

gray mold incidence was demonstrated since the?rst diseased

berries(1.7%of the total decay)were detected only after22

days of storage(Fig.1),while in non-treated fruit the onset of

the increase was observed after12days.The levels attained

at the end of storage(33days)were signi?cantly lower in

CO2-treated fruit than those observed in non-treated fruit.

3.3.Effect of high CO2levels on class I chitinase and

β-1,3-glucanase mRNA levels and chitinase activity in

table grapes during postharvest storage at low

temperature

In the skin of non-treated grapes,low-temperature stor-

age drastically increased levels of the Vcgns1mRNA;these

remained stable throughout storage,and a decrease in abun-

dance was observed only after33days.However,in CO2-

treated grapes although accumulation of the Vcgns1transcript

also increased rapidly at0?C,this increase was smaller than

in non-treated grapes(Fig.2A).Storage at0?C also induced

a slow but progressive accumulation of the Vcchit1

b tran-

script in the grape skin,reaching the maximum by day28

and decreasing slightly thereafter(Fig.2A).However,the

CO2treatment delayed accumulation of the class I chitinase

mRNA levels,increasing after22days and remaining stable

until the end of storage(Fig.2A).With regard to chitinase

activity(Fig.2B),it is interesting to note that although

activ-

Fig.1.Total decay(%)in non-treated and CO2-treated‘Cardinal’table grapes stored at0?C for12,22and33days.Values are the means of three replicate samples±

S.E.Fig.2.Effect of high CO2levels on Vcgns1and Vcchit1b mRNA accumula-tion in the skin of‘Cardinal’table grapes stored at0?C(A).Ten micrograms of total RNA from the skin was fractionated by gel electrophoresis,blotted and hybridized with the Vcchit1b and Vcgns1probes.The intensity of the bands was quanti?ed by scanning densitometry of the autoradiographs.Opti-cal densities values were normalized to the maximum value and expressed as percentage of relative accumulation(RA).The equivalence of RNA loading of the lanes was demonstrated by methylene blue staining.(B)Chitinase activity patterns in the skin of non-treated and CO2-treated‘Cardinal’table grapes during storage at0?C.Enzyme activity was expressed as absorbance at550nm h?1mg?1of protein.Data are averages of two separate experi-ments(n=6)and S.E.are shown by vertical bars.

ity did not increase progressively during storage at0?C as occurred with the Vcchit1b mRNA levels,the transient peaks in the activity were observed at the time of the increases in accumulation of the transcript(12and28days)(Fig.2A).By comparison,in CO2-treated grapes the transient increase in the chitinase activity was observed after22days of storage, when an increase in the accumulation of Vcchit1b transcript was observed.

3.4.Changes in class I chitinase gene expression, chitinase activity and total decay during the transfer of

CO2-treated and non-treated grapes to20?C

After12and33days of storage at0?C,changes in Vcchit1b gene expression(Fig.3A),chitinase activity (Fig.3B)and total fungal decay(Fig.3C)in CO2-treated and non-treated fruit transferred to20?C during2days, were analyzed.Upon transfer after12days of storage,the levels of Vcchit1b transcript and chitinase activity in non-treated grapes decreased slightly.In CO2-treated fruit a slight increase was observed in both Vcchit1b gene expression and chitinase activity.The transfer to20?C after33days of cold storage drastically increased the levels of Vcchit1b transcript

I.Romero et al./Postharvest Biology and Technology41(2006)9–15

13

Fig.3.The pattern of change of mRNA levels(A),chitinase activity(B) and total decay(C)in the skin tissues of non-treated and CO2-treated‘Car-dinal’table grapes stored12and33days at0?C and transferred to20?C for2days.(A)Ten micrograms of total RNA from the skin was fractionated by gel electrophoresis,blotted and hybridized with the Vcchit1b probe.The intensity of the bands was quanti?ed by scanning densitometry of the autora-diographs.Optical densities values were normalized to the maximum value and expressed as percentage of relative accumulation(RA).The equivalence of RNA loading of the lanes was demonstrated by methylene blue staining.

(B)Enzyme activity was expressed as absorbance at550nm h?1mg?1of protein.Data are averages of two separate experiments(n=6)and S.E.are shown by vertical bars.(C)Total decay(%)values are the means of three replicate samples±S.E.

in skin tissues of both non-treated and CO2-treated grapes, but this increase was even higher in non-treated ones.This sharp increase in Vcchit1b transcript did not correlate with the chitinase activity.However,it was consistent with the total decay increases observed in both series of samples.

4.Discussion

Advances in postharvest handling of table grapes,includ-ing the development of treatments for controlling storage decay while avoiding the use of chemicals,have been the focus of interest in recent years(Palou et al.,2002;Chervin et al.,2005).Most of the research has focused on the effective-ness of different postharvest treatments to counteract disease development in table grapes inoculated with B.cinerea.The use of controlled atmosphere(CA)packaging has been pro-posed as a suitable treatment to replace SO2fumigation as a means of controlling grape decay(Yahia et al.,1983;Crisosto et al.,2002;Art′e s-Hern′e ndez et al.,2003).However,in the case of high CO2concentrations,applied as a pretreatment for short periods of time,there is little information about its effectiveness in retarding the appearance of symptoms caused by fungal attack and its possible mode of action.Therefore, with a view to assess how effectively high CO2concentra-tions are able to activate speci?c defense mechanisms against fungal attack,we focused on an analysis of PR gene expres-sion in CO2-treated and non-treated grapes.Class I chitinase (Vcchit1b)and?-1,3-glucanase(Vcgns1)cDNAs were iso-lated from grapes of the‘Cardinal’cultivar of V.vinifera. The Vitis chitinase and?-1,3-glucanase analyzed here were structurally very similar to the corresponding proteins from Vitis or other species.The VcCHIT1b protein is composed of three domains present in the class I chitinase:a Cys rich chitin-binding domain,a Pro rich hinge region and a highly conserved catalytic domain.Moreover,the class I chitinase appeared to be very well preserved in Vitis,as the deduced VcCHIT1b protein was identical to the vacuolar class I chiti-nase from leaves of‘Ugni Blanc’(Robert et al.,2002)and cell cultures of‘Pinot Noir’(Busam et al.,1997).The predicted amino acid sequence of VcGNS1contains a preserved tryp-tophan residue,which is implicated in the interaction with the glucan substrate(Ori et al.,1990),and a preserved glutamate, which has been shown to act as a nucleophile in the catalytic mechanism(Varghese et al.,1994).The deduced amino acid sequence of VcGNS1contains both N-and C-terminal signal peptides,class I?-1,3-glucanases are synthesized as prepro-teins and the N-and C-terminal extensions are cleaved during or after transport of the protein to the vacuole(Shinshi et al., 1988).

While expression of chitinase and?-1,3-glucanase genes has been extensively studied in plants subjected to speci?c stress conditions,there is no information in response to high CO2levels during postharvest storage applied against fun-gal infection.Our results indicate that in table grapes cv. Cardinal,the enhanced expression of a cDNA encoding?-1,3-glucanase(Vcgns1)(Fig.2A)observed in non-treated grapes during low temperature storage was constrained by pretreatment with high CO2levels,using as a probe the full-length cDNA.Moreover,in these conditions we cannot?nd any relation between this gene and fungal infection.The marked accumulation of Vcgns1mRNA in non-treated grapes at the beginning of storage at0?C may indicate that factors other than fungal infection are involved in its induction.In this connection,mRNA accumulation of a class II and class III?-1,3-glucanase from tomato and mandarin,respectively, increased during chilling temperature storage(Ding et al., 2002;Sanchez-Ballesta et al.,2006).Although the effect of low temperature on the expression of?-1,3-glucanase requires further study,high CO2levels appears to be a clear effect in avoiding the induction of class I?-1,3-glucanase

14I.Romero et al./Postharvest Biology and Technology41(2006)9–15

genes.The accumulation of Vcchit1b transcript(Fig.2A)dur-ing low temperature storage was paralleled by the change in total decay(Fig.1),using as a probe the full-length cDNA.In this work we observed that total decay increased gradually in non-treated grapes stored at0?C.In CO2-treated grapes,on the other hand,total decay had not increased after22days of storage,and class I chitinase gene expression was delayed. With regard to chitinase activity,during low temperature stor-age the sharp transient increases in total activity matched the increase in Vcchit1b transcript levels.Moreover,a differ-ential increase in chitinase activity was observed when the increase in Vcchit1b transcript levels was above30%in both non-treated and CO2-treated grapes.Upon transfer to20?C after33days of storage at0?C,there was a sharp increase in the accumulation of Vcchit1b mRNA in both the treated and non-treated grapes,although it was smaller in the CO2-treated fruit.With regard to chitinase activity,the transfer to 20?C at the end of the storage period in non-treated fruit was associated with a decrease in the levels of chitinase activ-ity,although the expression of class I chitinase was sharply enhanced.At this time,chitinase activity in the skin tissues of non-treated grapes decreased signi?cantly,reaching values 45%lower that those quanti?ed in freshly harvested grapes and55%lower than in CO2-treated grapes.In CO2-treated grapes,contrary to what was observed in non-treated grapes, the chitinase activity increased by about73%with respect to the values prior to transfer.These results are consistent with the change in total decay observed in both series of samples.Effective control against B.cinerea and Penicil-lium digitatum has been reported by means of endochitinase combined in mixtures with other antifungal compounds(Ali et al.,2003).During transfer to20?C,the lack of correla-tion between Vcchit1b transcript levels and chitinase activity, mostly in non-treated grapes,could be explained in terms of the kinetic and regulatory properties of chitinase enzyme. Many factors,including different post-translational modi-?cations,could be involved in the modulation of chitinase activity.Several isoforms of chitinase have been identi?ed, and it is generally considered that these isoforms represent the products of different members of the chitinase gene family. Additional research is required to study possible mechanisms of regulation of chitinase activity and may provide some use-ful insights to help restrain fungal infection.

In this work a close link has been established between high CO2pretreatment and control of fungal decay.Our results indicate that the expression of class I chitinase and?-1,3-glucanase genes is not enhanced in CO2-treated grapes that are able to control fungal decay.However,in CO2-treated grapes,contrary to what was observed in non-treated grapes, there was an upward trend in chitinase activity at the time of maximum growth of fungal decay at20?C.We suggest that a mechanism other than induction of the tested PR genes renders grape berries less susceptible to natural postharvest fungal infection.Elsewhere,we reported that the applica-tion of20%CO2for short periods of time was effective in reducing the senescence-like responses in peel tissues of fruit (Escribano et al.,1997)and controlling speci?c processes associated with low temperature storage(Maldonado et al., 2002).Further analysis is needed to ascertain the mechanism whereby CO2treatment can in?uence the tolerance of table grape to fungal attack before the appearance of the?rst symp-toms and may provide some useful insights to help restrain fungal infection during prolonged low temperature storage. Acknowledgements

This work was supported by research grants(AGL2002-02308/ALI and AGL2005-04502/ALI)from CICYT(Spain). M.T.S.-B.and R.M.were supported by a postdoctoral con-tract from Comunidad de Madrid and by a fellowship from MCyT(Spain),respectively.The authors are grateful to Fru-taria SAT for providing tables grapes.

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Escribano,M.I.,Del Cura,B.,Mu?n oz,T.,Merodio,C.,1997.The effect of high carbon dioxide at low temperature on ribulose1,5-biphosphate carboxylase and polygalacturonase protein levels in cherimoya fruit.

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Lydakis,D.,Aked,J.,2003.Vapour heat treatment of Sultanina table grapes.I:control of Botrytis cinerea.Postharvest Biol.Technol.27, 109–116.

Maldonado,R.,Molina-Garc′?a,A.D.,Sanchez-Ballesta,M.T.,Escribano, M.I.,Merodio,C.,2002.High CO2atmosphere modulating the phe-nolic response associated with cell adhesion and hardening of Annona cherimola fruit stored at chilling temperature.J.Agric.Food Chem.

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经典中文英文翻译

经典中文的英译 但愿人长久，千里共婵娟。 We wish each other a long life so as to share the beauty of this graceful moonlight, even though miles apart. 独在异乡为异客，每逢佳节倍思亲。 A lonely stranger in a strange land I am cast, I miss my family all the more on every festive day. 大江东去，浪淘尽，千古风流人物。 The endless river eastward flows; with its huge waves are gone all those gallant heroes of bygone years. 二人同心，其利断金。 If two people are of the same mind, their sharpness can cut through metal. 富贵不能淫，贫贱不能移，威武不能曲，此之谓大丈夫。 It is a true great man whom no money and rank can confuse, no poverty and hardship can shake, and no power and force can suffocate. 海内存知己，天涯若比邻。 A bosom friend afar brings distance near.

合抱之木，生于毫末，九层之台，起于累土；千里之行始于足下。 A huge tree that fills one’s arms grows f rom a tiny seedling; a nine-storied tower rises from a heap of earth; a thousand li journey starts with the first step. 祸兮，福之所依；福兮，祸之所伏。 Misfortune, that is where happiness depends; happiness, that is where misfortune underlies. 见贤思齐焉，见不贤而内自省也。 On seeing a man of virtue, try to become his equal; on seeing a man without virtue, examine yourself not to have the same defects. 江山如此多娇，引无数英雄尽折腰。 This land so rich in beauty has made countless heroes bow in homage. 举头望明月，低头思故乡。 Raising my head, I see the moon so bright; withdrawing my eyes, my nostalgia comes around. 俱往矣，数风流人物，还看今朝。 All are past and gone; we look to this age for truly great men.

灯具类型及灯具知识

灯具类型 一旦我们知道所需要照明的是什么，下一步就得开始选择采用什么方式或灯具来进行照明。每个城市都有灯饰城，那些地方有各式各样，各种大小的灯具，大家可以利用这些灯具来完成我们所需要的上面所提及的一般照明呀，任务照明呀，重点照明呀。 灯具类型一：大厅或者大堂灯具（别墅里会见到：） 这种灯具能营造一种适宜的氛围，它所运用的是一般照明这种方式，起到欢迎来宾，确保他们能够安全地进入家里的其它区域。我们可以使用天花灯具、挂式灯具等安装在走道、楼道和进门的地方。 灯具类型二：花灯 花灯的样式正如其名，花样奇多花灯是一种能增加辉光的灯具，很适合用于餐厅等区域，能给我们的就餐、娱乐等活动进行一般性照明。它们有时也会被用于卧室，大厅、起居室，有时放到钢琴台顶上有是一种很有趣的照明方式。有些样式的花灯采用的是向下照明灯具组合，作为家庭活动、桌面游戏来提供任务照明方式，也可以用于桌面摆设的重点照明。花灯所采用的光源为白炽灯和卤钨灯这两种。值得提及的是上面这两种光源可以很轻松地进行调光，所以只需加一个调光控制器就可以控制光强来满足心理和活动这两方面的需求。 灯具类型三：吊灯 这种灯具于上面所提及的花灯类型有点内似，HOHO。但是它的外形较小一点的说。吊灯提供的是任务照明和一般照明。采用了环状或锥状等组件来防止眩光，它们通常被用于吊式安装，放到餐桌上，游戏桌上，（还有麻将桌上哟），橱房柜台上或其它场合。将它们放到桌子的末端，另外采用桌面台灯进行补光照明也是一种有趣的效果。同样的它们也可以采用调光控制器，使我们更加灵活地运用灯光来满足需求。 灯具类型四：天花灯（或吸顶灯） 天花灯用于一般照明。他们被运用到大厅、大堂、卧室、橱房、浴室、洗衣间、娱乐室等使用率较高的房间。它们采用的光源有白炽灯呀、荧光灯呀和节能灯这三种。 灯具类型五：壁灯 这种灯具通常用于补充式一般、任务和重点照明。通常被做为餐厅花灯的配角，也可以用于过道呀、卧室、起居室的照明。另外我们也会在浴室的洗潄台的镜子那里看到这种灯的

Barone中文操作手册

1.2运行程序 执行【开始】?【所有程序】?【Zebra BAR-ONE v5.0】?单击【Design Program】即可运行程 序，程序初始运行接口如下： 2 2.1菜单及按钮说明 软件运行后如下图所示: 菜单在最上面自左向右为:如下图 【File】-文件, 【Edit】-编辑, 【Veiw】-视图, 【Label】-标签, 【Options】-选项, 【ODBC】-数据库联接, 【Report】-报表, 【Window】-窗口, 【Help】-帮助 按钮在第二行从左向右依次为: 【新建文档】, 【打开文档】, 【保存文档】, 【剪切】, 【复制】, 【粘贴】, 【撤消】, 【重复】, 【指针】, 【条码】, 【线条】, 【圆】, 【字符】, 【变量】, 【图形】, 【测试打印】, 【打印】, 【放大】, 【缩小】, 【帮助】 2.2选择打印机??? 单击【File】?【Printer setup】?【Main printer】弹出如下图所示 ?在【Printer Type】选项选择Z105S/105SE-300dpi ?在【Port】选择COM1: 其它使用默认值. ?单击【OK】完成设定. 2.3新建标签文档 单击【File】?【New】即可。 2.4设置标签文档 ??单击【File】?【Label setup】,或单击【Label】?【Setup】出现对话框， 如下图所示： 【Label dimensions】中设定标签的宽度和高度, 【Width, Depth】, 【Margins】中设定上边距和左边距【Left, Top】, 【Units】中设定度量单位【mm】-毫米, 【inches】英寸,

中文姓氏的英文翻译对照表

中文姓氏的英文翻译对照表 中文姓氏的英文翻译对照表.txt我们用一只眼睛看见现实的灰墙，却用另一只眼睛勇敢飞翔，接近梦想。男人喜欢听话的女人，但男人若是喜欢一个女人，就会不知不觉听她的话。在互联网上混的都时兴起个英文名字，一是方便注册用户名，二是有个好英文名容易显得自己比较Cool。但是起英文名时，中文姓氏还是要保留的，并且姓氏一般都有专门的英文翻译，比如“刘德华”的英文名是Andy，刘姓对应的英文翻译是Lau，所以全称便是“Andy Lau”。当然了，我们一般人直接用汉语拼音作为姓氏的英文翻译也可以，但在比较正式的场合下，最好还是用相应的英文翻译。 姓氏的英文翻译跟汉语拼音是有一些细微差别的，这主要由中西方人发音的不同特点来决定的。比如，从声母上来看，D开头的姓，英文翻译对应的是T，G对应的是K，X对应的是HS，Z、J 一般对应的是C，韵母也会有一些细微差别。详细的，请参考如下中文姓氏的英文翻译对照表，正在起英文名的朋友可以看看。 A: 艾--Ai 安--Ann/An 敖--Ao B: 巴--Pa 白--Pai 包/鲍--Paul/Pao 班--Pan 贝--Pei 毕--Pih 卞--Bein 卜/薄--Po/Pu 步--Poo 百里--Pai-li C: 蔡/柴--Tsia/Choi/Tsai 曹/晁/巢--Chao/Chiao/Tsao 岑--Cheng 崔--Tsui 查--Cha

常--Chiong 车--Che 陈--Chen/Chan/Tan 成/程--Cheng 池--Chi 褚/楚--Chu 淳于--Chwen-yu D: 戴/代--Day/Tai 邓--Teng/Tang/Tung 狄--Ti 刁--Tiao 丁--Ting/T 董/东--Tung/Tong 窦--Tou 杜--To/Du/Too 段--Tuan 端木--Duan-mu 东郭--Tung-kuo 东方--Tung-fang E: F: 范/樊--Fan/Van 房/方--Fang 费--Fei 冯/凤/封--Fung/Fong 符/傅--Fu/Foo G: 盖--Kai 甘--Kan 高/郜--Gao/Kao 葛--Keh 耿--Keng 弓/宫/龚/恭--Kung 勾--Kou 古/谷/顾--Ku/Koo 桂--Kwei

灯具知识汇总

灯具知识汇总 灯具常识筒灯豆胆灯射灯天花灯 一般的尺寸有哪些？？宽度和高度？？主要谁能告诉我不同尺寸宽度和高度分 别是多少？？ 请专业人士回答，广告莫入，如果真正能解决问题，绝对是高分 首先说筒灯吧。 一般筒灯尺寸都很多。分家用还是公用了。家用有2寸，3寸，3寸半，4寸。开孔一般是7公分。8公分。9公分，10公分和12公分。。。一般高度比开孔尺寸多2公分左右。例如2寸的高度大概是到8公分。4寸的高度也不会超过12公分 豆胆灯的尺寸就比较多了。有单头。双头。三头。和四头。四头分别还有正方和厂房。而且豆胆的尺寸也很多公MR16（就是石英灯杯）MR70MR 90 MR111 太多了。 射灯目前我知道的有 4.5公分开孔的。不加灯杯高度大概2公分 灯杯高度大概4公分 5.5公分开孔的。7.5公分开孔的。 天花灯一般指装厨房洗手间或者过道嵌入式的类型。一般尺寸有30CM0*30CM,20CM*20CM ,16CM*16CM 高度都在6公分左右。 不是很齐全。但是大概我就知道这么多了。。 想要具体的。可以去灯饰店看看呀。。 灯具常识筒灯豆胆灯射灯天花灯有什么区别我想做灯饰，家装为主，店里面那些要上那些可以不用上货 满意回答 射灯和天花灯其实是一个概念，豆胆灯也和它们一样是用的灯杯，主要是局部照射，一般用于背景墙，电视墙。而筒灯则是上节能灯，属于散光，主要用于普通照明

单头豆胆射灯和筒灯哪一个照明效果更好一些？？ 2010-9-1 22:11 提问者：|浏览次数：563次 其他回答共3条 2010-9-1 23:10 |二级 主要是看你往什么地方照明了，如果是重点照明还是斗胆灯比较好。如果是大面积照明就选用筒灯，这两个照明效果不一样。 |评论 2010-9-2 00:29 |二级 筒灯里面装什么光源？不同光源效果不一样，节能灯和金卤灯就不一样，不知道你筒灯里面装什么光源 在什么情景下用什么样的灯我也不知道，你这个问题问的太肤浅了，补充全了再问！ |评论 2010-9-2 01:28 |十六级 斗胆灯和筒灯的使用界面不同，主要还是看你在哪一方面使用。 牛眼灯和豆胆灯和格栅灯的用途和区别 2011-6-20 14:58 提问者：匿名|浏览次数：729次 2011-6-27 12:37 满意回答 牛眼灯和斗胆灯是比较相似的用途都是聚焦光源突出被照物体的。 格栅灯一般指的是办公室，医院，教室内用的，起到一般室内照明用途的灯具 什么是豆胆灯？为什么叫豆胆灯？ 2008-11-17 19:24 提问者：|悬赏分：10|浏览次数：2140次 2008-11-17 21:45 满意回答 ①豆胆灯面板采用优质铝合金型材，经喷涂处理，呈闪光银色，防锈、防腐蚀。 ②反光罩采用进口高纯度阳极电化铝，经氧化处理，不易氧化，光束集中。性能：①配电子变压器，输入电压220V，频率50—60Hz ②适用光源：AR70 50W、75W、100W ③光效：8度聚光型，24度散光型。特点：①双环结构，光线方向可调节。②中心区域可增加35%的光亮度。安装方式：嵌入式适用场所：家具展厅、服装店.

功放与音箱匹配技巧与注意事项

功放与音箱匹配技巧与注意事项 对功放与音响之间的匹配问题，除了音色软搭配之外（音色搭配常说软硬之分，是根据设计者对音色走向的设计和用料，而具有的特征和个性）还有一些技术指标上的硬搭配。软搭配是经验积累和个人爱好以实际感受为主，硬搭配则以数据和基本技术常识来定夺，下列就来简述硬搭配有关方面的问题。 阻抗匹配 1. 真空管功放（胆机）与音箱匹配时，放大器的输出阻抗应与音箱阻抗相等，否则会出现降低输出功率和增大失真等现象。好在大都胆机都有可变输出阻抗匹配接口如4-8-16欧，与音箱阻抗匹配已趋简单。 2. 对于晶体管功放（石机）与音箱阻抗的匹配 A) 音箱阻抗比功放输出阻抗高时，除了输出功率不同程度的降低外，无其它影响。 B) 音箱阻抗比功放输出阻抗低时，输出功率相应成比例增加，失真度一般不会增加或增加一点点可忽略。但匹配时音箱阻抗不能太低，如低至2奥姆（指2只4奥姆音箱并联时），此时只有功放功率富裕量大，并使用性能良好的大功率管和多管并联推挽，一般对这样的功放无影响。反之，一般普通功放富裕量不大，而功放管的pcm、lcm不大，当音量又开得很大时，这时失真会明显增大，严重时机毁箱亡，切切注意。 功率匹配

1、从原则上来讲，音箱额定功率与功放额定功率不一致时，对于功放来说，它的功率大小只与音箱阻抗有关，而与音箱额定功率无关。无论音箱功率与功放功率是否相同，对功放工作无影响，只是对音箱本身安全有关。 2、如果音箱阻抗符合匹配要求，而承受功率比功放功率小，则推动功率充足，听起来很舒服。这就是常说的功放储备功率要大，才能充分地表现出音乐全部内涵，尤其是音乐中的低频部分，表现更为生动、有力。这是一种较好的匹配。 3、如果音箱的额定阻抗大于功放的额定功率，虽然二者都能安全的工作，但这时功率放大器推动功率显得不够，会觉得响度不足，往往出现已经开到饱和状态，失真加剧，仍感到力不从心。这是一种较差的匹配。 按阻尼系数匹配

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灯具安规知识 灯具安规知识 一．相关定义 1．灯具：凡是能分配，透出或转变一个或多个光源发出的光线的一种器具，并包括支撑、固定和保护光源必需的部件（但不包括光源本身），以及必需的电路辅助装置和将它们与电源连接的设施。 2．普通灯具：提供防止与带电部件意外接触的保护，但没有特殊的防尘、防固体异物和防水等级的灯具。 3．可移动式灯具：正常使用时，灯具连接到电源后能从一处移动到另一处的灯具。 4．固定式灯具：不能轻易的从一处移动到另一处的灯具，因为固定以致于这种灯具只能借助于工具才能拆卸。 5．嵌入式灯具：制造商指定完全或部分嵌入安装表面的灯具。 6．带电部件：在正常使用过程中，可能引起触电的导电部件。中心导体应当看作是带电部件。 7．EN安全特低电压（SELV－safety extra-low voltage）：在通过诸如安全隔离变压器或转换器与供电电源隔离开来的电路中，在导体之间或在任何导体与接地之间，其交流电压有效值不超过50V。 8．UL低压线路：开路电压不超过交流电压有效值30V的线路。 9．基本绝缘（EN）：加在带电部件上提供基本的防触电保护的绝缘。耐压应在 2U+1000V以上（U：当地的电网电压）。 10．补充绝缘（EN）：附加在基本绝缘基础上的独立的绝缘，用于基本绝缘失效时提供防触电保护。耐压值应在2U+1750V以上（单层）。 11．双层绝缘（EN）：基本绝缘与补充绝缘组成的绝缘，耐压值应在4U+2750V以上（即基本绝缘与补充绝缘耐压之和）。 12．增强绝缘（EN）：绝缘效果与双层绝缘相当的一种加强性绝缘。从总体上看，一般只为一层，但也可由多层组成，且各层不可明确进行分割并单独测量。耐压值应在 4U+2750V以上。 13．CLASS O级灯（EN）：仅以基本绝缘为电击保护措施的灯具，无接地等保护措施。 14．CLASS I级灯（EN）：除了基本绝缘为电击保护措施外，还采用了其它如接地等保护性措施的灯具。 15．CLASS II级灯具（EN）：采取双重绝缘或增加绝缘为电击保护措施的灯具。其绝缘效果不依赖于接地或安装条件。 16．CLASS III级灯（EN）：使用特低安全电压（SELV）为防电击保护方式的灯具。 17．普通可燃材料（normally flammable material）：材料的引燃温度至少为200℃，并且在此温度时该材料不至于变形或强度降低。例如木材及厚度大于2mm的以木材为基质的材料。 18．易燃材料（readily flammable material）：普通可燃材料和非可燃材料以外的一种材料。例如木纤维和厚度小于2的以木材为基质的材料。 19．非可燃材料（non-combustible material）：不能助燃的材料。例如金属、水泥等。 20：定型试验（type test）：对定型试验样品进行测试，其目的是检验某一给定产品的设计是否符合有关标准的要求，但通过定型测试后的产品在生产阶段是否符合标准要求，需要以测试报告及相关文件来保证。

英文翻译成中文

第四部分翻译 Part Ⅰ英译汉 练习： Unit 1 1.年轻时，他对学业漫不经心，加之他一直不愿考虑运动员以外的职业，到这时候，这一切终于给他带来了不幸。 2.护士们对不得不日复一日地参与欺骗病人的做法也许深恶痛绝，但要抵制却感到无能为力。 3.我不会在初版的《失乐园》上乱写乱画，就像我不会把一幅伦勃朗的原作连同一套蜡笔交给我的婴儿任意涂抹一样。 4.只有假设地球表面呈曲线状，这一现象才能得到解释。 5.鹿减少生存所需的能耗以增加越冬生存的机会，从生物学的角度看是合情合理的。 6.不论好坏，不论是何结果，美国人不仅会一概接受，还要去铲除那些反对者，尽管对于成千上万的人来说，这决定与自己的意愿背道而驰。 7.你可曾为了接电话在洗澡时从浴室冲出来，或是嚼着饭从饭桌旁站起来，或是昏昏沉沉的从床上爬起来，而结果却是有人打错了。 8.实际上，大把花钱的满足感大于商品本身带给他们的乐趣。 9.但是蓝色也可以表示伤感（我很伤感），白色常代表纯洁，尽管在中国，人们在婚礼上穿白的，在葬礼上穿黑的。 10. 晚上十点到十二点，美国处在权力真空状态——除了纽约广播公司总部和两家大的新闻机构之外，全国范围内就再没有别的信息中心。 Unit 2 1) 1800年英国与法国之间将爆发一场持续15后的大战。 2) 我相信，到1816年，英国将在滑铁卢村附近赢得一场伟大战役的胜利。 3) 然而，到1870年，对于英国来说，德国将成为一个比法国更具危险性的国家。 4) 在20世纪初，俄国、美国和日本将成为大国，而英国将不再是世界上最强大的国家了。 5) 反过来，农民的业绩大小取决于农业的组织形式，经济环境，市场结构这些与之息息相关的因素。 6) 他被接回来时，不停地跟人讲，一些可怕的怪物瞪着眼睛盯着他，把他带到了一个宇宙飞船上。 7) 烫伤大多数发生在老人和孩子身上，往往是由于浴室里水温太高而造成的。 8) 尽量多地了解可能发生的事情，这样你可以提前做好准备。 9) 市场的变化迫使很多网站关闭，而其它网站也仅是勉强维持。 10）因为在农民生产率低下的国家，需要劳动人口中大多数人种粮食，因此就没有多少人从事投资货物的生产或进行经济增长所必须的其它活动。 Unit 3 1. 在牛顿之前，亚里士多德已经发现物体的自然状态是静止的，除非有力作用于物体。所以运动着的物体会停下来。 2．人们在家中或是类似家的地方感觉最为亲密——和一个或几个亲近的人呆在一起——也就是在私人交谈的时候。 3．当一个人长时间在干道或高速公路上驾车行驶，就会存在两个问题：一是如何保持稳定的车速；二是如何确保他不撞上前面的车。 4．这个系统尤其适用于汽车拥挤的情况，因为电脑不仅能够控制车速，与前面车子的距离，还能够控制方向。

功放和音箱的接线方法

功放和音箱的接线方法 1、功放分定压式与定阻式： 定压功放一般用于公共场合的公共广播，其特点为单声道输出、高电压低电流输出。 定阻功放多用于专业场合，其特点为立体声输出、低电压高电流输出。 2、我们的功放都是定阻式，下面主要讲定阻功放与音箱。 定阻即是指负载的阻抗要与功放输出阻抗相匹配，所以只要你系统中连接的音箱总电阻与功放一致就行了，不管你的音箱串联、并联或者混联都行。 关于串联和并联的电阻计算公式在初中就学了： 串联时：R=R1+R2 并联时：R=1/(1/R1+1/R2) 比如说， 有2只16Ω的音箱，用我们的CS功放（4Ω/8Ω）去推，可以将音箱并联得到8Ω； 有1台16Ω的功放，要推我们的2只E-8（8Ω），可以将音箱串联得到16Ω； 有1台16Ω功放，要推4只16Ω的音箱，可以将其中两只并联，再将另外两只并联，最后把两组音箱串联得到16Ω； 在我们常用的方案里，1台CS2000功放推4只E-8音箱，就是把E-8两两并联，音箱阻抗变为4Ω，功放自适应为4Ω，功率也相应加大了。 本帖最后由SVSZ 于2011-7-22 16:33 编辑

1、先常规解释功放桥接的定义： 桥接模式(bridge mode)是利用功放内部的两个放大电路相互推挽，从而产生更大输出电压的方式，功放设定为桥接模式后，成为一台单声道放大器，只可以接受一路输入信号进行放大，输出端为两路功放输出的正端之间。 桥接的定义说得很清楚了，设置成桥接模式往往是因为功放的功率不够，而桥接模式下功放的输出功率一般为普通模式下的2-3倍。但是在桥接模式下功放只是单声道输出（推一只音箱，比如常用来推一只低音炮）。 2、桥接方法： 将功放的模式开关调至Bridge，然后把音箱线的正极接到功放左声道的正极，音箱线的负极接到功放右声道的正极，咱们SVS各款功放的桥接开关和接线方法详见下图： （CS系列功放桥接开关，按下状态为桥接模式，弹出状态为立体声模式） （H系列功放桥接开关，从上到下依次为立体声、单声道、桥接模式）

(完整版)LED灯具安规基础知识灯具分类打高压

LED灯具安规基础知识 一、灯具防护等级分类 灯具的分类方法很多，依照安全防护等级可以分为0类、I类、II类、III类。 1、0类灯具 工作电压是高压，防触电保护采用基本绝缘，而无其他防触电保护措施的灯具。此类灯具安全性能较差，目前欧美国家已不允许生产销售。0类灯具无符号标识。 特征：高压、无接地线、单层绝缘。 2、I类灯具 工作电压是高压，防触电保护采用单层绝缘基本绝缘外，还采用接地作为防触电保护的灯具。 I类灯具无符号标识，其内部可以包含有II类结构，即I类灯具内部分电气结构可以采用双绝缘的方式。 特征：高压、有接地、单层绝缘。 3、II类灯具 工作电压是高压，防触电保护采用双层绝缘的灯具。II类灯具用符号标识，其内部可以包含有III类结构。特征：高压、无接地、双层绝缘。 4、III类灯具 工作电压是安全电压的灯具。 III类灯具用符号标识。 特征：安全电压供电。 5.接地要求： 按照国标GB7000.1-2002的分类和IEC60598-1∶2003最新标准，在取消O类灯具后，只有Ⅰ、Ⅱ、Ⅲ类灯具的新规定，其接地要求如下： （1）Ⅰ类灯具的外露导电部分应接地：这是Ⅰ类灯具的附加安全措施要求所决定的；如果不作接地，就等于退回到O类灯具，安全无有效保证。 （2）Ⅱ类灯具不需要接地：因为他的附加安全措施不是靠接地，而是靠双层绝缘或加强绝缘来保证。 （3）Ⅲ类灯具不允许接地：因为它是用安全超低电压（SELV），低电压应使用隔离变压器与高电压隔离，并不应接地。 在新修订的国标GB7000.1-2007实施后，从立法上取消了O类灯具；而实际的灯具，大多数是Ⅰ类，所以应作接地。

功放和音箱的匹配

功放和音箱的匹配 功放与音箱的配接，即功率匹配是一项十分考人的问题，一定要把“音乐的忠实还原”放在第一位。在设计、安装一套音响系统时，不免遇到功放与音箱的配接问题。在音色方面，会注意其搭配上是否冷暖相宜、软硬适中，最终使整套器材还原音色呈中性，这仅是从艺术方面考虑。从技术方面考虑功放与音箱配接的要素有： 一、功率匹配 二、阻抗匹配 三、阻尼系数的匹配 四、灵敏度匹配 五、音色匹配 如果我们在配接时认识到上述五点，可使所用器材的性能得到最大、最充分的发挥。 1、功率匹配 为了达到高保真聆听的要求，额定功率应根据最佳聆听声压来确定。我们都有这样的感觉：音量小时、声音无力、单薄、动态出不来，无光泽、低频显著缺少、丰满度差，声音好像缩在里面出不来。音量合适时，声音自然、清晰、圆润、柔和丰满、有力、动态出得来。但音量过大时，声音生硬不柔和、毛糙、有扎耳根的感觉。因此重放声压级与声音质量有较大关系，规定听音区的声压级最好为80~85dB（A计权），我们可以从听音区到音箱的距离与音箱的特性灵敏度来计算音箱的额定功率与功放的额定功率。 功放电路的输出功率有多种名称，例如额定功率（RMS）、音乐功率、峰值音乐功率（PMPO）等，它们的含义互不相同，但应用最多、最重要的功率是额定功率。商家还经常制造出其它名称的功率，这些都是出于商业的宣传，或是躲避弱点、宣传优点的作法。严格的额定功率应当对频响范围、谐波失真、负载阻抗和信噪比等作出严格的规定，缺少这些限制条件的额定功率数值是没有价值的。额定功率应是一种综合性的技术指标。 功放的额定输出功率与音箱的额定输入功率应当相互适应。功放的额定功率应稍大于音箱的额定功率的1/4，例如，125W的功放宜推动100W左右的音箱。实用音箱都有一定的过载能力，其允许值为额定功放的1.5倍左右。晶体管功放的过载能力较强，当过载时其失真度变化较小。 在实际使用功放和音箱时，平时都达不到额定功率值，所使用的实际平均功率比较小，所实用的功率仅为额定功率的1/3--1/5。功率要适配、匹配，从表面看是两者额定功率相近，实际是指功率的储备量、富余量相适应；换言之，使功放和音箱长时间（例如8小时）工作于额定功率状态下（在规定的频响范围、失真度、信噪比格阻抗等条件限制下），都不能出现各种问题。在不降低限制条件的情况下，当增加音箱世界形势功放功率值时，售价也将飞速啬。在普通小听音房间条件下（例如20平方米以下），不需要选用输出功率过大的功放，额定功率60-80W（8欧）的功放已能完成一般的播放任务。 为了使音箱在受节目信号中的猝发强脉冲的冲击而不至于损坏或失真。这里有一个经验值可参考：所选取的音箱标称额定功率应是经理论计算所得功率的三倍。 电子管功放和晶体管功放相比，所需的功率储备是不同的。这是因为：电子管功放的过荷曲线较平缓。对过荷的音乐信号巅峰，电子管功放并不明显产生削波现象，只是使颠峰的尖端变圆。这就是我们常说的柔性剪峰。而晶体管功放在过荷点后，非线性畸变迅速增加，对信号产生严重削波，它不是使颠峰变圆而是把它整齐割削平。有人用电阻、电感、电容组成的复合性阻抗模拟扬声器，对几种高品质的晶体管功放进行实际输出能力的测试。结果表明，在负载有相移的情况下，其中有一台标称100W的功放，在失真度1%时实际输出功率仅有5W！由此对于晶体管功放的储备量的选取： 高保真功放：10倍民用高档功放：6~7倍民用中档功放：3~4倍而电子管功放则可以大大小于上