,甘肃农业大学食品科学与工程学院,兰州 730070Using Chlorine Dioxide Treatment to Promote Wound Healing of Postharvest Muskmelon Fruit
ZHENG XiaoYuan, WANG TiaoLan, ZHANG JingRong, JIANG Hong, WANG Bin, BI Yang,College of Food Science and Engineering, Gansu Agricultural University, Lanzhou 730070通讯作者:
收稿日期:2018-07-18接受日期:2018-09-13网络出版日期:2019-02-13
| 基金资助: |
Received:2018-07-18Accepted:2018-09-13Online:2019-02-13
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郑晓渊,Tel：18894310260;E-mail：
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郑晓渊, 王调兰, 张静荣, 姜红, 王斌, 毕阳. 二氧化氯处理促进厚皮甜瓜果实的采后愈伤[J]. 中国农业科学, 2019, 52(3): 512-520 doi:10.3864/j.issn.0578-1752.2019.03.011
ZHENG XiaoYuan, WANG TiaoLan, ZHANG JingRong, JIANG Hong, WANG Bin, BI Yang.
0 引言
【研究意义】厚皮甜瓜（Cucumis melon L.）是我国西北地区特色水果,由于果实个体较大,在采收和采后过程中易受机械损伤[1],而机械损伤造成的表面伤口为病原物的侵染提供了通道,加剧了采后腐烂的发生[2]。因此,有效降低伤口性病原菌的侵染率是采后厚皮甜瓜亟待解决的问题。【前人研究进展】不同果实表面形成的伤口具有不同程度的愈合能力,通过在伤口部位积累软木脂和木质素等具有保护作用的天然聚合物[3],从而抑制伤口部位水分的大量蒸腾,阻止病原物经由伤口的侵入[4]。近期研究发现,某些化学药物还具有促进伤口愈合的作用。例如,苯丙噻重氮可以促进采后梨果实的愈伤[5],脱落酸能提高采后番茄[4]和猕猴桃[6]果实的愈伤能力。ClO2是国际公认的A1级安全高效消毒剂,可杀灭病原物,对果蔬风味和品质无明显影响[7,8]。有报道表明,ClO2处理可减轻龙眼[9,10]和番茄果实[11]的采后病害,延缓苹果成熟衰老,减轻采后腐烂[12],还可一定程度上抑制鲜切哈密瓜的后熟[13]。而ClO2在减轻采后病害中的作用与增强果实苯丙烷代谢和提高氧化酶活性密切相关[14]。【本研究切入点】虽然已有ClO2诱导采后果实抗病性的报道,但该化合物是否影响厚皮甜瓜果实采后愈伤尚未见报道。【拟解决的关键问题】本研究以‘玛瑙’厚皮甜瓜果实为试材,用ClO2处理人工损伤的果实后在常温条件下进行愈伤,测定愈伤期间损伤果实的失重率以及接种果实的病情指数,观察愈伤组织的色度以及聚酚软木脂、聚酯软木脂和木质素的积累变化。分析氧化酶和苯丙烷代谢关键酶活性及其代谢产物的含量。评价ClO2处理对厚皮甜瓜果实采后愈伤能力的影响,为ClO2处理在厚皮甜瓜的采后应用提供方法和理论依据。1 材料与方法
1.1 材料与设备
供试‘玛瑙’甜瓜于2017年7月采自甘肃省民勤县收成乡露地大田,选取八成熟、外观整齐、大小一致、无病虫伤和机械伤的果实,单果套网套后装入瓦楞纸包装箱,于当天运抵实验室,在常温下（20—25℃,RH 70%—80%）贮藏待用。粉红单端孢（Trichothecium roseum）为甘肃厚皮甜瓜产区最常见的采后病原真菌[15],由本实验室提供,于PDA培养基上保存待用。
ClO2购自天津张大科技有限公司,有效浓度120 mg·g-1,于4℃冰箱保存。
刮皮刀（HF036型,阳江市阳东区焦点刀具有限公司,中国）;恒温培养箱（SPX-30085H-II型,上海新苗医疗器械制造有限公司,中国）;超净工作台（SW-CJ-2FD型,苏净集团苏州安泰空气技术有限公司,中国）;立式压力蒸汽灭菌锅（LDZX-30KBS 型,上海申安医疗器械厂,中国）;正置万能显微镜（CX21FS1C型,OLYMPUS公司,日本）;Ci6x分光光度仪（Ci6x型,日本爱色丽有限公司,日本）;台式高速冷冻离心机（3K30型,Sigma公司,德国）;紫外-可见光分光光度计（UV-2450 型,岛津,日本）。
1.2 方法
1.2.1 果实人工损伤及愈伤 参照姜红等[16]的方法并进行修改。果实先用清水冲洗,然后用1%的次氯酸钠浸泡1 min进行表面消毒,再用无菌水冲洗,晾干后用刮皮刀在果实的赤道部位分别刮出4条长30 mm、宽30 mm、深2 mm的伤口。在室温条件下暴露0.5 h后,将损伤的果实浸入25 mg?L-1的ClO2浸泡10 min,取出晾干后分别装入打孔的聚乙烯保鲜袋（25 cm×40 cm,厚度0.02 mm）,于常温、避光条件下进行愈伤,以清水处理作对照。每处理用果实120个,重复3次。1.2.2 愈伤效果的评价
1.2.2.1 失重率及病情指数的测定 失重率的测定采用重量法[17]。每处理用果实9个,重复3次。
病情指数的测定参照姜红等[16]的方法并修改。在培养了1周的T. roseum培养皿中加入一定量的无菌水,用涂布器刮下孢子用4层纱布过滤至锥形瓶中,在振荡器上振荡15 s,经过血球计数板计数配置成浓度为1×106个/mL的孢子悬浮液。分别在果实损伤后的第0、1、3、5、7天,用涂布器将20 μL配好的孢子悬浮液均匀涂于创口表面,晾干后装入打孔的聚乙烯保鲜袋中,常温培养7天后统计病情指数。每个处理用果实8个,重复3次。
\[病情指数=\frac {Σ（各病级伤口个数×发病级别）}{总伤口个数×最高发病级别} ×{100}\]
式中,发病级别的标准为：4级,创口表面全部发病;3级,创口表面3/4的面积发病;2级,创口表面1/2面积发病;1级,创口表面1/4面积发病;0级,创口表面不发病。
1.2.2.2 聚酚软木脂、聚酯软木脂和木质素沉积的观察 聚酚软木脂（suberin poly phenolic,SPP）和聚酯软木脂（suberin poly aliphatic,SPA）的沉积观察参照LULAI[18,19]的方法并修改。用不锈钢刀片垂直伤口表面切成厚0.2—0.3 mm,长和宽各为1 cm左右的薄片。采用如下步骤进行染色：用0.1%小檗碱（0.05%甲苯胺蓝）染色45 min后,先吸去染料,再用蒸馏水和75%酒精洗2—3遍,最后用95%酒精洗1—2遍,即脱去染料,紧接着在0.25%甲苯胺蓝（1%中性红）中放置1—2 min进行复染,最后用蒸馏水和75%酒精洗去染料,SPP（SPA）即染为紫蓝色。将染好色的薄片置于载玻片上,在显微镜下荧光观察拍照。每个果实切片4处,重复3次。
木质素的沉积观察参照ALBA等[20]的方法并修改。用不锈钢刀片垂直伤口表面切成厚0.2—0.3 mm,长和宽各为1 cm左右的薄片,滴加1%间苯三酚染色1.5 min后再加1—2滴浓盐酸,木质素即染为红色,置于显微镜下观察拍照。每个果实切片4处,重复3次。
愈伤组织的SPP、SPA和木质化细胞层的厚度根据文献[21]的方法通过IS Capture图像软件进行测量计算。
1.2.3 愈伤组织色度的测定 在愈伤的0、1、3、5和7 d用Ci6x分光光度仪垂直于愈伤组织表面进行色度的测定,依次测定L*、a*和b*值,每个处理测12处愈伤组织。
1.2.4 生化测定取样 参照BI等[22]的方法。在愈伤的0、1、3、5和7 d,用不锈钢刀片垂直伤口表面下取2—3 mm深的伤口组织3 g,用锡箔纸包好后用液氮冷冻,在-80℃超低温冰箱中保存备用。
1.2.5 苯丙氨酸解氨酶、过氧化物酶和多酚氧化酶的活性测定 苯丙氨酸解氨酶（phenylalnine ammonia- lyase,PAL）的测定参照LIU等[23]的方法并修改。取冷冻样品3 g,于5 mL硼酸-硼砂缓冲液（pH 8.8,含40 g?L-1聚乙烯吡咯烷酮（polyvinyl pyrrolidone,PVP）,2 mmol?L-1乙二胺四乙酸（ethylenediaminetetraacetic acid,EDTA）和5 mmol?L-1 β-巯基乙醇）中冰浴研磨成浆,在4℃、12 000×g条件下离心30 min,上层酶液即为粗酶液。反应体系包括：0.1 mL粗酶液,3 mL硼酸-硼砂缓冲溶液（50 mmol?L-1、pH 8.8）液,0.5 mL食物L-苯丙氨酸（20 mmol?L-1）,以蒸馏水为参比,测定反应体系混合10 s后在290 nm波长处的吸光值作为初始值（OD0）,将混合液在37℃水浴锅中保温1 h后在290 nm波长处的吸光值作为终止值（OD1）。以每小时吸光值变化值增加0.01为一个酶活性单位（U）,以U·g-1 FW表示。
过氧化物酶（peroxidase,POD）和多酚氧化酶（polyphenol oxidase,PPO）的测定参照LI[24]的方法。取冷冻样品3 g,于5 mL乙酸-乙酸钠缓冲液（pH 5.5,含1 mmol?L-1聚乙二醇（polyethylene glycol,PEG）,4%交联聚乙烯吡咯烷酮（crosslinking polyvingypyrrolidone,PVPP）和1%聚乙二醇辛基苯基醚（Triton X-100））中研磨成浆,在4℃、12 000×g条件下离心30 min,收集上层液用即为粗酶液。POD反应体系：3 mL 25 mmol?L-1愈创木酚,0.1 mL酶提取液,0.2 mL H2O2（5 mmol?L-1）。以蒸馏水为参比,在反应进行到15 s时测定混合液在470 nm波长处的吸光值2 min。以每分钟吸光值变化值增加1为一个酶活性单位（U）,以U·g-1 FW表示,重复3次。PPO反应体系：4 mL的乙酸-乙酸钠缓冲液（50 mmol?L-1、pH 5.5）,1 mL邻苯二酚溶液（50 mmol?L-1）,0.1 mL酶提取液。以蒸馏水为参比,在反应进行到15 s时测定混合液在420 nm波长处的吸光值2 min。以每分钟吸光值变化值增加1为一个酶活性单位（U）,以U·mg-1 FW表示。
1.2.6 总酚、类黄酮和木质素的含量测定 总酚和类黄酮的测定参照PIRIE等[25]的方法并作修改。取冷冻样品3 g,于预冷的4 mL HCL-甲醇溶液中冰浴研磨成浆,在4℃避光条件提取20 min,期间摇动数次,过滤收集上层清液待用。以1% HCL-甲醇溶液做为参比,分别测定滤液在280 nm和325 nm波长处的吸光度值作为总酚和类黄酮的含量,分别以OD280·g-1 FW和OD325·g-1 FW表示。
木质素的含量测定参照YIN等[26]的方法进行测定。取冷冻样品3 g,于预冷5 mL 95%乙醇中研磨成浆,在4℃,14 000×g条件下离心30 min,弃去上清液,将沉淀物依次用95%乙醇,乙醇（V）﹕正己烷（V）=1﹕2冲洗3次,将清洗后的沉淀物在60℃烘箱中干燥24 h后转移至离心管中,溶于1 mL 25%溴化乙酰冰醋酸溶液,70℃恒温水浴30 min后加入1 mL NaOH（2 mol?L-1）终止反应。最后加入2 mL冰醋酸和0.1mL盐酸羟胺（7.5 mol?L-1）,在4℃、12 000×g条件下离心30 min,取上清液0.5 mL并用冰醋酸定容至5 mL,在280 nm波长处测定吸光值,木质素含量以OD280·g-1 FW表示。
1.3 数据统计
上述测定均重复3次。全部数据用Excel 2010计算平均值和标准误（±SE）,用SPSS 19.0进行Duncan’s多重差异显著性分析及相关性分析（P<0.05）。2 结果
2.1 ClO2处理对愈伤期间果实失重率和病情指数的影响
愈伤期间,处理和对照果实的失重率均逐渐升高,但处理果实的失重率显著低于对照,第7天时,比对照低10.3%（P<0.05）（图1-A）。处理和对照果实的病情指数均随愈伤时间的延长逐渐下降,处理果实显著低于对照,第7天时,仅如对照的43.1%（P<0.05）（图1-B）。失重率和病情指数的结果表明,ClO2处理有效促进了厚皮甜瓜果实的采后愈伤。2.2 ClO2处理对果实伤口处SPP、SPA和木质素积累的影响
愈伤期间,处理和对照果实伤口处的SPP和SPA积累量均逐渐增加,处理果实的积累量在愈伤的中后期均显著高于对照（图2-A、B）。SPP和SPA的积累差异分别始于第1天和第3天,第7天时SPP和SPA的积累厚度分别比对照高25.3%和77.7%（P<0.05）（图3-A、B）。处理和对照果实伤口处的木质素积累始于愈伤中期,处理显著高于对照。在第7天时,处理果实木质素的积累厚度比对照高35.5%（P<0.05）（图3-C）。SPP、SPA和木质素的积累结果表明,ClO2有效促进了厚皮甜瓜果实伤口处的木栓化。图1
新窗口打开|下载原图ZIP|生成PPT图1ClO2处理对厚皮甜瓜果实愈伤期间失重率（A）和病情指数（B）的影响
*代表显著性差异(P<0.05)。下同
Fig. 1Effect of ClO2 treatment on weight loss (A) and disease index (B) of muskmelon fruit during wound healing
* indicate significant differences (P<0.05). The same as below
图2
新窗口打开|下载原图ZIP|生成PPT图2ClO2处理对伤口处SPP（A）、SPA（B）和木质素（C）积累的影响（×100）
P：聚酚软木脂 Suberin poly phenolic；A：聚酯软木脂 Suberin poly aliphatic；L：木质素 Lignin
Fig. 2Effect of ClO2 treatment on the accumulation of SPP (A), SPA (B) and lignin (C) of muskmelon wounded sites during wound-healing (×100)
图3
新窗口打开|下载原图ZIP|生成PPT图3ClO2处理对伤口处SPP（A）、SPA（B）和木质化（C）细胞层厚度的影响
Fig. 3Effects of ClO2 treatment on thickness of SPP (A), SPA (B) and lignified cell layers (C) of muskmelon wounded sites during wound-healing
2.3 ClO2处理对果实伤口处色度的影响
愈伤期间,处理和对照果实伤口处的L*值均先上升后下降,在愈伤的后期显著低于对照,第5天和第7天时,分别比同期对照低6.1%和5.8%（P<0.05）（图4-A）。处理和对照果实的a*值差异不显著（结果未显示）。两者b*值总体先降后升,在愈伤的前期和中期显著高于对照。第3天时,比对照高17.8%（P<0.05）（图4-B）。图4
新窗口打开|下载原图ZIP|生成PPT图4ClO2处理对伤口处的L*值（A）和b*值（B）的影响
Fig. 4Effects of ClO2 treatment on L* (A) and b* (B) of muskmelon wounded site during wound healing
2.4 ClO2处理对伤口处PAL、POD和PPO活性以及总酚、类黄酮、木质素含量的影响
愈伤期间,处理和对照果实伤口处的PAL活性均逐渐升高,但处理果实的PAL活性显著高于对照,第7天时,比对照高34.3%（P<0.05）（图5-A）。对照果实的POD和PPO活性随愈伤时间的延长逐渐升高,而处理果实的活性则先略有降低后显著升高,在愈伤的后期显著高于对照,第7天时,POD和PPO活性分别比对照高80.5%和15.7%（P<0.05）（图5-B、C）。处理果实伤口处的总酚、类黄酮和木质素含量在愈伤期间均呈先降后升的趋势,在愈伤的后期显著高于对照。第7天时,分别比对照高14.7%、16.8%和15.6%（P<0.05）（图5-D、E、F）。PAL、POD和PPO活性以及总酚、类黄酮和木质素含量的增加结果表明,ClO2激活了厚皮甜瓜果实伤口处的苯丙烷代谢以及氧化酶活性。图5
新窗口打开|下载原图ZIP|生成PPT图5ClO2处理对厚皮甜瓜果实伤口处PAL（A）、POD（B）和PPO（C）活性以及总酚（D）、类黄酮（E）和木质素（F）含量的影响
Fig. 5Effects of ClO2 treatment on the activity of PAL(A), POD(B) and PPO(C), and the content of total phenolic (D), flavonoids (E) and lignin (F) in muskmelon wounded sites during wound-healing
3 讨论
ClO2可通过增强苯丙烷代谢和提高氧化酶活性来诱导果实的采后抗病性[12]。本研究发现,ClO2处理可通过激活采后厚皮甜瓜果实伤口处的苯丙烷代谢及氧化酶活性,加速软木脂和木质素在伤口处的沉积,从而促进厚皮甜瓜果实的采后愈伤。苯丙烷代谢可合成愈伤组织形成所需的多种次生代谢产物,在果实愈伤中具有积极的作用[27]。PAL是苯丙烷代谢的限速酶[4],可催化苯丙烷代谢的第一步反应,使L-苯丙氨酸脱氨生成反式肉桂酸[27],反式肉桂酸又会进一步转化生成多酚和类黄酮以及木质素等愈伤组织的基本成分[28,29]。PAL的活性高低与果实的愈伤能力显著相关[6],果实的愈伤能力越强,其PAL活性就越高。本研究发现,ClO2处理显著提高了厚皮甜瓜伤口处PAL活性,该结果与赵明惠等[12]采用ClO2处理苹果后观察到的结果类似。苯丙烷代谢产生的肉桂酸、富马酸和咖啡酸等酚类物质[29],在细胞质内合成后被运送至细胞壁,与肉桂酸羟化酶催化形成的羟基肉桂酸和羟基肉桂酰醇在POD和H2O2的作用下氧化交联并开始沉积,形成SPP[30]。此外,伤口处的脂肪代谢也发生了显著的变化[31]。细胞内一些新的脂肪酸单体开始合成,主要包括超长链脂肪酸、1-链烷醇、ω-羟基脂肪酸和α,ω-二酸等,这些脂肪酸单体经质膜上的ATP结合通道转运蛋白被运送至膜外,在质膜和细胞壁间聚合形成SPA[30,31]。但这些脂肪酸单体或低聚物如何和甘油组装形成SPA尚有待揭示。在番茄果实上的研究结果表明,SPP和SPA都对病原物具有抵抗作用,但两者之间存在着差异。其中,SPP对细菌性病害有防御作用,SPA对真菌性病害有抵抗作用[32]。至于SPP和SPA在甜瓜果实愈伤中的功能是否与番茄一致尚有待证实。本研究观察到,ClO2处理促进了SPP、SPA以及木质素的积累,对于SPP的促进作用要先于SPA和木质素。苯丙烷代谢形成的4-香豆酸、阿魏酸和芥子酸等是木质素的合成前体,这些酚酸首先在CAD的作用下还原,形成相应的醇后再通过POD的作用聚合为木质素[33]。木质素是苯丙烷代谢的终产物,是细胞壁次生壁的组成物质,木质素在保持水分和维持细胞结构稳定中发挥着重要作用[28]。木质素也是伤口周皮的主要成分,可使细胞壁更加坚固[34],从而在伤口表面形成一个有效的物理屏障,限制病原物从伤口处获取营养,提高果实对病原物侵染的抵抗能力[35]。黄酮类物质在伤口处的含量随PAL活性的提高而增加[6]。黄酮类物质作为抗氧化剂,具有较强的抗氧化和自由基清除能力,可直接抑制真菌的孢子萌发和菌丝生长[33]。本研究发现,ClO2处理在愈伤后期显著提高了POD活性,促进了总酚、类黄酮和木质素的积累。但在愈伤前期,ClO2处理的POD活性以及总酚、类黄酮和木质素含量均显著低于对照,这可能与ClO2抑制POD活性和苯丙烷代谢相关。
本研究发现,ClO2处理可显著提高厚皮甜瓜果实伤口处的PPO活性。处理果实伤口处L*值高于对照,b*值低于对照的结果表明,PPO参与了愈伤组织的形成,处理果实伤口处的L*值在0 d显著高于对照可能源于ClO2的漂白作用。在愈伤中由于细胞内膜被破坏,液泡中的酚类底物会和PPO发生反应,氧化为醌,醌再进一步聚合为黑色或褐色的物质[36]。这些聚合物不仅引起果实组织褐变,而且可直接抑制病原菌生长,钝化病原菌分泌的胞外酶[37],该结果与WEI[38]等在猕猴桃愈伤期间观察到的结果一致。
4 结论
ClO2采后处理可有效降低损伤果实的失重率和损伤接种果实的病情指数,促进厚皮甜瓜的采后愈伤。ClO2处理对采后厚皮甜瓜愈伤的促进作用与激活果实苯丙烷代谢,提高POD和PPO活性,促进SPP、SPA和木质素在伤口处的积累密切相关。参考文献 原文顺序
文献年度倒序
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被引期刊影响因子
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DOI:10.1007/s00299-014-1727-zURLPMID:25504271 [本文引用: 1]
Abstract Suberin is a lipid-phenolic biopolyester deposited in the cell walls of certain boundary tissue layers of plants, such as root endodermis, root and tuber peridermis, and seed coats. Suberin serves as a protective barrier in these tissue layers, controlling, for example, water and ion transport. It is also a stress-induced anti-microbial barrier. The suberin polymer contains a variety of C16-C24 chain-length aliphatics, such as ω-hydroxy fatty acids, α,ω-dicarboxylic fatty acids, and primary fatty alcohols. Suberin also contains high amounts of glycerol and phenolics, especially ferulic acid. In addition, non-covalently linked waxes are likely associated with the suberin polymer. This review focusses on the suberin biosynthetic enzymes identified to date, which include β-ketoacyl-CoA synthases, fatty acyl reductases, long-chain acyl-CoA synthetases, cytochrome P450 monooxygenases, glycerol 3-phosphate acyltransferases, and phenolic acyltransferases. We also discuss recent advances in our understanding of the transport of suberin components intracellularly and to the cell wall, polymer assembly, and the regulation of suberin deposition.
DOI:10.1016/j.postharvbio.2016.04.002URL [本文引用: 3]
The development of wound periderm is vital to prevent water vapor loss and pathogen invasion in wounded fruit. The effect of abscisic acid (ABA) on wound-healing in harvested tomato fruit was evaluated in this study. Wounded tomato fruit were treated with ABA or fluridone (FLD, an inhibitor of ABA biosynthesis), respectively, and allowed to wound-heal at 20掳C in darkness for 4days. Weight loss of tomato fruit reflected the intuitionistic effects of different treatments during wound-healing. Autofluorescence and histochemical staining demonstrated the development of suberized wound periderm in harvested tomato fruit at 3 4day after wounding. Alkanoic acids,n-alkanes, unsaturated fatty acids and pentacosane represented the major components in the suberin. ABA-treated fruit showed enhanced autofluorescence, histochemical intensity and suberin deposition along with increased activities of phenylalanine ammonia-lyase (PAL) and peroxidase (POD). FLD treatment, however, alleviated the features of suberization and enzyme activities during wound-healing. The results suggest that ABA is involved in the stimulation of wound-induced suberization in harvested tomato fruit.
[本文引用: 1]
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DOI:10.1016/j.scienta.2017.06.039URL [本文引用: 3]
Wound-induced suberization is an essentially protective healing process for fruit to reduce water loss and avoid infecting. However, cognate mechanisms that regulate this process are little known. To expand our knowledge of suberization induced by wounding, a wound-healing investigation together with metabolite profiling study was conducted in postharvest kiwifruit ( Actinidia deliciosa ). The development of suberization in wounded fruit was demonstrated by autofluorescence observation and toluidine blue staining at 1 4 day (d) after wounding. Activities of phenylalanine ammonia-lyase (PAL), cinnamyl-alcohol dehydrogenase (CAD) and peroxidase (POD) in wound-healing tissue were enhanced by abscisic acid (ABA). The constituent analysis of suberin including polyphenolics (SPP) and polyaliphatics (SPA) proved that exogenous ABA increased the content levels of total phenols, total flavonoids and alkanes, alkenes, alcohols, alkane acids, olefine acids, esters, glycerides and vitamin E in wound-healing tissue. Results suggested that ABA stimulated suberization through the activation of PAL, CAD and POD to accelerate wound-healing of wounded kiwifruit.
DOI:10.1016/S0740-0020(02)00129-6URL [本文引用: 1]
The efficacy of chlorine dioxide (ClO 2) gas in inactivating a mixture of Escherichia coli O157:H7 (C7927, EDL933, 204P) on different apple surfaces was investigated. The bacteria were spotted onto the calyx and stem cavities, and the skin at 3, 5, or 8 log cfu site 611, air dried, then treated with ClO 2 gas at 21°C and 90–95% relative humidity. Bacterial populations were determined using surface plating, membrane transfer plating, or most probable number method. Bacterial log reductions increased with both increase of ClO 2 concentration and treatment time. At least 3-log reductions were achieved after the following ClO 2 gas treatments: 12.0 mg l 611 for 10 min or 3.3 mg l 611 for 20 or 30 min on the calyx cavities, and 12.0 mg l 611 for 10 min, 4.8 mg l 611 for 20 min, or 3.3 mg l 611 for 30 min on the stem cavities. A 7.2 mg l 611 treatment for 30 min showed the highest log reduction on the calyx (6.5±0.7 log) and stem cavities (4.1±0.2 log), respectively. More than a 5-log reduction on the skin was achieved by ClO 2 gas treatment with 7.2 mg l 611 for 10 min or 3.3 mg l 611 for 20 or 30 min. A treatment with 12.0 mg l 611 for 10 min, 7.2 mg l 611 for 20 min, or 4.8 mg l 611 for 30 min completely inactivated the 8 log cfu site 611 bacteria initially inoculated on the skin, which was determined by an end-point method. It was concluded that ClO 2 gas treatment was a promising non-thermal pathogen reduction technique for apples.
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DOI:10.1016/j.postharvbio.2013.12.016URL [本文引用: 1]
Pericarp browning reduces both the shelf-life and market value of harvested longan fruit stored at room temperature. Our study investigated the efficiency of chlorine dioxide (ClO2) fumigation at reducing pericarp browning of longan (Dimocarpus longan Lour.) cv. Daw. Fresh longan fruit were fumigated with 0 (control), 2.5, 5, 10 and 25mg/L ClO2 for 10min, before being packed in cardboard boxes, and stored at 25C, RH 825% for 7 days. Fruit treated with ClO2 had a lower browning index, but higher hue angle (true color), L* (lightness) and b* (yellowness) values than non-treated fruit. The 10 and 25mg/L ClO2 treatments were the most effective at extending shelf-life from 1 to 5 days, compared with the control, by reducing pericarp browning, the activities of polyphenol oxidase (PPO) and peroxidase (POD), disease development and by maintaining the highest total phenolic content. However, quality acceptance of fruit treated with 10mg/L ClO2 was higher than fruits treated with 25mg/L, as determined by odor and flavor. Consequently, ClO2 fumigation at a concentration of 10mg/L was considered to be the most effective treatment to reduce pericarp browning of longan, whilst maintaining fruit quality.
DOI:10.3791/55400URLPMID:28448049 [本文引用: 1]
A controlled-release chlorine dioxide (ClO2) pouch was developed by sealing a slurry form of ClO2 into semipermeable polymer film; therelease properties of the pouch were monitored in containers with or without fruit. The pouch was affixed to the inside of a perforated clamshell containing grape tomatoes, and the effect on microbial population, firmness, and weight loss was evaluated during a 14 day storage period at 20 C. Within 3 days, the ClO2 concentration in the clamshells reached 3.5 ppm and remained constant until day 10. Thereafter, it decreased to 2ppm by day 14. The ClO2 pouch exhibited strong antimicrobial activity, reducing Escherichia coli populations by 3.08 log CFU/g and Alternariaalternata populations by 2.85 log CFU/g after 14 days of storage. The ClO2 treatment also reduced softening and weight loss and extended the overall shelf life of the tomatoes. Our results suggest that ClO2 treatment is useful for extending the shelf life and improving the microbial safety of tomatoes during storage without impairing their quality.
[本文引用: 3]
[本文引用: 3]
DOI:10.1111/ijfs.12149URLMagsci [本文引用: 1]
The effects of chlorine dioxide (ClO2) on respiration and ethylene synthesis of fresh-cut melon fruit and the possible mechanisms involved were investigated. Fresh-cut ‘Hami’ melon fruit fumigated with gas ClO2 in sealed container for 12 h and then stored at 5 °C with 95% relative humidity (RH) for 19 days. Results showed that fruit treated with ClO2 resulted in lower rates of the total respiration, alternative pathway respiration, cytochrome pathway respiration and ethylene production. Furthermore, the expressions of ethylene biosynthesis-related genes, including CmACS2, CmACO1 and CmACO3 were reduced by ClO2 treatment. Taken together, it is suggested that ClO2 treatment might be an effective way to delay ripening of fresh-cut ‘Hami’ melon, partially due to the reduced respiration and ethylene biosynthesis.
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DOI:10.17660/ActaHortic.2006.712.45URL [本文引用: 1]
Acibenzolar-S-methyl (ASM) is a chemical activator of systematic resistance in many plants. The effect of postharvest dipping with different concentrations of ASM was studied in Hami melons (cvs. New Queen and 8601). A concentration at 200 mg/L was the most effective treatment for reducing decay severity caused by and . Higher concentration (300 mg/L) failed to promote better resistance against decay-causing agent and to cause phytotoxicity. ASM did not demonstrate any fungicide effect in vitro and suppressed lesion diameter in treated melons, indicating that disease resistance was induced. Efficacy of suppression against lasted 7 and 10 days for 07New Queen08 and 07860108 cultivars in ASM treated fruit. The protection of ASM was associated with the activation of peroxidase (POD), chitinase (CHT) and phenylalanine ammonia lyase (PAL) in treated melons.
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DOI:10.1016/j.postharvbio.2010.08.006URLMagsci [本文引用: 1]
The effects of edible coatings, Semperfresh64 (SF), acid-soluble chitosan (ACH), water-soluble chitosan (WCH), calcium caseinate (CC), and sodium alginate (SA) on the fruit quality of fresh blueberries during storage was studied in 2006 and 2008. Fruit were washed in 200 μL L 611 chlorinated water before applying coatings, packaged in vented or non-vented clam-shell containers, and then stored at 2 °C for 1 week, followed by storage at room temperature (20 °C) for up to 15 d for quality evaluation. The ACH, WCH, and WCH + SA coatings helped reduce the decay rate of ‘Duke’ or ‘Elliott’ fruit during room temperature storage. Results from 2006 showed that SF coating decreased weight loss of ‘Duke’ after 6 d of room temperature storage, CC-coated ‘Elliott’ fruit had delayed fruit ripening as evidenced by higher TA, lower pH, and greater firmness than control during storage, and washing and coating did not significantly affect antioxidant capacity and total phenolics content of ‘Duke’ and ‘Elliott’. Fruit in non-vented containers had reduced weight loss and increased firmness than those in vented containers as demonstrated in 2008 study. Our results suggest that edible coatings have potential for retaining quality of pre-washed, ready-to-eat fresh blueberries under commercial storage conditions, when appropriate coating material, container, and method of applying the coatings are used.
DOI:10.3109/10520299209110065URLPMID:1504180 [本文引用: 1]
A technique is described which uses the lipid fluorochrome neutral red as a cytochemical probe to detect the hydrophobic domain of the lignosuberin matrix in native and wound periderm of potato tuber. Toluidine blue O is used as a counterstain to quench autofluorescence. The neutral red technique appears to be specific for the hydrophobic/lipid domain of suberin and is significantly more sensitive than Sudan III and IV. The fluorochrome was extensively used on paraffin-embedded tissue with excellent results but also worked on freehand sections of fresh periderm tissue. In tuber tissue undergoing wound-healing, the pattern of suberin fluorescence obtained with the neutral red probe was identical in specificity to the color pattern obtained with Sudan III/IV, but somewhat different than that observed when berberine was used. Results obtained with the neutral red probe and berberine probe visually demonstrated that during ligno-suberin biosynthesis, the depositions of hydrophobic/lipid and phenolic/lignin-like components in potato tuber periderm were separate processes. The deposition of these components does not necessarily require their simultaneous presence because the fluorescence from these probes showed that the components were not consistently present together on the cell walls.
DOI:10.1006/pmpp.1998.0179URL [本文引用: 1]
Rapid suberization of wounded potato tubers is critical in avoiding infection by subsp. (a causal organism of bacterial soft rot) and (a causal organism of fungal dry rot) in cut seed and stored potatoes. However, until now the reason for the differential development of resistance to bacterial and then fungal penetration during suberization has not been shown to be related to the differential deposition of the two major suberin components (phenolic and aliphatic domains) during wound-healing. Tubers of four varieties of diverse genetic background were wounded and inoculated with subsp. throughout a 5-day time course and throughout an 11-day time course during wound-healing (18 C and 98% RH). During wound-healing, the tubers were examined at the cellular level for deposition of suberin phenolic and aliphatic domains. The percentage of inoculated tubers which became infected was determined for each wound-healing time point and was related to the deposition of suberin phenolic and aliphatic domains. Total resistance to infection by subsp. occurred after the completion of phenolic deposition on the outer tangential wall of the first layer of cells (2 3 days). However, this suberin phenolic matrix offered no resistance to fungal infection by even after phenolic deposition was complete on adjoining radial and inner tangential cell walls of the first layer of cells. Resistance to fungal infection did not begin to develop until after deposition of the suberin aliphatic domain was initiated. Total resistance to fungal infection was attained after completion of deposition of the suberin aliphatic domain within the first layer of suberizing cells (5 7 days). These results indicate that the suberin phenolic domain provides resistance to infection by subsp. but not infection by They further suggest that deposition of the suberin aliphatic domain is responsible for final resistance to infection by This is believed to be the first evidence indicating separate depositional patterns, at the cellular level, for the two major domains of suberin and separate roles for each of these domains in the development of resistance to bacterial and fungal infection during suberization.
DOI:10.1034/j.1399-3054.2000.100403.xURL [本文引用: 1]
A preliminary characterization of a phenoloxidase from extracts of soluble and ionically-bound cell wall proteins of peach ( Prunus persica L. Batsch, cv. Redhaven) endocarp is described in the present study to establish differences with peroxidases from the same plant tissue. The phenoloxidase activity was detected mainly in the first stage of peach fruit growth, while peroxidase activity and lignin content increased along the second stage of growth. There were clear differences between the two enzymes. The phenoloxidase had a pI value of 5.6, different from those of peroxidases isoenzymes with various pIs ranging from 3.6 to 9.6. The oxidase molecular mass was 112 kDa, similar to other phenoloxidases described in the literature, while all peroxidase isoenzymes showed a molecular mass of around 40 kDa. The specific activities of phenoloxidase against different substrates and its inhibition by various effectors suggest that the endocarp oxidase described here is probably a metal-dependent polyphenol oxidase, displaying attributes of both catechol oxidase (EC 1.10.3.1) and laccase (EC 1.10.3.2).
DOI:10.1016/j.postharvbio.2006.05.013URL [本文引用: 1]
This paper presents a study on the wound healing processes in sweetpotatoes ( Ipomoea batatas Lam.) when exposed to tropical conditions typical for marketing (RH 50–73%, T 25–30 °C). The physiological processes during healing were revisited. At low humidities (65% ± 10) the depth of the lignified layer i.e. the thickness of the desiccated cell layers was affected by both cultivar and humidity. Some cultivars consistently failed to produce a lignified layer and for others the layer was often not continuous. The continuity of the lignified layer was more important for effectiveness of wound healing than the actual thickness. A method for assessing efficiency of wound healing based on assessing the continuity of lignified layers was developed, and called the lignification score. Wound healing efficiency as measured by the lignification score was found to be a major factor for the shelf-life of sweetpotato cultivars. Lignification of wounds correlated with reduced rate of weight loss and reduced susceptibility to microbial infection. A high dry matter content in cultivars correlated with a low lignification score. This relationship was consistent for five trials, including 34 cultivars.
[本文引用: 1]
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DOI:10.1016/j.scienta.2013.06.041URL [本文引用: 1]
Muskmelons (Cucumis melo L.) are major economic crops in the northwestern part of China, and postharvest decay of fruit is serious. In order to reduce postharvest decay and prolong the storage time, the effect of hot water dipping (HWD) on nature decay and mechanisms involved were studied when muskmelon fruit (cv. Yujinxiang) were dipped in hot water at 53C for 3min. The results showed that postharvest HWD effectively (p<0.01) reduced the decay incidence, 18.9% lower than that in control fruit after 18 days of storage. HWD noticeably enhanced the activities of phenylalanine ammonialyase (PAL), cinnamate-4-hydroxylase (C4H), 4-Coumarate: CoA ligase (4CL), polyphenoloxidase (PPO) and peroxidase (POD), and accumulated phenolic compounds, flavonoid, lignin and hydroxyproline-rich glycoproteins (HRGPs). The treatment effectively maintained fruit firmness by suppressing the activities of endo-1,4- d-glucanase (EGase), glucosidase ( Glu), polygalacturonase (PG) and pectinesterase (PME), and promoting the accumulation of suberin and callose. And the data showed a higher correlation between fruit firmness and decay incidence (R2=0.8933). Furthermore, HWD could clean the surface of fruits, melt the epicuticular waxes, cover and seal the stomata. These results indicated that postharvest HWD reduced decay incidence by inducing disease resistance and maintaining the firmness in muskmelon fruit. Our data suggest that HWD has the potential to reduce or/and substitute chemical fungicides to control postharvest decay of muskmelon fruits.
DOI:10.1104/pp.58.4.468URLPMID:16659699 [本文引用: 1]
Sucrose (0.04 to 0.12 M) induces accumulation of both total phenolics and anthocyanin in leaf discs of grapevine (Vitis vinifera L.) incubated in intermittent light. Abscisic acid (20 μM) and 2-chloroethyl phosphonic acid (60 μM) act synergistically with the sucrose to enhance its induction of both total phenolics and anthocyanin. The magnitude of this interaction depends on leaf age. Nitrate (30 mM) inhibits sucrose induction of phenolics and anthocyanin. Levels of total phenolics and anthocyanin changed independently.
[本文引用: 1]
DOI:10.1016/j.jprot.2017.11.018URLPMID:29191746 [本文引用: 2]
Abstract Quick suberin-based healing after wounding played a protective role for plant to prevent further damage. In this study, the stimulative effect of exogenous abscisic acid (ABA) on wound suberization in postharvest kiwifruit was evaluated through suberin staining with toluidine blue O as well as the determination of suberin phenolics and aliphatics in wound tissue. Furthermore, to reveal the regulatory involvement of ABA in wound suberization, comparative quantitative proteomics and transcriptomics analyses based on iTRAQ and qRT-PCR technique were performed. In proteomics levels, a total of 95 protein species consistently showed differential abundance between ABA and control, including 29 down-regulated and 66 up-regulated protein species. The Kyoto Encyclopedia of Genes and Genomes (KEGG) with protein-protein interaction analyses revealed that ABA mainly affected the antioxidant system, phenylpropanoid metabolism and lipid metabolism associated with wound suberization. Based on the data of proteomics analysis, the differential expressions of genes encoding 11 selected protein species were confirmed by qRT-PCR analyses. GSH-Px, MDHAR, SOD, APX, POD, PAL, CCR, PPO, CYP86B1, DGGT and KCS11 were likely to be the key enzymes that involved the response of ABA to stimulate wound suberization by mediating the antioxidant system, phenylpropanoid metabolism and lipid metabolism. BIOLOGICAL SIGNIFICANCE: Kiwifruit is susceptible to physical injury causing postharvest deterioration during harvest, transportation and storage. Therefore, quick healing is important for maintaining the postharvest quality of injured fruit. This work elucidated the potential role of ABA and the proteomic mechanism of its regulation in wound suberization of postharvest kiwifruit. Copyright 2017 Elsevier B.V. All rights reserved.
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URL [本文引用: 2]
The physiology and biochemistry of resistance and susceptibility to tuber skinning/excoriation wounds, wound-healing and wound-related defects are of global importance because of the magnitude of the resulting food and financial losses. Wound related losses are difficult to determine because of the large range of associated infections, bruise defects, water vapor loss and various quality issues. Collectively, minor to serious wounding/bruising can average 40%, resulting in huge financial losses and the creation of contracts with incentives to reduce these wound-related losses. Many rot type diseases found in stored potatoes gain entry through wounds that did not heal quickly. This chapter is intended to cover important physiological and biochemical research that impacts these costly wound related issues. Skinning wounds are difficult to control during harvest unless the tuber periderm has matured so that the skin is set and resistant to excoriation. The physiology of tuber skin-set, i.e. resistance to skinning/excoriation injury, is only beginning to be studied. The structure of tuber periderm and maturational changes that result in resistance to tuber skinning injury are of central importance in developing physiological approaches to enhance skin-set and reduce associated losses; the current status of this research area is summarized. The process of wound-induced suberization to heal skinned, cut, and so called bruised areas covers a vast research plane. The induction and regulation of suberization, composition, biosynthetic pathways and macromolecular assembly, and molecular structure of suberin are not fully known. Consequently, suberin is somewhat of an enigma that is often misunderstood and poorly described in conjunction with wound-healing and wound-periderm development; the plane of suberin research is summarized including what is currently considered appropriate terminology and description of suberin. Various wound-related defects are described and discussed.
DOI:10.1111/tpj.13820URLPMID:29315972 [本文引用: 2]
Wound‐induced suberin deposition involves the temporal and spatial coordination of phenolic and fatty acid metabolism. Phenolic metabolism leads to both soluble metabolites that accumulate as defense compounds as well as hydroxycinnamoyl derivatives that form the basis of the poly(phenolic) domain found in suberized tissue. Fatty acid metabolism involves the biosynthesis of very long chain fatty acids, 1‐alkanols, ω‐hydroxy fatty acids and α,ω‐dioic acids that form a poly(aliphatic) domain, commonly referred to as suberin. Using the ABA biosynthesis inhibitor fluridone (FD), we reduced wound‐induced de novo biosynthesis of ABA in potato tubers, and measured the impact on the expression of genes involved in phenolic metabolism (StPAL1, StC4H, StCCR, StTHT), aliphatic metabolism (StCYP86A33, StCYP86B12, StFAR3, StKCS6), metabolism linking phenolics and aliphatics (StFHT) or acyl chains and glycerol (StGPAT5, StGPAT6), and in the delivery of aliphatic monomers to the site of suberization (StABCG1). In FD‐treated tissue, both aliphatic gene expression and accumulation of aliphatic suberin monomers were delayed. Exogenous ABA restored normal aliphatic suberin deposition in FD‐treated tissue, and enhanced aliphatic gene expression and poly(aliphatic) domain deposition when applied alone. By contrast, phenolic metabolism genes were not affected by FD treatment, while FD + ABA and ABA treatments slightly enhanced the accumulation of polar metabolites. These data support a role for ABA in the differential induction of phenolic and aliphatic metabolism during wound‐induced suberization in potato.
DOI:10.1111/j.1469-8137.2011.04047.xURLPMID:22296281Magsci [本文引用: 1]
090004During harvest, fleshy berry tomato fruits (Solanum lycopersicum) were wounded at their stem scar. Within 3 d, this wound was rapidly sealed by a process covering the wound site with a membranous layer which effectively protects the tomato fruit from excessive water loss, nutrient elution and the entry of pathogens.090004Chemical analysis of the de novo synthesized stem scar tissue revealed the presence of aromatic and aliphatic components characteristic of the biopolyester suberin.090004Gene expression patterns associated with suberization were identified at the stem scar region. Changes in the relative abundance of different transcripts suggested a potential involvement of the plant hormone abscisic acid (ABA) in the wound-healing processes.090004The amount of ABA present in the stem scar tissue showed a significantly increased level during wound healing, whereas ABA-deficient mutants notabilis, flacca and sitiens were largely devoid of this rise in ABA levels. The mutant fruits showed a retarded and less efficient suberization response at the stem scar wound, whereas the rate and strength of this response were positively correlated with ABA content. These results clearly indicate in vivo the involvement of ABA in the suberization-based wound-healing processes at the stem scar tissue of tomato fruits.
DOI:10.1146/annurev.pp.30.060179.000541URL [本文引用: 2]
Summary This chapter contains sections titled: Introduction Experimental Procedure Results and Discussion Conclusions
DOI:10.1017/S0025315400044969URLPMID:20232915 [本文引用: 1]
Abstract This study investigated the effects of heat treatment (hot air at 38 degrees C for 4 days) on wound healing in Gala and Red Fuji apple fruits (Malus domestica Borkh.) and the possible mechanism. Wounded apples were healed at either 20 or 38 degrees C for 4 days. During the treatment, ethylene, phenylalanine ammonia-lyase (PAL), peroxidase (POD), polyphenol oxidase (PPO), hydrogen peroxide (H(2)O(2)), and phenolic and lignin contents were measured. Following the treatment, healed wounds were inoculated with Penicillium expansum, Botrytis cinerea, and Colletotrichum acutatum, and then the decay development was observed. Results revealed that the influence of heating on wound healing in apple fruit was cultivar dependent. Compared with fruits healed at 20 degrees C, heating at 38 degrees C had a pejorative effect on wound healing in Gala apples. However, identical treatment enhanced wound healing in Red Fuji apples. Heating sharply reduced ethylene evolution, PAL and POD activity, and the accumulation of phenolic compounds and lignin around wounds in Gala apples. Alternatively, in Red Fuji apples, treatment at 38 degrees C significantly improved ethylene evolution and peroxide (H(2)O(2)) content at the first two days of treatment. In addition, both PAL and POD activities, and contents of phenolic compounds and lignin around wounds increased. Our findings suggest that this discrepancy in the effect of heat treatment on wound healing is due to different effects on ethylene evolution in cultivars of apple fruit.
DOI:10.1016/S0925-5214(99)00073-3URL [本文引用: 1]
The effect of gamma irradiation on lignin biosynthesis during wound healing in potato tubers was studied by [U- 14C] phenylalanine incorporation into lignin and monitoring the activities of key enzymes involved in the lignification process. There was a 40% reduction in lignin biosynthesis during wound healing in response to gamma irradiation. The level of the first enzyme involved in lignin biosynthesis, phenylalanine ammonia lyase (PAL), was five-fold higher in irradiated potatoes than in control tubers during wound healing. However the level of another key enzyme, cinnamyl alcohol dehydrogenase (CAD) was found to be 30% less in irradiated potatoes. There was no significant change in peroxidase activity and its isozyme pattern during wound healing. Differential regulation of different enzymes of lignin biosynthesis in response to gamma irradiation may be responsible for the decreased lignin biosynthesis.
DOI:10.1104/pp.113.3.685URLPMID:12223637 [本文引用: 1]
Abstract Polyphenol oxidases (PPOs) are encoded by a highly conserved, seven-member gene family clustered within a 165-kb locus on chromosome 8 of tomato (Lycopersicon esculentum). Using gene-specific probes capable of differentiating between PPO A/C, PPO B, PPO D, and PPO E/F, we examined the spatial and temporal expression of this gene family during vegetative and reproductive development. RNA blots and in situ hybridization using these probes showed that although PPO expression is primarily confined to early stages of development, the steady-state mRNA levels of these genes are subject to complex patterns of spatial and temporal regulation in vegetative and reproductive organs. Young tomato leaves and flowers possess the most abundant PPO transcripts. PPO B is the most abundant in young leaves, whereas in the inflorescence PPO B and E/F transcripts are dominant. Differential expression of PPOs is also observed in various trichome types. PPO A/C are specifically expressed in type I and type IV trichomes. In contrast, PPO D is only expressed in type VI trichomes. Type I, IV, and VI trichomes possess PPO E/F transcripts. Immunolocalization verified the translational activity of PPOs identified by in situ hybridization and suggested cell-type-specific, developmentally programmed PPO turnover. In addition, immunolocalization demonstrated the accumulation of PPO in specific idioblast cells of stems, leaves, and fruits.
DOI:10.1016/j.phytochem.2006.08.006URLPMID:16973188 [本文引用: 1]
The more recent reports on polyphenol oxidase in plants and fungi are reviewed. The main aspects considered are the structure, distribution, location and properties of polyphenol oxidase (PPO) as well as newly discovered inhibitors of the enzyme. Particular stress is given to the possible function of the enzyme. The cloning and characterization of a large number of PPOs is surveyed. Although the active site of the enzyme is conserved, the amino acid sequence shows very considerable variability among species. Most plants and fungi PPO have multiple forms of PPO. Expression of the genes coding for the enzyme is tissue specific and also developmentally controlled. Many inhibitors of PPO have been described, which belong to very diverse chemical structures; however, their usefulness for controlling PPO activity remains in doubt. The function of PPO still remains enigmatic. In plants the positive correlation between levels of PPO and the resistance to pathogens and herbivores is frequently observed, but convincing proof of a causal relationship, in most cases, still has not been published. Evidence for the induction of PPO in plants, particularly under conditions of stress and pathogen attack is considered, including the role of jasmonate in the induction process. A clear role of PPO in a least two biosynthetic processes has been clearly demonstrated. In both cases a very high degree of substrate specificity has been found. In fungi, the function of PPO is probably different from that in plants, but there is some evidence indicating that here too PPO has a role in defense against pathogens. PPO also may be a pathogenic factor during the attack of fungi on other organisms. Although many details about structure and probably function of PPO have been revealed in the period reviewed, some of the basic questions raised over the years remain to be answered.
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