Tsantili Eleni, Gapper Nigel E, Arquiza J M R Apollo, Whitaker Bruce D, Watkins Chris B
Department of Horticulture, Cornell University, Ithaca, New York 14853, USA.
J Agric Food Chem. 2007 Jun 27;55(13):5267-76. doi: 10.1021/jf063775l. Epub 2007 May 31.
Relationships among alpha-farnesene synthesis and oxidation, ethylene production and perception, antioxidative enzyme activities, and superficial scald development in fruit of three commercial apple cultivars were investigated at the biochemical and gene transcriptional levels. Scald-susceptible Cortland and Law Rome and scald-resistant Idared apples were untreated or treated with the ethylene action inhibitor 1-methylcyclopropene (1-MCP) and stored for up to 25 weeks at 0.5 degrees C. Separate blushed (red) and unblushed (green) peel tissue samples were taken at harvest and after 2, 4, 6, 10, 15, 20, and 25 weeks of storage. Large increases in peel tissue concentrations of alpha-farnesene and its conjugated trienol (CTol) oxidation products occurred in untreated Cortland and Law Rome and were about 4-9-fold greater than those in Idared. In both Cortland and Law Rome, accumulation of CTols in green peel was nearly twice that in red peel. 1-MCP treatment delayed and attenuated alpha-farnesene and CTol accumulation in each cultivar. Activities of peroxidase (POX) and catalase (CAT) were lower in red peel than in green peel, with the exception of CAT in Law Rome, whereas no effects of 1-MCP on enzyme activities were detected except for Cortland. In control fruit, internal ethylene concentrations (IECs) increased during the first 4-6 weeks to reach highest levels in Cortland, intermediate levels in Law Rome, and low levels in Idared. In 1-MCP-treated fruit, IECs increased gradually to modest levels by 25 weeks in Cortland and Law Rome but were almost nil in Idared. Expression patterns of the alpha-farnesene synthase gene MdAFS1, the ethylene receptor gene MdERS1, and the ethylene biosynthetic genes MdACS1 and MdACO1 were generally in accord with the patterns of alpha-farnesene and ethylene production. In particular, MdAFS1 and MdACS1 showed similar patterns of expression in each cultivar. Among the controls, transcript levels increased more rapidly in Cortland and Law Rome than in Idared during the first few weeks of storage. In 1-MCP-treated fruit, transcript abundance in Cortland and Law Rome rose to untreated control levels after 10-15 weeks but remained low in Idared. Scald symptoms were restricted to unblushed skin, and the incidence in controls after 25 weeks was nearly 100% in Cortland and Law Rome compared with 1% in Idared. 1-MCP treatment reduced scald incidence to 14, 3, and 0% in Cortland, Law Rome, and Idared, respectively. Overall, the results support the proposed role of CTols in scald induction and indicate that alpha-farnesene synthesis is tightly regulated by ethylene. However, gene transcription alone does not account for the big differences in ethylene and alpha-farnesene production in Cortland, Law Rome, and Idared apples.
在生化和基因转录水平上，研究了三个商业苹果品种果实中α-法尼烯合成与氧化、乙烯产生与感知、抗氧化酶活性以及表面烫伤发展之间的关系。对易发生烫伤的科特兰（Cortland）和罗马美（Law Rome）以及抗烫伤的艾达红（Idared）苹果进行了如下处理：不处理或用乙烯作用抑制剂1-甲基环丙烯（1-MCP）处理，然后在0.5摄氏度下储存长达25周。在收获时以及储存2、4、6、10、15、20和25周后，分别采集有红晕（红色）和无红晕（绿色）的果皮组织样本。未处理的科特兰和罗马美苹果果皮组织中α-法尼烯及其共轭三烯醇（CTol）氧化产物的浓度大幅增加，比艾达红苹果中的浓度高约4 - 9倍。在科特兰和罗马美苹果中，绿色果皮中CTols的积累量几乎是红色果皮中的两倍。1-MCP处理延缓并减弱了每个品种中α-法尼烯和CTol的积累。除了罗马美苹果中的过氧化氢酶（CAT）外，红色果皮中过氧化物酶（POX）和CAT的活性低于绿色果皮，而除了科特兰苹果外，未检测到1-MCP对酶活性有影响。在对照果实中，内部乙烯浓度（IECs）在最初4 - 6周内升高，在科特兰苹果中达到最高水平，在罗马美苹果中为中等水平，在艾达红苹果中为低水平。在1-MCP处理的果实中，科特兰和罗马美苹果中的IECs在25周时逐渐增加到适度水平，但在艾达红苹果中几乎为零。α-法尼烯合成酶基因MdAFS1、乙烯受体基因MdERS1以及乙烯生物合成基因MdACS1和MdACO1的表达模式总体上与α-法尼烯和乙烯产生的模式一致。特别是，MdAFS1和MdACS1在每个品种中表现出相似的表达模式。在对照中，储存的最初几周内，科特兰和罗马美苹果中的转录水平比艾达红苹果中增加得更快。在1-MCP处理的果实中，科特兰和罗马美苹果中的转录丰度在10 - 15周后升至未处理对照水平，但在艾达红苹果中仍保持较低水平。烫伤症状仅限于无红晕的果皮，25周后，对照中科特兰和罗马美苹果的发病率接近100%，而艾达红苹果中为1%。1-MCP处理分别将科特兰、罗马美和艾达红苹果的烫伤发病率降低至14%、3%和0%。总体而言，结果支持了CTols在烫伤诱导中所起的作用，并表明α-法尼烯合成受乙烯严格调控。然而，仅基因转录并不能解释科特兰、罗马美和艾达红苹果在乙烯和α-法尼烯产生方面的巨大差异。
