Hayama Hiroko, Shimada Takehiko, Fujii Hiroshi, Ito Akiko, Kashimura Yoshiki
National Institute of Fruit Tree Science (NIFTS), 2-1 Fujimoto, Tsukuba, Ibaraki 305-8605, Japan.
J Exp Bot. 2006;57(15):4071-7. doi: 10.1093/jxb/erl178. Epub 2006 Oct 31.
To investigate the role of ethylene in peach fruit softening during ripening, stony hard peach fruit, in which ethylene production is suppressed during ripening, were treated with various concentrations of ethylene. There was no noticeable decrease in flesh firmness without ethylene treatment, while applied ethylene, in the range 0.1-100 microl l(-1), resulted in fruit softening. Furthermore, the fruit softened more rapidly when the applied ethylene concentration was higher. When ethylene treatment was interrupted, the degree of softening was greatly reduced. These results indicated that continuous ethylene treatment was required for the initiation and progression of fruit softening and that ethylene concentration is also an important factor in regulating the rate of softening. Eight genes, which putatively encode cell wall metabolism-related proteins, were investigated for mRNA accumulation patterns in the two different softening phenotypes of melting and stony hard peaches. All of the mRNAs investigated accumulated in fruit of the melting-flesh "Akatsuki" during ripening. By contrast, in the stony hard-flesh "Manami", the mRNAs for a putative endopolygalacturonase (PpPG), an alpha-L-arabinofuranosidase/beta-xylosidase (PpARF/XYL), and an expansin (PpExp3) showed either much lower levels or did not accumulate, and were identified as softening-related genes. Interruption of ethylene treatment indicated that these genes were regulated at the transcriptional level, and quickly responded to the presence or absence of ethylene before the softening response occurred, suggesting that ethylene directly regulates the transcription of these softening-related genes. These results suggested that cell wall metabolism, causing a rapid loss of firmness in peach fruit, may be controlled by ethylene at the transcriptional level.
为研究乙烯在桃果实成熟软化过程中的作用，对在成熟过程中乙烯生成受抑制的硬石桃果实施加不同浓度的乙烯。未进行乙烯处理时，果肉硬度无明显下降，而施加0.1 - 100微升/升范围内的乙烯会导致果实软化。此外，施加的乙烯浓度越高，果实软化越快。当乙烯处理中断时，软化程度大幅降低。这些结果表明，果实软化的起始和进程需要持续的乙烯处理，且乙烯浓度也是调节软化速率的重要因素。研究了八个可能编码细胞壁代谢相关蛋白的基因在溶质型和硬石型两种不同软化表型桃果实中的mRNA积累模式。在溶质型“明月”桃果实成熟过程中，所有研究的mRNA均有积累。相比之下，在硬石型“真珠”桃中，一个假定的内切多聚半乳糖醛酸酶（PpPG）、一个α-L-阿拉伯呋喃糖苷酶/β-木糖苷酶（PpARF/XYL）和一个扩展蛋白（PpExp3）的mRNA水平极低或未积累，这些基因被确定为与软化相关的基因。乙烯处理中断表明这些基因在转录水平受到调控，并且在软化反应发生之前能快速响应乙烯的有无，这表明乙烯直接调控这些与软化相关基因的转录。这些结果表明，导致桃果实硬度快速丧失的细胞壁代谢可能在转录水平受乙烯调控。
