Department of Agronomy, Food, Natural Resources, Animals, and Environment, University of Padova, Agripolis, 35020 Legnaro, Italy.
Plant Physiol. 2013 Apr;161(4):1952-69. doi: 10.1104/pp.112.208470. Epub 2013 Feb 26.
Apple (Malus domestica) fruitlet abscission represents an interesting model system to study the early phases of the shedding process, during which major transcriptomic changes and metabolic rearrangements occur within the fruit. In apple, the drop of fruits at different positions within the cluster can be selectively magnified through chemical thinners, such as benzyladenine and metamitron, acting as abscission enhancers. In this study, different abscission potentials were obtained within the apple fruitlet population by means of the above-cited thinners. A metabolomic study was conducted on the volatile organic compounds emitted by abscising fruitlets, allowing for identification of isoprene as an early marker of abscission induction. A strong correlation was also observed between isoprene production and abscisic acid (ABA) levels in the fruit cortex, which were shown to increase in abscising fruitlets with respect to nonabscising ones. Transcriptomic evidence indicated that abscission-related ABA is biologically active, and its increased biosynthesis is associated with the induction of a specific ABA-responsive 9-cis-epoxycarotenoid dioxygenase gene. According to a hypothetical model, ABA may transiently cooperate with other hormones and secondary messengers in the generation of an intrafruit signal leading to the downstream activation of the abscission zone. The shedding process therefore appears to be triggered by multiple interdependent pathways, whose fine regulation, exerted within a very short temporal window by both endogenous and exogenous factors, determines the final destiny of the fruitlets.
苹果（Malus domestica）幼果脱落代表了一个有趣的模型系统，可用于研究脱落过程的早期阶段，在此期间，果实内部会发生重大的转录组变化和代谢重排。在苹果中，通过使用诸如苄氨基嘌呤和噻苯隆等作为脱落促进剂的化学疏除剂，可以选择性地放大簇中不同位置果实的脱落。在本研究中，通过上述疏除剂在苹果幼果群体中获得了不同的脱落潜力。对脱落幼果释放的挥发性有机化合物进行了代谢组学研究，鉴定出异戊二烯是脱落诱导的早期标志物。还观察到异戊二烯的产生与果实皮层中的脱落酸（ABA）水平之间存在很强的相关性，与未脱落的幼果相比，脱落的幼果中 ABA 水平增加。转录组学证据表明，与脱落相关的 ABA 具有生物活性，其生物合成的增加与特定的 ABA 响应的 9-顺式-环氧类胡萝卜素双加氧酶基因的诱导有关。根据一个假设模型，ABA 可能与其他激素和第二信使短暂合作，在产生导致脱落区下游激活的果实内信号中发挥作用。因此，脱落过程似乎是由多个相互依赖的途径触发的，这些途径的精细调节，是由内源和外源因素在很短的时间窗口内共同作用决定的，决定了幼果的最终命运。
