Three apple cultivars with different peel colour and known ripening dynamics were examined throughout development and on-tree ripening to unravel how the hormonal crosstalk may influence colour changes. Our results indicate that the colour of ripe apples in ‘Granny Smith’ and ‘Opal^®’ cultivars was primarily influenced by chlorophyll levels masking the contribution of other pigments, whilst the development of red colour in the ‘Royal Gala’ was not only due to an important loss of chlorophyll during ripening but also to anthocyanins accumulation. The interplay amongst indole-3-acetic acid (IAA), ethylene and abscisic acid (ABA) seemed to control pigment content during the later stages of development, indicating that variations in the hormonal profile contribute to colour differences in ripe apples. In ‘Granny Smith’ apples, basal levels of IAA, ethylene and ABA were associated with the inhibition of chlorophyll loss, which was responsible for its green colour, despite the presence of high carotenoid levels. In contrast, the peel of ‘Opal^®’ and ‘Royal Gala’ apples underwent a degreening process facilitated by the IAA-mediated activation of ethylene metabolism, in a crosstalk facilitated by MdARF5. The accumulation of anthocyanins in the peel of ‘Royal Gala’ apples seemed to be regulated in an ethylene-dependent manner, with MdMYB1 acting as the mediator between ethylene signalling and the anthocyanins biosynthesis and vacuolar transport pathways. On the other hand, the decline in carotenoid content during fruit development in the three cultivars appeared to be regulated at the catabolic level through ABA and its derivatives and possibly also facilitated by ethylene-mediated mechanisms. Notably, chlorophyll levels, crucial for the observed colour changes, were likely controlled by MdGLK1, a transcription factor involved in chloroplast biogenesis, working in coordination with ethylene-dependent catabolic enzymes. Overall, understanding the cultivar-specific hormonal regulation of apple colour provides valuable insights for developing preharvest and postharvest strategies to ensure an optimal fruit colour aligned with consumer preferences.

对具有不同果皮颜色和已知成熟动态的三个苹果品种的整个发育和树上成熟进行了检查，以揭示激素串扰如何影响颜色变化。我们的结果表明，“Granny Smith”和“Opal ^® ”品种中成熟苹果的颜色主要受到叶绿素水平的影响，掩盖了其他色素的贡献，而“Royal Gala”中红色的形成不仅是由于成熟过程中叶绿素的重要损失，而且也会影响花青素的积累。 3-吲哚乙酸 (IAA)、乙烯和脱落酸 (ABA) 之间的相互作用似乎控制着发育后期的色素含量，这表明激素分布的变化导致了成熟苹果的颜色差异。在“澳洲青苹果”中，IAA、乙烯和ABA的基础水平与叶绿素损失的抑制有关，叶绿素损失是其绿色的原因，尽管类胡萝卜素水平很高。相比之下，‘Opal®’和‘Royal Gala’苹果的果皮^经历了由 IAA 介导的乙烯代谢激活促进的程度化过程，在MdARF5促进的串扰中。 “Royal Gala”苹果果皮中花青素的积累似乎以乙烯依赖性方式进行调节，MdMYB1充当乙烯信号传导与花青素生物合成和液泡运输途径之间的介质。另一方面，三个品种果实发育过程中类胡萝卜素含量的下降似乎是通过ABA及其衍生物在分解代谢水平上调节的，也可能是通过乙烯介导的机制促进的。值得注意的是，叶绿素水平对于观察到的颜色变化至关重要，很可能是由MdGLK1控制的，MdGLK1 是一种参与叶绿体生物发生的转录因子，与乙烯依赖性分解代谢酶协同工作。总体而言，了解苹果颜色的品种特异性激素调节为制定采前和采后策略提供了宝贵的见解，以确保最佳的水果颜色符合消费者的喜好。