Application of a Rapid and Sensitive Method for Hormonal and Vitamin E Profiling Reveals Crucial Regulatory Mechanisms in Flower Senescence and Fruit Ripening

Knowledge of ripeness and regulation of postharvest processes is an important tool to prevent loss of commercial value in both fruit and cut flower markets. The joint analysis of hormones and vitamin E levels can reveal complex interactions between hormones and oxidative stress as key regulators of postharvest processes. Profiling of both groups of metabolic compounds was performed during the ripening of non-climacteric fruits (red raspberry, Rubus idaeus L.) and senescence of ethylene-insensitive flowers (Dutch Iris, Iris x hollandica L.). After an initial extraction of the sample, without further purification steps, the hormonal profile was analyzed by UPLC-MS/MS and vitamin E levels were measured by HPLC. This methodological approach was very fast and had enough sensitivity for the analysis of small samples. Raspberry fruit maturation was characterized by a decline of cytokinin levels [zeatin, zeatin riboside, 2-isopentenyl adenine, and isopentenyl adenosine (Z, ZR, 2-iP, and IPA, respectively)] and gibberellins (GA₁ in particular). Exogenous application of ABA prevented δ-tocopherol loss during fruit ripening. Iris floral senescence was also under strict hormonal control, also mediated by cytokinins and gibberellins. Z, ZR, 2-iP, GA₉, and GA₂₄ levels decreased in inner tepals, whereas the level of IPA decreased in style-merged-to-stigma tissues, thus suggesting tissue-specific roles for different hormones. α-Tocopherol levels decreased during senescence of inner tepals, hence suggesting enhanced oxidative stress. In conclusion, the rapid and sensitive hormonal and vitamin E profiling presented here can help in understanding the key physiological processes underlying fruit ripening and floral senescence.