Phenolic compounds as biochemical markers of senescence in woody ornamental flowers of Malus crabapple

Polyphenol intermediates accumulate predominantly in peripheral parts of floral tissues and play various roles in tissue homeostasis. A limited ornamental flower shelf life is caused by early tissue senescence, otherwise known as programmed cell death (PCD), which is characterized by processes such as DNA degradation, reduction in protein content and others. However, the role of polyphenols during PCD is poorly understood. In this study, we evaluated polyphenols as potential biochemical markers during developmental changes associated with PCD. Malus crabapple flowers were exposed to low (LT = 13 ± 2 °C), room (RT = 23 ± 2 °C), and high (HT = 30 ± 2 °C) temperatures to induce different levels of PCD. HT treatment was associated with enhanced H2O2 and MDA content, which subsequently caused lower protein concentration and induced DNA degradation. Conversely, substantially higher protein content, lesser DNA degradation, and lower H2O2 and MDA accumulation were observed following RT and LT treatments. Furthermore, significantly higher concentrations of phenolic acids, flavanols, and anthocyanins were observed following both RT and LT treatments, more so for the latter, due to up-regulation of structural genes such as MpPAL, MpDFR, MpLDOX, and MpUFGT. Similarly, following HT treatment that induced a higher rate of PCD, the accumulation of dihydrochalcone and flavonols was significantly enhanced and associated with increased expression of MpCHS and MpFLS. Phenolic contents are determined via precise regulation of a highly conserved set of structural genes, indicating their functional importance. Therefore, it was assumed that individual phenolic intermediates or discrete diverse classes of polyphenol compounds may be utilized as biochemical markers of PCD in woody ornamental flowers of Malus crabapple.