Physiological and Biochemical Analysis Revealing the Key Factors Influencing 2-Phenylethanol and Benzyl Alcohol Production in Crabapple Flowers

Floral scent (FS) plays a crucial role in the ecological functions and industrial applications of plants. However, the physiological and metabolic mechanisms underlying FS formation remain inadequately explored. Our investigation focused on elucidating the differential formation mechanisms of 2-phenylethanol (2-PE) and benzyl alcohol (BA) by examining seven related enzyme concentrations and the content of soluble sugar, soluble proteins, carbon (C) and nitrogen (N), as well as the C/N ratio. The findings revealed that the peak content of 2-PE in <i>M.</i> ‘Praire Rose’ and BA in <i>M.</i> ‘Lollipop’ occurred during the end flowering stage (S4) and flowering stage (S3) periods, respectively. The enzyme concentration change trends of phenylpyruvate decarboxylase (PDL), phenylacetaldehyde reductase (PAR), soluble protein, C, N, and C/N ratio changes during the S3-S4 period in <i>M.</i> ‘Praire Rose’ and <i>M.</i> ‘Lollipop’ were entirely opposite. Correlation and PCA analysis demonstrated that the content of CYP79D73 (a P450) and N, and the C/N ratio were key factors in 2-PE production in <i>M.</i> ‘Praire Rose’. The production of BA in <i>M.</i> ‘Lollipop’ was more influenced by the content of phenylacetaldehyde synthase (PAAS), CYP79D73, and soluble sugar. As CYP79D73 exits oppositely in correlation to 2-PE (<i>M.</i> ‘Praire Rose’) and BA (<i>M.</i> ‘Lollipop’), it is hypothesized that CYP79D73 was postulated as the primary factor contributing to the observed differences of 2-PE (<i>M.</i> ‘Praire Rose’) and BA (<i>M.</i> ‘Lollipop’) formation. These results carry significant implications for crabapple aromatic flower breeding and the essential oil industry etc.