###### Abstract  
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 \(M\). 'Praire Rose' and BA in \(M\). '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 \(M\). 'Praire Rose' and \(M\). 'Lollipop' were entirely opposite. Correlation and PCA analysis demonstrated that the content of CYP9D73 (a P450) and N, and the C/N ratio were key factors in 2-PE production in \(M\). 'Praire Rose'. The production of BA in \(M\). 'Lollipop' was more influenced by the content of phenylacetaldehyde synthase (PAAS), CYP9D73, and soluble sugar. As CYP9D73 exits oppositely in correlation to 2-PE (_M_. 'Praire Rose') and BA (_M_. 'Lollipop'), it is hypothesized that CYP9D73 was postulated as the primary factor contributing to the observed differences of 2-PE (_M_. 'Praire Rose') and BA (_M_. 'Lollipop') formation. These results carry significant implications for crabapple aromatic flower breeding and the essential oil industry etc. crabapple; 2-phenylethylanol; benzyl alcohol; enzyme; C/N 2024 13 202 Additionally, 2-PE has widespread application in various industries, contributing to the production of diverse flavors, fragrances, cosmetics, and food processing [13; 14]. BA has been considered a pollinator-attractant in a diversity of pollination syndromes [15; 16]. The synthesis of 2 PE and BA is relevant across various industries and fields, from fragrance and flavoring to pharmaceuticals and chemical research, making it an important topic of study and exploration. Notably, 2-PE and BA are synthesized through the same precursor, L-phenylalanine (L-Phe). The synthesis of 2-PE involves two key steps: the conversion of L-Phe to phenylacetaldehyde (PALD), followed by the transformation of PALD into 2-PE [17; 18]. While phenylacetaldehyde reductase (PAR) has been identified as the enzyme responsible for the second step in the synthesis of 2-PE, the first step displays notable variations among different plant species [18]. In \(R\). 'Hoh-Jun' and \(R\). _damascena_ Mill., aromatic amino acid decarboxylase (AADC) has been identified as the enzyme that converts L-Phe to the intermediate compound PALD [9]. Conversely, in _Petunia hybrida_ cv. Mitchell plants, phenylacetaldehyde synthase (PAAS) is the enzyme responsible for converting L-Phe [19]. Roses also employ a third enzyme called aromatic amino acid aminotransferase (AAAT), which catalyzes the formation of phenylpyruvate acid from L-Phe. This intermediate can then be further converted to PALD by phenylpyruvate acid decarboxylase (PDL) [20]. In the case of _Plumeria rubra_, the pathway for 2-PE production involves an intermediate (E/Z)-PAOx, which was catalyzed by a cytochrome P450 family 79D protein (PrCYP79D73) [21]. BA, a key component in the characteristic FS of common crabapple species and cultivars [8], is produced through phenylalanine ammonia-lyase (PAL). PAL also catalyzes the deamidation of L-Phe as part of the overall process. Benzaldehyde, originating from cinnamic acid and a precursor to BA, is generated through both CoA-dependent \(\beta\)-oxidation and CoA-independent non-\(\beta\)-oxidation pathways in the petunia [22; 23]. The enzyme BPBT (benzyl alcohol/phenylethanol benzylotransferase) plays a crucial role in promoting the synthesis of benzyl benzoate along with phenethyl benzoate [24; 25; 26].