Alterations in carbon and nitrogen metabolism under phenylalanine ammonia-lyase inhibition in winter triticale seedlings

This study aimed to assess the impact of phenylalanine ammonia-lyase (PAL) inhibition on the carbon and nitrogen metabolism of winter triticale seedlings using 4-hydroxybenzoic acid hydrazide (HBH, 10⁻³ M), with particular attention to sugar accumulation and changes in polyamine and proline content. The HBH treatment did not significantly affect leaf water potential but caused a significant decrease in osmotic potential values, indicating an increase in leaf osmotic potential. PAL inhibition was primarily reflected by a significant decrease in cinnamic acid content (free and cell wall-bound), the direct product of PAL enzymatic activity. The HBH treatment reduced the content of several soluble and cell wall-bound phenolics, e.g. ferulic, benzoic, and chlorogenic acids. HBH application indirectly affected sugar content, increasing glucose and trehalose levels while decreasing fructose, sucrose, and oligosaccharides. Moreover, HBH also indirectly altered nitrogen metabolism by increasing proline levels and modulating the content of both free and cell wall-bound polyamines. Additionally, HBH application resulted in an increase in the dry mass of both shoots and roots, suggesting a stimulatory effect on biomass accumulation during the early growth stage. These findings demonstrate that PAL inhibition has broader implications indirectly affecting carbohydrate and nitrogen-related pathways. At the level of primary metabolism, altered sugar and polyamine profiles, along with increased proline content, suggest a disruption of the carbon-nitrogen balance, indicating that PAL activity contributes to maintaining metabolic homeostasis under non-stress conditions. Regarding secondary metabolism, the reduction in phenolic compounds confirms PAL's crucial role in phenylpropanoid biosynthesis and highlights its regulatory function in coordinating secondary metabolite production.