Methyl Jasmonate and α-aminooxi-β-phenyl Propionic Acid Alter Phenylalanine Ammonia-Lyase Enzymatic Activity to Affect the Longevity and Floral Scent of Cut Tuberose

Longevity is a determining factor of the marketability of cut flowers, and is therefore a key target in commercial floriculture. Floral scent is another important factor in the popularity of cut flowers. The phenylpropanoid pathway is one of the key pathways in floral scent production. The first step of this pathway is catalyzed by the enzyme phenylalanine ammonia-lyase (PAL). Here, we evaluated the pre-harvest foliar application of a PAL promoter (methyl jasmonate [MeJA]) and a PAL inhibitor (α-aminooxi-E-phenyl propionic acid [AOPP]) on the physiological parameters, floral scent, and longevity of cut tuberose flowers (Polianthes tuberosa L.). Relative water content (RWC) was significantly affected by foliar application of treatments. The highest and lowest RWCs were observed in plants treated with AOPP (3 mM) and the control, respectively. Catalase (CAT) enzyme activity was not significantly affected by treatments, while peroxidase (POD) activity was significantly affected. Foliar application significantly affected stem water uptake and the 3 mM AOPP resulted in the highest stem water uptake. A GC-MS analysis of floral scent volatiles detected 37 different compounds, with the most abundant being methyl benzoate, benzyl benzoate, pentacosane, and methyl salicylate. The pre-harvest foliar application of MeJA increased the total scent of tuberose, as well as increasing the relative abundances of methyl benzoate and methyl salicylate and reducing the benzyl benzoate and pentacosane content. In contrast, the foliar application of AOPP decreased the total floral scent; while the relative amount of pentacosane increased, the methyl benzoate and methyl salicylate contents decreased. Both treatments extended the longevity of the tuberose flowers; however, the flowers of the AOPP-treated plants lasted longer than those treated with MeJA which could be due the different effects of these treatments on RWC, antioxidant enzymes activity, and/or stem water uptake. These results indicate that PAL plays an important role in the generation of floral scent and the extension of longevity in cut tuberose.