The form, dose, and method of application of vermicompost differentiate the phenylpropene biosynthesis in the peltate glandular trichomes of methylchavicol chemotype of Ocimum basilicum L.

Abstract

Peltate glandular trichomes (PGTs) in basil (Ocimum basilicum L.) are ideal for studying phenylpropanoid metabolism, as they allow for the elimination of the effects of primary plant metabolism. In this study, we aimed to investigate the effects of 0, 10%, and 25% doses of both solid and tea forms of vermicompost on phenylpropanoid metabolism in PGTs of the methylchavicol chemotype of basil. The experiment based on the analysis of the gene expression (PAL, 4CL, EGS, EOMT, CVOMT) and the accumulation of phenylpropene (eugenol, chavicol, methyleugenol, methylchavicol) in PGTs after vermicompost treatment. Our results showed that the application of solid vermicompost (SV) to the root zone of basil at 10% and 25% significantly reduced the expression of EOMT and CVOMT to below 0.1 from 2.43 and 3.85, respectively. The application of 10% solid vermicompost (SV) to basil soil resulted in a decrease in methyleugenol and methylchavicol accumulation approximately by 50% and 52%, respectively. Further application of 25% (SV) resulted in a total decrease of approximately 76% and 51% in methyleugenol and methylchavicol accumulation, respectively. Application of 10% vermicompost tea (VT) to basil leaves resulted in a significant increase in chavicol accumulation (243%) and methyleugenol accumulation (613%) in basil essential oil, as well as upregulation of EOMT and CVOMT gene expression approximately by 391-fold and 1,155-fold, respectively, compared to control plants. Furthermore, application of 25% VT resulted in a significant increase in eugenol accumulation (665%) and methylchavicol accumulation (56%), as well as downregulation of EOMT and CVOMT gene expression approximately by 31-fold and 9-fold, respectively, compared to control plants. These findings suggest that VT application can modulate the accumulation of important phenylpropenes in basil through regulation of gene expression. In addition, the use of vermicompost tea has been shown to significantly enhance the levels of phenylpropenes in basil, which are important contributors to the herb's aroma and antimicrobial activity. This suggests that the application of VT can play a crucial role in determining the quality of basil in terms of its secondary metabolites, making it a valuable tool in phytoremediation practices. Overall, our results demonstrate the effectiveness of vermicompost on phenylpropene biosynthesis and the utility of PGTs composed of a single cell type for the study of secondary metabolic processes in plants.