Estresses abióticos em poliploides sintéticos de Lippia alba

Abstract

Lippia alba (Verbenaceae) is a native species of the American continent, widely distributed in Brazil. It is popularly known as melissa, lemon balm and field rosemary, among others. It is a perennial shrubby and its branches easily root when they touch the soil. Its leaves are rich in essential oils of economic and biotechnological interest. L. alba stands out for being a polyploid complex, with wide morphological, genetic and phytochemical variation. It is also known that the chemical composition of terpenes is directly related to the DNA content of the species. Polyploidy has an impact on the morphology, physiology and production of secondary metabolites, giving to the polyploids particular traits, such as better tolerance to adverse conditions like water deficit and salinity. Synthetic polyploidy is an additional tool for understanding the evolution of organisms, especially plants, and evaluate the effects of the increasing of the genome size. In this study, we used a synthetic triploid individual of L. alba to evaluate the effects of water and salt stress on biochemical, genetic and chemical composition of the essential oils. In addition, we described the process of inducing synthetic polyploidy from a synthetic triploid of L. alba to obtain hexaploids using colchicine (0.2%) and analyzed the immediate effects of the induced chromosome duplication. We observed that the abiotic stresses increased the content of total soluble proteins under water stress and altered the expression of genes related to the terpene production pathway in both treatments. The polyploidy induction initially showed the formation of mixoploids. Treatment with colchicine increased the mortality rate, altered the time of development and the pattern of gene expression. In addition, over the evaluation period, we observed that plants that were initially mixoploid reverted to their initial triploid state. The opposite was observed as well. Overall, this work contributes for the understanding of the process of inducing polyploidy in Lippia alba and its effects on neopolyploids, as well as provides new insights into the responses of synthetic polyploid plants under water and salt stress.