Water stress modulates terpene biosynthesis and morphophysiology at different ploidal levels in Lippia alba (Mill.) N. E. Brown (Verbenaceae).

Monoterpenes are the main component in essential oils of Lippia alba. In this species, the chemical composition of essential oils varies with genome size: citral (geraniol and neral) is dominant in diploids and tetraploids, and linalool in triploids. Because environmental stress impacts various metabolic pathways, we hypothesized that stress responses in L. alba could alter the relationship between genome size and essential oil composition. Water stress affects the flowering, production, and reproduction of plants. Here, we evaluated the effect of water stress on morphophysiology, essential oil production, and the expression of genes related to monoterpene synthesis in diploid, triploid, and tetraploid accessions of L. alba cultivated in vitro for 40 days. First, using transcriptome data, we performed de novo gene assembly and identified orthologous genes using phylogenetic and clustering-based approaches. The expression of candidate genes related to terpene biosynthesis was estimated by real-time quantitative PCR. Next, we assessed the expression of these genes under water stress conditions, whereby 1% PEG-4000 was added to MS medium. Water stress modulated L. alba morphophysiology at all ploidal levels. Gene expression and essential oil production were affected in triploid accessions. Polyploid accessions showed greater growth and metabolic tolerance under stress compared to diploids. These results confirm the complex regulation of metabolic pathways such as the production of essential oils in polyploid genomes. In addition, they highlight aspects of genotype and environment interactions, which may be important for the conservation of tropical biodiversity.

Accessions of Brazilian ginseng (Pfaffia glomerata) with contrasting anthocyanin content behave differently in growth, antioxidative defense, and 20-hydroxyecdysone levels under UV-B radiation.

Ultraviolet-B (UV-B) radiation is an elicitor of secondary metabolites in plant tissue culture, but the effects on 20-hydroxyecdysone (20E) are still unclear. The 20E may show biotechnological, pharmacological, medical, and agrochemical applicability. Here, we use Pfaffia glomerata, a medically important species, to understand the impacts of UV-B radiation on their physiological performance, the expression of key genes involved in the 20E biosynthesis, and the 20E content. Two accessions (A22 and A43) of plants 20 days old grown in vitro were exposed to 0 (control), 2 (6.84 kJ m-2), and 4 (13.84 kJ m-2) h UV-B radiation for 20 consecutive days. Our data showed that UV-B reduced glucose concentration in A22 and A43 under 4 h of exposure (29 and 30%, respectively), while sucrose concentration increased (32 and 57%, respectively). UV-B also differentially impacted the accessions (A22 and A43), where the A22 under 4 h of UV-B had reduced total dry weight (8%) and electron transport rate (31%); in contrast, A43 did not change. Also, only A22 had increased POD activity under 4 h of UV-B (66%), as well as increased gene expression of the 20E pathway and the 20E content under 2 and 4 h of UV-B in leaves (28 and 21%, respectively) and roots (16 and 13%, respectively). This differential performance to UV-B can be explained by the contrasting anthocyanin contents. Notably, A43 displayed 56% more anthocyanin to the former, a possible defense against UV-B. In conclusion, UV-B radiation is a potential elicitor for increasing 20E content in P. glomerata grown in vitro.