Hernandulcin Production in Cell Suspensions of Phyla Scaberrima: Exploring Hernandulcin Accumulation through Physical and Chemical Stimuli.

Hernandulcin (HE) is a non-caloric sweetener synthesized by the Mexican medicinal plant Phyla scaberrima. Herein we present the results of HE production through cell suspensions of P. scaberrima as well as the influence of pH, temperature, biosynthetic precursors and potential elicitors to enhance HE accumulation. The incorporation of mevalonolactone (30-400 mg L-1 ) farnesol (30-400 mg L-1 ), AgNO3 (0.025-0.175 M), cellulase (5-60 mg L-1 ; 0.3 units/mg), chitin (20-140 mg L-1 ) and (+)-epi-α-bisabolol (300-210 mg L-1 ) to the cell suspensions, resulted in a differential accumulation of HE and biomass. Among elicitors assayed, chitin, cellulase and farnesol increased HE production from 93.2 to ∼160 mg L-1 but, (+)-epi-α-bisabolol (obtained by a synthetic biology approach) increased HE accumulation up to 182.7 mg L-1 . HE produced by the cell suspensions was evaluated against nine strains from six species of gastrointestinal bacteria revealing moderate antibacterial activity (MIC, 214-465 µg mL-1 ) against Staphylococcus aureus, Escherichia coli and Helicobacter pylori. Similarly, HE showed weak toxicity against Lactobacillus sp. and Bifidobacterium bifidum (>1 mg mL-1 ), suggesting a selective antimicrobial activity on some species of gut microbiota. According to our results, chitin and (+)-epi-α-bisabolol were the most effective molecules to enhance HE accumulation in cell suspensions of P. scaberrima.

A species-level phylogenetic study of the Verbena complex (Verbenaceae) indicates two independent intergeneric chloroplast transfers.

Two major impediments to infer plant phylogenies at inter- or intra- species level include the lack of appropriate molecular markers and the gene tree/species tree discordance. Both of these problems require more extensive investigations. One of the foci of this study is examining the phylogenetic utility of a combined chloroplast DNA dataset (>5.0kb) of seven non-coding regions, in comparison with that of a large fragment (ca. 3.0kb) of a low-copy nuclear gene (waxy), in a recent, rapidly diversifying group, the Verbena complex. The complex includes three very closely related genera, Verbena (base chromosome number x=7), Glandularia (x=5), and Junellia (x=10), comprising some 150 species distributed predominantly in South and North America. Our results confirm the inadequacy of non-coding cpDNA in resolving relationships among closely related species due to lack of variation, and the great potential of low-copy nuclear gene as source of variation. However, this study suggests that when both cpDNA and nuclear DNA are employed in low-level phylogenetic studies, cpDNA might be very useful to infer organelle evolutionary history (e.g., chloroplast transfer) and more comprehensively understand the evolutionary history of organisms. The phylogenetic framework of the Verbena complex resulted from this study suggests that Junellia is paraphyletic and most ancestral among the three genera; both Glandularia and Verbena are monophyletic and have been derived from within Junellia. Implications of this phylogenetic framework to understand chromosome number evolution and biogeography are discussed. Most interestingly, the comparison of the cpDNA and nuclear DNA phylogenies indicates two independent intergeneric chloroplast transfers, both from Verbena to Glandularia. One is from a diploid North American Verbena species to a polyploid North American Glandularia species. The other is more ancient, from the South American Verbena group to the common ancestor of a major Glandularia lineage, which has radiated subsequently in both South and North America. The commonly assumed introgressive hybridization may not explain the chloroplast transfers reported here. The underlying mechanism remains uncertain.

Aerenchyma tissue development and gas-pathway structure in root of Avicennia marina (Forsk.) Vierh.

The aerenchyma differentiation in cable roots, pneumatophores, anchor roots, and feeding roots of the mangrove plant, Avicennia marina (Verbenaceae) was analyzed using a light microscope and scanning electron microscope. In all types, cortex cells were arranged in longitudinal columns extending from the endodermis to the epidermis. No cells in the cortex had intercellular spaces at the root tip (0-150 microm), and aerenchyma started developing at 200 microm from the root apex. The aerenchyma formation was due to cell separation (schizogeny) rather than cell lysis. The cell separation occurred between the longitudinal cell columns, forming long intercellular spaces along the root axis. During aerenchyma formation, the cortex cells enlarged longitudinally by 1.8-3.9 times and widened horizontally by 2.2-2.9 times. As a result, the aerenchyma had a pronounced tubular structure that was radially long, elliptical or oval in cross section and that ran parallel to the root axis. The tube had tapering ends, as did vessel elements, although there were no perforated plates. The interconnection between neighboring tubes was made by abundant small pores or canals that were schizogenous intercellular spaces between the wall cells. All aerenchyma tubes in the root were interconnected by these small pores serving as a gas pathway.