Cristini Milech

Potential allelopathic and antibacterial activity from Alternanthera philoxeroides

Alternanthera philoxeroides is a promising species in the search for new molecules with biological effects. To accelerate this bioprospection process of A. philoxeroides, the chosen methods (allelopathy and discdiffusion technique) are excellent alternatives. The purpose of this study was to evaluate the allelopathic effects and verify the antibacterial properties of extracts from A. philoxeroides. To evaluate the antibacterial activity, disc diffusion technique was used with five reference strains. The germination test was conducted with the extracts at concentrations of 0, 1.0, 2.0 e 3.0 mg mL-1 in a petri dish with 30 lettuce seeds and for the growth trial 10 seeds were used. The experimental design was completely randomized in factorial 4 × 2 × 4 (four extracts, two sources, four concentrations), with four replicates.The results indicate that the lettuce germination was influenced by ethyl acetate fraction obtained from leaves of A. philoxeroides at the highest concentrations; however, the germination speed and the radicle growth were significantly affected by all the extracts starting at 1mg mL-1 concentration. Those results demonstrate allopathic effect of different extracts of this plant, although they have not interfered with the strains growth used in this experiment.

Validation of reference genes for RT-qPCR studies in Stevia rebaudiana in response to elicitor agents

Stevia rebaudiana is an important source of natural steviol glycosides and is of increasing interest in various fields of study. Therefore, understanding the molecular processes regulating its metabolism is of great importance. In this study, the stability of seven reference genes (18S ribosomal RNA, Actin, Aquaporin, Calmodulin, Eukaryote elongation factor 1-α, Malate dehydrogenase, and Ubiquitin) under the effect of three stress-related elicitors (methyl jasmonate, salicylic acid, and spermidine) was evaluated in stevia plants. We used RefFinder software, which makes use of the four main currently available algorithms for reference gene selection: geNorm, NormFinder, BestKeeper, and the Comparative ∆Ct method. The results indicated that Ubiquitin and Actin can be used as reference genes under all tested experimental conditions. The genes, 18S ribosomal RNA, traditionally used as a reference gene, along with Calmodulin, showed the lowest stability. The expression of Deoxyxylulose-5-phosphate synthase and Kaurenoic acid hydroxylase genes was used to confirm the validated reference genes, showing that inadequacy of the reference gene may lead to erroneous results. This is the first study on the stability of reference genes in Stevia rebaudiana plants, and is of great relevance for further analysis of the gene expression of the steviol glycoside biosynthetic pathway.

Produção de pigmentos em calos de Alternanthera sessilis mediados por reguladores de crescimento e luz

Among the compounds produced by plants, pigments such as betalains have received attention from both food and pharmaceuticals industries. The Alternanthera sessilis species produces these pigments, though in small quantities, and so it is necessary to increase production. Thus, many studies use elicitors that are capable of triggering physiological or morphological responses in plants. The objective was to establish callus production in A. sessilis grown under different combinations of growth regulators and light qualities and to assess whether these factors can increase betalain and flavonoid production. Leaf and internodal explants in MS medium with different growth regulators were used to obtain calli, which were subsequently transferred to a betacyanin induction medium remaining for 40 days under different light qualities (white, blue, red, and dark). The most suitable treatment for callus formation and subsequent betalain and flavonoid induction was to combine a medium containing 6.7 μmol L 2,4-D and 9.0 μmol L BAP and blue light. Physical elicitation by light combined with appropriate concentration of growth regulators on calli can increase production of commercially important metabolites.