Relationship between aluminum stress and caffeine biosynthesis in suspension cells of Coffea arabica L.

Toxicity by aluminum is a growth-limiting factor in plants cultivated in acidic soils. This metal also promotes signal transduction pathways leading to the biosynthesis of defense compounds, including secondary metabolites. In this study, we observed that Coffea arabica L. cells that were kept in the dark did not produce detectable levels of caffeine. However, irradiation with light and supplementation of the culture medium with theobromine were the best conditions for cell maintenance to investigate the role of aluminum in caffeine biosynthesis. The addition of theobromine to the cells did not cause any changes to cell growth and was useful for the bioconversion of theobromine to caffeine. During a short-term AlCl3-treatment (500µM) of C. arabica cells kept under light irradiation, increases in the caffeine levels in samples that were recovered from both the cells and culture media were evident. This augmentation coincided with increases in the enzyme activity of caffeine synthase (CS) and the transcript level of the gene encoding this enzyme (CS). Together, these results suggest that actions by Al and theobromine on the same pathway lead to the induction of caffeine biosynthesis.

Antioxidant capacity and total phenolic content in fruit tissues from accessions of Capsicum chinense Jacq. (Habanero pepper) at different stages of ripening.

In the past few years, there has been a renewed interest in studying a wide variety of food products that show beneficial effects on human health. Capsicum is an important agricultural crop, not only because its economic importance, but also for the nutritional values of its pods, mainly due to the fact that they are an excellent source of antioxidant compounds, and also of specific constituents such as the pungent capsaicinoids localized in the placental tissue. This current study was designed to evaluate the antioxidant capacity and total phenolic contents from fruits tissues of two Capsicum chinense accessions, namely, Chak k'an-iik (orange) and MR8H (red), at contrasting maturation stages. Results showed that red immature placental tissue, with a Trolox equivalent antioxidant capacity (TEAC) value of 55.59 µmols TE g(-1) FW, exhibited the strongest total antioxidant capacity using both the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the CUPRAC methods. Placental tissue also had the highest total phenolic content (27 g GAE 100 g(-1) FW). The antioxidant capacity of Capsicum was directly related to the total amount of phenolic compounds detected. In particular, placentas had high levels of capsaicinoids, which might be the principal responsible for their strong antioxidant activities.

Isolation of functional total RNA from Argemone mexicana tissues

RNA extraction from recalcitrant plant tissues is frequently complicated by the presence of secondary metabolites, polysaccharides and polyphenols. These compounds may co precipitate with RNA, often rendering it unsuitable for either cDNA synthesis or hybridization in northern blot analyses and therefore, interfering with the gene analysis expression in such tissues. We have developed an efficient RNA extraction method from A. mexicana tissues. The procedure includes the use of polyvinylpolypyrrolidone (PVPP), to remove secondary metabolites, proteins and polyphenols, and a two-step precipitation with LiCl, to eliminate polysaccharides, and thus increasing RNA yield. The quality of the resulting RNA was evaluated spectrophotometrically and by agarose gel electrophoresis. Moreover, the RNA obtained by this method, could be used directly for both RT-PCR and northern blot analysis, without any further purification.

Agrobacterium-mediated transient transformation of Mexican prickly poppy (Argemone mexicana L)

Shoot apex, leaf primordia, leaf sections and roots from Mexican prickly poppy seedlings, were inoculated with Agrobacterium tumefaciens harboring the binary vector pCAMBIA2301, which contained the beta-glucuronidase (uid A) gene. Histochemical beta-glucuronidase (GUS) assay in infected explants showed transient gus gene expression between 3 and 12 days after inoculation. To our knowledge, this is the first report of A. mexicana susceptibility to A. tumefaciens-mediated genetic transformation.