The impact of nanotechnology in the field of agricultural sciences creates the need to study in greater detail the effect of products offering nanoparticles for application in plant species of agricultural interest. The objective of this study was to determine the response of stevia (Stevia rebaudiana B.) in vitro to different concentrations of AgNPs (silver nanoparticles), as well as to characterize and identify their absorption, translocation and accumulation mechanisms. Nodal segments of stevia grown in MS medium supplemented with AgNPs (0,12.5, 25, 50,100 and 200 mg L⁻¹) were used. After 30 days of in vitro shoot proliferation, the number of shoots per explant, shoot length, chlorophyll content, dry matter content and the metallic silver (Ag) content of the plants were quantified. In addition, characterization, transport and accumulation of silver nanoparticles were performed by microscopic analysis. AgNPs were shown to be present in epidermal stem cells, within vascular bundles and in intermembrane spaces. In leaves, they were observed in ribs and stomata. The current and future use of AgNPs in agricultural sciences opens up the possibility of studying their effects on different plant species.

Background: Hormesis is considered a dose–response phenomenon characterized by growth stimulation at low doses and inhibition at high doses. The hormetic response by silver nanoparticles (AgNPs) on in vitro multiplication of sugarcane was evaluated using a temporary immersion system. Methods: Sugarcane shoots were used as explants cultured in Murashige and Skoog medium with AgNPs at concentrations of 0, 25, 50, 100, and 200 mg/L. Shoot multiplication rate and length were used to determine hormetic response. Total content of phenolic compounds of sugarcane, mineral nutrition, and reactive oxygen species (ROS) was determined. Results: Results were presented as a dose–response curve. Stimulation phase growth was observed at 50 mg/L AgNPs, whereas inhibition phase was detected at 200 mg/L AgNPs. Mineral nutrient analysis showed changes in macronutrient and micronutrient contents due to the effect of AgNPs. Moreover, AgNPs induced ROS production and increased total phenolic content, with a dose-dependent effect. Conclusion: Results suggested that the production of ROS and mineral nutrition are key mechanisms of AgNP-induced hormesis and that phenolic accumulation was obtained as a response of the plant to stress produced by high doses of AgNPs. Therefore, small doses of AgNPs in the culture medium could be an efficient strategy for commercial micropropagation.

The aim of this study was to determine the pungency level of different accessions of Habanero peppers. The high-performance liquid chromatography (HPLC) technique was used to evaluate the content of total capsaicinoids in the whole fruit, placenta, and pericarp of 18 accessions of Habanero pepper from the germplasm bank of the Capsicum chinense species maintained in the Scientific Research Center of Yucatan [Centro de Investigación Científica de Yucatán (CICY)]. Thirteen of these accessions belonged to the “orange type”, four to the “red type”, and one to the “yellow type”. During the study, the plants were cultivated and maintained under greenhouse conditions and the fruit was harvested only when it was completely ripe on the plant. The results show considerable intraspecific diversity for this characteristic as well as the existence of cultivars of this species that surpass the levels of pungency reported for Habanero peppers under the conditions evaluated.

As an alternative to conventional lighting systems, light emitting diode (LED) has been demonstrated to be an artificial flexible lighting source for commercial micropropagation. The objective of this study was to determine the effects of different LED light quality on in vitro shoot proliferation and growth of Vanilla planifolia. To evaluate shoot proliferation, axillary bud cuttings (3 to 5 mm in diameter) of V. planifolia were used as explants and cultivated on Murashige and Skoog basal medium supplemented with 9.55 µM of 6-benzylaminopurine. To evaluate in vitro growth, unrooted shoots (2 cm in length) were used as explants cultivated on Murashige and Skoog basal medium without plant growth regulators. All explants were exposed to a 16 h photoperiod for 60 days under five different lights: fluorescent lamp, white LED, blue LED, red LED and blue plus red LED mixtures (Blue + Red = 1:1). The results indicated a clear increase in the number of shoots per explant under Fluorescent Lamp, White LED and Blue+Red LED light; these treatments produced more than 10 shoots. Shoot length was more than 3 cm in cultures under Blue, Red and Blue+Red (1:1) LEDs, and less than 3 cm in Fluorescent Lamp and White LEDs. Our results also showed that fresh weight, dry weight and dry matter were greatest in shoots under Blue+Red LED light. For shoot growth, plant height, number of leaves, number and length of roots, fresh weight, dry weight, dry matter and chlorophyll content were greater under Fluorescent Lamp and White LED. In conclusion, White or Blue+Red LED light may be used as an alternative light source for shoot proliferation, while White LED may be used for growth in vitro. These results demonstrate the effectiveness of light qualities using LEDs for micropropagation of V. planifolia. Key words: Light quality, micropropagation, orchid, chlorophyll.