Castor (Ricinus communis L.) differential cell cycle and metabolism reactivation, germinability, and seedling performance under NaCl and PEG osmoticum: Stress tolerance related to genotype-preestablished superoxide dismutase activity.

Castor (Ricinus communis) is a relevant industrial oilseed feedstock for many industrial applications, being globally mainly cultivated by smallholder farmers in semiarid areas, where abiotic stresses predominate. Therefore, susceptible to generating reactive oxygen species (ROS) and subsequent oxidative stress, compromising cell metabolism upon seed imbibition and germination, seedling and crop establishment, and yield. The present study evaluated the consequences of water restriction by Polyethylene glycol (PEG) and Sodium chloride (NaCl) on cell cycle and metabolism reactivation on germinability, seedling growth, and vigor parameters in 2 commercial castor genotypes (Nordestina and Paraguaçu). PEG water restriction inhibited germination completely at -0.23 MPa or higher, presumably due to reduced oxygen availability. The restrictive effects of NaCl saline stress on germination were observed only from -0.46 MPa onwards, affecting dry mass accumulation and the production of normal seedlings. In general, superoxide dismutase (SOD) activity increased in NaCl -0.23 MPa, whereas its modulation during the onset of imbibition (24h) seemed to depend on its initial levels in dry seeds in a genotype-specific manner, therefore, resulting in the higher stress tolerance of Nordestina compared to Paraguaçu. Overall, results show that Castor germination and seedling development are more sensitive to the restrictive effects of PEG than NaCl at similar osmotic potentials, contributing to a better understanding of the responses to water restriction stresses by different Castor genotypes. Ultimately, SOD may constitute a potential marker for characterizing castor genotypes in stressful situations during germination, early seedling, and crop establishment, and a target for breeding for Castor-improved stress tolerance.

Modulation of NF-YB genes in Ricinus communis L. in response to different temperatures and developmental stages and functional characterization of RcNF-YB8 as an important regulator of flowering time in Arabidopsis thaliana.

We have characterized the NF-YB gene family in R. communis using bioinformatics, ecotopic expression, and transcriptomics. A total of 14 RcNF-YB genes were identified in R. communis genome using the conserved NF-YB region. This number is similar to what is found in A. thaliana (13 genes) and O. sativa (11 genes), whereas it is considerably lower to what is found in P. trichocarpa (21 genes) and S. lycopersycum (29 genes). Several regulatory cis-elements were identified in the promoter region, including low temperature, defense and stress, MIC, MYB, and abscisic acid. RcNF-YB is strongly modulated by temperature and it is dependent on the stage of germination. In general, RcNF-YB genes showed higher expression levels in dry seeds and early imbibition (EI) samples as compared to later stages of seedling development. Ectopic expression of RcNF-YB8 reduced flowering time in Arabidopsis reducing the time required for the formation of the first visible bud, the time required to open the first flower, and the time required for the formation of the first visible silique. At the end of the life cycle, ectopic expression of RcNF-YB8 affected plant height (PH), silique length (SL), the total number of silique per plant, 1000-seed weight, and seed size. Our data demonstrated the role of RcNF-YB8 in flowering time, plant height and seed production, and it shows that it may constitute a key target gene for breeding superior R. communis genotypes.

Metabolite profiling of Ricinus communis germination at different temperatures provides new insights into thermo-mediated requirements for successful seedling establishment.

Ricinus communis seeds germinate to a high percentage and faster at 35 °C than at lower temperatures, but with compromised seedling establishment. However, seedlings are able to cope with high temperatures at later stages of seedling establishment if germination occurred at lower temperatures. Our objective was to assess the biochemical and molecular requirements of R. communis germination for successful seedling establishment at varying temperatures. For that, we performed metabolite profiling (GC-TOF-MS) and measured transcript levels of key genes involved in several energy-generating pathways, such as storage oil mobilization, ß-oxidation and gluconeogenesis of seeds germinated at three different temperatures. We identified a thermo-sensitive window during seed germination in which high temperatures compromise seedling development, most likely by down-regulating some energy-generating pathways. Overexpression of malate synthase (MLS) and glycerol kinase (GK) genes resulted in higher starch levels in Nicotiana benthamiana leaves, which highlights the importance of these genes in energy-generating pathways for seedling establishment. Additionally, we showed that GABA, which is a stress-responsive metabolite, accumulated in response to the water content of the seeds during the initial phase of imbibition. Herewith, we provide new insights into the molecular requirements for vigorous seedling growth of R. communis under different environmental conditions.

Metabolite profiling, antioxidant and antibacterial activities of Brazilian propolis: Use of correlation and multivariate analyses to identify potential bioactive compounds.

The production of propolis by honeybees results from a selective collection of exudates from various plant species and present many potentialities in the pharmaceutical industry. The objective of this study was to investigate the chemical profile of Brazilian propolis, as well as their in vitro antioxidant and antibacterial activities. Gas chromatography-mass spectrometry was applied for chemical profiling of propolis extracts. Total phenolic compounds were quantified by Folin-Ciocalteu and antioxidant properties were assessed by 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay. Antibacterial activity was assessed against Staphylococcus aureus, Bacillus subtilis, and Micrococcus luteus. Correlation and multivariate statistical analysis were used to identify potential bioactive compounds in the extracts. Twenty-nine metabolites were identified along with 34 other metabolites that were classified into the following classes: triterpenoids (12), acetyltriterpenoids (3), sesquiterpenes (6), steroids (4), and hydrocarbons (9). The antioxidant capacity (IC50) ranged from 21.50 to 78.77µg/mL, whereas the content of total phenolic compounds ranged from 31.88 to 204.30mg GAE/g of dry weight. Total phenolic compounds and methyl retinoate showed a positive correlation with the antioxidant capacity, whereas tetradecanal, γ-palmitolactone and ethyl hydrocinnamate showed a negative correlation. Different sets of metabolites are shown to correlate with the antibacterial activity of the extracts, which is largely dependent on the type of microorganism. This innovative approach allowed us to identify likely bioactive compounds in the extracts, although the mechanism(s) underlying antibacterial activity encompass a complex trait, which might involve synergistic effects.