Modification of Leaf Glucosinolate Contents in Brassica oleracea by Divergent Selection and Effect on Expression of Genes Controlling Glucosinolate Pathway.

Modification of the content of secondary metabolites opens the possibility of obtaining vegetables enriched in these compounds related to plant defense and human health. We report the first results of a divergent selection for glucosinolate (GSL) content of the three major GSL in leaves: sinigrin (SIN), glucoiberin (GIB), and glucobrassicin (GBS) in order to develop six kale genotypes (Brassica oleracea var. acephala) with high (HSIN, HIGIB, HGBS) and low (LSIN, LGIB, LGBS) content. The aims were to determine if the three divergent selections were successful in leaves, how each divergent selection affected the content of the same GSLs in flower buds and seeds and to determine which genes would be involved in the modification of the content of the three GSL studied. The content of SIN and GIB after three cycles of divergent selection increased 52.5% and 77.68%, and decreased 51.9% and 45.33%, respectively. The divergent selection for GBS content was only successful and significant for decreasing the concentration, with a reduction of 39.04%. Mass selection is an efficient way of modifying the concentration of individual GSLs. Divergent selections realized in leaves had a side effect in the GSL contents of flower buds and seeds due to the novo synthesis in these organs and/or translocation from leaves. The results obtained suggest that modification in the SIN and GIB concentration by selection is related to the GSL-ALK locus. We suggest that this locus could be related with the indirect response found in the GBS concentration. Meantime, variations in the CYP81F2 gene expression could be the responsible of the variations in GBS content. The genotypes obtained in this study can be used as valuable materials for undertaking basic studies about the biological effects of the major GSLs present in kales.

Effect of temperature stress on the early vegetative development of Brassica oleracea L.

BACKGROUND: Due to its biennual life cycle Brassica oleracea is especially exposed to seasonal changes in temperature that could limit its growth and fitness. Thermal stress could limit plant growth, leaf development and photosynthesis. We evaluated the performance of two local populations of B. oleracea: one population of cabbage (B. oleracea capitata group) and one population of kale (B. oleracea acephala group) under limiting low and high temperatures. RESULTS: There were differences between crops and how they responded to high and low temperature stress. Low temperatures especially affect photosynthesis and fresh weight. Stomatal conductance and the leaf water content were dramatically reduced and plants produce smaller and thicker leaves. Under high temperatures there was a reduction of the weight that could be associated to a general impairment of the photosynthetic activity. CONCLUSIONS: Although high temperatures significantly reduced the dry weight of seedlings, in general terms, low temperature had a higher impact in B. oleracea physiology than high temperature. Interestingly, our results suggest that the capitata population is less sensitive to changes in air temperature than the acephala population.

Identification of antioxidant capacity -related QTLs in Brassica oleracea.

Brassica vegetables possess high levels of antioxidant metabolites associated with beneficial health effects including vitamins, carotenoids, anthocyanins, soluble sugars and phenolics. Until now, no reports have been documented on the genetic basis of the antioxidant activity (AA) in Brassicas and the content of metabolites with AA like phenolics, anthocyanins and carotenoids. For this reason, this study aimed to: (1) study the relationship among different electron transfer (ET) methods for measuring AA, (2) study the relationship between these methods and phenolic, carotenoid and anthocyanin content, and (3) find QTLs of AA measured with ET assays and for phenolic, carotenoid and anthocyanin contents in leaves and flower buds in a DH population of B. oleracea as an early step in order to identify genes related to these traits. Low correlation coefficients among different methods for measuring AA suggest that it is necessary to employ more than one method at the same time. A total of 19 QTLs were detected for all traits. For AA methods, seven QTLs were found in leaves and six QTLs were found in flower buds. Meanwhile, for the content of metabolites with AA, two QTLs were found in leaves and four QTLs were found in flower buds. AA of the mapping population is related to phenolic compounds but also to carotenoid content. Three genomic regions determined variation for more than one ET method measuring AA. After the syntenic analysis with A. thaliana, several candidate genes related to phenylpropanoid biosynthesis are proposed for the QTLs found.

Identification of metabolic QTLs and candidate genes for glucosinolate synthesis in Brassica oleracea leaves, seeds and flower buds.

Glucosinolates are major secondary metabolites found in the Brassicaceae family. These compounds play an essential role in plant defense against biotic and abiotic stresses, but more interestingly they have beneficial effects on human health. We performed a genetic analysis in order to identify the genome regions regulating glucosinolates biosynthesis in a DH mapping population of Brassica oleracea. In order to obtain a general overview of regulation in the whole plant, analyses were performed in the three major organs where glucosinolates are synthesized (leaves, seeds and flower buds). Eighty two significant QTLs were detected, which explained a broad range of variability in terms of individual and total glucosinolate (GSL) content. A meta-analysis rendered eighteen consensus QTLs. Thirteen of them regulated more than one glucosinolate and its content. In spite of the considerable variability of glucosinolate content and profiles across the organ, some of these consensus QTLs were identified in more than one tissue. Consensus QTLs control the GSL content by interacting epistatically in complex networks. Based on in silico analysis within the B. oleracea genome along with synteny with Arabidopsis, we propose seven major candidate loci that regulate GSL biosynthesis in the Brassicaceae family. Three of these loci control the content of aliphatic GSL and four of them control the content of indolic glucosinolates. GSL-ALK plays a central role in determining aliphatic GSL variation directly and by interacting epistatically with other loci, thus suggesting its regulatory effect.

Environmental and genetic effects on yield and secondary metabolite production in Brassica rapa crops.

Twelve Brassica rapa varieties grown, such as turnip green and turnip top, were evaluated in seven environments to determine the environmental and genotypic variables that have an influence on crop production and on the content of glucosinolates and phenolic compounds. Factorial regression analysis showed that, in general, crop production was favored by high temperatures all along the crop cycle. However, the lack of a period of intense cold could be a limiting factor. The metabolite content seems to be regulated by extreme temperatures (daily maximum and minimum temperatures) rather than by average daily temperatures. With regard to genotypic covariables, turnip top production was significantly affected by traits related to the vegetative development and time to flowering. Meanwhile, turnip green production was largely affected by a sinapoyl derivative compound, which is a precursor of cell wall components. Cross-talk between glucosinolate biosynthesis and phenylpropanoid signaling pathways is suggested.

The natural compound trans-chalcone induces programmed cell death in Arabidopsis thaliana roots.

Chalcone (1,3-diphenyl-2-propen-1-one) is an aromatic ketone precursor of important molecules in plants such as flavonoids or anthocyanins. Its phytotoxicity has been demonstrated on different plant species, but to date little is known about the mechanisms of action of this secondary metabolite at plant cellular level. Detailed analysis by light and transmission electron microscopy (TEM) was conducted to examine the root meristems' ultrastructure of control and chalcone-treated Arabidopsis seedlings. Mitochondrial dysfunction was analysed by measuring mitochondrial membrane potential with JC-1 fluorochrome. Finally, acridine orange/ethidium bromide staining was used for the detection of programmed cell death. Microscopy revealed tissue alterations, inhibition of root hair formation and important changes after 7 and 14 d at the chalcone IC(50) value. Chalcone-treated cells showed signs of programmed cell death such as mitochondrial condensation, disruption of organelles and chromatin fragmentation. Acridine orange/ethidium bromide staining confirmed the programmed cell death, which could be induced by the reduction of mitochondrial transmembrane potential (ΔΨ(m)) that was detected after chalcone treatment. These results confirm the phytotoxic activity of chalcone on Arabidopsis seedlings, the alteration of mitochondrial membrane potential and the induction of programmed cell death.

pH dependence of the interaction between rhodamine B and the water-soluble poly(sodium 4-styrenesulfonate).

The binding of rhodamine B (RB) to the polyanion containing aromatic groups poly(sodium 4-styrenesulfonate) (PSS) is studied by separation and spectroscopic techniques at pH between 2 and 7. Significant binding is found at pH below 5, together with a red-shift of the RB maximum of absorbance to 564 nm, and RB fluorescence quenching. The dependence of the pH is related with protonation of RB molecules. Fluorescence quenching is a consequence of a more hydrophobic environment and may occur on territorially or site-specifically bound molecules, and/or on self-aggregated molecules in a hydrophobic polymer domain. Remarkably, the basicity of RB is increased by the influence of the polymer.