Abstract
Methyl jasmonate (MeJA) spray treatments were applied to the kale varieties ‘Dwarf Blue Curled Vates’ and ‘Red Winter’ in replicated field plantings in 2010 and 2011 to investigate alteration of glucosinolate (GS) composition in harvested leaf tissue. Aqueous solutions of 250 µM MeJA were sprayed to saturation on aerial plant tissues four days prior to harvest at commercial maturity. The MeJA treatment significantly increased gluconasturtiin (56%), glucobrassicin (98%), and neoglucobrassicin (150%) concentrations in the apical leaf tissue of these genotypes over two seasons. Induction of quinone reductase (QR) activity, a biomarker for anti-carcinogenesis, was significantly increased by the extracts from the leaf tissue of these two cultivars. Extracts of apical leaf tissues had greater MeJA mediated increases in phenolics, glucosinolate concentrations, GS hydrolysis products, and QR activity than extracts from basal leaf tissue samples. The concentration of the hydrolysis product of glucoraphanin, sulforphane was significantly increased in apical leaf tissue of the cultivar ‘Red Winter’ in both 2010 and 2011. There was interaction between exogenous MeJA treatment and environmental conditions to induce endogenous JA. Correlation analysis revealed that indole-3-carbanol (I3C) generated from the hydrolysis of glucobrassicin significantly correlated with QR activity (r = 0.800, P<0.001). Concentrations required to double the specific QR activity (CD values) of I3C was calculated at 230 µM, which is considerably weaker at induction than other isothiocyanates like sulforphane. To confirm relationships between GS hydrolysis products and QR activity, a range of concentrations of MeJA sprays were applied to kale leaf tissues of both cultivars in 2011. Correlation analysis of these results indicated that sulforaphane, NI3C, neoascorbigen, I3C, and diindolylmethane were all significantly correlated with QR activity. Thus, increased QR activity may be due to combined increases in phenolics (quercetin and kaempferol) and GS hydrolysis product concentrations rather than by individual products alone.
Highlights
Epidemiological studies have reported that the intake of Brassica vegetables is inversely correlated with cancer risk, and this association is stronger than those between cancer and fruit and vegetable consumption in general [1]
Methyl jasmonate (MeJA) treatment significantly increased quinone reductase (QR) activity in the combined apical and basal leaf extracts of the two different kale species extracts over two years except for the DBCV cultivar in 2011 (Figure 1B)
A previous study reported that MeJA treatment increased phenolic and flavonoid concentrations in kale leaves primarily in the form of the flavonoids, quercetin and kaempferol [10]
Summary
Epidemiological studies have reported that the intake of Brassica vegetables is inversely correlated with cancer risk, and this association is stronger than those between cancer and fruit and vegetable consumption in general [1]. Kale (Brassica oleracea L. acephala) is a frequently consumed leafy vegetable. In certain regions like on the Iberian Peninsula, kale (Brassica oleracea acephala group) leaves and flower buds are grown and harvested for consumption throughout the year [2]. Napus kales have good cold tolerance so that they can be grown anywhere in the US over a broader range of growing seasons and are used as animal forage. Cultivars of Brassica napus are thought to have originated from a chance hybridization between Brassica rapa and Brassica oleracea, the Red Russian type of kales were bred by artificial hybridization (http:// seedambassadors.org/Mainpages/still/napuskale/napuskale.htm). The ‘Red Winter’ cultivar was derived from Red Russian kale types
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