ABSTRACT
Cabbage (Brassica oleracea) and watercress (Nasturtium officinale) produce glucobrassicin (GBS) and gluconasturtiin (GNST), precursors of chemopreventive compounds. Their accumulation is affected by environmental signals. We studied the impact of the red to far-red light (R/FR) ratio on GBS concentration in red â³Ruby Ballâ³ and green â³Tiaraâ³ cabbage. Foliar shading, via weed surrogates that competed with cabbage plants for specific durations, induced R/FR variation among treatments. â³Ruby Ballâ³ GBS concentrations were the highest when R/FR within the canopy was the lowest. â³Tiaraâ³ was unaffected by competition. The same trend was observed in a controlled environment using R and FR LEDs without weeds present. â³Ruby Ballâ³ subjected to an R/FR = 0.3 treatment had 2.5- and 1.4-fold greater GBS concentration compared to R/FR = 1.1 and 5.0 treatments combined. Watercress given end-of-day (EOD) R and/or FR pulses after the main photoperiod had the lowest GNST concentrations after an EOD FR pulse but the highest concentrations after an R followed by FR pulse.
Subject(s)
Brassica , Nasturtium , Glucosinolates , Indoles , LightABSTRACT
BACKGROUND: Glucobrassicin (GBS) and its hydrolysis product indole-3-carbinol are important nutritional constituents implicated in cancer chemoprevention. Dietary consumption of vegetables sources of GBS, such as cabbage and Brussels sprouts, is linked to tumor suppression, carcinogen excretion, and cancer-risk reduction. High-performance liquid-chromatography (HPLC) is the current standard GBS identification method, and quantification is based on UV-light absorption in comparison to known standards or via mass spectrometry. These analytical techniques require expensive equipment, trained laboratory personnel, hazardous chemicals, and they are labor intensive. A rapid, nondestructive, inexpensive quantification method is needed to accelerate the adoption of GBS-enhancing production systems. Such an analytical method would allow producers to quantify the quality of their products and give plant breeders a high-throughput phenotyping tool to increase the scale of their breeding programs for high GBS-accumulating varieties. Near-infrared reflectance spectroscopy (NIRS) paired with partial least squares regression (PLSR) could be a useful tool to develop such a method. RESULTS: Here we demonstrate that GBS concentrations of freeze-dried tissue from a wide variety of cabbage and Brussels sprouts can be predicted using partial least squares regression from NIRS data generated from wavelengths between 950 and 1650 nm. Cross-validation models had R2 = 0.75 with RPD = 2.3 for predicting µmol GBS·100 g-1 fresh weight and R2 = 0.80 with RPD = 2.4 for predicting µmol GBS·g-1 dry weight. Inspections of equation loadings suggest the molecular associations used in modeling may be due to first overtones from O-H stretching and/or N-H stretching of amines. CONCLUSIONS: A calibration model suitable for screening GBS concentration of freeze-dried leaf tissue using NIRS-generated data paired with PLSR can be created for cabbage and Brussels sprouts. Optimal NIRS wavelength ranges for calibration remain an open question.
