Can narrow-bandwidth light from UV-A to green alter secondary plant metabolism and increase Brassica plant defenses against aphids?

Abstract

Light of different wavelengths is essential for plant growth and development. Short-wavelength radiation such as UV can shift the composition of flavonoids, glucosinolates, and other plant metabolites responsible for enhanced defense against certain herbivorous insects. The intensity of light-induced, metabolite-based resistance is plant- and insect species-specific and depends on herbivore feeding guild and specialization. The increasing use of light-emitting diodes (LEDs) in horticultural plant production systems in protected environments enables the creation of tailor-made light scenarios for improved plant cultivation and induced defense against herbivorous insects. In this study, broccoli (Brassica oleracea var. italica) plants were grown in a climate chamber under broad spectra photosynthetic active radiation (PAR) and were additionally treated with the following narrow-bandwidth light generated with LEDs: UV-A (365 nm), violet (420 nm), blue (470 nm), or green (515 nm). We determined the influence of narrow-bandwidth light on broccoli plant growth, secondary plant metabolism (flavonol glycosides and glucosinolates), and plant-mediated light effects on the performance and behavior of the specialized cabbage aphid Brevicoryne brassicae. Green light increased plant height more than UV-A, violet, or blue LED treatments. Among flavonol glycosides, specific quercetin and kaempferol glycosides were increased under violet light. The concentration of 3-indolylmethyl glucosinolate in plants was increased by UV-A treatment. B. brassicae performance was not influenced by the different light qualities, but in host-choice tests, B. brassicae preferred previously blue-illuminated plants (but not UV-A-, violet-, or green-illuminated plants) over control plants.

Blue Light Treatment but Not Green Light Treatment After Pre-exposure to UV-B Stabilizes Flavonoid Glycoside Changes and Corresponding Biological Effects in Three Different Brassicaceae Sprouts

“…Nevertheless, blue light was not able to further increase flavonoid glycosides and hydroxycinnamic acids in Brassicaceae sprouts. However, in broccoli, kaempferol-3-feruloyl-sphoroside-7-glucoside and kaempferol-3-caffeoyl-sophoroside-7-glucoside were increased after blue light treatment alone, without any UV pre-treatment ( Rechner et al, 2017 ). Blue light was able to increase total phenolics of lettuce ( Johkan et al, 2010 ).…”

Ultraviolet-A Radiation Stimulates Growth of Indoor Cultivated Tomato (Solanum lycopersicum) Seedlings

“…Such effects have been attributed to blue/UV-A absorbing cryptochromes, which can play a role in shade avoidance (Keller et al, 2011). However, there are also studies that reported that UV-A radiation decreased plant height (D ader et al, 2014;Rechner et al, 2017). In this context, more evidence is needed to corroborate speculations about UV-A radiation playing a functional role in countering the shade-acclimated phenotype.…”

Flavonoid Glycosides in Brassica Species Respond to UV-B Depending on Exposure Time and Adaptation Time

“…In contrast, traditional farming techniques increase sunlight and simultaneously UV radiation during plant growth and ripening to increase secondary plant metabolites that contribute to flavor and color, e.g., reduction of leaves in the vine during berry ripening [ 16 , 17 ]. Recent studies, however, have highlighted the regulatory properties of low, ecologically relevant UVB levels that trigger the accumulation of certain flavonoids, known for their high antioxidant activity, in Brassica species [ 11 , 18 , 19 , 20 , 21 ] and other species [ 14 , 22 ]. Flavonoid enrichment also affects plant quality and is important in meeting consumer preferences for fruits and vegetables, including growth and appearance, aroma/smell, flavor, color, and compounds that promote plant and human health [ 14 ].…”