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.
Highlights
Arthropod pests like aphids (Hemiptera: Aphididae) can damage horticultural plants by removing assimilates, producing honeydew, and transmitting viruses [1]
Plant height was higher (p < 0.01) for plants treated with green light (515 nm) than for plants treated with UV-A light (365 nm), violet light (420 nm), or blue light (470 nm) (Fig 2B)
The present study investigated the effects of different narrow-bandwidths of light on the growth of broccoli plants, on the concentrations of glucosinolates and flavonol glycosides in the plants, and on the interaction between the plants and the aphid B. brassicae, which is a specialized herbivore of Brassica spp
Summary
Arthropod pests like aphids (Hemiptera: Aphididae) can damage horticultural plants by removing assimilates (phloem-feeding), producing honeydew, and transmitting viruses [1]. (Brassicaceae; broccoli) can be increased by treatment with UV-B or UV-A radiation [5,6] This light-induced increase in plant metabolites results from the stimulation of specific photoreceptors followed by the activation of a signal transduction chain and the triggering of transcription factors and genes involved in secondary metabolite biosynthesis [2]. Expression of these genes shifts the composition of metabolites in the plant, and changes in specific secondary plant metabolites can enhance or decrease the susceptibility to certain herbivorous insects [2, 7]. In addition to UV-B and UV-A, other light qualities, e.g., blue, green, and red, may induce the biosynthesis of certain plant metabolites such as flavonoids and glucosinolates and alter the resistance of the plant [8,9,10,11,12,13]
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