Advancing Understanding of LED Light Impacts on Plant Phytonutrient Content for Application into Hydroponically Grown Leafy Greens

Sutton, Phoebe and Toledo-Ortiz, Gabriela and McAinsh, Martin and Bosch, Christine (2023) Advancing Understanding of LED Light Impacts on Plant Phytonutrient Content for Application into Hydroponically Grown Leafy Greens. PhD thesis, Lancaster University.

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Abstract

The majority of global population increases in the 21st Century will be concentrated in urban centres, where ‘Hidden hunger’, diets devoid of micronutrients, is common. Vertical farming is uniquely poised to address this shortfall due to its ability to produce food intensively under tailored LED lighting spectra. This thesis explores the contribution of light wavelengths and signalling pathways on the genetic expression of nutrient biosynthesis genes for carotenoid (pro-Vitamin A), tocopherol (Vitamin E) and ascorbic acid (Vitamin C) pathways, essential micronutrients that must be consumed via the diet, in Arabidopsis (Chapter 2). In addition, the impact of spectral quality on the growth and content of these nutrients was evaluated in Basil (Chapter 3) and Coriander (Chapter 4), two high value herbaceous crops commonly grown hydroponically in vertical farms. Using publically available transcriptomic datasets, it was found that the transcriptional response of flux controlling genes to light quality in Arabidopsis was unique to each gene, but in general, MEP pathway genes are stimulated by red light (RL), whereas carotenoids are upregulated by both RL and blue light (BL). This study also found a novel increase in expression of tocopherol and ascorbic acid biosynthesis genes to BL. Crucially these responses were linked with photoreceptor input and associated light signalling components, including circadian input in all four pathways examined. This thesis also examines the content of these phytonutrients and growth responses in two crop species, Basil and Coriander, grown under differing light regimes in controlled environments. The best overall commercially viable growth of Basil and Coriander was found in 25% BL 75% RL (B25R75) and B50R50, respectively. Whereas, ascorbic acid increases were associated with RL in Basil, and tocopherol and ascorbic acid increased with BL in Coriander. This research has contributed new mechanistic understandings into the light regulation of phytonutrient pathways in Arabidopsis, and provided important insights into the differing effects of LED lighting regimes on phytonutrient content in valuable crop species. Such work constitutes a step towards the application of tailored spectra into Controlled Environment Agriculture and realising the potential of light quality to provide fresh and nutritious produce to urban populations.