Abstract

Field cultivation of pigment-rich crops for use as natural dyes and functional phytochemicals is constrained by seasonal and site variability, by the land and water demands of large-scale field production, and by the environmental and regulatory concerns increasingly attached to synthetic colorants. Controlledenvironment hydroponic systems address these constraints directly: They decouple pigment production from soil and season and allow reproducible manipulation of the root-zone chemical environment as a lever on pigment biosynthesis. Anthocyanins, carotenoids, battalions, and chlorophylls are the four principal pigment families with established or emerging value as renewable colorants and functional phytochemicals. This review synthesizes verified evidence on how nitrogen, potassium, phosphorus, iron speciation, light quality, and bio stimulant inputs influence pigment accumulation in hydroponically grown crops, and integrates this with the transcriptional architecture, principally the MYB-bHLHWD40 complex, the COP1-HY5 light-signaling hub, and phosphate-starvation signaling through PHR1, that governs these responses. Confirmed findings include a 461.7 percent increase in anthocyanin concentration in carrot microgreens treated with a legume-derived protein hydrolysate [1], genotypedependent phenolic responses to nutrient solution strength in red versus green lettuce spanning approximately a five-fold decrease to an eleven-fold increase across phenolic subclasses [2], a direct molecular link between phosphate starvation and anthocyanin gene expression through PHR1 binding of F3’H and LDOX promoters [3], and engineering-scale anthocyanin enrichment in tomato through heterologous transcription factor expression [4]. This review is deliberately conservative: claims that could not be traced to a verifiable primary source have been removed rather than retained in qualified form, and the resulting evidence base, while narrower than is typical for reviews in this area, is intended to be fully reliable for downstream citation.

Keywords:Hydroponics; Natural dyes; Pigment biosynthesis; Nutrient management; Transcription factors; Anthocyanins; Carotenoids; Controlled-environment agriculture; Microgreens