Mechanism of bract reddening in guzmania

To clarify the mechanism of Guzmania bract reddening, we conducted the following investigation from three aspects. First, we determined the pigments contained in the red Guzmania bracts, observed tissue anatomy, and performed the color reaction test, spectral scanning analysis, and HPLC (High Performance Liquid Chromatography) analysis of the bracts. The results confirmed that the red substance distributed in the fence tissue of the bracts is anthocyanin (a flavonoid substance with an absorption wavelength of 510nm) composed of cyanidin (red) and pelargonium (orange -red), the yellow substances distributed throughout the mesophyll tissue of the bracts are mainly flavones (absorption wavelengths of 291nm and 328nm) and carotenoids (absorption wavelengths of 438nm and 467nm), and the green substance distributed in sponge tissue of the bracts is chlorophyll (absorption wavelengths of 440nm and 468nm). Second, to explore the molecular mechanisms of changes in flavonoids and chlorophyll, we used HPLC, RT-Qpcr (Quantitative Reverse Transcription Polymerase Chain Reaction), and other methods to detect changes in flavonoids and chlorophyll contents and the gene expression of key enzymes for corresponding metabolic processes. The results confirmed that bract reddening was caused by accumulated flavonoids and reduced chlorophyll content, while the reduction in chlorophyll was caused by a decrease in chlorophyll synthesis and a significant increase in chlorophyll degradation. Finally, we examined dynamic changes in ethylene release from the bracts and expression patterns of key enzymatic genes in ethylene biosynthesis. It was confirmed that the biosynthesis of ethylene increased in the bracts, further promoting the process of bract reddening. This study on the mechanism of bract color formation has practical significance for improving bract color and ornamental quality through breeding and guiding production practices.