EN
Anthocyanins impart red, purple and violet colour to many flowers and fruits, mainly to attract pollinators and seed dispersers, but their function and biosynthetic regulation in foliages of several plants are less studied. The red and green forma of Ocimum tenuiflorum differ in anthocyanin accumulation in leaves and provide an excellent system for exploring the course of its regulation. It was observed that red forma gradually changed to green upon transfer to a particular greenhouse with limited transmission of ultraviolet light (both UV-B and UV-A). The sequential monitoring of anthocyanin content confirmed positive correlation between visible and ultraviolet light intensity with leaf colour and antioxidant activities. An ultra-performance liquid chromatography method of < 3.5 min was developed for rapid and precise quantification of anthocyanidins. Expressions of PAL, CHS and CHI were down-regulated by low light in both forma. The F3H and F3'H genes had reduced expression in both forma and were supported by reduced levels of cyanidin in red forma plants within greenhouse. The expression of late biosynthetic genes, DFR and LDOX, also plummeted within the greenhouse. The regulatory transcription factors bHLH and WD40 were severely down-regulated within the greenhouse suggesting that bHLH and WD40 control the expression of F3'H, DFR and LDOX to regulate the biosynthesis of anthocyanin pigments in leaves of O. tenuiflorum, whereas the expression of Myb remained almost unaffected.