The role of light on foliage colour development in coleus (Solenostemon scutellarioides (L.) Codd)

Many coleus (Solenostemon scutellarioides (L). Codd) varieties change pigmentation when exposed to high light intensity: they increase anthocyanin amount and decrease chlorophyll content. The physiological and molecular mechanisms involved in this phenomenon have been investigated in two independent experiments using two related coleus varieties ‘Royal Glissade’ (RG) and ‘UF06-1-06’ (UF). The developmental stage of a leaf had a minimum effect on colouration. Light intensity affected the rate of colour transition, anthocyanin and chlorophyll concentrations, and plant growth. Foliage colour was affected by a complex interaction between anthocyanin and chlorophyll. The isolation and expression analysis of several structural and regulatory genes involved in the anthocyanin biosynthetic pathway, and the genes Lchb2 and CBS, an indicator of cellular energy status are reported. Results indicate a close similarity between transcript amount and anthocyanin accumulation and its rate was tightly associated with light intensity. Differences in foliage colour between RG and UF are due to different sensitivity to light, probably affecting chlorophyll content and F3H and UFGT expression.