Responses to Low Phosphorus in High- and Low- Anthocyanin Coleus (Solenostemon scutellaroides) and Maize (Zea mays)

Foliar anthocyanin production is frequently induced by phosphorus deficiency, but the adaptive significance of increased anthocyanin production under P stress, if any, remains unknown. In this study we hypothesised that if anthocyanin expression is an adaptive response to mitigate the stress effects of P deficiency, genotypes with constitutive anthocyanin expression would have greater tolerance to P stress than low anthocyanin-producing genotypes. Four studies were conducted in greenhouse, outdoor chamber and field conditions to compare genetically similar maize and coleus plants with contrasting anthocyanin accumulation (i.e. 'red-leafed' vs 'green-leafed'). In low-P treatments, anthocyanin production did not consistently result in greater photosynthesis or biomass. In coleus, red-leafed phenotypes showed lower chlorophyll a/b ratios suggesting photoprotection by anthocyanins against degradation of light harvesting complex proteins. However, the opposite trend was observed in maize, where red-leafed phenotypes showed greater chlorophyll a/b ratios and lower q_P (oxidation state of PSII). Based on results from the various treatments and growth conditions of this study, it could not be concluded that high foliar anthocyanin production confers a general functional advantage under low-P stress. More research comparing inducible vs constitutive production may help elucidate the role of anthocyanin biosynthesis in P deficiency responses.