The colours of plant leaves, flowers and fruits are provided by different pigments. Among them, carotenoids are health-promoting antioxidants produced in virtually all plant organs. In leaves, they participate in photosynthesis and photoprotection. In flowers, they colour petals to attract pollinators. And in fruits, they accumulate at the ripe stage to provide not only distinctive pigments, but also nutrients for animals to eat them and disperse the seeds. Light normally stimulates the biosynthesis of carotenoids and regulates the development of storage structures to accommodate these lipophilic pigments. Thus, carotenoid levels decrease when plants become shaded in high-density environments, and they are usually very low in dark-grown organs such as roots or in seedlings that germinate underground. Work with the model plant Arabidopsis thaliana has revealed the molecular factors that transduce light signals to boost carotenoid biosynthesis and storage in coordination with photosynthetic development when seedlings emerge from the soil and expose their leaves to sunlight. The same factors appear to control leaf carotenoid contents when light conditions change in day/night cycles or in response to shade. Strikingly, recent discoveries suggest that light-related factors have been recruited during evolution to promote carotenoid accumulation in tomatoes (fruits) and carrots (roots).
Plant colours come to light