When are red juvenile leaves mature enough to be green? The coordination of anthocyanin decline with photosynthetic maturity

Juvenile leaves in high-light environments commonly appear red due to anthocyanin pigments, which play a photoprotective role during light-sensitive ontogenetic stages.  The loss of anthocyanin during leaf development presumably corresponds to a decreased need for photoprotection, as photosynthetic maturation allows leaves to utilize higher light levels more efficiently.  However, the relationship between photosynthetic development and anthocyanin decline has yet to be quantitatively described.  In the current study, anthocyanin concentration was measured against chlorophyll content, lamina thickness, anatomical development, and photosynthetic CO₂ exchange in developing leaves of three deciduous-tree species.  In all three species, anthocyanin disappearance corresponded with development of ~50% mature photopigment concentrations, ~80% mature lamina thickness, and differentiation of the mesophyll into palisade and spongy layers.  Photosynthetic gas exchange correlated positively with leaf thickness and chlorophyll content (per unit area) and negatively with anthocyanin concentration.  Species with more rapid photosynthetic maturation also lost anthocyanin earliest in development.  Chlorophyll a/b ratios increased as leaves matured, consistent with a shading effect of anthocyanin.  These results suggest that anthocyanin re-assimilation is linked closely with chloroplast and whole-leaf developmental processes, supporting the idea that anthocyanins protect tissues until light-processing and carbon-fixation processes have matured to adequately balance energy capture with utilization.