The selective advantages of anthocyanins in developing leaves of mango and cacao.
Lee D. W., Brammeier S., Smith A. P.
Author Affiliation: Florida International University, Miami, FL 33199, USA.
Biotropica 19 : 40-49
Abstract : Flushing and mature leaves of young cocoa trees, cv. Amelonado, and mature mango trees, cv. Tommy Atkins, growing in Miami were analysed and measured during March-May. Leaf temperatures, diffusion resistance and photosynthetic photon flux density (incident to the upper leaf surface) were also recorded. The leaves of both species grew rapidly and continually; from an initial length of 5 cm, maximum leaf expansion was completed in one week. Leaves lost their anthocyanic coloration and matured during the following week. Levels of both anthocyanins and total phenols fluctuated during leaf expansion, but in both species anthocyanin levels fell with maturity whereas phenol levels remained high. Young leaves had lower absorptances than old leaves at most wavelengths (in the range 250-750 nm); absorptances were highest at 300 nm because of the presence of phenolic compounds. Developing leaves of both species showed considerably more diffusion resistance than mature leaves; in general, temperatures did not differ significantly between leaves of different ages. Although developing leaves contained appreciable concentrations of anthocyanins these comprised only a small proportion of the total phenolic content. It would seem that anthocyanins did not play an important role as a screen against ultraviolet radiation, a mechanism for elevating leaf temperature, a means of defence against herbivory or as part of a physiological mechanism.