Functional significance of anthocyanins in peduncles of Sambucus nigra

• We test a signalling function and a physiological function for peduncle anthocyanins.
• Peduncle reddening required exposure to sunlight.
• Anthocyanins reduced the transmission of green light to subjacent chlorenchyma.
• Quantum efficiencies of photosystem II were higher in red than in green peduncles.
• Following light stress, Fv/Fm decreased more significantly in green peduncles than in red.

Anthocyanin accumulation in reproductive organs is normally assumed to attract animals as dispersers, yet in leaves and stems these pigments may also serve a number of protective roles. Here, we tested the requirements of both a physiological function, that anthocyanins provide photoprotection, and a communicative function, that anthocyanic reddening enhances frugivory, for Sambucus nigra peduncles which turn red prior to fruit ripening. We found that peduncle reddening required exposure to sunlight, and that the sub-epidermal anthocyanins significantly reduced the transmission of green light to subjacent chlorenchyma. Under saturating white light, quantum efficiencies of photosystem II were higher in red than in green peduncles. Following light stress, the decline in Fv/Fm was significantly greater for green portions of peduncle compared to red portions on the same organ. In contrast, we found that avian frugivory was not consistently greater for those infructescences bearing the reddest peduncles, and therefore found little evidence of a communicative function for peduncle reddening. Because peduncle senescence begins prior to fruit maturation, anthocyanins in these sterile parts of reproductive organs may confer protective benefits similar to those postulated for senescing autumn leaves.