Background
Abaxially anthocyanic leaves of deeply-shaded understorey plants play important ecological significance for the environmental adaption. In contrast to the transient pigmentation in other plants, anthocyanins are permanently presented in these abaxially red leaves, however, the mechanism for the pigment maintenance remains unclear. In the present study, we investigated phenolic metabolites that may affect pigment stability and degradation in
Excoecaria cochinchinensis
(a bush of permanently abaxial-red leaves), via a comparison with
Osmanthus fragrans
(a bush of transiently red leaves).
Results
High levels of galloylated anthocyanins were identified in the
Excoecaria
but not in the
Osmanthus
plants. The galloylated anthocyanin showed slightly higher stability than two non-galloylated anthocyanins, while all the 3 pigments were rapidly degraded by peroxidase (POD) in vitro. High levels of hydrolysable tannins [mainly galloylglucoses/ellagitannins (GGs/ETs)] were identified in
Excoecaria
but none in
Osmanthus
. GGs/ETs showed inhibition effect on POD, with IC50 ranged from 35.55 to 83.27 μM, correlated to the markedly lower POD activities detected in
Excoecaria
than in
Osmanthus
. Strong copigmentation was observed for GGs/ETs and anthocyanins, with more than 30% increase in the red intensity of non-galloylated anthocyanin solutions. In the leaf tissue, the hydrolysable tannins were observed to be co-localized with anthocyanins at the abaxial layer of the
Excoecaria
leaves, correlated to the low POD activity, more acidity and increased red intensity of the tissue.
Conclusion
The results suggest that the
Excoecaria
leaves accumulate a distinct group of phenolic metabolites, mainly GGs/ETs, at the abaxial layer, which prevent anthocyanin degradation and increase the pigment stability, and consequently lead to the permanent maintenance of the red leaves.
Electronic supplementary material
The online version of this article (10.1186/s12870-019-1903-y) contains supplementary material, which is available to authorized users.