Diurnal and acclimatory responses of violaxanthin and lutein epoxide in the Australian mistletoe Amyema miquelii

This study investigated the chloroplast pigment content of the Australian mistletoe Amyema miquelii (Lehm. ex Miq.) Tiegh. over diurnal periods in sun- and shade-acclimated leaves. Amyema miquelii exhibited the typical higher plant complement of neoxanthin, the xanthophyll cycle pigments, lutein, chlorophylls a and b and carotene. Substantial levels of lutein epoxide were also present. Interestingly, diurnal light exposure elicited a decrease in lutein epoxide that paralleled the decrease in violaxanthin. Compared with shade-acclimated leaves, sun leaves exhibited reduced lutein epoxide and violaxanthin levels and higher chlorophyll a/b ratios. It is clear that the pools of violaxanthin and lutein epoxide respond in parallel to both diurnal light changes and sun- shade acclimation, although there seemed to be some differences in the recovery characteristics. These results raise a question as to whether lutein and lutein epoxide cycling may provide an auxiliary means of energy dissipation for some species.