Composition of photosynthetic pigments and photosynthetic characteristics in green and yellow sectors of the variegated Aucuba japonica 'Variegata' leaves

Aucuba japonica 'Variegata' is a widely used ornamental shrub with green-yellow variegated leaves. In this study, the formation of leaf variegation and photosynthetic characteristics in green and yellow sectors were investigated. There were no marked anatomical differences in tissue organization between the green and yellow sectors. At the cellular level, it was observed that the chloroplasts in the yellow leaf tissue were vacuolated. Besides, the pigment contents of the yellow leaf tissue were obviously lower than those in the green areas, and a very low intensity of chlorophyll auto-fluorescence was generated from the yellow areas. Furthermore, significantly lower values of F0, Fm, Fv/Fm, ФPSII and non-photochemical quenching (NPQ) were noticed in yellow sectors compared to the green ones, indicating that the yellow leaf tissue was less photoprotected than the green area. In addition, the yellow sectors showed lower net photosynthesis and dark respiration rates compared to the green leaf tissue. Immunofluorescence showed large amounts of ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) in green leaf tissue, while only faint fluorescence was detected in the yellow sectors. As a whole, the results of this study suggest that the leaf variegation of A. japonica 'Variegata' is “pigment type” and that this pigment-related leaf variegation affects photosynthetic light use in the variegated leaves. These findings also shed light on the coloration mechanism of ornamental plant foliage.