Chloroplast structure and function in wild-type and aurea-type leaves of the Japanese spindle-tree over their life span

摘要

The evergreen leaves of the Japanese spindle-tree (Euonymus japonicus Thunb. 'Aureo-marginatus') are adapted to endure repeated freezing and thawing during the winter. We investigated the physiological and morphological characteristics of the chloroplasts in young, overwintering, and overwintered wild-type and aurea-type leaves. When developing in the shade, both leaf types during their life span maintained a well-developed thylakoid system in their chloroplasts. The photosynthesis rates were also similar. When growing in intense sunlight, the áurea variety contained chloroplasts with a reduced thylakoid system, but photosynthesis was less reduced. In spring, overwintered leaves of both varieties clearly showed ultrastructural and physiological characteristics of senescence. The senescence in áurea leaves exposed to full sunlight was more pronounced.