Isomers of rhodoxanthin in reddish brown leaves of gymnosperms and effect of daylight intensity on the contents of pigments during autumnal coloration

Abstract

The major red carotenoids in autumnal, colored leaves were analyzed in seven species and one variety that belong to two families of gymnosperms. The red carotenoids in leaves of all species and variety were rhodoxanthin, which was separated into three geometric isomers, (6Z, 6′Z)-rhodoxanthin, (6Z)-rhodoxanthin and (all E)-rhodoxanthin. The effects of daylight intensity on the content and composition of the leaf pigments of autumnal coloration were studied with leaves ofCryptomeria japonica (evergreen) andTaxodium distichum (deciduous) grown under different grades of shade. Histological observation showed that many reddish particles of rhodoxanthin were observed inside chromoplasts on the sunny side of a leaf at the early stage of coloration and that the content of the reddish particles was decreased toward the shady side from the sunny side of a leaf. The transition from chloroplasts to chromoplasts was observed and cells at different stage of coloration independently existed in the mesophyll tissue of a leaf. The content of rhodoxanthin became maximum when the daylight intensity was 4.1–7.4 MJ m−2 day−1 and the daily mean temp. was below 8.1 C inCryptomeria, and 3.1–8.3 MJ m−2 day−1 and 13.4 C inTaxodium.