© 2004 Heron Publishing—Victoria, Canada
Seasonal changes in the xanthophyll cycle and antioxidants in sun-exposed and shaded parts of the crown of Cryptomeria japonica in relation to rhodoxanthin accumulation during cold acclimation
Quingmin Han (1, 2), Shinichiro Katahata (3), Yoshitaka Kakubari (3) and Yuzuru Mukai (3)
1. Department of Plant Ecology, Forestry and Forest Products Research Institute (FFPRI), Ibaraki 305-8687, Japan / 2. Corresponding author (qhan@ffpri.affrc.go.jp) / 3. Faculty of Agriculture, University of Shizuoka, Shizuoka 422-8529, Japan / Received September 2, 2003; accepted October 31, 2003; published online April 1, 2004
Summary
Xanthophyll rhodoxanthin, which is present in sun-exposed needles of certain gymnosperms in winter, may have a photoprotective
role during long-term cold acclimation. To examine how cold acclimation processes vary within tree crowns and to examine putative
correlations between xanthophyll cycle pigments (VAZ), rhodoxanthin and the water–water cycle in photoprotection, we monitored
seasonal changes in the activities of two key antioxidant enzymes (ascorbate peroxidase (APX) and glutathione reductase (GR)),
pigment composition and chlorophyll fluorescence parameters in sun and shade needles of crowns of the gymnosperm Cryptomeria japonica D. Don. Although APX and GR activities in both sun and shade needles were higher in winter than in summer when assayed at
20 °C, differences between seasons were less pronounced when enzymatic activities in summer and winter were assayed at 20
and 5 °C, respectively. These results suggest that increases in the potential activity of antioxidant enzymes in winter is
an adaptation that helps counterbalance reductions in absolute enzyme activity caused by low temperature, and thus allows
the photoprotective capacity of the water–water cycle in C. japonica to be maintained at a roughly constant value throughout the year. In shade needles, the concentration of VAZ increased in
winter, but no rhodoxanthin accumulated. Photosynthetic activity was maintained in winter. In sun needles, however, the electron
transport rate (ETR) and photochemical quenching (qP) decreased to their lowest values in December, just before the accumulation of rhodoxanthin, which coincided with the highest
amount of VAZ. Changes in rhodoxanthin concentration mirrored changes in VAZ concentration from January to March. Winter values
of ETR and qP were comparable with summer values after accumulation of rhodoxanthin, indicating that rhodoxanthin may play a more important
role than the VAZ cycle in protecting the photosynthetic apparatus from photodamage in winter. Photosynthetic activity may
be modulated, as a result of the interception of light by rhodoxanthin, to match the extent to which absorbed light energy
can be utilized in winter when the VAZ cycle is unable to operate effectively because of low temperatures.
Keywords:
ascorbate peroxidase, electron transport rate, glutathione reductase, light, low temperature, non-photochemical quenching,
photochemical efficiency of PSII, photoinhibition, water–water cycle.
