First published online September 3, 2004; 10.1104/pp.104.047977
Plant Physiology 136:2700-2709 (2004)
© 2004 American Society of Plant Biologists
BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES
The Capacity of Green Oilseeds to Utilize Photosynthesis to Drive Biosynthetic Processes1
Sari A. Ruuska,
Jörg Schwender and
John B. Ohlrogge*
Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
Seeds of many plant species are green during embryogenesis. To directly assess the influence of light on the physiological status of green oilseeds in planta, Brassica napus and soybean (Glycine max) seeds were rapidly dissected from plants growing in the light or dark. The activation state of malate dehydrogenase, which reflects reduced thioredoxin and NADP/NADPH ratios, was found to be as high in seeds exposed to light as in leaves and to decrease in the dark. Rubisco was highly activated (carbamylated) in both light and dark, most likely reflecting high seed CO2 concentrations. Activities of Rubisco and phosphoribulokinase were sufficient to account for significant refixation of CO2 produced during B. napus oil biosynthesis. To determine the influence of light on oil synthesis in planta, siliques on intact plants in full sunlight or detached siliques fed 3H2O were partly covered with aluminum foil. Seeds from light and dark sections were analyzed, and fatty acid accumulation was found to be higher in seeds exposed to light than seeds from dark sections. The spectrum of light filtering through silique walls and the pigment composition of developing B. napus embryos were determined. In addition to a low chlorophyll a/b ratio, the carotenoid pigments of seeds can provide additional capture of the green light that filters through siliques. Together, these results demonstrate that even the low level of light reaching seeds plays a substantial role in activating light-regulated enzymes, increasing fatty acid synthesis, and potentially powering refixation of CO2.
1 This work was supported by the Department of Energy (grant no. DE–FG02–87ER13729) and the National Science Foundation (grant no. MCB 98–17882). Acknowledgment is also made to the Michigan Agricultural Experiment Station for its support of this research.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.047977.
* Corresponding author; e-mail ohlrogge{at}msu.edu; fax 517–353–1926.
Received June 8, 2004;
returned for revision July 14, 2004;
accepted July 15, 2004.
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