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Evidence for Light-Stimulated Fatty Acid Synthesis in
Soybean
Fruit1
Jennifer R. Willms,
Christophe Salon2, and
David B. Layzell*
Department of Biology, Queen's University at Kingston, Kingston,
Ontario, Canada K7L 3N6
In
leaves, the light reactions of photosynthesis support fatty acid
synthesis but disagreement exists as to whether this occurs in green
oilseeds. To address this question, simultaneous measurements of the
rates of CO2 and O2 exchange (CER and OER,
respectively) were made in soybean (Glycine max L.)
fruits. The imbalance between CER and OER was used to estimate the
diverted reductant utilization rate (DRUR) in the equation: DRUR = 4 × (OER + CER). This yielded a quantitative measure of the rate
of synthesis of biomass that is more reduced per unit carbon than
glucose (in photosynthesizing tissues) or than the substrates of
metabolism (in respiring tissues). The DRUR increased by about 2.2-fold
when fruits were illuminated due to a greater increase in OER than
decrease in CER. This characteristic was shown to be a property of the
seed (not the pod wall), to be present in fruits at all developmental
stages, and to reach a maximal response at relatively low light. When
seeds were provided with 13CO2, light reduced
12CO2 production but had little effect on
13CO2 fixation. When they were provided with
18O2, light stimulated
16O2 production but had no effect on
18O2 uptake. Together, these findings indicate
that light stimulates fatty acid synthesis in photosynthetic oilseeds,
probably by providing both ATP and carbon skeletons.
1
This work was supported by the Natural Sciences
and Engineering Research Council of Canada with a research grant to
D.B.L. and a postgraduate fellowship to J.R.W.
2
Present Address: Unite de Malherbiologie et
d'Agronomie Institut National de la Recherche Agronomique, BV 1540, 17 rue Sully, 21034 Dijon cedex, France.
*
Corresponding author; e-mail layzelld{at}biology.queensu.ca; fax
613-533-6617.
Plant Physiol. (1999) 120: 1117-1128
Copyright Clearance Center: 0032-0889/99/120//12
© 1999 American Society of Plant Physiologists
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