Journal of Experimental Botany, Vol 49, 1105-1111, Copyright © 1998 by Oxford University Press
P Eastmond and S Rawsthorne
Plastids isolated from developing leaves and embryos of oilseed rape
(Brassica napus L.) were incubated with substrates in
the light or the dark, with or without exogenous ATP. Incorporation of
HCO-3, and carbon from a range of substrates into
fatty acids and/or starch by leaf chloroplasts was absolutely
light-dependent and was unaffected by provision of ATP. Incorporation of
HCO-3 into fatty acids and/or starch by embryo
plastids was also light-dependent. However, the light-dependent rates
attained, when expressed on a comparable basis, were less than 32% of those
from Glc6P (plus ATP), which was the most effective substrate for starch
and fatty acid synthesis. In the light alone the rates of carbon
incorporation from Glc6P, pyruvate and acetate into fatty acids, and from
Glc6P into starch by embryo plastids were less than 27% of the respective
ATP-dependent (dark) rates. Light had no effect on these ATP-dependent
rates of synthesis by embryo plastids. While transporter activities for
both glucose and Glc6P were present in embryo plastids, leaf chloroplasts
did not have the latter activity. It is concluded that light at
in vivo levels can contribute energy to carbon
metabolism in embryo plastids. However, this contribution is likely to be
small and these plastids are therefore largely dependent upon interaction
with the cytosol for the ATP, reducing power and carbon precursors that are
required for maximal rates of starch and fatty acid
synthesis.Keywords: Brassica
napus L., oilseed rape, chloroplast, embryo plastid, fatty acid
synthesis, starch synthesis.
ARTICLES
Comparison of the metabolic properties of plastids isolated from developing leaves or embryos of Brassica napus L
John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK; Corresponding author; e-mail: steve.rawsthorne@bbsrc.ac.uk
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