First published online March 7, 2002; 10.1104/pp.010879
Plant Physiol, April 2002, Vol. 128, pp. 1417-1427
Biochemical and Molecular Inhibition of Plastidial Carbonic
Anhydrase Reduces the Incorporation of Acetate into Lipids in Cotton
Embryos and Tobacco Cell Suspensions and Leaves1
Chau V.
Hoang2 and
Kent D.
Chapman*
Department of Biological Sciences, Division of Biochemistry and
Molecular Biology, University of North Texas, Denton, Texas
76203
Two cDNAs encoding functional carbonic anhydrase (CA) enzymes were
recently isolated from a non-photosynthetic, cotyledon library of
cotton (Gossypium hirsutum) seedlings with putative plastid-targeting sequences (GenBank accession nos. AF132854 and
AF132855). Relative CA transcript abundance and enzyme activity
increased 9 and 15 times, respectively, in cotton embryos during the
maximum period of reserve oil accumulation. Specific sulfonamide
inhibitors of CA activity significantly reduced the rate of
[14C]acetate incorporation into total lipids in cotton
embryos in vivo, and in embryo plastids in vitro, suggesting a role for
CA in plastid lipid biosynthesis. CA inhibitors did not affect
acetyl-coenzyme A carboxylase activity or total storage protein
synthesis. Similar results were obtained for two other plant systems:
cell suspensions (and isolated plastids therefrom) of tobacco
(Nicotiana tabacum), and chloroplasts isolated from
leaves of transgenic CA antisense-suppressed tobacco plants (5% of
wild-type CA activity). In addition, tobacco cell suspensions treated
with the CA inhibitor ethoxyzolamide showed a substantial loss of
CO2 compared with controls. The rate of
[14C]acetate incorporation into lipid in cell suspensions
was reduced by limiting external [CO2] (scrubbed air),
and this rate was further reduced in the presence of ethoxyzolamide.
Together, these results indicate that a reduction of CA activity
(biochemical or molecular inhibition) impacts the rate of plant lipid
biosynthesis from acetate, perhaps by impairing the ability of CA to
efficiently "trap" inorganic carbon inside plastids for utilization
by acetyl-coenzyme A carboxylase and the fatty acid synthesis machinery.
1
This work was supported by the Herman Frasch
Foundation (grant no. 427-HF97).
2
Present address: Department of Pharmacology, University
of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9041.
*
Corresponding author; e-mail chapman{at}unt.edu; fax
940-565-4136.
© 2002 American Society of Plant Physiologists
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