PLANT PHYSIOLOGY , Vol 105, Issue 1 119-125, Copyright © 1994 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Activity in the Endosperm of Maize vivipary Mutants
K. B. Moore and K. K. Oishi
Department of Molecular and Cellular Biology (K.B.M., K.K.O.), Departmemnt of Plant Sciences,(K.K.O.), and Committee on Genetics (K.K.O.), University of Arizona, Tucson, Arizona 85721
During seed maturation the levels of the rate-limiting enzyme of isoprenoid
biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR)
decrease while the levels of the isoprenoid compund abscisic acid (ABA)
increase. In the present study, we demonstrate that HMGR specific activity
is inversely correlated with endogenous ABA levels in Zea mays endosperm
during seed development. HMGR specific activity and ABA levels were
measured in the endosperm of the maize vivipary mutuants vp2, vp5, and vp7,
which are defective in ABA biosynthesis, and vp1, which is defective in an
ABA response element. Reduced ABA levels were observed in the endosperm of
vp2, vp5, and vp7, whereas HMGR activity levels were higher compared with
wild-type sibling endosperm activity. HMGR activities were increased by as
much as 37% (vp2), 45% (vp5), and 58% (vp7) in the mutants. Endosperm HMGR
activity in the vp1 mutant was also increased (41%) relative to wild-type
siblings, even though vp1 does not have reduced ABA levels. In addition,
exogenous ABA inhibits HMGR activity 34 to 50% in maize roots. These
results sugggest the HMGR activity levels during seed development are
regulated via a Vp1-dependent signal transduction pathway that is affected
by the reduced ABA content of vp2, vp5, and vp7 endosperm.