PLANT PHYSIOLOGY , Vol 114, Issue 3 1095-1101, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Regulation of Acyltransferase Activity in Immature Maize Embryos by Abscisic Acid and the Osmotic Environment
F. Pacheco-Moises, L. Valencia-Turcotte, M. Altuzar-Martinez and R. Rodriguez-Sotres
Departmento de Bioquimica, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Mexico D.F. 04510, Mexico
Maize (Zea mays L.) embryos, isolated from the developing seed and
incubated in dilute buffer, show reduced triacylglycerol (TAG) synthesis,
and accumulation stops after 24 h. Synthesis and accumulation can be
maintained at high levels if the incubation medium contains abscisic acid
(ABA) and/or a high osmotic concentration. Radiolabeled free fatty acids
accumulate at higher levels in embryos that contain less TAG, and acetyl
coenzyme A carboxylase activity remains essentially unchanged under all of
the conditions tested. In contrast, the activities of the acyltransferases
required for TAG synthesis remain high only in embryos incubated with ABA
and/or a high osmotic concentration. Dose-response curves showed that 4
[mu]M of ABA or mannitol at -1.0 MPa elicits a full response; both values
are within the range considered to be physiological. The TAG synthesis
capacity and diacylglycerol acyltransferases activity lost by pretreatment
of the embryos can be restored by re-exposure to ABA or high osmoticum.
Germination is not involved because isolated scutellum halves showed the
same changes in enzyme activity found in the whole embryo but did not
germinate. Our results provide direct evidence for the regulation of
TAG-synthesizing activities in maize embryos by ABA and the osmotic
potential of the environment.
