PLANT PHYSIOLOGY , Vol 114, Issue 1 55-62, Copyright © 1997 by American Society of Plant Biologists
|
BIOCHEMISTRY AND ENZYMOLOGY |
The Spatial Distribution of Sucrose Synthase Isozymes in Barley
J. Guerin and P. Carbonero
Laboratorio de Bioquimica y Biologia Molecular, Departamento Biotecnologia-UPM, Escuela Tecnica Superior Ingenieros Agronomos, 28040 Madrid, Spain
The sucrose (Suc) synthase enzyme purified from barley (Hordeum vulgare L.)
roots is a homotetramer that is composed of 90-kD type 1 Suc synthase (SS1)
subunits. Km values for Suc and UDP were 30 mM and 5 [mu]M, respectively.
This enzyme can also utilize ADP at 25% of the UDP rate. Anti-SS1
polyclonal antibodies, which recognized both SS1 and type 2 Suc synthase
(SS2) (88-kD) subunits, and antibodies raised against a synthetic peptide,
LANGSTDNNFV, which were specific for SS2, were used to study the spatial
distribution of these subunits by immunoblot analysis and
immunolocalization. Both SS1 and SS2 were abundantly expressed in
endosperm, where they polymerize to form the five possible homo- and
heterotetramers. Only SS1 homotetramers were detected in young leaves,
where they appeared exclusively in phloem cells, and in roots, where
expression was associated with cap cells and the vascular bundle. In the
seed both SS1 and SS2 were present in endosperm, but only SS1 was apparent
in the chalazal region, the nucellar projection, and the vascular bundle.
The physiological implications for the difference in expression patterns
observed are discussed with respect to the maize (Zea mays L.) model.
