INFLUENCE OF NITROGEN-SOURCE ON THE GROWTH, PROLAMIN CONTENT, AND GLUTAMINE-SYNTHETASE ISOZYME PROFILES OF ENDOSPERM-DERIVED SUSPENSION-CULTURES OF MAIZE
Mj. Muhitch et Fc. Felker, INFLUENCE OF NITROGEN-SOURCE ON THE GROWTH, PROLAMIN CONTENT, AND GLUTAMINE-SYNTHETASE ISOZYME PROFILES OF ENDOSPERM-DERIVED SUSPENSION-CULTURES OF MAIZE, Journal of plant physiology, 144(2), 1994, pp. 215-221
In order to assess the suitability of endosperm-derived suspension cul
tures (EDSC) as a model system for nitrogen metabolism in intact maize
kernel endosperm, the isozyme complements of glutamine synthetase (GS
), a key enzyme of nitrogen metabolism in higher plants, were compared
from both tissue sources. Anion exchange profiles revealed five GS is
ozymes from intact endosperm. These same isozymes were also found in E
DSC, although in very different relative proportions, along with a six
th isozyme with elution characteristics corresponding to the chloropla
st GS from maize leaves. Isoelectric focusing under denaturing conditi
ons followed by immunoblotting revealed the presence of five GS subuni
ts from both intact endosperm and EDSC. The relative abundance of the
GS isozymes and subunits from intact endosperm changed strikingly with
development. Developmental changes in the isozyme patterns were less
dramatic in the EDSC. Culturing the EDSC on alternative nitrogen sourc
es changed the relative proportions of isozymes and affected growth an
d zein accumulation. It was concluded that while the EDSC do resemble
intact endosperm in that they express the same GS subunits, the differ
ences in the relative proportions of those subunits and the correspond
ing isozymes and differences in developmental changes make extrapolati
ons of results obtained from studies of nitrogen metabolism using the
endosperm suspension cultures to the intact endosperm inappropriate.