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Accumulation and conversion of sugars by developing wheat grains. 4. Effects of phosphate and potassium ions in endosperm slices
Author(s) -
RIJVEN A. H. G. C.,
GIFFORD R. M.
Publication year - 1983
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/1365-3040.ep11589214
Subject(s) - endosperm , starch , chemistry , sucrose , phosphate , potassium , biochemistry , apoplast , substrate (aquarium) , potassium phosphate , nuclear chemistry , chromatography , organic chemistry , biology , cell wall , ecology
. Transverse slices through developing grains of Triticum aestivum cv. SUN 9E 16 d after anthesis were incubated in simple defined media with various radioactive labels. In some enzymic assays slices were pretreated with 2.5% Triton X‐100 or with 5% butanol to remove cellular membranes and endogenous substrates. Endogenous potassium leaked from endosperm slices into 30mol m −3 sucrose while sucrose was converted partly into starch. Exogenous alkali‐ions, except Li + , stimulated conversion of sucrose to insoluble matter, specifically to starch with K + . Starch synthetase activity of Triton‐pretreated slices was stimulated by K + at both high and low substrate ADPG concentration, but was not affected by phosphate (25 mol m −3 ). Phosphate in the medium had no effect on incorporation of sucrose or glucose into alcohol‐insoluble material or starch in fresh slices (internal inorganic phosphate (P,) concentration was about 11 mol m −3 ). Three‐ to four‐fold contrasts in internal P i level, achieved by prolonged preincubations in different media, did not show an inhibition of starch synthesis by P i . However, phosphate (25mol m −3 ) inhibited starch synthesis, that was mediated by ADPG pyrophosphorylase in butanol‐pretreated endosperm slices by 15–18%. It is concluded that starch synthesis in wheat endosperm is not regulated directly by apoplastic P i ; level.