Accumulation and conversion of sugars by developing wheat grains. 4. Effects of phosphate and potassium ions in endosperm slices |
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Authors: | A H G C RIJVEN R M GIFFORD |
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Institution: | Division of Plant Industry, CSIRO, PO Box 1600, Canberra City, ACT 2601, Australia |
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Abstract: | Abstract. 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 Pi level, achieved by prolonged preincubations in different media, did not show an inhibition of starch synthesis by Pi. 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 Pi; level. |
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Keywords: | Triticum aestivum Gramineae wheat starch synthesis developing endosperm phosphate potassium |
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