New Zealand Journal of Crop and Horticultural Science abstracts
Alternate routes for starch synthesis in developing grains of wheat and
sorghum: indirect evidence through its regulation by inorganic phosphates
and organic acids
RABINDRA RANDHAWA
RANGIL SINGH
Department of Biochemistry
Punjab Agricultural University
Ludhiana 141004
Punjab, India
Abstract The path of carbon from sucrose to starch in
developing grains appears to be different in wheat (
Triticum aestivum)
and sorghum (
Sorghum bicolor). In this paper we present indirect
evidence in support of this hypothesis. Detached ears, carrying actively
metabolising grains, were cultured in complete liquid media manipulated with
respect to inorganic phosphates and organic acids.
14C-incorporation
studies indicated a higher level of metabolism of sucrose before starch
formation in sorghum grain as compared to that in wheat grain. Starch and
protein contents drastically decreased in sorghum grain in response to
exogenously-supplied inorganic phosphate and inorganic pyrophosphate. In
contrast, these inorganic phosphates had no such effect on starch and protein
accumulation in wheat grain. [[alpha]]-ketoglutarate and citrate in
sucrose-free culture medium increased the starch content of wheat grain.
Conversely, these organic acids markedly decreased the starch content of
sorghum grain. This difference in the response of wheat and sorghum grains to
inorganic phosphates and organic acids leads us to suggest that whereas triose
phosphates act as precursors of starch in sorghum grain, hexose phosphates
and/or adenosine 5[[minute]]-diphosphoglucose may act as direct precursors of
starch in wheat grain. This hypothesis is supported by the observation of
higher specific activities of some selected glycolytic enzymes, such as
phosphoglucoisomerase, ATP-dependent phosphofructokinase, fructose
1,6-bisphosphate aldolase, and triose phosphate isomerase in sorghum grain as
compared to those in wheat grain.
Keywords inorganic phosphates; liquid culturing; organic
acids; starch synthesis; sorghum; wheat
H97-22
Received 6 June 1997; accepted 28 January 1998
PDF file of entire paper: medium quality (889K); (scanned from paper original: notes about this process)
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