Regulation of growth and storage product metabolism in cultured kernels of maize
Singletary, George William
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https://hdl.handle.net/2142/22140
Description
Title
Regulation of growth and storage product metabolism in cultured kernels of maize
Author(s)
Singletary, George William
Issue Date
1989
Doctoral Committee Chair(s)
Below, Frederick E.
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Biochemistry
Biology, Plant Physiology
Language
eng
Abstract
Maize (Zea mays L.) kernel growth and grain yield are functions of endosperm starch accumulation. In vitro seed culture was used to study the influence of assimilate supply on the growth and composition of maize endosperm and to determine how various metabolic events in developing endosperm are related to starch accumulation. Immature kernels were grown to maturity on liquid medium containing different concentrations of C (as sucrose) and N (as an amino acid mixture). Endosperm starch and protein syntheses responded to N supply in much the same way as do kernels grown on the intact plant. Protein accumulation was generally independent of sucrose concentration in the medium, while starch synthesis was reduced by low C supply. Extremely low or high concentrations of N also interfered with starch metabolism, possibly through a deficiency in metabolic enzymes or an osmotic imbalance. The relationship between starch and protein accumulation was dependent, at least in appearance, under low N and independent otherwise.
To study metabolism in relation to starch accumulation, kernels were grown on medium with: (a) zero N ($-$N), (b) N optimum for growth (+N), or (c) $-$N from 3 to 20 days after pollination followed by +N until maturity ($-$/+N). Endosperm starch and protein accumulation were greatly reduced in $-$N kernels, but enhanced in $-$/+N, relative to $-$N, endosperm. A reciprocity occurred between endosperm concentrations of free sugars and amino-N. Endosperm growth of N stressed kernels ($-$N, $-$/+N) was not limited by C substrate but, instead, by an apparent inability to utilize reducing sugars and a low content of albumin/globulin proteins. Of nine C metabolism enzymes assayed, only sucrose synthase and PPi-linked phosphofructokinase increased in activity concurrent with the promotion of starch accumulation in $-$/+N kernels. Greater activity of PPi-linked phosphofructokinase in $-$/+N endosperm may have been related to the enhanced utilization of reducing sugars. Electrophoretic analysis indicated additional proteins (albumin/globulins) that changed in relative amount in association with changes in starch accumulation. These data suggest that sucrose synthase, PPi-linked phosphofructokinase, and/or specific albumin/globulin proteins may have important roles in the regulation of starch synthesis in maize endosperm.
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