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Metabolism and Enzymology

Response of Enzymes and Storage Proteins of Maize Endosperm to Nitrogen Supply ¹

Department of Agronomy, University of Illinois, Urbana, Illinois 61801, Seed Biosynthesis Research Unit, U.S. Department of Agriculture, Agricultural Research Service, Northern Regional Research Center, Peoria, Illinois 61604

To examine the effects of N nutrition upon endosperm development, maize (Zea mays) kernels were grown in vitro with either 0, 3.6, 7.1, 14.3, or 35.7 millimolar N. Kernels were harvested at 20 days after pollination for determination of enzyme activities and again at maturity for quantification of storage products and electrophoretic separation of zeins. Endosperm dry weight, starch, zein-N, and nonzein-N all increased in mature kernels as N supply increased from zero to 14.3 millimolar. The activities of sucrose synthase, aldolase, phosphoglucomutase, glutamate-pyruvate transaminase, glutamate-oxaloacetate transaminase, and acetolactate synthase increased from 1- to 2.5-fold with increasing N supply. Adenosine diphosphate-glucose pyrophosphorylase and both ATP- and PPi-dependent phosphofructokinases increased to lesser extents, while no significant response was detected for hexose kinases and glutamine synthetase. Nitrogen-induced changes in enzyme activities were often highly correlated with changes in final starch and/or zein-N contents. Separation of zeins indicated that these peptides were proportionately enhanced by N supply, with the exception of C-zein, which was relatively insensitive to N. These data indicate that at least a portion of the yield increase in maize produced by N fertilization is induced by a modification of kernel metabolism in response to N supply.

¹ Cooperative investigations of the Illinois Agricultural Experiment Station, Department of Agronomy, University of Illinois, Urbana and the U.S. Department of Agriculture, Agricultural Research Service, Peoria, IL. This study was a part of Project No. 15-0371 of the Agricultural Experiment Station, College of Agriculture, University of Illinois.

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