Source‐Sink Control of Grain Composition in Maize Strains Divergently Selected for Protein Concentration

Abstract

A long‐term divergent selection program for concentration of grain protein in maize (Zea mays L.) has produced the Illinois High (IHP) and Low (ILP) Protein strains, which differ greatly in yield and grain composition. The objective of this study was to determine the relative contribution of maternal (source) and zygotic (sink) factors in eliciting the characteristic differences in grain protein concentration. Changes in accumulation and partitioning of dry matter and reduced N during the grain‐filling period were determined on field‐grown plants in 1984 and 1985. Immature kernels of both strains were also grown to maturity in vitro on liquid media that contained various concentrations of N (amino acid mixture ranging in N from 0 to 100 mM). In both years, field‐grown IHP plants had greater total N accumulation (79% more at physiological maturity), more extensive N remobilization from vegetative tissue (43% of that present at anthesis, compared with 19%), and higher N partitioning values (62 vs. 43%) than ILP plants. When grown in vitro, N supply had a large effect on grain protein percentage for IHP but a small effect for ILP. In contrast, dry weight of ILP kernels responded markedly to N supply, while the response of IHP was more tempered. Based on these data, it appears that the distinction in grain protein composition between IHP and ILP results from the coordination of genetic differences in assimilate uptake and remobilization by the vegetation with different utilization efficiencies of the kernel.