Partitioning into Maize Grain N Fractions of N Absorbed Through the Roots Before and After Pollination

The abundance of N in various fractions in maize (Zea mays L.) grain was compared in two genotypes, a normal hybrid (Pioneer 3369A) and its opnque-2 (0-2) counterpart (L3369). Plants were grown in the greenhouse in sand cultures irrigated daily with nutrient solutions containing 3.75 mM N as NO, ion. At anthesis the plant cultures were divided into sets, one set continuing to be irrigated with the same solution, but with 15N added, and the other set irrigated with a solution of the same composition except that the N was omitted. The plants were sampled at 12, 24 and 36 days after pollination. Post-anthesis N nutrition affected the composition of the vegetative growth but had no effect during the sampling period on yields or amounts of N in the grain. At 12 days post-pollination there were no differences between the two genotypes in N partitioning, with about 50% of the N present as nonprotein N (NPN). At 24 and 36 days over 75% more N was present as zein in the normal genotype as in the 0-2, while the latter contained a much higher proportion of N as NPN. The albumin-globulin and glutelin fractions were slightly greater in the 0-2 . The N absorbed after pollination was partitioned among the grain protein fractions similarly to N absorbed prior to pollination. The nature of the NPN fraction needs to be considered in evaluating effects on crop quality of an elevated N supply.