Protein concentration has major impacts on wheat product quality; therefore, this trait is a high priority in wheat improvement efforts. An allele from a wild relative of wheat at locus Gpc-B1 on chromosome 6BS that increases grain protein concentration (GPC) was recently reported to be associated with early senescence. We introgressed this allele into the adapted hard red spring wheat cultivars ‘Scarlet' and ‘Tara 2002' via marker-assisted backcross breeding (MABB). The objectives of this study were to: (1) assess differences in rates of plant senescence, N translocation, and N assimilation in grain among isogenic BC₅F₅ derivatives of Scarlet and Tara 2002 with and without the high GPC allele; and (2) compare the physiological responses conferred by this allele under irrigated and non-irrigated field production conditions. Three MABB-derived genotypes with and 3 without the high GPC allele were evaluated for each genetic background, along with the recurrent parents. Replicated field trials in 2006 and 2007 were planted in Pullman, WA as split-plots, with irrigation (with or without) as the main plot factor and allele composition (with or without the high GPC allele) as the subplot factor. Field results from 2006 suggested that the rate of growing degree day accumulation impacted the rate of senescence. To confirm this, replicated greenhouse studies were conducted in 2007 using the same genotypes to compare rates of senescence under controlled environmental conditions. Chlorophyll degradation rates in flag leaves and changes in peduncle color were collected to compare senescence rates between genotypes and treatments. Free amino acids and total protein N levels were measured in flag leaves and developing grains to compare N translocation and assimilation rates among genotypes between treatments. Data were used to assess the effect of the Gpc-B1 locus on GPC and end-product quality under different environmental conditions and in different genetic backgrounds.