Variation in the capacity for organic nitrogen acquisition along the root length of rice and wheat

Oligopeptides constitute an important yet understudied component of soil's dissolved organic nitrogen (DON) pool, representing a primary breakdown product of proteins. However, the mechanisms of oligopeptide uptake and utilisation by crop roots remain poorly understood in a plant nutrition context. We investigated the rate and spatial uptake pattern of 14C-labelled alanine and di- to pentapeptides of alanine in wheat and rice under sterile hydroponic conditions. Both species demonstrated the capacity to absorb N through amino acids and oligopeptides, with rice roots showing higher peptide uptake than wheat. Specifically, alanine absorption exceeded peptide uptake by 3-7-fold in rice and 6-9-fold in wheat. Using phosphor imaging, we demonstrated that alanine and oligopeptide uptake occurred throughout the root system, with the highest accumulation in the root tip and root hair regions. Further, spatial analysis revealed that peptide absorption rates in rice were 2-5 times higher in the 0-1 cm root section and 1.5-4 times higher in the 1-2 cm section compared to corresponding wheat root segments. We conclude that plants can directly take up amino acids and oligopeptides to acquire exogenous N, with marked differences occurring among species in both uptake efficiency and spatial uptake patterns.