Pre-anthesis reserve utilization for protein and carbohydrate synthesis ingrains of wheat

We assessed the contribution of pre-anthesis reserve C to protein and carbo hydrate deposition in grains of wheat (Triticum aestivum L.) using a new ap proach comprised of steady-state C-13/C-12 labeling and separation of the p rotein and carbohydrate fractions of mature grains. Experiments were perfor med with two spring wheat cultivars (Kadett and Star) grown with differenti al N fertilizer supply over 2 years. Pre-anthesis reserves contributed betw een 30% and 47% of the C in protein and 8% to 27% of the C in carbohydrates of grains. Partitioning of pre-anthesis C among the grain fractions was st rongly dependent on the C/N (w/w) ratio in mobilized preanthesis biomass (r (2) = 0.92). There appeared to be no significant exchange of pre-anthesis C between amino acids and carbohydrates during redistribution. The mean appa rent efficiency of mobilized carbohydrate-C use in grain filling (MECHO, es timated as the mass of pre-anthesis C deposited in grain carbohydrates per gram of preanthesis C mobilized from carbohydrates in vegetative plant part s) was 0.72, whereas that of protein-C (MEP) was 0.56. However, MEP and MEC HO varied among treatments. MECHO increased with increasing contributions o f water-soluble carbohydrates to total preanthesis carbohydrate mobilizatio n. MEP decreased with increasing residence time of protein in vegetative bi omass. Possible causes for variability of MEP and MECHO are discussed.