The utilization of pre-anthesis reserves in grain filling of wheat. Assessment by steady-state (CO2)-C-13/(CO2)-C-12 labelling

Significant mobilization of protein and carbohydrates in vegetative plant p arts of wheat regularly occurs during grain filling. While this suggests a contribution of reserves to grain filling, the actual efficiency of mobiliz ed assimilate conversion into grain mass (ME) is unknown. In the present st udy the contribution of pre-anthesis C (C fixed prior to anthesis) to grain filling in main stem ears of two spring wheat (Triticuin aestivum L.) cult ivars was determined by C-13/C-12 steady-state labelling. Mobilization of p re-anthesis C in vegetative plant parts between anthesis and maturity, and the contributions of water-soluble carbohydrates (WSC) and protein to pre-a nthesis C mobilization were also assessed. Experiments were performed with two levels of N fertilizer supply in each of 2 years. Pre-anthesis reserves contributed 11-29% to the total mass of C in grains at maturity. Pre-anthe sis C accumulation in grains was dependent on both the mass of pre-anthesis C mobilized in aboveground vegetative plant parts (r(2) = 0.87) and ME (de fined as g pre-anthesis C deposited in grains per g pre-anthesis C mobilize d in above-ground vegetative plant parts; r(2) = 0.40). ME varied between 0 .48 and 0.75. The effects of years, N fertilizer treatments and cultivars o n ME were all related to differences in the fractional contribution of WSC to preanthesis C mobilization. Multiple regression analysis indicated that C from mobilized pre-anthesis WSC may be used more efficiently in grain fil ling than C present in proteins at anthesis and mobilized during grain fill ing. Possible causes for variability of ME are discussed.