Exploring nitrogen remobilization for seed filling using natural variation in Arabidopsis thaliana.

Nineteen Arabidopsis accessions grown at low (LOW N) and high (HIGH N) nitrate supplies were labelled using (15)N to trace nitrogen remobilization to the seeds. Effects of genotype and nutrition were examined. Nitrate availability affected biomass and yield, and highly modified the nitrogen concentration in the dry remains. Surprisingly, variations of one-seed dry weight (DW(1S)) and harvest index (HI) were poorly affected by nutrition. Nitrogen harvest index (NHI) was highly correlated with HI and showed that nitrogen use efficiency (NUE) was increased at LOW N. Nitrogen remobilization efficiency (NRE), as (15)N partitioning in seeds ((15)NHI), was also higher at LOW N. The relative specific abundance (RSA) in seeds and whole plants indicated that the (14)NO(3) absorbed post-labelling was mainly allocated to the seeds (SEEDS) at LOW N, but to the dry remains (DR) at HIGH N. Nitrogen concentration (N%) in the DR was then 4-fold higher at HIGH N compared with LOW N, whilst N% in seeds was poorly modified. Although NHI and (15)NHI were highly correlated to HI, significant variations in NUE and NRE were identified using normalization to HI. New insights provided in this report are helpful for the comprehension of NUE and NRE concepts in Arabidopsis as well as in crops and especially in Brassica napus.