1. NMR approach to evaluate impact of nitrogen supply on the senescence process of Brassica napus leaves under field conditions

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]SPEE [ADD1_IRSTEA]Sûreté alimentaire

International audience

English. During leaf senescence, improved remobilization of nutrients from old leaves to growing organs may represent an adaptive response of Brassica napus plants to the decrease in nitrogen (N) input. Therefore characterization of the natural genotypic variability of leaf remobilization efficiency should allow providing relevant information for crop improvement. It has been recently demonstrated that NMR transverse relaxation times can be used to monitor leaf senescence process through senescence associated cell and tissue structural modifications [1-2]. The impact of N deficiency on these changes has also been demonstrated on Brassica Napus plants grown under controlled conditions [3]. The aim of the present work was to investigate by NMR a plant response to nitrogen fertilization under field conditions. Two genotypes of winter oil seed rape (Brassica napus, cv Aviso and Express) with different tolerance to N deficiency were assessed. A mobile NMR lab [4] was brought into the field allowing NMR measurements without plant uprooting. Transverse relaxation times were measured on leaf discs cut from the leaves of each leaf rank of the plant studied. A CPMG sequence with a 90°-180° pulse spacing of 0.2ms and 64 averages were used. The genotypic response to N depletion was evaluated through dry mass production and seed yield. The results obtained in two different genotypes showed that despite a great variability of the macro and micro environmental factors, the NMR relaxation provided robust indicators of the structural changes that occurred during leaf development. The pattern of these changes differed between genotypes in lower N regime due to their different responses to the decrease in N input. This study presents an important step toward the use of NMR relaxometry for field phenotyping of nitrogen fertilization response.