Grain legume seed filling in relation to nitrogen acquisition: A review and prospects with particular reference to pea

Seed filling depends not only on the instantaneous supply of C and N, but also on their remobilisation from vegetative organs. C supply during seed filling depends mostly on current photosynthesis, but N assimilation and N-2 fixation decline during seed filling, with newly acquired N generally insufficient for the high seed demand. As seeds are strong sinks for mobilised nutrients, seed growth becomes metabolically closely associated with N remobilisation. N remobilisation from vegetative tissues to filling seeds interacts with photosynthesis since it induces senescence, which reduces the seed filling period. Hence improved grain legume seed filling requires either reduced dependency on N remobilisation or enhanced N supply. This latter might be obtained either by prolonging the activity of symbiotic fixation, increasing the potential for root assimilation of soil mineral N or optimising complementarity between both N acquisition pathways, which does not affect the quantity and the quality of the seed reserves.