Effects of altered source–sink relationships on N allocation and vegetative storage protein accumulation in Brassica napus L.

Abstract

Growth, N allocation and involvement of vegetative storage protein (VSP) in the temporary N accumulation were evaluated in field conditions of oilseed rape grown with altered source–sink relationships (by leaf halving or removal of stem, flowers or pods). As compared to control plants, removal of half the leaves early in the vegetative period-induced delayed flowering, a lower accumulation of the taproot 23 kDa VSP and finally a decreased pod production. Stem removal, when flower buds were still covered by leaves, increased taproot biomass and its N concentration but prevented taproot VSP accumulation. Continuous removal of flowers or pods increased the shoot growth and N uptake duration (for deflowered plants). When foliar senescence finally occurred in plants continuously subjected to flower or pod removal, the N was allocated in a large proportion to buffering organs (taproot and stem) and it led to an increased and late VSP accumulation without subsequent mobilization. In control plants, N stored as VSP was remobilized during late pod filling concomitant with stem and taproot sink to source transition. A summarized scheme of N source–sink relationships during the growth cycle is presented where the 23 kDa VSP may act as an N storage buffer in response to an asynchronism between mobilization of foliar N and N requirements for seed formation.