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Remobilization of leaf S compounds and senescence in response to restricted sulphate supply during the vegetative stage of oilseed rape are affected by mineral N availability

Dubousset, L., Abdallah, M., Desfeux, A.S., Etienne, P., Meuriot, F., Hawkesford, M.J., Gombert, J., Ségura, R., Bataillé, M.P., Rezé, S., Bonnefoy, J., Ameline, A.F., Ourry, A., Dily, F. Le, Avice, J.C.
Journal of experimental botany 2009 v.60 no.11 pp. 3239-3253
Brassica napus var. napus, gene expression, leaves, senescence, shoots, sulfates, sulfur, transporters, vegetative growth
The impact of sulphur limitation on the remobilization of endogenous S compounds during the rosette stage of oilseed rape, and the interactions with N availability on these processes, were examined using a long-term ³⁴SO[Formula: see text] labelling method combined with a study of leaf senescence progression (using SAG12/Cab as a molecular indicator) and gene expression of the transporters, BnSultr4;1 and BnSultr4;2, involved in vacuolar sulphate efflux. After 51 d on hydroponic culture at 0.3 mM ³⁴SO[Formula: see text] (1 atom% excess), the labelling was stopped and plants were subject for 28 d to High S-High N (HS-HN, control), Low S-High N (LS-HN) or Low S-Low N (LS-LN) conditions. Compared with the control, LS-HN plants showed delayed leaf senescence and, whilst the shoot growth and the foliar soluble protein amounts were not affected, S, ³⁴S, and SO[Formula: see text] amounts in the old leaves declined rapidly and were associated with the up-regulation of BnSultr4;1. In LS-LN plants, shoot growth was reduced, leaf senescence was accelerated, and the rapid S mobilization in old leaves was accompanied by decreased ³⁴S and SO[Formula: see text], higher protein mobilization, and up-regulation of BnSultr4;2, but without any change of expression of BnSultr4;1. The data suggest that to sustain the S demand for growth under S restriction (i) vacuolar SO[Formula: see text] is specifically remobilized in LS-HN conditions without any acceleration of leaf senescence, (ii) SO[Formula: see text] mobilization is related to an up-regulation of BnSultr4;1 and/or BnSultr4;2 expression, and (iii) the relationship between sulphate mobilization and up-regulation of expression of BnSultr4 genes is specifically dependent on the N availability.