A specific method of 34S labelling provides evidence that sulphate assimilation occurs in developing seeds and pod walls of Brassica napus L. subjected to ample or limited S nutrition.
BACKGROUND
Seeds from different species actively assimilate sulphur (S) from sulphate. This has never been proved for Brassica napus L., a high S demanding plant, especially with regard to S limitation. The role of pod walls in the assimilation and allocation of S in well-fed and sulphate-limited conditions also needs to be clarified.


METHODS
Freshly harvested seeds and pod walls from plants well-supplied (HS) or limited with sulphate (LS) from the 'visible buds' stage were subjected to a nutrient solution containing (34)S-sulphate (10 atom% excess) for 24 h. The (34)S labelling of the sulphate and protein fractions was determined with an elemental analyser connected to a continuous flow isotope ratio mass spectrometer. The amino acid profiles of seeds and pod walls were also determined by ion-exchange chromatography.


RESULTS
The 24 h of (34)S-sulphate feeding treatment leads to an important production of proteins in HS and LS seeds, associated with a decrease in numerous amino acid contents. The treatment also leads to an incorporation of (34)S in seeds and pod walls proteins in both HS and LS conditions. The incorporation of (34)S in proteins was not different between HS and LS seeds, but was lower in LS than in HS pod walls, related to a higher incorporation in the other organic S compounds.


CONCLUSIONS
This study provides evidence that Brassica napus seeds and pod walls are able to assimilate sulphate in HS and LS conditions, and that the LS condition leads to enhancement of the sulphate assimilation capacity of pod walls, which may be of crucial importance for the allocation of S to developing seeds.
Normandie Univ, France; UCBN, UMR INRA-UCBN 950 Ecophysiologie Végétale, Agronomie & nutritions N.C.S., F-14032, Caen, France; INRA, UMR INRA-UCBN 950 Ecophysiologie Végétale, Agronomie & nutritions N.C.S., F-14032, Caen, France.
Philippe
P
D'Hooghe
Marie-Paule
MP
Bataillé
Jacques
J
Trouverie
Jean-Christophe
JC
Avice
D018533:Biomass; D029688:Brassica napus / Q000737:chemistry / Q000378:metabolism*; D002852:Chromatography, Ion Exchange; D013058:Mass Spectrometry; D010940:Plant Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D012639:Seeds / Q000737:chemistry* / Q000378:metabolism*; D013431:Sulfates / Q000378:metabolism*; D013455:Sulfur / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D013460:Sulfur Isotopes
D010940:Plant Proteins; D013431:Sulfates; D013460:Sulfur Isotopes; D013455:Sulfur