S-deficiency responsive accumulation of amino acids is mainly due to hydrolysis of the previously synthesized proteins - not to de novo synthesis in Brassica napus.
To characterize the mechanisms of amino acid accumulation under sulphur (S)-deficiency and its physiological significance in Brassica napus, stable isotopes (15) N and (34) S were employed. The plants were exposed for 9 days to S-deficient conditions (0.05 mM vs 1.5 mM sulphate). After 9 days of S-deficiency, leaf-osmotic potential and total chlorophyll content significantly decreased. S uptake decreased by 94%, whereas N uptake and biomass were not significantly changed. Using (15) N and (34) S labelling, de novo synthesis of amino acids and proteins derived from newly absorbed NO(3)             (-)  and SO(4)             (2)             (-)  and the content of N and S in the previously synthesized amino acids and proteins were quantified. At the whole plant level, S-deficiency increased the pool of amino acids but resulted in strong decrease of incorporation of newly absorbed NO(3)             (-)  and SO(4)             (2)             (-)  into amino acids by 22.2 and 76.6%, respectively, compared to the controls. Total amount of N and S incorporated into proteins also decreased by 28.8 and 62.1%, respectively. The levels of (14) N- and (32) S-proteins (previously synthesized proteins) strongly decreased, mainly in mature leaves. The data thus indicate that amino acid accumulation under short-term S-deficiency results from the degradation of previously synthesized proteins rather than from de novo synthesis.
Department of Animal Science, Institute of Agricultural Science and Technology, College of Agriculture & Life Science, Chonnam National University, Buk-Gwangju, P.O Box 205, Gwangju, 500-600, South Korea.
Bok-Rye
BR
Lee
Sowbiya
S
Muneer
Kil-Yong
KY
Kim
Jean-Christophe
JC
Avice
Alain
A
Ourry
Tae-Hwan
TH
Kim
D000596:Amino Acids / Q000378:metabolism*; D029688:Brassica napus / Q000187:drug effects / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D006868:Hydrolysis; D009566:Nitrates / Q000494:pharmacology; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism; D009587:Nitrogen Isotopes / Q000032:analysis; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000378:metabolism; D013431:Sulfates / Q000494:pharmacology; D013455:Sulfur / Q000032:analysis / Q000172:deficiency* / Q000378:metabolism; D013460:Sulfur Isotopes / Q000032:analysis
D000596:Amino Acids; D009566:Nitrates; D009587:Nitrogen Isotopes; D010940:Plant Proteins; D013431:Sulfates; D013460:Sulfur Isotopes; D002734:Chlorophyll; D013455:Sulfur; D009584:Nitrogen