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Titre :
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Modelling of the flows and partitioning of carbon and nitrogen in the holoparasite Cuscuta reflexa Roxb And its host Lupinus albus L .2. Flows between host and parasite and within the parasitized host
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Auteurs :
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W. Jeschke ;
P. Baumel ;
N. Rath ;
F. Czygan ;
P. Proksch
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Type de document :
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article/chapitre/communication
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Année de publication :
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1994
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Format :
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801-812
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Langues:
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= Anglais
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Mots-clés:
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Cuscuta reflexa
;
Lupinus albus
;
parasitism
;
carbon
;
nitrogen
;
phloem
;
xylem
;
transport
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Résumé :
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A recently developed empirically based modelling technique was used to quantify uptake, flow and utilization of C and N in Lupinus albus L., uninfected and parasitized by Cuscuta reflexa Roxb. plants over a 12 d period during flowering and early fruit setting of the host. The modelling combined data on molar C:N ratios in host phloem and pressure-induced xylem sap, net increments of C and N in host and parasite plant parts and respiratory losses of C. The modelling of the solute transfer between host and Cuscuta was achieved by assuming non-specific intake from the xylem. The models predicted that Cuscuta derived 99.5% of its carbon and 93.6% of its nitrogen demand from the host phloem. The overriding sink strength of the parasite diverted most of the basipetally translocated host assimilates and massively competed with the host root and inhibited fruit setting. Carbon incorporation in Cuscuta consumed 56%, respiration 24% and secretion by extrafloral nectaries 1.8% of the ourrent host photosynthate. Root respiration was inhibited by 59% and carbon was mobilized from host root and leaves. Competition by the parasite for N was even more severe and Cuscuta incorporated nitrogen equalling 223% of current fixation, but N-2 fixation of the host was severely restricted to 37%. Withdrawal of N from host phloem led to severe losses of N from leaves and the root and marked decreases in N concentration. It required massive xylem-to-phloem transfer of N, because the xylem as the major supply route for N was not exploited substantially by Cuscuta. The results are discussed in relation to likely causes for parasite-induced pathogenic effects, suggesting that Cuscuta affected the host adversely by depriving it mainly of its nitrogen, but that causal to incipient nitrogen deficiency and restricted N-2 fixation was the superior sink potential of Cuscuta, which prevented adequate supply of assimilates to the nodulated root. The dominating sink potential of Cuscuta is compared with the similarly strong sink competition exerted by fruits at the stage of seed filling in annual plants.
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Source :
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Journal of Experimental Botany - 0022-0957, vol. 45, n° 275
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