SUMMARYThe protein content of seeds determines their nutritive value, downstream processing properties and market value. Up to 95% of seed protein is derived from amino acids that are exported to the seed after degradation of existing protein in leaves, but the pathways responsible for this nitrogen metabolism are poorly defined. The enzyme pyruvate,orthophosphate dikinase (PPDK) interconverts pyruvate and phosphoenolpyruvate, and is found in both plastids and the cytosol in plants. PPDK plays a cardinal role in C 4 photosynthesis, but its role in the leaves of C 3 species has remained unclear. We demonstrate that both the cytosolic and chloroplastic isoforms of PPDK are up-regulated in naturally senescing leaves. Cytosolic PPDK accumulates preferentially in the veins, while chloroplastic PPDK also accumulates in mesophyll cells. Analysis of microarrays and labelling patterns after feeding 13 C-labelled pyruvate indicated that PPDK functions in a pathway that generates the transport amino acid glutamine, which is then loaded into the phloem. In Arabidopsis thaliana, overexpression of PPDK during senescence can significantly accelerate nitrogen remobilization from leaves, and thereby increase rosette growth rate and the weight and nitrogen content of seeds. This indicates an important role for cytosolic PPDK in the leaves of C 3 plants, and allows us to propose a metabolic pathway that is responsible for production of transport amino acids during natural leaf senescence. Given that increased seed size and nitrogen content are desirable agronomic traits, and that efficient remobilization of nitrogen within the plant reduces the demand for fertiliser applications, PPDK and the pathway in which it operates are targets for crop improvement.

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Summary: Résumé: Zusammenfassung A putative graminicide‐resistant biotype of E. indica (L.) Gaertn. and a wild (graminicide sus ceptible) biotype were compared with regard to their growth, development and resistance to ary‐loxyphenoxypropionate and cyclohexanedione herbicides in controlled environment studies. The resistant biotype produced much lower amounts of shoot biomass (46% less) but flow ered earlier and allocated a higher proportion and amount of biomass into seed‐bearing struc tures compared with the wild type. The resistant biotype survived the application of 50 g a.i. ha−1 of clethodim, tralkoxydim, sethoxydim, fluazi‐fop‐butyl, fenoxaprop‐ethyl and diclofop methyl with the greatest resistance being shown to the aryloxyphenoxypropionates. At rates of >1000 g a.i. ha−1, tralkoxydim achieved superior con trol to that of fluazifop‐butyl. Even at rates of 4000 g a.i. ha−1, some 50% of the resistant test plants survived the application of fluazifop‐bu‐tyl. The trait for graminicide resistance did not appear to be strongly heritable, as assessed by the growth and survival of a graminicide‐treated F1 population grown in isolation. It is concluded that widespread graminicide resistance in E. in dica is unlikely to develop from this biotype. Études comparatives de biotypes d'Eleusine indicata résistant et sensible aux herbicides à action antigraminée Un biotype d'Eleusine indica (L.) Gaertn., supposé résistant aux herbicides à action antigraminée, a été comparé en conditions contrôlées à un biotype sauvage (sensible) en ce qui concerne la croissance, le développement et la résistance aux herbicides aryoxyphénoxypropioniques et cyclohexanediones. Le biotype résistant produisait beaucoup moins de biomasse aérienne (‐46%) mais fleurissait plus tôt et attribuait aux structures porteuses de graines une proportion et une quantité plus importantes de biomasse. Le biotype résistant survivait à un traitement à la dose 50 g ha−1 de clethodime, de tralkoxydime, de séthoxydime, de fluazifop‐butyle. de fénoxaprop‐éthyle et de diclofop‐méthyle, la plus grande résistance se manifestant à l'égard des aryloxyphénoxypropioniques. à des doses >1000 g m.a. ha−1, le tralkoxydime était plus efficace que le fluazifop‐butyle. Même à des doses 4000 g m.a. ha−1, environ 50% des plantes résistantes survivaient à un traitement au fluazifop‐butyle. Le caractère conférant la résistance aux herbicides à action antigraminée n'a pas montré de forte héritabilité, celle‐ci étant estimée par la croissance et la survie d'une population F1 traitée aux herbicides à action antigraminée et cultivée en isolement. En conclusion, il est peu probable qu'une résistance aux herbicides à action antigraminée se répande chez E. indicaà partir de ce biotype. Untersuchungen an Graminizid‐resistenten und ‐toleranten Biotypen von Eleusine indica An einem wahrscheinlich Graminizid‐resistenten und einem toleranten Biotyp von Eleusine indica (L.) Gaertn. wurden Wachstum, Entwicklung und Empfindlichkeit gegenüber Aryloxyphenoxypropionat‐ und Cyclohexandion‐Her‐bizi...

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