Does root glutamine synthetase control plant biomass production in Lotus japonicus L.?

To investigate the contribution of root cytosolic glutamine synthetase (GS) activity in plant biomass production, two different approaches were conduc ted using the model legume Lotus japonicus. In the first series of experime nts, it was found that overexpressing GS activity in roots of transgenic pl ants leads to a. decrease in plant biomass production. Using N-15 labelling it was shown that this decrease is likely to be due to a lower nitrate upt ake accompanied by a redistribution to the shoots of the newly absorbed nit rogen which cannot be reduced due to the lack of nitrate reductase activity in this organ. In the second series of experiments, the relationship betwe en plant growth and root GS activity was analysed using a series of recombi nant inbred lines issued from the crossing of two different Lotus ecotypes, Gifu and Funakura. It was confirmed that a negative relationship exists be tween root GS expression and plant biomass production in both the two paren tal lines and their progeny. Statistical analysis allowed it to be estimate d that at least 13% of plant growth variation can be accounted for by varia tion in GS activity.