Studies of the effects of nitrate on the 14C partitioning between tissues of P. erosus showed that, whereas in control plants the major photosynthate sinks were the shoot apices, root nodules and tubers, in plants given 20 msmallcap˜M KNO3, 14C accumulated in leaf proteins and starch and less was partitioned to tubers or root nodules. A large decline in nodule total radioactivity due to a 3-fold reduction in nodule wt in response to nitrate was accompanied by only a 36% decline in specific radioactivity (radioactivity/g FW) of nodules. In addition tuber wt/plant declined by 51% whereas the tuber specific activity was unaffected. The negative effect of nitrate on nodules and tubers was consistent with the carbohydrate-deprivation hypothesis as a main cause of the nitrate inhibition of tuberous legume nodules.