Effect of methionine sulfoximine on nitrogen metabolism and externally supplied ammonium assimilation in kidney bean.

L-Methionine sulfoximine (MSO) at concentration 1.25 mM in vivo causes the inhibition of glutamine synthetase (GS) in both roots and leaves of young seedlings of kidney bean following the accumulation of high levels of ammonia and decrease in amounts of free amino acids that is more pronounced in leaves. The inhibition of GS by MSO in leaves in the case of externally supplied 5 mM (15NH4)2SO4 assimilation leads to ammonia accumulation and the decrease in the amounts of glutamine and glutamic acid and the intensity of the incorporation of 15N into them. In roots the inhibition of GS is not followed by the decrease of 15N content into glutamate. It is concluded that the pathway of ammonia primary assimilation in leaves is via GS and glutamate synthase (GOGAT), while in roots glutamate dehydrogenase also plays an important role in this process.