Effect of photorespiratory metabolites, inhibitors and methionine sulphoximine on the accumulation of ammonia in the leaves of mung bean and Amaranthus

Abstract

The free ammonia (NH₃) level, and its accumulation in the presence of methionine sulphoximine (MSO) were investigated in the leaves of a C₃ (Vigna radiata) and a C₄ (Amaranthus edulis) plant, both in the presence and absence of photorespiratory inhibitors, isonicotinyl hydrazide (INH) or α-hydroxypyridine methane sulphonate (α-HPMS) as well as when fed with photorespiratory intermediates, glycolate or glycine. The endogenous level of free NH₃ was slightly greater in the C₄ than in the C₃ plant in control treatments but when NH₃ assimilation was blocked with MSO, the difference was reversed. The inhibition of MSO-induced accumulation of NH₃ by INH and α-HPMS was four times more effective in Vigna (C₃) than in Amaranthus (C₄). Glycine feeding enhanced the NH₃ accumulation with MSO and the enhancement was similar in both C₃ and C₄ plants. However, NH₃ accumulation with MSO and glycolate feeding was more in the C₃ than in the C₄ plant. The increase in MSO-induced NH₃ accumulation on glycine or glycolate feeding were inhibited ny INH or α-HPMS, respectively.