1-Aminocyclopropane-1-carboxylate-dependent biosynthesis of ethylene in soils of different texture

Summary1-Aminocyclopropane-1-carboxylic acid (ACC) is an established intermediate in methionine-derived ethylene (C2H4) biosynthesis in plants. This study reports concentration-dependent ACC-derived C2H4 biosynthesis in two differently textured soils (silt clay loam and fine loam). The gas chromatographic analysis showed that addition of up to 10 mmol l−1 ACC significantly stimulated C2H4 biosynthesis in both soils while no C2H4 was detected in sterilized soils amended with a sterilized ACC solution. Kinetic analysis revealed that the ethylene-forming enzyme (EFE)-mediated reaction was more linear in the silt clay loam (R2=0.992) than in the fine loam soil (R2=0.668) when reaction velocity (V) was plotted against substrate concentration [S] that ranged from 2.5 to 10 mmol l−1. Within this range of [S], a first-order reaction was observed. Amendment of soils either with glucose (C source) or NH4NO3 (N source) strongly inhibited ACC-dependent C2H4 production. Maximum C2H4 production in both soils was recorded at a substrate concentration of 10 mmol l−1 when reaction mixture was maintained at a pH of 7.0 and incubated for a period of 120 h at 35 °C while shaking. Among the nine trace elements tested, seven showed a positive effect on ACC-dependent biosynthesis of C2H4 in both soils, while Fe(III) and Ag(I) inhibited the biotransformation of ACC into C2H4. However, three of the five tested electron complexes, added at 1.0 mmol l−1, had inhibitory effects on ACC-derived C2H4 biosynthesis while mannitol and hydroquinone stimulated C2H4 production in both soils. The addition of antibiotics (1.0 mmol l−1) to ACC-amended soils significantly reduced C2H4 production in both soils. Overall, C2H4 production from ACC was greater in the silt clay loam soil than in the fine loam soil. Knowledge of the factors affecting C2H4 biosynthesis in soil could be of great significance since even very low concentrations (ppb) of C2H4 in the root environment are known to affect plant growth dramatically.