An osmotic agent, -0.9 MPa D-Mannitol, imitating drought stress in mungbean roots, was used to investigate the relationship between redox system in plant. plasma membrane and elongation growth under drought stress. Results showed that -0.9 Mpa D-Mannitol significantly similarly inhibited the elongation, H+ extrusion and NADH oxidative activity in the growing zone of mungbean hypocotyl. Within 24 hours, they were reduced by D-Mannitol up to 49.1%, 44.1% and 49.2%, respectively. 1.0cm long hypocotyl segments from the seedlings grown in DI water (control) were floated for 12h in the dark at room temperature in 4 solutions respectively: CK0 (pH7.0 buffer only), N(+ 0.2 mmol(.)L(-1)NADH), D(+0.02 mmol(.)L(-1) Actinomycin D) and ND(NADH + Actinomycin D); The hypocotyl segments from the seedlings grown in -0.9 MPa D-Mannitol (treatment for 24h) were floated for 12h in other 4 solutions correspondingly, and all 4 contained -0.9 MPa a Mannitol in pH7.0 buffer. Then the length of hypocotyls and pH of solution were assayed. Actinomycin D, the specific inhibitor of NADH oxidase, could inhibit growth of isolated hypocotyl by 41.2% (control) and 31.8% (treatment) respectively. Applied NADH could enhance their growth up to 27.8% (control) and 14.2% (treatment) respectively, but such effect could be counteracted by actinomycin D. Under drought stress, H+ extrusion rate were reduced 34.4% by Actinomycin D. Applied NADH could enhance H+ extrusion to 20% (control) and 14% (treatment), respectively. Under drought stress, inhibited elongation growth of mungbean hypocotyls may relate to the NADH oxidase in the PM redox system, with the regulation role being carried out through H+ extrusion.
