Abscisic Acid Stimulation of Nitrate Reductase Activity in Potato Tuber Slices: Effect of Inhibitors of Protein and Nucleic Acid Synthesis

摘要

Pretreatment of potato tuber slices with ABA for 22 hr, in the absence of exogenous NO3resulted in stimulation of nitrate reductase activity (NRA) and increase in endogenous NO3content. The increased tissue NO3level suggests the conversion of organic nitrogen to NO3. Upon transferring slices to 25 mM KNO3there was a marked stimulation of NRA and NO3accumulation.Addition of cycloheximide (CHM) at the start of ABA pretreatment abolished the NRA response but stimulated NO3accumulation. Actinomycin D (ACTD) pretreatment stimulated NRA and maintained a high level of activity throughout the incubation period. In combination with ABA ACTD suppressed the ABA response during the first 10 hr of incubation after which there was a slight increase.With fresh unpretreated slices CHM alone and in combination with ABA suppressed NRA throughout the incubation period while ACTD slightly reduced activity during the first 10 hr before stimulating it. Combined pretreatment with ABA and ACTD elicited the greatest stimulation of NRA.Abscisic acid stimulated NRA only after 24 hr but significantly enhanced tissue NO3accumulation which was suppressed by CHM alone and in combination with ABA but not affected by the other treatments.These results suggest that the ABA response requires protein synthesis but may be independent of RNA transcription. These findings support the view that mRNA for nitrate reductase translation is stable in some tissues. Both ABA and ACTD probably enhanced NRA by suppressing the production of inhibitory substances thereby reducing normal fluctuations in enzyme activity.