Evidence for Substrate Induction of a Nitrate Efflux System in Barley Roots.

AUTOR(ES)

Aslam, M.

RESUMO

Induction of an NO3- efflux system in intact barley (Hordeum vulgare L.) roots was demonstrated. Since the measurement of NO3- efflux is dependent on its accumulation, experiments were devised to facilitate accumulation under noninducing conditions. This was accomplished by incubating seedlings in 10 mM NO3- in the presence of RNA and protein synthesis inhibitors. Under these conditions NO3- uptake is mediated by constitutive high- and low-affinity transport systems. Control roots were incubated with 1.0 mM NO3-. This resulted in the accumulation of similar levels of NO3- in both treated and control roots; however, cytoplasmic NO3- efflux from inhibitor-treated roots was much lower than from control roots. Following a brief lag period, efflux rates increased rapidly in the presence of NO3- for 8 to 12 h. The NO3- efflux system was also induced by ambient NO2-. After induction the efflux system was relatively stable in the presence of RNA and protein synthesis inhibitors as long as NO3- or NO2- was present. These results suggest that NO3- efflux may be an inducible system requiring both RNA and protein synthesis, as does induction of the uptake system. The efflux system, however, has a much slower turnover rate than the uptake system.

Documentos Relacionados

• A Soluble Pyridine Nucleotide Oxidase System from Barley Roots. 1
• Substrate Induction of Nitrate Reductase in Barley Aleurone Layers 1
• Active sodium and potassium transport in cells of barley roots.
• Inhibition of Ion Absorption and Respiration in Barley Roots. 12
• Ionic Species in Orthophosphate Absorption by Barley Roots. 1