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Asian Journal of Agriculture and Development (AJAD) - Call for papers!

Enhancement of Nitrate Reductase in Tomato (Lycopersicon esculentum)

(Vietnam), Doctor of Philosophy (University of the Philippines Los Baños)

Dissertation Abstract:

 

Experiments were conducted on tomato; (1) to optimize the conditions for the in vivo determination of endogenous nitrate reductase activity (NRA, EC 1.6.6.1) and enhanced NRA (by nitrate) and simultaneously explore the possibility of using the ratio of enhanced NRA to endogenous NRA as a new approach for predicting nitrogen requirement, and (2) to investigate the product-enhancible characteristics of this enzyme.

Acceptable concentrations of KNO3 and propanol found for the assay medium were 0.02 M and 1.5 percent, respectively. As enhancing medium, 0.1 M potassium phosphate was significantly better than distilled water, primarily owing to the presence of phosphate ion. The optimum concentration for enhancement was found to be 0.1 M, regardless of nitrogen fertilization levels. Maximum enhanced NRA was obtained from 6 to 12 hours of enhancement (≤ 4°C) for morning sampling, and from 6 hours to overnight for afternoon sampling. The ratio enhanced NRA to endogenous NRA was not affected by sampling time, although their absolute values varied diurnally.

Results of several experiments using optimum conditions for enhancement showed the inability of nitrate to enhance NRA to any considerable extent, regardless of nitrogen fertilization rates; the ratio of enhanced NRA to endogenous NRA never exceeded two. While more conclusive data are necessary, these observations tend to indicate that this new approach may not be applicable to tomato.

Nitrate, as a product of the enzyme, was found to enhance NRA considerably. Studies on the mechanism of enhancement revealed that it was brought about by activation. On so doing, nitrate was speculated to compete with enzyme inhibitions for regulatory site of the enzyme. Cyanide and molybdo-moiety are very possible candidates for such inhibition and binding site, respectively.