Glutamate Dehydrogenase Isomerization: A Simple Method for Diagnosing Nitrogen, Phosphorus, and Potassium Sufficiency in Maize (Zea mays L.)

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Journal of Agricultural and Food Chemistry


Improved nutrient-use efficiency in cropping systems is needed to increase farm income and to minimize possible nutrient emission to the environment. Plant glutamate dehydrogenase (GDH) offers a means for improved diagnosis of the nutrient status of crops. Zea mays L. DK-68 was fertilized with nutrient solutions containing different ratios of nitrogen, phosphorus, and potassium (N, P, K). Maize shoot GDH was fractionated to its population of isoenzyme by Rotoforation followed with native PAGE. The GDH of the control maize had the complete set of 28 isoenzymes. Fertilization of the maize with N1P1K1 did not repress the 14 anodal but did repress the 14 cathodal isoenzymes. As the P content of the fertilizer increased in the sequence N0P0K0, N1P0K1, N0P1K0, N1P1K1, N0P2K0, and N0P4K0, the amination maximum velocity (Vmax) of the enzyme decreased curvilinearly in the sequence 310, 246, 140, 130, 108, and 83 μmol min-1 mg-1, respectively. The highest dry matter yield occurred when the fertilizer contained 1-3 mM Pi, which was thus the nutrient deficiency-sufficiency interphase. In the GDH integration of the signals from the N, P, and K so as to respond with a characteristic isoenzyme population pattern, the signal from N superseded that from K; in turn, the signal from P superseded those from N and K. Signal integration was therefore based on the dominance by the most nucleophilic nutrient. In this case, the decreasing order of nucleophilic dominance was PO43- > NH4+ > K+.

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