Responses of the fructose-1,6-bisphosphatase and glutamate dehydrogenase activities of alfalfa to boron, gypsum, and limestone amendments of soil

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Plants cultivated on acid soils that contain toxic levels of Al 3+ usually produce low yields. A multi-factorial treatment of gypsum (G), boron (B), and limestone (Lm) was applied to such soil in order to determine the biochemical basis of the best management plan for ameliorating the soil acidity for sustainable growth of alfalfa. The alfalfa shoots were subjected to analysis for hexose, protein, nucleotide, and chlorophyll (Chl) contents, fructose 1,6-bisphosphatase (FBPase) activity, and the RNA synthetic activity of glutamate dehydrogenase (GDH). Hexose and protein contents of control alfalfa without B and G, but with Lm (672 g m -2) amendment were 0.87 and 38.30 g, respectively, per kg shoot. Increasing the G doses at fixed moderate doses of 0.15 and 0.30 g m -2 B decreased the FBPase activity by ∼53 and ∼31 %, respectively. However, increasing the B doses at higher fixed G (1 kg m -2 = G 1.0) increased the FBPase activity by ∼91 % thus indicating that G 1 optimized the saccharide metabolism by neutralizing the soil acidity. In the absence of B, increasing the G doses also maximized the hexose and Chl contents, but minimized the nucleotide amount. In the absence of G, increasing the B doses maximized the RNA synthetic activity of GDH, but lowered the hexose and Chl contents as well as the FBPase activity without affecting the protein contents, thereby permitting the selection of B (0.45 g m -2) with Lm as the best amendment for the sustainable growth of alfalfa. Treatment with 0.45 g B and 0.5 kg G (= G 0.5) induced the strongest B-Ca antagonism by maximizing the hexose and Chl contents but severely suppressing the FBPase activity and the RNA synthetic activity of GDH. Therefore, the coordinate optimization of saccharide metabolism through the G-dependent neutralization of soil acidity, and of RNA metabolism through the B-dependent detoxification of Al 3+ are the biochemical options for the mitigation of the adverse effects of soil acidity for the optimization of sustainable alfalfa production.

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