Malate dehydrogenase in the Fusarial wilt disease of peas

• Published in: Physiological plant pathology Vol. 7; no. 2; pp. 99,IN1,107 - 106,IN2,111
• Main Authors: Reddy, M.N., Stahmann, M.A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.1975
• Subjects: Fusarium oxysporum
• ISSN: 0048-4059
• DOI: 10.1016/0048-4059(75)90001-6

During development of wilt disease in peas caused by Fusarium oxysporum f. sp. pisi race 1, the specific activity of malate dehydrogenase (MDH) of stem tissue, at 12 to 14 days after inoculation, was increased 280% above that of noninfected plants. This increased specific activity in infected plants was accompanied by an appearance of one, new electrophoretically fast moving isozyme which could not be found in the noninfected plants or in the fungus. The new isozyme in infected plants was a cytoplasmic protein and contained about 21% of the total activity. Wilt development in plants was accompanied by a decrease in mitochondrial malate dehydrogenase and an increase in soluble malate dehydrogenase. Partially purified malate dehydrogenase from plant and fungal tissue had an optimum pH at 7·5 for the reduction of oxaloacetate, and for the oxidation of malate the optimum pH was at 9. The binding affinity of the enzyme was increased upon infection; the Michaelis constants for oxaloacetate and NADH of the enzyme from infected plants was about half that of noninfected plants. The MDH had a maximum velocity for the oxaloacetate at 12 and 50 μ m from noninfected and infected plants, respectively; above these concentrations, oxaloacetate became inhibitory. On heating crude extracts at 55 °C, all fungal MDH was destroyed within 5 min, that from noninfected tissue within 22 min, while 40 min were required for the total loss of activity from infected tissue. Heating acrylamide gels after electrophoresis at 50 °C for 180 min inactivated all the isozymes from noninfected plants and fungus, whereas heating up to 320 min did not destroy all the isozymes from the infected plants. Aspartate and glutamate increased the activity of the MDH from plants and fungus. Citrate, isocitrate, succinate, α-ketoglutarate, fumarate, maleate and asparagine caused a partial inhibition of the enzyme from noninfected and infected plants; the same compounds except for succinate and asparagine also showed an inhibitory effect on the fungal enzyme. The alteration of physical and chemical properties of malate dehydrogenase following infection and the possible rôle of this altered enzyme in pathogenesis are discussed.