ENZYMES OF THE PHENYLPROPANOID PATHWAY IN SOYBEAN INFECTED WITH MELOIDOGYNE-INCOGNITA OR HETERODERA-GLYCINES

Transcription of genes encoding several enzymes and the activity of so me of these enzymes of the phenylpropanoid pathway leading to synthesi s of chemical and physical barriers for defense of plants against root pathogens was estimated in susceptible and resistant soybean infected with Heterodera glycines race 3 or with Meloidogyne incognita race 3. Transcription of genes encoding phenylalanine ammonia lyase (PAL) and the activity of this enzyme increased in resistant, but not susceptib le, soybean cultivars after nematode infection. Likewise, transcriptio n of the gene encoding 4-coumaryl CoA ligase and activity of this enzy me were enhanced in resistant, but not susceptible, soybean cultivars after nematode infection. Activity of PAL decreased in susceptible soy bean after H. glycines or M. incognita infection. Transcription of enz ymes later in the phenylpropanoid pathway leading to glyceollin synthe sis increased in both resistant and susceptible soybean in response to nematode infection; the increase was greater in resistant cultivars. These results suggest possible reasons for the rapid induction of glyc eollin synthesis immediately after infection of resistant soybean cult ivars with H. glycines or M. incognita and the failure of this respons e in infected, susceptible soybean cultivars. Nematode infection had n o effect on the activity of enzymes in the branch of the pathway leadi ng to lignin synthesis.