Activity of nitrogen assimilation enzymes in soybean seedlings infected with hemibiotrophic fungi

Abstract

The purpose of this research was to compare how soybean seedlings (Glycine max L., cultivar Bečejka) cope with different nutrition acquisition strategies of hemibiotrophic fungi: Rhizoctonia solani Kühn and Sclerotinia sclerotiorum (Lib.) de Bary. Severe changes at morphological and histological level after inoculation with both fungi were accompanied by significant changes in nitrogen assimilation enzymes activities in leaves and roots of 21-day-old soybean plants. Infected seedlings had decreased nitrate reductase (NR) (2-fold the amount of control, on average) and glutamate synthase (GS) activity (40-60%), except in leaves infected with S. sclerotiorum. Glutamate dehydrogenase (GDH) activity increased 46-75% after the pathogen infection, being highest during R. solani infection. High GDH values in infected organs (0.26-0.47 μmol NADH mg-1 protein) point to enhanced nitrogen remobilization process from infected tissue, possibly to restrict available nutrients to pathogens, among other things beneficial to plant. Differences in GS and GDH activities in the same organs depending on pathogen infection showed that plants cope differently with these fungi at this stage of development, or that time of switching from bio- to necrotrophic lifestyle differs between investigated pathogens. Due to adaptable lifestyle of hemibiotrophic fungi, mechanistic details that allow pathogen to control host metabolic pathways are unknown, and for this reason the understanding of plant nutrient acquisition could be of great importance in the development of novel disease control strategies.