Effect of auxins and ectomycorrhizal elicitors on wall-bound proteins and enzymes of spruce [Picea abies (L.) Karst.] cells

Summary Elicitors of the ectomycorrhizal fungus Hebeloma crustuliniforme and auxins (IAA, NAA and 2,4-D) were tested for their effects on apoplastic proteins and enzymes of suspension cultured cells of Picea abies (L.) Karst. The ectomycorrhizal elicitor increased the amount of some ionically wall-bound proteins (36, 28, 24, 21 kDa) and decreased the amount of others (61, 22 kDa). The elicitor triggered an H₂O₂ burst and enhanced the peroxidase (EC 1.11.1.7) activity of the Picea cells by increasing one of the two wall-bound peroxidase isoforms. Auxins significantly suppressed the elicitor induction of peroxidase but did not influence the elicitor-triggered H₂O₂ burst. The elicitors and auxin did not change the amount and the pattern of wall-bound invertase isoforms (EC 3.2.1.26) of spruce cells. However, auxin reduced the uptake of glucose by spruce cells and increased the acidification of the cell culture medium. Since Hebeloma lacks apoplastic invertase as well as a sucrose uptake system, utilization of plant-derived sucrose depends on the apoplastic plant invertase activity. Although the host invertase is constitutive, the fungus might be able to increase this invertase activity within a mycorrhiza by lowering the pH of the interface towards the pH optimum of the enzyme via the action of auxin. This fungus-released hormone could increase the H⁺ extrusion of plant cells by activation of the plant membrane H⁺-ATPases. Additionally, an auxin-dependent suppression of glucose uptake by cortical root cells could improve the glucose supply for the fungus. Furthermore, the fungal auxin might suppress the elicitor induced formation of defense enzymes, such as peroxidase.