Changes in protein biosynthesis during the differentiation ofPisolithus–Eucalyptus grandisectomycorrhiza

Abstract

Protein biosynthesis in Pisolithus – Eucalyptus grandis ectomycorrhiza was related to the stage of ectomycorrhizal development using two-dimensional polyacrylamide gel electrophoresis of proteins labelled by in vivo incorporation of35S radiolabelled amino acids. Nineteen-day-old seedlings were radiolabelled and the primary root was divided into 1-cm segments. With increasing distance from the tip of the primary root, the lateral roots developed as follows: segment 1, no lateral tips; segment 2, three lateral tips, 1–4 days old; segment 3, five lateral tips, 3–8 days old; segment 4, five lateral tips, 7–12 days old. Six-day-old ectomycorrhizas were fully formed with a mantle and Hartig net. During ectomycorrhizal development, there was a decrease in all plant proteins and differential accumulation of fungal proteins. The apical segment of the primary root had a biosynthesis profile very similar to that of noninoculated roots. By contrast, the other segments of the primary root, with attached lateral roots, had biosynthesis profiles that were similar to those of the free-living hyphae. Thus, plant biosynthesis was shown to be predominantly associated with the primary root meristem. The domination of the fungal partner in the protein biosynthesis of developing ectomycorrhiza is probably a consequence of stimulated fungal growth and the corresponding decrease in plant meristematic activity. Ectomycorrhizal development was associated with a differential accumulation of fungal polypeptides and the appearance of a group of symbiosis-related acid fungal polypeptides between 27 and 37 kDa. As the polypeptides were present in a similar magnitude throughout ectomycorrhizal development (lateral tips 1–12 days old), it is suggested that they function as structural proteins associated with mantle formation. Keywords: ectomycorrhizal development, Eucalyptus, Pisolithus, protein biosynthesis, symbiosis-related polypeptides.