Occurrence and expression of acid phosphatase of Hymenoscyphus ericae (Read) Korf & Kernan, in isolation or associated with plant roots

Abstract

Summary. The activity of acid phosphatase produced in pure culture by the endomycorrhizal fungus Hymenoscyphus ericae (Read) Korf & Kernan (H. ericae LPA 2) was inhibited by high phosphorus levels, alkaline pH, fluoride, molybdate and mannosidase, and activated by concanavalin A. Over 80% of the enzyme activity was due to two wall-bound acid phosphatase isozymes with the characteristics of mannose-rich glycoproteins. Antiserum was raised against the major, low-molecularweight wall isozyme and its activity tested by immunoblotting and ELISA. The antiserum cross reacted 100~ with exocellular (excreted) and 28~ with cytoplasmic cellular fractions of H. ericae (LPA 2) cultures, and showed high reactivity with other strains of H. ericae but not with fungal isolates from Erica hispidula L. or E. mauritanica L. Ultrastructural localization of acid phosphatase by cytoenzymology and indirect immunogold labelling confirmed its association with the fungal wall in pure culture and showed that the influence of a high phosphorus level, fluoride and molybdate is through inactivation of the enzyme. Intense acid phosphatase activity, sensitive to the latter inhibitors, was also present on external hyphae growing over a host or non-host root but it was weak or absent from intracellular hyphae where these developed within a host root. Indirect immunolabelling confirmed that this acid phosphatase was of fungal origin and that the specific inhibitory effect of host cells is due to inactivation of the enzyme rather than repression of its synthesis. Possible implications of fungal acid phosphatase in ericoid endomycorrhizal infection processes are discussed together with mechanisms that may be regulating the enzyme activity.

Ericoid mycorrhizal fungi: cellular and molecular bases of their interactions with the host plant

“…Glucose and mannose residues have been identified in situ on the fibrillar sheath by using ConA lectin (Bonfante et al 1987), and the occurrence of these residues has been confirmed by HPLC analysis of extracted material. These observations, together with reports on the presence of immunogenic ) and enzymatic glycoproteins (Straker et al 1989;Lemoine et al 1992), indicate that the cell surface of ericoid fungi is a complex molecular mosaic, which may play important functions during the early stages of interaction with the host plant.…”

Phosphodiesterase as mycorrhizal P sources

“…As established for the monoesterase by Straker & Mitchell (1986) and Lemoine et al (1992) most diesterase activity appears to be associated with the cell wall, since activity of whole mycelium was t>'pically two orders of magnitude higher than that in culture filtrates. Activities of the two enzymes against the pNP-labelled substrates were almost identical for cultures grown on DNA (Figs 5, 8) whereas in the -P cultures the monoesterase was higher than the diesterase for culture filtrate (P < 0-001) and whole mycelium, although in the latter case the difference was not significant (P > fl'O5).…”

“…The pH optimum for the phosphomonoesterase in H. ericae (pH 5-5-6-0) is somewhat higher than for phosphodiesterase, but similar to values reported by other workers. For example, Lemoine (1992) found that in the type isolate of H. ericae, (Read, 1974) the pH optimum of phosphomonoesterase was 4-5, whereas an isolate obtained in France had an optimum of pH 6'0.…”

“…Although there have been many studies of phosphomonoesterases produced by ericoid mycorrhizal fungi, including measures of activity (Pearson & Read, 1975); substrate specificity (Mitchell & Read, 1981;Straker & Mitchell, 1986), kinetics (Straker, 1986); effects of natural and artificial inhibitors (Straker 1986;Shaw & Read, 1989); and immunocytochemicai characterization and localisation of phosphatase (Lemoine et al, 1992), there is no evidence to date of phosphodiesterase activity in ericoid endophytes.…”

Analysis of acid invertase and comparison with acid phosphatase in the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf and Kernan

“…The ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf and Kernan produces high levels of acid phosphatase (Pearson and Read 1975;Straker and Mitchell 1986;Lemoine et al 1992). The enzyme has been localized by both cytochemistry and immunogold labelling in the isolated fungus and in the fungus associated with a host plant, and shown to be a predominantly Correspondence to: C. J. Straker wall-bound and hyphal-surface glycoprotein (Gianinazzi- Lemoine et al 1992).…”