THE BIOLOGY OF MYCORRHIZA IN THE ERICACEAE: X. THE UTILIZATION OF PROTEINS AND THE PRODUCTION OF PROTEOLYTIC ENZYMES BY THE MYCORRHIZAL ENDOPHYTE AND BY MYCORRHIZAL PLANTS.

The ability of the ericoid mycorrhizal endophyte to utilize a range of proteins as substrates for growth is assessed in liquid culture and in mycorrhizal association with host plants. Some aspects of proteolytic enzyme production are also investigated. The fungus readily utilizes the soluble protein bovine serum albumin (BSA) as sole nitrogen and carbon source, and produces lower yields on less soluble plant and animal proteins. Maximum yields of endophyte on all substrates were obtained in the pH range 3 to 5. Infection provides a significant enhancement of plant growth on agar over this pH range on most of the proteins. Yields and nitrogen contents of mycorrhizal plants grown on cellulose sheets with BSA as sole N source were significantly higher than those of the uninfected controls, which were unable to use protein. Using a chromogenic substrate it was shown that the pH optimum for enzyme activity is comparable with that for utilization of protein in pure culture and in mycorrhizal association. Non-mycorrhizal plants produced negligible proteolytic activity. The significance of these observations is discussed in relation to the nutrition of both host and fungus in the natural environment, and the broader ecological implications of the results are assessed.