THE ROLE OF SOURCE-SINK RELATIONSHIPS IN TRANSLOCATION DURING SCLEROTIAL FORMATION BY MORCHELLA-ESCULENTA

Sclerotia formed by Morchella esculenta were developed on square split plates. A trough separated two different media, effecting total separ ation between the sclerotia developing on one side, and the mycelium o n the other. The translocation of two sugars, [C-14]-D-glucose, or its analog, [C-14]-3-O-methyl glucose, placed in the trough, was quantita tively measured during six stages of growth and sclerotial development . During this period, the direction of translocation changed three tim es: during extension of the colony, translocation was toward the hypha l tips of the mycelium; when the mycelium reached the edge of the plat e, reverse translocation was observed, as a result of sclerotial forma tion; at maturation, the direction of translocation reversed again. In control experiments, the use of lanolin on the trough to prevent the wick effect, or ethylene oxide vapour to kill the fungus, showed that translocation to sclerotia was not the result of capillary action. The velocity of translocation was much greater than the utilization of nu trients in the developing sclerotia, probably due to sink strength. Mo st of the radioactivity was lost into the agar medium (up to 80% of th e total radioactivity), rather than accumulating in the fungus. It is suggested that this loss originated from excess nutrients which were n ot converted to insoluble reserve materials. The labelled compounds th at were lost to the medium were later reabsorbed by the mycelium, duri ng the mature stage of sclerotial formation