Ahmad Iftikhar, Carleton Terry J, Malloch David W, Hellebust Johan A
Department of Botany, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada M5S 3B2.
New Phytol. 1990 Nov;116(3):431-441. doi: 10.1111/j.1469-8137.1990.tb00529.x.
Blended colonies of the ectomycorrhizal fungus, Laccaria bicolor (R. Mre.) Orton, grew axenically as a suspension of fine hyphae in a defined buffered medium with glucose (doubling time 1-2 d) but not acetate as the carbon source, and either ammonium or nitrate as nitrogen sources. A number of amino acids were found to be excellent nitrogen sources for this basidiomycete, but were less effective as sources of carbon. During post-exponential growth in medium containing inorganic nitrogen, the fungal symbiont released amino acids. L. bicolor has the enzymatic potential to assimilate ammonium by the activities of glutamine synthetase, NADH-glutamate dehydrogenase and NADPH-glutamate dehydrogenase. It also contains highly active aspartate and alanine aminotransferases. The activities of glutamine synthetase, NADPH-glutamate dehydrogenase and aspartate aminotransferase were greater in the presence of nitrate than in the presence of ammonium and declined as the culture aged, suggesting a biosynthetic role for these enzymes. In contrast, the activities of NADH-glutamate dehydrogenase and alanine aminotransferase increased during post-exponential growth, and also in cultures growing on amino acids as a carbon source, suggesting a catabolic role for these enzymes.
外生菌根真菌双色蜡蘑（Laccaria bicolor (R. Mre.) Orton）的混合菌落，在含有葡萄糖的特定缓冲培养基中作为细菌丝悬浮液无菌生长（倍增时间为1 - 2天），但不能以乙酸盐作为碳源，可使用铵盐或硝酸盐作为氮源。已发现多种氨基酸是这种担子菌的优质氮源，但作为碳源的效果较差。在含有无机氮的培养基中指数生长后期，真菌共生体释放氨基酸。双色蜡蘑具有通过谷氨酰胺合成酶、NADH - 谷氨酸脱氢酶和NADPH - 谷氨酸脱氢酶的活性来同化铵的酶促潜力。它还含有高活性的天冬氨酸和丙氨酸转氨酶。在硝酸盐存在下，谷氨酰胺合成酶、NADPH - 谷氨酸脱氢酶和天冬氨酸转氨酶的活性高于铵盐存在时，且随着培养时间延长而下降，表明这些酶具有生物合成作用。相比之下，NADH - 谷氨酸脱氢酶和丙氨酸转氨酶的活性在指数生长后期以及以氨基酸作为碳源生长的培养物中增加，表明这些酶具有分解代谢作用。
