1NOR r, A NIC SOURCES OF NITROGE N 



247 



Day incubation at 30° C 



Figure 4. The effect of nitrogen assimilation on pH in Karlingia (Rhizophlyctis) 

 rosea. Redrawn from Haskins and Weston (227), bv permission of the American 

 Journal of Botany. 



amino acids can be formed from glutamate by transamination (p. 267). 

 Secondary roles in ammonium assimilation may be filled by reactions 

 which incorporate free ammonia into alanine, aspartic acid or gluta- 

 mine. Respiratory breakdown of glucose is obviously necessary to 

 supply the carbon skeleton. 



One of the best established physiological correlates of ammonium 

 assimilation from such salts as the sulfate, nitrate, or chloride is the 

 rapid and often quantitatively large drop in pH consequent upon 

 preferential utilization of the cation. Typical data are shown in Figure 

 4. The generality of this reaction may be emphasized by listing a few 

 of the fungi in which careful observation demonstrates the phenomenon 

 beyond question: 



Alternaria solani (391), Aspergillus niger (496), Chaetomium funi- 

 cola (477), Choanephora cucurbitarum (43), Chytridium sp. (113), 

 Diplocarpon rosae (482), Entomophthora spp. (604), Myrothecium 

 verrucaria (122), Mycosphaerella pinodes (45), Penicillium spp. (119, 

 254), Phymatotrichum omnivorum (520), Piricularia oryzae (406), 

 Psalliota bispora (546), Pythium spp. (459), Polyporus spp. (221), 

 Verticillium spp. (221, 256), Xylaria mali (221). 



In many, if not most, of the instances cited the decrease in pH was 

 sufficient to reduce growth. Practically, several remedies exist: use 



