Rothamsted Symposium on Trace Ele ments 50 



References 



1. Anderson, A. J., Thomas, M. P. and Oertel, A. C, 1946: Plant 

 responses to molybdenvmi as a fertilizer (Coiinc. Sci. Inst. Res. Commonw. 

 Australia Bull. 198). 



2. Arnon, D. I. and Stout, P. R., 1939: Molybdenum as an essen- 

 tial element for higher plants (Plant Physiol. 14:599-602). 



3. BoRTELS, H., 1930: Molybdan als Katalysator bei der biologischen 

 Stickstoffbindung (Arch. Mikrobiol. 1:333-342). 



4. HuDiG, J. and Meyer, C, 1925 and 1926: De ontginningsziekte en 

 haar bestrijding (De Veldbode). 



5. Mulder, E. G., 1938: Over de beteekenis van koper voor de groei 

 van planten en microorganismen (Thesis, Wageningen). 



6. Mulder, E. G., 1948: Importance of molybdenum in the nitrogen 

 metabolism of microorganisms and higher plants (Plant and Soil 1:94-119). 



7. Steinberg, R. A., 1936: Relation of accessory growth substances to 

 heavy metals including molybdenvun, in the nutrition of Aspergillus niger 

 (J. Agr. Research 52:439-448). 



Points from Discussion of Pa^er hy Dr. Mulder 



Prof. Burstrom:— 



1) You have demonstrated a relation between nitrate and 

 molybdenum very convincingly, but in your experiments with 

 Azotohacter you have given the amount of organic nitrogen per 

 culture. I suppose that you have growth responses parallelling the 

 amounts of utilized nitrogen. Why can you not conclude that 

 there is a direct relation between molybdenum and nitrate as- 

 similation? 



2) Have you been able to find nitrite or other presumed inter- 

 mediates in your experiments with or without molybdenum? 



Dr. Mulder:— 



1) The amount of organic nitrogen in the cells of Azotohacter 

 may be used to measure growth. If nitrate is being added, as a 

 source of nitrogen, we observe a direct relation between nitrate 

 assimilation and molybdenum. 



2) No tests for such compounds have been carried out. 



Prof. Arnon:— 



Your results with higher plants suggest that Mo is involved in 

 NO3 reduction whereas those with Azotohacter indicate that Mo 

 is needed for nitrogen fixation. Now if we assume that Azotohac- 

 ter fixes atmospheric nitrogen by reduction i.e. combination with 

 hydrogen rather than oxidation i.e. combination with O2, then it 

 would appear that Mo is not performing the same function in the 

 two classes of organisms. 



