86 THE BIOCHEMISTRY OF B VITAMINS 



The relation of pantothenic acid to the growth of green plants has been 

 studied. 38 Aseptically grown alfalfa seedlings were found to respond to 

 pantothenic acid by increased growth, but when the plants had developed 

 for several days, they were assayed and found to contain much more 

 pantothenic acid than could be accounted for other than by synthesis. 

 These experiments, carried out in the author's laboratory, were performed 

 at a time when minute amounts of nearly pure pantothenic acid were 

 available, and there is no reason to doubt the substantial biological purity 

 of the preparations used. The only criticism of the demonstration of 

 pantothenic acid synthesis by green plants was the failure to show at the 

 end of the experiment that molds and other bacteria were entirely absent 

 from the sand cultures. While there was no macroscopic evidence of mold 

 or bacterial growth, the resistance of some spores to autoclaving may 

 introduce a small uncertainty. 



Pyridoxal, Pyridoxamine, Pyridoxine 



Especially because of relatively recent clarification with respect to the 

 chemical nature of the "B 6 group" of vitamins, the available information 

 regarding their biosynthesis is relatively unsatisfactory. Studies involving 

 "vitamin B 6 " have revealed that of the approximately 40 bacteria about 

 which information is available, about one-half are stimulated by or re- 

 quire it, and the other half either are known to synthesize it or have been 

 shown at least not to require it for growth. The five organisms studied by 

 Thompson 5 all produced it. 



Just how the results of such studies would appear if all three forms 

 of the vitamin were taken into account is not entirely clear. It is certain, 

 however, that the three forms are not always interchangeable in nature, 

 since some organisms are unable to convert pyridoxine into the active 

 pyridoxal form, 42 and the form which predominantly exists differs from 

 source to source. Pyridoxine appears to be a relatively inactive storage 

 form which occurs predominantly in metabolically inactive seeds (p. 36) . 



Yeasts, molds and fungi which are able to grow on simple media pro- 

 duce at least one form of the vitamin because assays by a yeast method, 

 which responds to all forms, indicates the universal presence of these, 

 as well as the other B vitamins (p. 60). By x-ray induction a mutant 

 strain of Neurospora crassa was produced early in the investigations of 

 Beadle and Tatum, 43 which is unable to grow unless pyridoxine, pyridoxa- 

 mine or pyridoxal is added to the medium. For this organism the three 

 forms are interchangeable, and the x-ray has destroyed a gene which is 

 essential for the building of any of the forms. 



The same uncertainty exists with respect to the mode of production 

 of the "B G group" during the growth of green plants as exists in connec- 



