360 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1940 



A particularly perplexing question has been raised by the report 

 of one group of workers that the carbohydrate requirements of 

 excised tomato roots may be satisfactorily met by either glucose or 

 sucrose, while in another laboratory glucose has been found entirely 

 unsuited for the growth of the same species of roots. 



As has been mentioned, a satisfactory nutrient medium consisted 

 of known substances with the exception of yeast extract which, 

 although it comprised only one-hundredth of 1 percent of the total 

 solution, was nevertheless indispensable. Roots placed in nutrient 

 solution lacking the yeast extract ceased growth within a few days. 

 Since yeast extract contains a great variety of materials the first 

 problem was the identification of the substance or substances 

 responsible. 



In 1937, within the course of a few months, workers in three 

 laboratories announced that the yeast extract could be partially or 

 entirely replaced by vitamin Bi, a substance of which the composi- 

 tion was known and which can be prepared synthetically. Subse- 

 quent investigation has indicated that vitamin Bj, or thiamin, alone 

 is not an adequate substitute for the yeast extract and that maximal 

 growth can be obtained only when additional materials are supplied. 

 Since there is not, as yet, complete agreement as to the nature of 

 these additional factors a tabulation of the findings of the labora- 

 tories which have contributed the bulk of our information on the 

 nutrition of excised roots is instructive. 



Bonner 



Robbins 



White 



February 1937: Vitamin Bi com- 

 pletely replaces and is superior to 

 yeast extract for pea roots. 



September 1037: Vitamin Bi alone 

 only partially replaces yeast ex- 

 tract for pea roots. A mixture of 

 16 amino acids is capable of sub- 

 stittitinp for that portion of the 

 yeast extract activity which is not 

 due to vitamin Bi. The mixture 

 of vitamin Ri plus amino acids is 

 equal or superior to yeast extract. 



December 1938: Thiamin plus am- 

 ino acids is not a complete sub- 

 stitute for yeast extract. Nico- 

 tinic acid Is also an essential 

 growth factor for pea roots. The 

 amino acids are not essential. 



October 1939: Pea roots ^row better 

 whnn supplied with thiamin plus 

 nicotinic acid thsn in yeast ex- 

 tract. Radish roots also require 

 vitamin Bi and nicotinic acid. 

 Flax roots require viatmin Bj but 

 not nicotinic acid. Growth of 

 tomato roots continues indefi- 

 nitely If the yeast extract is re- 

 placed by vitamin Bi plus vita- 

 min Bs but the rate is inorea.sed if 

 nicotinic acid also Is furnished. 



March 1937: Yeast extract may 

 bo partially replaced by vita- 

 min Bi for tomato roots. 

 Growth is improved by the 

 addition of supplementary 

 mineral elements but is still 

 less than in yeast extract. 



July 1937: The entire thiamin 

 molecule need not be fur- 

 nished. Equal or better 

 growth of tomato roots is ob- 

 tained by supplying the thi- 

 Bzole portion of the vitamin Bi 

 molecule. 



January 1939: Addition of nico- 

 tinic acid or an amino acid 

 mixture is of no benefit to 

 tomato Toots supplied with 

 thiamin. Addition of vitamin 

 B( increases the growth sev- 

 eral-fold. 



March 1939: Growth of tomato 

 roots supplied with thiamin 

 plus vitamin Bj is several 

 times as great as in yeast ox- 

 tract. In the presence of vita- 

 min B« the appearance of the 

 roots is abnormal. Evidence 

 of the occurrence, in various 

 sugars, of an additional, as yet 

 unidentified, growth factor 

 has been obtained. 



July 1937: Two fractions, active 

 in the growth of tomato roots, 

 can be separated from yeast. 

 One of these can be replaced by 

 a mixture of 9 amino acids; the 

 other fraction can be replaced 

 by vitamin Bi provided that a 

 mixture of 12 supplementary 

 inorganic salts is also supplied. 

 Yeast extract is not equaled, 

 however, even by the vitamin 

 Bi plus the amino acids plus the 

 accessory salts. 



April 1938: Reduction of the num- 

 ber of accessory inorganic com- 

 pounds to four (supplying man- 

 ganese, boron, zinc, and iodine) 

 in a medium containing thiamin 

 and the 9 amino acids gives 

 growth of tomato roots nearly 

 equal to that in yeast extract 



July 1939: No single one of the 9 

 amino acids is indispensable for 

 tomato roots and the entire 

 mixture may be replaced by 

 glycine which is structurally the 

 most simple of the amino acids. 

 For sunflower roots the thiamin 

 plus glycine medium is far 

 superior to yeast extract whereas 

 clover roots grow very poorly 

 in It. 



