82 



BIOCHEMICAL SYSTEMATICS 



Antiserum against subcotyledonous tissue of seedlings against 

 sera from the following sources: 



subcotyledons 100 



leaf 23.7 



Antiserum against leaf tissue tested against sera from the 

 following sources: 



leaf 100 



subcotyledons 53.4 



cotyledons 8 



There is no question but that there are serological differences 

 among the organs investigated. Kloz et al. stated that the protein 

 characters of cotyledons (reserve proteins) showed weakest cross re- 

 actions between species of different genera, indicating that generic dif- 

 ferences were more pronounced in these organs. These authors 

 presented the hypothesis that the protein characters of the sub- 

 cotyledonous and leaf tissues are phylogenetically older than storage 

 protein of the cotyledons and therefore emphasize the common 

 origin of taxa more than do characters which have undergone 

 differentiation at later stages of evolution. Although the hypothesis is 

 interesting and, if valid, of theoretical importance, it may be an over- 

 simplification. Presumably, in this instance what one is measuring are 

 differences which parallel and reflect the evolution of several genera 

 of a single tribe at a time when the cotyledons had already made 

 their evolutionary appearance. It is therefore possible that in some 

 cases more subsequent specialization appeared in organs such as leaves 

 than appeared in cotyledonous proteins. In any event, the major 

 point, that serological differences exist among different tissues within 

 a plant, should not be obscured by further attention to the second 

 question. 



Wright (1960) has refined, further, investigation of organ 

 specific antigens. By combining ultracentrifugation and immuno- 

 diffusion he was able to demonstrate an antigen in the microsome 

 fraction of three-day old coleoptile tissue of wheat. In order to ex- 

 clude non-microsomal antigens, the antiserum was first absorbed with 

 the supernatant of the microsome fraction. The precipitin band 

 associated with the microsome fraction of three-day coleoptile tissue 

 was absent from coleoptile tissue of a younger age and from root and 

 leaf tissue. These data imply, in the words of the author, "that a non- 

 organ specific meristematic pattern of antigens has superimposed upon 

 it, during differentiation, a combination of proteins characteristic of 

 differentiated cells." 



