68 



THE FLOWERING PROCESS 



flowering, even though respiration is known to be part of the 

 flowering process. In spite of such complications, careful use of 

 anti-metabolites might yield valuable information about the bio- 

 chemistry of flowering. 



3. Reversal of Antimetabolite Inhibition by a Metabolite 



Based upon these principles, we can choose compounds to test 

 in the flowering process (in the manner described in Chapter 5 — 



I 2 3 4 5 6 



CONCENTRATION OF METABOLITES 



7 8 



(xlO~-M) 



Figure 9-9 



Effects upon flowering of an anti-metabolite (5-fluorouracil — 5-FU) 

 applied in the presence of increasing concentrations of metabolite (uracil, 

 thymidine, or orotic acid), as compared to effects of the metabolite 

 applied alone. The metabolites alone have no significant effect, and 

 only the orotic acid overcomes the inhibitory effects of 5-FU. Data 

 from Frank Salisbury and James Bonner, 1960, Plant Physiol. 35, 



173-177. 



see Fig. 5-7). We can use anti-metabolites and any other substances 

 known to influence the plant's biochemistry, such as growth regu- 

 lators or even inorganic compounds such as cobaltous ion. But 

 how can we know what biochemical step is being influenced ? With 



