10 

 their studies, Peck et al . (1957) stated that gibberellic acid presents 

 no apparent hazard either to the individual who uses the material for 

 agricultural purposes or to the individual who consumes products on 

 which gibberellic acid or its salts have been used. 



Biosynthesis and Metabolism 



Much of the information available to date on gibberellin biosyntheis 

 has come from studies utilizing cultures of Gibberella fujikuroi (Saw.) 

 Wr. Barendse (1974) noted that although the pathway of biosynthesis in 

 higher plants is less well known, studies involving higher plants 

 suggest that the pathway follows the same scheme as found in Gibberella 

 fujikuroi . Birch et al . (1958) confirmed the fact that GA^ has a 

 di terpenoid nature by feeding radioactive-labelled acetate or mevalonate to 

 cultures of Gibberella fujikuroi . By examining relative amounts and 

 positions of the label, they were able to suggest a biosynthesis pathway 

 which was later confirmed (Salisbury and Ross, 1978). 



The basic pathway of biosynthesis of gibberellic acid described by 

 Birch et al . (1958), Barendse (1974), and Salisbury and Ross (1978) 

 results in the following sequence of compounds: acetyl coenzyme A; 

 mevalonic acid; isopentenyl pyrophosphate; geranylgeranyl pyrophosphate, 

 a 20-carbon compound which serves as the donor for all gibberellin car- 

 bon atoms (Salisbury and Ross, 1978); copalyl pyrophosphate; kaurene; 

 kaurenol ; kaurenal ; kaurenoic acid; and GA,~ aldehyde which is the first 

 true gibberellane ring system. This aldehyde of GA^ is converted 

 either directly to other gibberellins or to GA^, a 19-carbon compound, 

 which is interconverted to other gibberellins (Barendse, 1974; Salisbury 

 and Ross, 1978). 



