11 



Once formed, gibberellins can be readily converted to bound 

 inactive forms in which they are stored or translocated for release at 

 the proper location and physiological time (Lang, 1970; Barendse, 1974; 

 Salisbury and Ross, 1978). Glucosides are the most prominent known 

 bound form of gibberellin (Barendse, 1974; Salisbury and Ross, 1978). 

 Salisbury and Ross (1978) indicate that other unidentified bound forms 

 are also known to exist, some of which appear to be stable protein- 

 gibberellin conjugates. 



Sites of Synthesis 



Major sites of gibberellin synthesis are developing seeds, apical 

 buds, young leaves, and root tips (Barendse, 1974; Salisbury and Ross, 

 1978). Lockhart (1957) implicated the shoot tip as the site of gib- 

 berellin synthesis by restoring growth in decapitated pea seedlings by 

 applying GA 3> The diffusion technique of Jones and Phillips (1964) 

 later confirmed these results and also identified root tips as sites of 

 synthesis. The diffusion technique is based on the following principle: 

 if the amounts of diffusible gibberellins obtained in an agar block over 

 a period of time exceeds the amounts of extractable gibberellins in the 

 same organ, active biosynthesis or conversion occurs in the organ. 

 Barendse (1974) reviewed the role of plant roots in gibberellin synthe- 

 sis and reported that root tips were the site of conversion of inactive 

 forms of gibberellin synthesized in apical buds to more active forms. 

 Salisbury and Ross (1978) stated that repeated excision of parts of the 

 root system markedly reduced the amount of gibberellin in plant 

 foliage which may partially explain why root pruning inhibits shoot 

 growth. Developing seeds are generally considered to be sites of 



