12 

 synthesis based on observations that they contain large concentrations 

 and many types of gibberellins and the fact that accumulation of gib- 

 berellins is inhibited by growth retardants (Baldev et al . , 1965; 

 Barendse, 1974; Salisbury and Ross, 1978). 



Transport 



Gibberell in-like substances have been isolated from both phloem 

 and xylem (Audus, 1972). Hoad and Bowen (1968) isolated gibberellins in 

 seive tube sap of several species which indicated phloem transport. 

 Exogenously applied GA., follows a distribution pattern within the plant 

 and rate of movement typical of substances moving within the phloem 

 (McComb, 1964; Chin and Lockhart, 1965). Barendse (1974) cited various 

 studies which documented xylem transport of gibberellins in a number of 

 species including sunflower, peas, grapes, birch, maple, apple, and pear. 

 According to Salisbury and Ross (1978), the transport pathway from young 

 leaves into the stem below is uncertain, but does not involve vascular 

 transport because young actively growing leaves import but rarely export 

 through either xylem or phloem. Kato (1958a) conducted translocation 

 studies with pea stems and indicated that gibberellic acid does not show 

 a pattern of polar translocation. CI or (1967) confirmed these findings 

 utilizing tritium-labeled GA.,. However, these experiments utilized 

 concentrations of GA 3 which far exceeded physiological levels and may 

 have affected normal movement of the growth substance (Jacobs and 

 Kaldeway, 1970). Subsequent investigations by Jacobs and Kaldeway 

 (1970) and Jacobs and Pruett (1973) utilizing physiological levels of 

 GA., revealed that GA-, exhibits strong basipetal polar movement in Zea 

 mays roots and Coleus petioles. As with auxins, cortex and pith are 



