13 

 believed to be involved. Thus, the evidence indicates that gibbe renins 

 and their conjugates are readily transported in the entire conductive 

 system of plants; however, the physiological significance of this 

 transport has not been determined (Barendse, 1974). 



Mode of Action 



The literature contains numerous reviews of the physiological, 

 morphological, and biochemical mechanisms of action of gibberellins. 

 Addicott (1970) stated that gibberellic acid has probably been tested 

 more widely for its effects on higher plants than any other naturally 

 occurring substance. However, contradictory results were frequently 

 obtained from seemingly similar experiments. Addicott (1970) and Low 

 (1974) explain the differing results in terms of physiological con- 

 ditions of the experimental material, i.e., age, size, nutrient and 

 light availability, temperature, species, and type of tissue studied. 

 All of these factors have been shown to alter the level of other endoge- 

 nous hormones in the experimental tissues and thus change the plant's 

 sensitivity to the exogenous gibberellic acid (Low, 1974). As an 

 example, Goya! and Baijal (1980a and 1980b) reported different responses 

 between varieties of the same species of rice. The following discussion 

 of the mode of action of gibberellic acid presents the most commonly 

 accepted responses. 



Typical morphological effects of sensitive species to gib- 

 berellin treatments include germination of dormant seeds (Stuart and 

 Cathey, 1961; Chen, 1974), growth of dormant buds (Shafer and Monson, 

 1958), stimulation of flowering and inflorescence size (Stowe and 

 Yamaki , 1957; Stuart and Cathey, 1961; Weaver, 1972, Krishnamoorthy, 



