18 



(c) Some of the saccharides are converted to storage carbohydrates 

 (starches and fructans); others are utilized in respiratory metabolism 

 or enter metabolic pathways leading to synthesis of cellular components. 



(d) Respiratory cellular energy (ATP) is used by endergonic processes 

 such as active transport and synthetic pathways. 



(e) Cell wall components and properties are adjusted in order to 

 allow for cellular growth. 



(f) Protein synthesis is stimulated in order to allow for growth. 

 Many of these proteins are specific enzymes needed for catalyzation of 

 growth metabolism. 



(g) The asterisks in Figure 1 represent possible control points at 

 which gibberellins are thought to regulate key metabolic pathways. 



The above discussion indicates that most workers have concentrated 

 on metabolic pathways to explain gibberellin actions. An increasingly 

 popular explanation is in terms of alterations of membrane permeability 

 (Rappaport, 1980). Wood and Paleg (1972) were the first to clearly 

 demonstrate that gibberellic acid can influence the permeability of 

 model membranes. Wood and Paleg (1972) proposed that effects on sub- 

 cellular membrane permeability were due a biophysical alteration of one 

 or more of the membrane components through some sort of bond formation. 

 Involvement of endoplasmic reticulum and increased enzyme synthesis 

 was summarized by Mann (1974) and further confirmed with electron 

 microscopy by Pyliotis et al . (1979). However, as noted by Kaufman 

 (1974), no one mechanism has been ell uci dated for gibberellins and 

 regulatory sites of this hormone appear to occur at several points in 

 plant growth metabolism. 



