Stimulation of Respiration in Relation to Growth 



GEORGE S. AVERY, JR. 



THE widespread natural occurrence of plant growth substances is 

 one of the striking physiological attributes of the plant kingdom. 

 From higher plants to lower plants hardly an organism, or any of its 

 parts, has ever been tested and found to be without hormones. This 

 wide distribution of such substances in plants, in the light of their 

 high physiological activity, argues for their having some sort of universal 

 role in metabolism. 



There is ample circumstantial evidence to connect these substances 

 with the stimulation of respiration. For example, seeds of certain plants 

 which have been carefully investigated are known to possess a hormone 

 precursor which is hydrolyzed in the course of germination, giving a 

 continuous high level of hormone supply during early growth. This 

 high hormone supply goes hand in hand with the accelerated respiration 

 and growth which is typical of germinating seeds. The growing root 

 and stem tips of plants, as well as the cambium, constitute another 

 example: meristems are regions characterized by the rapid production of 

 new cells, the basis of which is the synthesis of new protoplasm. Wherever 

 new protoplasm is produced hormone concentration is high as are the 

 respiration and growth rates. In spite of these commonly known facts, 

 to date there is surprisingly little experimental evidence hnking hormone 

 concentration with the stimulation of respiration, and growth. 



Now briefly as to how phytohormones exercise their growth-regulating 

 roles. We have the simple picture that growth responses, in higher plants 

 at least, depend on differential distribution of phytohormones in their 

 tissues and on the relationship of these hormones to other substances 

 which are important in growth. If it is finally shown that hormones 

 exert their growth-controlling influence through respiration, it seems to 



