Hoagland _146_ plant Nutrition 



deficiency of knowledge of respiratory systems in 

 higher plants. Various systems apparently operate 

 and the problem of their relative importance and roles 

 in different processes remains to be solved. In the 

 potato tuber tissue, as investigated by Steward and 

 Preston, the accumulation of potassium salts is ac- 

 companied by oxidase activity, with the oxidation of 

 phenolic compounds. Brown and Goddard find evi- 

 dence that wheat embryos and barley seedlings con- 

 tain a cytochrome oxidase, but in mature leaves no 

 evidence for the function of this oxidase was found. 

 The period has apparently arrived for more extensive 

 exploration of respiratory systems of higher plants, 

 comparable with that carried out by those who have 

 worked on muscle and yeast. 



At the heart of the whole question of salt ac- 

 cumulation in its relation to biochemistry is the nature 

 of the energetic coupling of metabolism to the active 

 transport of salt. At the present time no technique 

 is available to measure the energy utilized in these 

 particular processes. In theory, the expenditure of 

 energy required would be extremely small. Specula- 

 tively, one possible approach to the problem might be 

 envisaged as a development of a recently discussed 

 theory of biochemists who have devoted themselves to 

 research on biochemical processes in which energy is 

 applied to other cellular activities. The notable ex- 

 ample is found in studies on muscle. 



The essence of the biochemical theory referred to 

 has been outlined by Lipman (1941) and by Kalckar 

 (1941). The utilization of energy made available by 

 respiration is associated with the formation and break- 

 down of phosphorylated compounds. Certain types of 

 these compounds contain energy-rich phosphate bonds, 

 from which energy can be yielded to cellular processes. 

 The relation of the energy-rich phosphate linkages to 

 contractility of muscle tissue has been more definitely 

 considered than one that might be postulated for the 

 movement of solutes against activity gradients. Con- 



