The Plant as a Metabolic Unit 231 



Temperature Influences 



The expectation is that the metabolic activities of root cells gov- 

 erning the accumulation of solutes should have a high tem- 

 perature coefficient over certain ranges of temperature, and 

 ample experimental evidence is now available to support this 

 expectation. In barley roots, for example, the accumulation of 

 mineral elements has a high temperature coefficient in the range 

 6° 0.-24° C, but the rate of accumulation may increase with 

 temperature up to 30° C, or higher, at least over a brief period 

 of time. The lower temperature limit for accumulation has not 

 yet been determined, but it is probably not far below 5°-6° C. 

 It is, however, interesting that accumulation of mineral solutes 

 can proceed slowly even at this low temperature. 



A typical example of temperature influence on accumulation 

 (for potassium) is given in figure 3. Barley plants were grown in 

 nutrient solution for approximately three weeks and then the 

 root systems were excised. These excised root systems were im- 

 mersed in solutions of potassium salts and subjected to varying 

 temperatures for limited periods of time, under conditions of 

 aeration suitable for high respiratory activity. The temperature 

 coefficients indicated are of a high order and in no way sug- 

 gestive of simple diffusion processes. It is evident, rather, that 

 temperature is influencing metabolic rates and that these are 

 controlling the rate of accumulation of potassium. When the en- 

 tire plant is studied, other complicating factors enter. 



The results cited are not restricted to the barley plant. Very 

 similar temperature relations have been observed in experiments 

 with Nitella cells and storage tissues. The temperature coeffi- 

 cients for the accumulation of different elements are not neces- 

 sarily identical, but it must be emphasized that temperature 



