Lecture 7 — 175 — Potassium Nutrition 



potassium is further complicated by the fact that 

 nitrate must be reduced and the role of potassium, 

 if any, in this reduction is not understood. 



The potassium supply has indirectly a relation to 

 respiration of plant tissues. In the experiments of 

 Gregory's laboratory on barley plants low potassium 

 was found to be correlated with increase of respiration, 

 when sugar concentration in the plant was not too low. 

 More specifically the respiration was correlated with 

 protein content and also amino-acid content. High 

 content of amino acid is present under some potassium 

 deficiency conditions. Gregory (1937), however, does 

 not conclude that potassium is primarily associated 

 with protein synthesis, but rather with the main- 

 tenance of the protoplasmic content. In the absence 

 of sufficient potassium rapid proteolysis is thought to 

 occur. Steward and Preston (1941), on the other 

 hand, find in their experiments with potato discs that 

 potassium absorption enhances respiration and protein 

 synthesis. They worked with aerated potato tuber 

 cells which under the experimental conditions were 

 capable of growth and in which a progressive gain 

 in protein occurred with the utilization of a substrate 

 of amino acids. A contrast was found in this respect 

 between these experiments and some of those con- 

 ducted with leaves of grass plants. Other difficulties 

 arise in comparing results of different investigators 

 on leaf metabolism because the effects of age of the 

 leaves are not always considered. 



One of the outstanding difficulties of understanding 

 what roles potassium plays, aside from a function in 

 buffer systems, is that no indispensable organic com- 

 binations of potassium have been discovered and that 

 nearly all potassium ordinarily exists in inorganic 

 form. At one period many articles appeared on the 

 possible function of the radio-activity of one of the 

 naturally occurring isotopes of potassium. Little has 

 been said of this hypothesis recently. The radio- 

 activity is exceedingly feeble and no confirmed evi- 



