382 Mineral Nutrition of Plants 



DISCUSSION 



The summary of data in the literature concerning the effect of 

 mineral deficiency on amino acids and protein shows how greatly the 

 results of various investigators have differed. A certain degree of uni- 

 formity has been introduced, perhaps unwarranted, by comparing the 

 mean values obtained in all experiments. Another procedure, namely, 

 comparison of the number of positive results with negative results, 

 might also have been used. A brief computation will disclose that six 

 out of nine of the investigators with phosphorus, and fifteen of seven- 

 teen with potassium obtained an increase in amino acids and a relative 

 decrease in protein of the leaves with deficiency. Sulfur deficiency re- 

 sulted in similar reactions without exception. Since the greater num- 

 ber of experiments deal with potassium and phosphorus in the order 

 given and only limited information is available for the other elements, 

 these may be taken to indicate that any mineral deficiency results in a 

 disturbance of protein metabolism. Only in a few instances did the 

 analytical data indicate an unchanged proportion of amino acids to 

 protein in either leaves or stems as a result of deficiency. 



This interpretation is also supported by the data of those experimental 

 results of greater uniformity due in part to the use of large samples — 

 for example, those of Sideris and Young {40, 4/), Nightingale et al. 

 (j/, ^2) and Wall (59, 60). Steinberg, Bowling, and McMurtrey ($0) 

 were able to demonstrate that marked increases in free amino acids took 

 place in leaves of field-grown tobacco. Large samples of 50 to 100 leaves 

 were used and positive results were obtained in each case (calcium, 

 magnesium, potassium, phosphorus, nitrogen, and boron) in accordance 

 with the severity of symptoms displayed. 



The mean values for nitrogen, phosphorus, and potassium deficiency 

 in successive leaves as they matured were determined by Richards and 

 Templeman (j6) and are shown in Table X. Nitrogen deficiency did 

 not alter the relative proportion of amino acid and protein. Phosphorus 

 deficiency caused a rise in amino acids and a fall in protein. Potassium 

 deficiency also led to a rise in amino acids, while protein remained 

 unchanged. It might be noted in this connection that the authors' con- 

 clusion that increased amino acids with potassium deficiency are the 



