1 1 2 BIOCHEMICAL SYSTEMATICS 



the plant is in circumstances which encourage protein breakdown. 

 Additionally, the amides, glutamine and asparagine, are extremely 

 sensitive to modifications of plant growth. Pleshkov et al. (1959) 

 compared the free amino acid content of corn leaves and roots grown 

 in a complete nutrient medium and grown in media minus nitrogen, 

 phosphorus, or calcium, respectively. With prolonged deficiency in 

 each case the amino acids decreased sharply, the greatest decrease 

 being evident in aspartic and glutamic acids, alanine, serine, and gly- 

 cine. In contrast to the nitrogen deficient plants, which responded by 

 a drop in free amino acid content within twenty-four hours after re- 

 moval from the complete medium, the phosphorus and potassium 

 deficient sets showed a slight increase in the amino acid content 

 during the first week, followed by a rapid decrease with prolonged 

 deficiency. Possingham (1956) found that in tomato plants cultured 

 in media deficient in copper, zinc, manganese, or iron, the free amino 

 acid fraction actually increased while in molybdenum deficient plants 

 the free amino acid fraction decreased. When molybdenum was 

 added, there was a rapid upswing in free amino acid content inter- 

 preted to reflect the role of molybdenum in nitrate reduction and 

 nitrogen uptake (Possingham, 1957). Although qualitative differences 

 were not great, an example such as the appearance of pipecolic acid 

 in iron and manganese deficient plants, while absent in controls, is 

 notable. A similar situation reported by Coleman (1957) occurs in flax. 

 In this plant citrulline, not previously found in flax, occurs in mod- 

 erate concentration in sulfur deficient plants. Possingham (1956) 

 noted that the relative amounts of amino acids changed in a different 

 pattern with each type of deficiency. The systematic implications of 

 these last observations are that, if one is interested in discovering 

 whether the enzyme system leading to the production of a substance 

 is present and not merely whether the plant normally accumulates 

 the substance, exposure to various types of physiological stress may 

 provide the opportunity in some cases. 



There are other more recent studies, similar in principle to 

 those of Possingham cited above; for example, Tso and McMurtrey 

 (1960) found that, in general, mineral deficiencies other than N caused 

 an increase in the free amino acids of tobacco plants and variations 

 in the relative concentrations of amino acids. ^ Such evidence serves 

 to support the concept that apparently metabolically labile sub- 

 stances such as amino acids provide less reliable data than do meta- 

 bolic end products which accumulate. ^ 



4 Mineral deficiencies also affect the accumulation of other groups of substances, 

 for example, alkaloids, anthocyanins, and so on, but generally not so directly, hence as 

 quickly, as the common amino acids. 



