Potassium Effect on Protein Formation and Amino Acid Turnover in Developing Wheat Grain 1

Earlier investigations have shown that the potassium ion (K + ) promotes grain protein synthesis. It is not yet known whether this K + effect is directly related to the requirement of K + for formation of peptide bonds or is more indirectly related to the translocation of amino acids into developing grain. Wheat ( Triticum aestivum L. “Kolibri”) was grown in solution culture to study the N transformations in developing grain of wheat. At two K levels (K 1 :0.3 and K 2 :2.0 me/liter) plants were treated with 15 N labeled ammonium nitrate for 2 days (2 weeks after anthesis) and then grain samples were obtained from both K treatments periodically until full maturation. Initially, grain from the K 2 treatment contained almost twice as much free amino acids as grain from the K 1 treatment. This treatment difference gradually disappeared with grain development. The 15 N label in the free amino acids declined faster in grain from the K 2 treatment. Concomitant with this decline the 15 N content of the grain proteins increased with the K 2 treatment exceeding the K 1 treatment. Potassium increased the rate of amino acid translocation into the grain as well as the conversion of amino acids into grain proteins (albumin, globulin, prolamin, and glutelin). The accumulation of free amino acids hi the K 2 treated grain suggests the influence of K was stronger on the translocation of amino acids into the grain than the conversion into proteins. The K concentration of the grain was not influenced greatly by K treatment, whereas, stalk and leaf levels showed remarkable differences. It is concluded that an indirect effect of K + on grain protein formation results from amino acid translocation into the grain and not from the influence of K + on peptide bond formation. The heaviest 15 N label was found in glutamine, whereas glutamate showed the highest rate of N turnover.