Amino and amide nitrogen content of the potato, Solanum tuberosum, and its relation to a shoot inhibition phenomenon

Abstract

Solarium tuberosum L. plants grown in non-nutritive media exhibit a shoot inhibition in light which follows normal tuber dormancy. Shoot inhibition is expressed as retardation of leaf development. Physiological age, injury, and nitrate fertilization appeared to be factors in overcoming the inhibition. Studies included comparison of inhibited and non-inhibited shoots fertilized with nitrate and ammonium N sources and analysis of amino-N and amide-N concentrations. Nitrate fertilization produced normal plants. Ammonium fertilized plants remained inhibited, although it was apparent that ammonium was absorbed. Estimates of concentrations of amino-N and amide-N indicated that while nitrate fertilization produced morphologically normal plants, plant nitrogen reserves were not being metabolized. High amino-N and amide-N levels were found in storage tissues of ammonium fertilized plants indicating that absorbed ammonium was being assimilated into organic compounds, but not utilized for immediate growth. Visible ninhydrin absorption spectra of alcoholic extracts were analyzed. Each tissue showed a distinct complement of amino acids and amides and the composition was relatively unaffected by external nitrogen sources. Glutamine may play a significant role in amino-N and amide-N storage in inhibited shoots. Possible mechanisms involved in limiting amino-N and amide-N are discussed.