Effects of tritiated water on the metabolism and germination of jack pine seeds

Abstract

Tritium, imbibed as tritiated water, which evoked the germination of jack pine, was recovered from alcohol-soluble and insoluble components of seeds. At 12 h, tritium labeled nonexchangeably a few but not all free amino acids. By 96 h, all amino acids contained tritium but in seeds killed by heat no radioactive amino acids were detected. Radioactivity in glutamic acid, alanine, proline, and γ-aminobutyric acid implicated key roles for α-ketoacids and semialdehydes during germination. Two neutral fractions accounted for over 80% of the tritium in alcohol-soluble compounds.Levels of tritium above 1.0 mCi/ml water per gram dry seed inhibited water intake after 1 h and inactivated the germination of seeds by 96%. The total soluble N and amide content were also significantly reduced as alanine N increased. Specific activities of glutamine and γ-aminobutyric acid but not of all amino acids were proportional to tritium dose. Radioactivity in glutamine was not associated with the amide N supporting the specific labeling by tritium at the α-carbon of glutamic acid. At high levels of tritium radioactivity was concentrated in the insoluble (protein) fraction and was accompanied by brittleness of tissues and subcellular disruption. Tritium although localized mostly in the cytoplasm was more concentrated per unit area throughout chromatin regions of the nucleus than in the cytoplasm.