Tritium Incorporation From Tritium Water as an Index of Metabolism

<p>Part A The metabolism of mustard (Sinapis alba) seeds wet at sub-germination temperatures has been studied using tritium incorporation as an index of metabolism. The theory and scope of the method are discussed. The enzymic reactions known in 1964 are surveyed one by one, suggesting which will, or will not, incorporate tritium from THO into specified metabolites, or cannot be confidently predicted either way. Improvements have been made in the chromatography procedure. At 0°, many of the normal germination chemical reactions proceed, but about one tenth as fast as at 24°. Amino-acids are being metabolised within 2 h of wetting the seeds, and malic and citric acids within 4 h. Within 24 h lipids and fructose are undergoing reactions. An unidentified compound “M”, not reported in normal germination, is being metabolised within 48 h. Another aberration from normal is the absence of detectable succinate metabolism. Labelling of the solid residue (insoluble in ethanol and in water) always occurs, shown to be largely non-metabolic. To explain the non-germination of seeds at temperatures near 0°, it is hypothesized that the Krebs cycle is qualitatively altered, perhaps by “wasting away” of glutamate to 4-aminobutyrate instead of its routing into the Krebs cycle as alpha-oxoglutarate. Part B A method has been developed for studying the metabolism of dry seeds, spores and pollen by exposure to THO vapour. Dry Pinus radiata pollen labels many compounds. A few have been identified and are common metabolites. It may be that the metabolism of dry pollen is not qualitatively different from its germination reactions. Dry mustard seeds and spores of the fungus Pithomyces chartarum give, in contrast to pollen, patterns of incorporation very different from those in early germination.</p>