Studies of early reactions occurring in germinating Sinapis alba seeds

Abstract

The work described in this thesis is an attempt to trace some of the metabolism that occurs in the early stages of the germination of Sinapis alba seeds. Spedding and Wilson D.J. Spedding and A.T. Wilson,Phytochemistry,7, 897 (1968) have shown that when Sinapis alba seeds are germinated in the presence of tritiated water, the amino-acids γ-aminobutyric acid, glutamic acid, aspartic acid and alanine are the first to be labelled with tritium. Spedding and Wilson D.J. Spedding and A.T. Wilson,Phytochemistry,7, 897 (1968) proposed several feasible reactions that would give rise to this incorporation of the tritium label. This included the reversible transamination of the four amino acids mentioned and the decarboxylation of glutamic acid to produce labelled γ-aminobutyric acid. In order to use classical biochemical techniques, methods were developed which involved grinding up the seed to give a powder. This powder still carried out some of the same reactions as the original seeds. Attention was focused on γ-aminobutyric acid as it is obviously an important metabolite but at present has little known metabolic function. Experiments with C-14 labelled substrates showed that the enzymes present in the ground up seeds could irreversibly convert L-glutamic acid to γ-aminobutyric acid and it is suggested that this occurs in whole seeds. Some preliminary work was carried out using C-14-labelled amino-acids to investigate the transaminase activity of the ground up seeds. Whilst results showed no such activity, the possibility of transamination occurring in whole seeds cannot be entirely eliminated. The labelling pattern obtained when the seed powder was imbibed with tritiated water was similar to that of whole seeds except that the metabolism of lipid-like material (that is, material which travelled with the solvent front of paper chromatograms) was implicated much earlier. An attempt was made to discover the nature of the lipid-like material that had incorporated a tritium label. This material was resolved into two components. One appeared to be a neutral lipid or an ester, and the other a neutral phosphatide.