Studies on the germination of Sinapis alba seeds

Abstract

Two techniques have been used to study the metabolism of Sinapis alba (white mustard) seeds during germination. Tritiated water (THO) has been used as the aqueous medium for initiating the reactions of germination and a comparative investigation has been made of the changes that are observed in the labelling pattern as a result of different external conditions. The total pool size of each of several amino acids has been measured after the seed has been allowed to metabolise for a specified time. The effect of the partial pressure of carbon dioxide above the seed has been investigated, using tritiated water. Active metabolism was found to occur throughout the first 24 hours under atmospheres of 100% CO2 and 10% CO2, 90% N2. After 24 hours under the pure carbon dioxide, lactic acid, GABA, alanine, glutamic acid and malic acid were found to be significantly labelled. Under the anaerobic atmosphere with 10% CO2 added, lactic acid, alanine, and glutamic acid were heavily labelled, and GABA, glutamine and malic acid were more lightly labelled. To separate the effect caused by the high partial pressure of CO2 and the absence of O2, seeds were allowed to imbibe under a mixture of 80% CO2 and 20% O2. After 24 hours under this mixture, lactic acid, alanine, glutamic acid and malic acid were heavily labelled and glutamine and GABA were moderately labelled. After 24 hours under air, glutamic, malic and aspartic acids were relatively heavily labelled and lactic acid, alanine, glutamine and sucrose were moderately labelled. S. alba seeds have been found to recover rapidly when placed in air after 24 hours imbibition under CO2 A. W. Missen. M. Sc. Thesis. Victoria University of Wellington. (1968). The metabolism during early recovery was investigated using THO. Five minutes in air did not cause detectable changes from the pattern obtained after 24 hours imbibition of THO under CO2. After 80 minutes in air, lactic acid, GABA and alanine were heavily labelled, glutamine, glutamic acid and malic acid were lightly labelled. After 3 hours in air, lactic acid, GABA and alanine are relatively heavily labelled, malic and glutamic acids, sucrose and glutamine are much more heavily labelled relative to lactic acid than they were after 80 minutes. A technique was developed so that seeds could imbibe THO at pHl under air. Active metabolism was observed throughout the first 24 hours following wetting of the seeds. After 24 hours imbibition, GABA, alanine and aspartic acid were relatively heavily labelled, glutamic acid was moderately labelled and a weakly labelled, unidentified, ninhydrin-positive compound was observed. Measurement of total pool sizes of certain amino-acids present in the seed during aerobic imbibition showed that the following were involved in active metabolism during the first 5 minutes; aspartic and glutamic acids, alanine, glycine, phenylalanine and valine. The apparent importance of the first three compounds confirms previous results obtained using THO. The latter three have been hitherto unsuspected of being involved in early metabolism. After longer periods of imbibition, proline and serine increase in concentration, and are thought to be important metabolites during this period. Studies of anaerobic metabolism using the amino-acid analyser showed that during the first 24 hours, alanine, serine, aspartic acid and possibly glutamic acid and glycine are involved in metabolism. An attempt using gas chromatography to measure the pool sizes of organic acids was not completed successfully in the time available, although the results suggested that the lactic acid concentration rose during imbibition under hydrogen, as suggested by work with tritiated water.