The role of metabolic adaptation in the avoidance of soaking injury in seeds

Abstract

Seeds of a range of crop species were classified according to their ability to germinate after presowing soaking treatments of varying severity. The differences in soaking tolerance were then compared with changes in several metabolic parameters to determine the importance of metabolic adaptation in the avoidance of soaking injury in seeds. After seed soaking treatments those species most susceptible to injury exhibited the highest respiration rates under nitrogen. At the same time the species with the highest respiration rates under nitrogen showed more rapid utilization of their seed reserves. This was demonstrated as a positive correlation of respiration rate under nitrogen against the fall in sucrose content of seeds on soaking. A similar positive correlation of respiration under nitrogen with alcohol content and with fall in sucrose content on soaking seeds was found. However, when the malic acid content of, seeds was assayed the reverse trend was shown, where malic acid was negatively correlated both with respiration under nitrogen and with the fall in sucrose content on soaking seeds. Thus the changes in the alcohol and malic acid contents of seeds on soaking were negatively correlated with each other. Analysis of lactic acid content of soaked seeds was expressed as the percentage of the three anaerobic products measured (ie. alcohol plus malic acid plus lactic acid) and gave a significant negative correlation against respiration rate under nitrogen' on soaking seeds. Parallel studies of both alcohol and malic dehydrogenases were conducted after soaking seeds. The activity of alcohol dehydrogenase was highest in those species which were least tolerant of soaking injury, while the Michaelis constants for alcohol dehydrogenase with respect to acetaldehyde were low in species intolerant of soaking injury but higher in species tolerant of this treatment. Enhanced metabolic damage was observed as a result of both high (30°C) and of low temperature (0°C) soaking treatments, but only in species which were normally susceptible to soaking injury. In studies on a single species (Pisum sativum) metabolic injury followed a similar course to the above studies in high but not in low temperature soaking treatments. Studies on the enzyme invertase showed grossly enhanced activity with a rise in temperature. This increased activity was also related to germination counts.