The effect of soaking injury in bean seeds on aspects of the oxidative pentose phosphate pathway in embryonic axes

Submerging Phaseolus vulgaris cv. Top Crop seeds in air-saturated water for 16 h markedly depresses subsequent germination. This is termed soaking injury. Soaking injury does not occur in seeds soaked in CO2-saturated water. Previous studies have shown that soaking injury can be alleviated by drying seeds or removing seed coats. Submergence therefore leads to a situation in bean seeds which is similar to secondary dormancy. As with dormant seeds, C-6/C-1 ratios of embryonic axes of seeds soaked in air-saturated water remained high (0.8-1.0) during and after soaking. This was paralleled by low activities of glucose-6-phosphate dehydrogenase (EC.1.1.49) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44). In axes of seeds soaked in CO2-saturated water and in unsoaked seeds C-6/C-1 ratios declined steadily during soaking/imbibition and reached values of around 0.3 after germination. Slight increases of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities occurred in the pre-germination phase. This was followed by a massive increase after radicle emergence. Synthesis of the plastid isoenzymes was a post-germinative event. It appears that soaking injury depresses protein synthesis. Lack of oxidative pentose phosphate pathway activity appears to be a causative factor in soaking injury.