The capacity for protein synthesis in embryonic axes of Phaseolus vulgaris L. cv. Top Crop seeds was reduced markedly by soaking in airsaturated and CO2-saturated water. The former treatment induces soaking injury while the latter treatment prevents injury. After soaking, the capacity for protein synthesis in axes of seeds soaked in air-saturated water declined and the pattern of synthesis remained almost similar to that at the time of termination of soaking. However, the capacity and pattern of protein synthesis in axes of seeds soaked in CO2-saturated water recovered subsequent to soaking and approached that of non-soaked seeds.

Electroconductivity tests are currently used for seed vigour assessment. They are rapid and simple and after further development, they may yet provide the seed industry with a non-destructive alternative to the standard germination test, which is thoroughly destructive to the sample, time consuming, and expensive. Seed injury, a result of soaking required by the electroconductivity test, was evaluated using high quality Zea mays L. seeds responding to successive imbibition/dryback cycles. If the soaking time is brief, injury to the seeds should be minimal, thus permitting successive tests on the same sample. We tested 5 imbibition/dryback cycles (C) and 5 imbibition periods, or cycle durations (CD) of 2, 4, 6, 7 and 8 h. Dryback periods lasted 5–7 d at room temperature. Seeds were permitted to dry back to 10% moisture. Electroconductivity readings were obtained at the end of each CD for each C. Each treatment (C × CD) sample, n=100 seeds, was germinated at 25°C for 7 d; radicle lengths were measured after 3 d. The experiment was repeated yielding a total of 50 observations. Viability and vigour losses were measured in response to successive C and increasing CD. Five cycles of 6 h each resulted in only a 10% loss of viability, but a 20% loss of relative vigour, confirming that vigour is more sensitive to the testing procedure. Cycles had the greatest effect on loss of seed quality since 45% of the readily leachable electrolytes were lost from the seeds during the first soaking period. There was no interaction between C and CD.

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, C6/C1 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 C6/C1 ratios declined steadily during soaking/imbibition and reached values of around 0.3 after germination. Slight increases ofglucose-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.