Thiamine (vitamin B1) deficiency in germinating seeds of Phaseolus vulgaris L-exposed to soaking injury

Exogenous application of thiamine (vitamin BI) during imbibition improved g ermination and seedling development of bean (Phaseolus vulgaris L. cv. Lass o) seeds, which were exposed to soaking injury by submergence. Leaching of the vitamin into the incubation medium was not increased in submerged seeds . However, translocation of the thiamine reserves from the cotyledons to th e seedling axis was reduced in response to soaking injury. After exogenous application of free thiamine to the seeds, thiaminediphosphate (TDP), which is the physiologically active coenzyme form of thiamine, accumulated in th e seedling axis of submerged seeds, suggesting an increased demand for thia mine-dependent metabolic reactions in these tissues. Limited oxygen supply of the seeds during the soaking period induces a shift from respiration to fermentation of carbohydrates. Neither thiamine-dependent ethanolic ferment ation, nor ATP production or adenylate energy charge (AEC) of the seedling axis were affected by exogenous thiamine application, suggesting that there is no limitation of thiamine-dependent reactions in the energy metabolism of the seedlings. Thus the physiological mechanisms improving germination a nd seedling development of submerged seeds in response to thiamine seed tre atment are still not clear.