GERMINATION AND WATER RELATIONS OF IMMATURE SOYBEAN SEED

The water content (g kg-1 and mg seed-1) water, osmotic, and turgor po tentials of immature fresh soybean [Glycine max (L.) Merrill] seed, ha rvested at different stages of development, were measured during imbib ition on germination towels. Seeds that had accumulated 25% or more of their maximum dry weight germinated (radicle protrusion) more than 90 %. The water content of all fresh immature seeds increased when the se eds were placed on germination towels. The initial water content (g kg -1), prior to placing the seeds on the germination towels, was a funct ion of stage of development. Thus, the water content after imbibition was also a function of the stage of development and was always higher than that associated with germination of mature seed. The movement of water into seeds on germination towels caused the water and osmotic po tential of the axes to increase (become less negative) and the turgor potential to decrease. When immature seeds were incubated in 250 mM su crose, water moved into the seed but there was no change in osmotic po tential of the axis and no germination. When these seeds were shifted from sucrose to water, the osmotic potential of the axes increased and the seeds germinated. These data indicate that immature fresh seeds t ake up water before they germinate, just as mature seeds do. However, the change in water status of the axis may be more important in regula ting germination than movement of water into the seed.