GERMINATION OF FRESH, IMMATURE SOYBEAN SEED - EFFECT OF THE PRE-GERMINATION LIGHT ENVIRONMENT

Immature soybean [Glycine max (L.) Merrill] seeds usually continue nor mal growth and development in in vitro culture in media with high osmo larity. The effect of the pre-culture light environment on germination of immature seeds during in vitro culture was investigated by exposin g plants to various light regimes before seeds were placed in culture media which contained 200 mM sucrose, 62.5 mM asparagine, 10 mM methio nine and other minor nutrients. There was a significant negative linea r relationship (r(2) = 0.75) between germination (radicle protrusion t hrough the testa) in culture and average solar radiation for five days before culture for control seed from greenhouse and field experiments . Placing plants in reduced radiation or complete darkness for 2 to 13 days before culture increased germination. This response could be rev ersed by placing the plants in light again before culturing. Longer da rk treatments were required in the field to get similar responses. The light reduction treatments reduced soluble sugar levels and increased the osmotic potential of the axes. There was a significant negative l inear relationship (r(2) = 0.52) between axis osmotic potential and ge rmination across field and greenhouse\experiments. In vitro germinatio n was associated with changes in axis osmotic potential that were caus ed by the light treatments. The light treatment effect was probably me diated by changes in photosynthesis. These data support the contention that seed water status is involved in regulating the shift from devel opment to germination.