ENDO-BETA-MANNANASE ACTIVITY DURING DORMANCY ALLEVIATION AND GERMINATION OF WHITE SPRUCE (PICEA-GLAUCA) SEEDS

It is not known how embryos of seeds of the Pinaceae protrude from the ir enclosing tissues to complete germination. Prior to protrusion of t he radicle there is an increase in endo-beta-1,4-mannanase (EC 3.2.1.7 8) activity associated with weakening of the micropylar megagametophyt e/nucellus from seeds of white spruce (Picea glauca [Moench.] Voss). M annanase activity is present as three isoforms (pi values 5.0, 4.8, 4. 7) in both the embryo and surrounding structures (megagametophyte and nucellus) prior to and during imbibition. Activity of all the isoforms increases in the chalazal and micropylar megagametophyte during germi nation. Activity then declines after the testa splits, typically 1 day prior to radicle protrusion, due partially to its leaching from the s eed into the surrounding water. Activity increases in the cotyledons a nd axis as the embryo commences elongation Seeds from dormant seedlots exhibit a lower germination percentage, relative to seeds from nondor mant seedlots, and the force necessary for the embryo to puncture the surrounding structures tends to be greater. Although similar mannanase activities are present in unimbibed seeds of dormant and nondormant s eedlots, during germination, enzyme activity in seeds of dormant seedl ots is lower. Moist chilling alleviates dormancy in the seeds of the P inaceae and, during 3 weeks of this treatment, mannanase activity slow ly increases. After 3 weeks of moist chilling and regardless of whethe r the seedlot was dormant or not prior to moist chilling, the force ne cessary to puncture the micropylar megagametophyte and nucellus is low er, and the speed of germination greater. Seeds from previously dorman t seedlots also complete germination to a greater percentage, relative to unchilled seeds from dormant seedlots. Upon transfer to 25 degrees C, mannanase activity in moist-chilled seeds decreases during germina tion of all seedlots regardless of their previous dormancy status.