The interaction of light and low temperature on breaking the dormancy of Chara vulgaris oospores

Germination and dormancy-breaking requirements have been investigated of Chara vulgaris, L. oospores harvested from surface sediments and from the plants of two lakes, Schumacher and Little Pearl in the locality of Timmins, northern Ontario. Oospores exhibited contrasting germination rates of 4–5% for fresh and 28–45% for sedimentary oospores. Dormancy of sedimentary oospores was readily broken by after-ripening for 60 days at 4 °C followed by exposure to white or red light, or by gibberellic acid (GA) in light (49–74% germination), whereas fresh oospores were less responsive (12–22% germination) to such treatments. Treatment of oospores by stratification or with GA or exposure to red light caused the induction of α-amylase activity. Abscisic acid reduced the effect of stratification and inhibited the GA-enhanced germination of sedimentary oospores, providing evidence of the participation of a phytochrome mechanism and hormonal regulation in the breaking of oospore dormancy. These results indicate that C. vulgaris oospores exhibit primary dormancy when first released from the parent plant, which is broken by exposure to low temperature, followed by secondary dormancy which is broken by a further period of stratification and exposure to light. Oospores from both lakes responded similarly to the dormancy-breaking treatments, but their overall viabilities were significantly different.