Dissecting seed dormancy and germination in Aquilegia barbaricina, through thermal kinetics of embryo growth.

Threshold-based thermal time models provide insight into the physiological switch from the dormant to the non-dormant germinating seed., This approach was used to quantify the different growth responses of the embryo of seeds purported to have morphophysiological dormancy ( MPD) through the complex phases of dormancy release and germination. Aquilegia barbaricina seeds were incubated at constant temperatures (10-25 °C) and 25/10 °C, without pre-treatment, after warm+cold stratification (W+C) and GA3 treatment. Embryo growth was assessed and the time of testa and endosperm rupture scored. Base temperatures ( Tb) and thermal times for 50% (θ50) of embryo growth and seed germination were calculated., W+C enabled slow embryo growth. W+C and GA3 promoted rapid embryo growth and subsequent radicle emergence. The embryo internal growth base temperature ( Tbe) was ca. 5 °C for W+C and GA3-treated seeds. GA3 treatment also resulted in similar Tb estimates for radicle emergence. The thermal times for embryo growth (θe50) and germination (θg50) were four- to six-fold longer in the presence of GA3 compared to W+C., A. barbaricina is characterised by a multi-step seed germination. The slow embryo growth during W+C reflects continuation of the maternal programme of development, whilst the thermal kinetics of both embryo and radicle growth after the removal of physiological dormancy are distinctly different. The effects of W+C on the multiphasic germination response in MPD seeds are only partially mimicked by 250 mg·l−1 GA3. The thermal time approach could be a valid tool to model thermal kinetics of embryo growth and radicle protrusion. [ABSTRACT FROM AUTHOR]