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

Abstract

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 GA treatment. Embryo growth was assessed and the time of testa and endosperm rupture scored. Base temperatures (T ) and thermal times for 50% (θ ) of embryo growth and seed germination were calculated. W+C enabled slow embryo growth. W+C and GA promoted rapid embryo growth and subsequent radicle emergence. The embryo internal growth base temperature (T ) was ca. 5 °C for W+C and GA -treated seeds. GA treatment also resulted in similar T estimates for radicle emergence. The thermal times for embryo growth (θ ) and germination (θ ) were four- to six-fold longer in the presence of GA 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 GA . The thermal time approach could be a valid tool to model thermal kinetics of embryo growth and radicle protrusion.

Seed ecology of the geophyte Conopodium majus (Apiaceae), indicator species of ancient woodland understories and oligotrophic meadows

“…Presumably, the thermal control of different growth phases varies, as shown for embryo growth and radicle emergence in Aquilegia barbaricina Arrigoni & E.Nardi ( Ranunculaceae ; Porceddu et al . ). In Heracleum spondylium L. ( Apiaceae ), cold temperatures promote embryo growth by stimulating the conversion of the proteins stored in the endosperm into soluble nitrogen compounds, promoting radicle emergence (Stokes ).…”

Seeds of future past: climate change and the thermal memory of plant reproductive traits

“…physical dormancy). Most recently, Porceddu et al (2017) made a first attempt to model embryo growth (i.e. morphological dormancy) by quantifying cardinal temperatures specific to embryo growth inside the seed.…”

Differential Interpretation of Mountain Temperatures by Endospermic Seeds of Three Endemic Species Impacts the Timing of In Situ Germination

“…In this model, seeds accumulate units of thermal time to germinate for a percentile g of the population, and when some dormancy is present seed germination may be predicted in relation to thermal time accumulation above a gradually changing base temperature ( T b ) [ 18 ]. Furthermore, as reported recently by Porceddu et al [ 19 ] for Aquilegia barbaricina Arrigoni & E.Nardi, this approach may be applied also to identify the thermal thresholds ( T b and θ ) requirements for embryo growth within the seed. Thermal time models have been shown to be robust and have many purposes, including predicting seed germination in the field (i.e., [ 20 , 21 , 22 ]), assessing the impact of different simulated climate warming scenarios on seed dormancy release and germination [ 23 , 24 ], and identifying the role of diurnally alternating temperatures in seed responses to climate change [ 25 ].…”

“…sandalioticum (hereafter R. sandalioticum ) are endospermic and contain a linear underdeveloped embryo ( sensu [ 42 ]). The seeds of these species show morphophysiological dormancy (MPD) [ 19 , 43 , 44 ]. Warm (25 °C for three months) followed by a cold stratification (5 °C for 3 months) release dormancy in A. barbaricina [ 19 ], while warm stratification (25 °C for three months) is required for dormancy break in seeds of P. corsica and R. sandalioticum [ 43 , 44 ].…”

“…The seeds of these species show morphophysiological dormancy (MPD) [ 19 , 43 , 44 ]. Warm (25 °C for three months) followed by a cold stratification (5 °C for 3 months) release dormancy in A. barbaricina [ 19 ], while warm stratification (25 °C for three months) is required for dormancy break in seeds of P. corsica and R. sandalioticum [ 43 , 44 ]. Although these species were thoroughly studied under laboratory controlled conditions [ 19 , 43 , 44 ], how the seed germination kinetics of these species interact with their natural habitat (e.g., favourable environmental conditions for seed dormancy release, embryo growth, and radicle protrusion) needs to be investigated in order to supplement the limited knowledge present in the literature about the thermal control of MPD-type seeds.…”