Abstract
Pinus bungeana Zucc. ex Endl. is an endemic conifer tree species in China with high ornamental value. In order to investigate favorable conditions for seed germination and explore the germination inhibition mechanism of this species at high temperatures, the effects of temperature, light, and storage on the mean germination time (MGT), speed of germination (SG), and total germination percentage (TGP) are evaluated here. Seeds that have either been kept still or entered into a state of dormancy at high temperature are assessed here by a recovery experiment. Furthermore, the contribution of covering layers on thermo-inhibition is analyzed here, including the way they work. This has been realized by the structural observation and via the determination of the abscisic acid (ABA) content. The results show that seeds germinate to a high percentage (approximately 90%) at temperatures of 15 or 20 °C, with or without light, whereas higher temperatures of 25 or 30 °C impeded radicle protrusion and resulted in the germination percentage decreasing sharply (within 5%). Inhibition at high temperatures was thoroughly reversed (bringing about approximately 80% germination) by placing the ungerminated seeds in favorable temperatures and incubating them for an additional 30 days. Dry cold storage did little to reduce the temperature request for germination. Embryo coverings, especially the nucellar membrane, and ABA levels both had a dominant role in seed germination regulation in response to temperature. Under favorable temperature conditions, the levels of ABA significantly decreased. Germination occurred when the levels dropped to a threshold of 15 ng/g (FW (Fresh Weight)). Incubation at a high temperature (25 °C) greatly increased ABA levels and caused the inhibition of radicle protrusion.
Highlights
Seed germination is where the youngest form of a plant resumes its normal physiological activities, and it is the starting point of growth for plants
A two-way analysis of variance (ANOVA) indicated that the total germination percentage (TGP), speed of germination (SG), and mean germination time (MGT) of Pinus bungeana seeds were all significantly different among the incubation temperatures
The light condition was not a limiting factor for the radicle protrusion of Pinus bungeana seeds, but the temperature was the critical factor for germination
Summary
Seed germination is where the youngest form of a plant (an embryo) resumes its normal physiological activities, and it is the starting point of growth for plants. The germination behavior of seeds is related to the time of seed produced and the moment elapsed from the seed settling This behavior is owed to the environmental conditions undergone by the mother plant during seed maturation and those undergone by the seeds after settling [3]. To prevent seedlings from being damaged after germination, physiological reactions may occur in seeds to cope with the high-temperature environment in which they are placed. This ecological requirement can be considered as an adaptation strategy to guarantee favorable conditions for seedling development and survival in some species [7]
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