Final answer:
Seed germination is influenced by complex hormone signaling pathways involving ABA and GA, as well as environmental cues like light and temperature. Altered protein expression in response to stressors like aluminum treatment can also affect germination. Seeds may require specific conditions, such as light exposure, vernalization, or scarification, to break dormancy and begin germination.
Step-by-step explanation:
The timing and percentage of seed germination can be affected by various hormones, with abscisic acid (ABA) and gibberellins (GA) typically exerting opposing actions. ABA usually inhibits germination and promotes dormancy, while GA promotes germination.
However, studies indicate that a more intricate hormone signaling system may be involved, as seen in tomato seeds where changes in ABA- and GA-related proteins did not correlate with germination rate under aluminum (Al) treatment.
Nonetheless, the altered expression of proteins like mitogen-activated protein kinase (MAPK) in Al-treated radicles suggests that other signaling pathways are significantly involved in the germination process. Moreover, the repression of seed oil body-associated proteins such as caleosin and oleosin during Al treatment can make the seeds more susceptible to dehydration stress, which could impact germination timing and success.
Environmental factors also play a critical role in seed germination. Darkness usually inhibits germination whereas light conditions, such as red and far-red light, may promote it.
The process of vernalization, or exposure to cold, is often required before certain seeds can germinate, particularly in temperate climates; this ensures seeds do not germinate prematurely during warm spells in winter. Treatment options such as scarification are often used to induce germination in seeds with tough coats.