I'm sure there are many different ways for seeds of different species, but what is a general rule? Is it some kind of ideal temperature & wetness that triggers a chemical reaction? What factors stimulate seeds to germinate?
Certain conditions are necessary for seed germination:
- Moisture — seeds dry out during dispersal, but at germination the cells need to absorb water in order to rehydrate so that metabolic reactions can take place, which will eventually lead to the growth of the embryo tops and shoot. Furthermore, some seeds contain a hormone that inhibits germination and water is needed in order to wash it out of the seed. The water needed for these processes is absorbed by the micropyle.
- Warmth — many of the metabolic events of germination use enzymes, and these are sensitive to temperatures. Temperature will often be used as a trigger for germination.
- Oxygen — many of the metabolic events that occur during germination use energy. This energy is produced by aerobic respiration.
Many metabolic processes take place at the start of germination, such as the synthesis of giberrellin, this is a plant hormone that stimulates mitosis and cell division in the embryo. Other plant hormones include Abscisic acid (ABA), which regulates seed dormancy and germination. It has been found to stop germination once it has been placed in the soil, it causes the seed to enter a period of dormancy. This allows the seed to remain dormant until when the conditions are more favorable for the seed to grow.