Germination
The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, ferns, bacteria, and the growth of the pollen tube from the pollen grain of a seed plant.
The seed of a vascular plant is a small package produced in a fruit or cone after the union of male and female reproductive cells.
Under proper conditions, the seed begins to germinate and the embryo resumes growth, developing into a seedling.
The most important external factors include right temperature, water, oxygen or air and sometimes light or darkness.
Often this depends on the individual seed variety and is closely linked to the ecological conditions of a plant's natural habitat.
[2] In some definitions, the appearance of the radicle marks the end of germination and the beginning of "establishment", a period that utilizes the food reserves stored in the seed.
Germination and establishment as an independent organism are critical phases in the life of a plant when they are the most vulnerable to injury, disease, and water stress.
In epigeal germination, the hypocotyl elongates and forms a hook, pulling rather than pushing the cotyledons and apical meristem through the soil.
Once it reaches the surface, it straightens and pulls the cotyledons and shoot tip of the growing seedlings into the air.
Once the pollen grain lands on the stigma of a receptive flower (or a female cone in gymnosperms), it takes up water and germinates.
[2] Since most plants carry both male and female reproductive organs in their flowers, there is a high risk of self-pollination and thus inbreeding.
The initial formation and subsequent elongation of the germ tube in the fungus Aspergillus niger has been captured in 3D using holotomography microscopy.
Each cell is of a tubular shape, but the conidial anastomosis tube forms a bridge that allows fusion between conidia.
For example, in zygomycetes the thick-walled zygosporangium cracks open and the zygospore inside gives rise to the emerging sporangiophore.
In the bryophytes (e.g., mosses and liverworts), spores germinate into protonemata, similar to fungal hyphae, from which the gametophyte grows.
In ferns, the gametophytes are small, heart-shaped prothalli that can often be found underneath a spore-shedding adult plant.
[2] Bacterial spores can be exospores or endospores which are dormant structures produced by a number of different bacteria.
The seed needs to be able to determine when is the perfect time to germinate and they do that by sensing environmental cues.
When red light is present, PHYB is converted to its active form and moves from the cytoplasm to the nucleus where it upregulates the degradation of PIF1.
The authors also looked at how NO and GA effects the vacuolation process of aleurone cells that allow the movement of nutrients to be digested.
NO may also lead to the decrease in sensitivity of abscisic acid (ABA), a plant hormone largely responsible for seed dormancy.
Step 3: This marks the final step in the germination of the seed, where the cotyledons are expanded, which are the true leaves. Note: Temperature must be kept at an optimum level.
