Following fertilisation, the new seed is carried in fruit and can finally give rise to a new plant through germination at a location potentially further away than the parent plant. Fruit serves this spreading purpose by containing nutrients appealing to various animals which consume them and expel their seeds through defecation at a more distant place.
Seeds and fruit can develop into a multitude of shapes, sizes and arrangements in different flowering plants.
Broad beans have been cultivated for food for thousands of years, and are a great source of protein and folate.
In this case, the whole pod is the “fruit” while the bean is the seed. The testa is the outer coat that protects the embryo against dehydration and infection by outside agents.
The hilum is the scar left on the seed following its detachment from the wall of the ovary.
The micropyle was initially the opening through which the pollen entered the ovule for pollination, and now can serve to direct the emerging seedling out into the ground during germination. This can happen after a period of dormancy during which the seedling does not develop. This can help the plant save energy, and only develop in good conditions. Hydration of the seed can kickstart germination.
The plant hormone gibberellin has a role in ending dormancy, hence regulating germination.
Gibberellins regulate seed germination, stem elongation, leaf growth, producing pollen and flowering.
Since many of these growth and flowering processes are light-dependent, their development is photomorphogenesis which means development of structure driven by light.
This is achieved via a plant receptor that is light-sensitive called phytochrome. It’s a protein-based molecule with a chromophore group at the centre called bilin. It absorbs light in the red and far-red end of the light spectrum, and hence acts as a detection mechanism which informs the plant of the duration of day and night to control flowering, as well as for the circadian rhythm.
The red (r) and far-red (fr) forms of phytochrome transition between states according to the presence of sunlight. When the far-red, active form becomes abundant, it initiates chemical reactions that start the processes of growth and flowering. The top half of phytochrome is the receptor part sensitive to light, while the bottom, rounded half is the part that catalyses chemical reactions to enact the changes based on the detection of light.
Light stimulates the action of gibberellin, which stimulates the breakdown of stored starch into active sugars which enable seedling growth and together with water encourage the continued expression of the relevant protein products in the seedling such as amylase which breaks down starch.
The radicle section of the embryo is first to emerge and start downwards growth, while the plumule continues its upward growth above soil.
Maize (corn) is the largest product in terms of quantity made, surpassing wheat and rice in terms of human crop and livestock production. Some is consumed directly, with large quantities going to animal feed and secondary products like corn starch and corn syrup.
Here, the kernels are the seeds with each one containing some familiar things: the large, nutritious endosperm, the seedling itself with a plumule and shoot and root meristems (the source of flowers and roots respectively) as well as new terms.
The cotyledon is the source of the leaf, while the aleurone is a protein store. All in all, they contribute different parts to the developing seedling during germination.