What is a Seed?
This article gives us an overview of a seed. So, to start a seed is a part that forms the basis of any plant. After the fertilization process, the ovules form seeds. A seed generally consists of a seed coat and also an embryo. This embryo of a seed contains three parts
- Radicle,
- Embryonal axis
- One cotyledon, in the case of wheat, maize, or Two cotyledons in the case of gram and pea.
A seed is almost there in all fruits and it is the seed that one plants in order to get a new plant. Therefore, the seed is the most important plant of a plant and is generally defined as a matured ovule comprising an embryo. The embryo is also known as a miniature plant that is not developed and reserves food. This is fully covered by a protective seed coat. Flowering plants cannot be grown with seeds. They are mainly responsible for the production of many trees, fruits, and flowers. However, seeds are capable of producing only in a proper and suitable environment that has the correct temperature, right moisture content as well as sunlight. The gymnosperm's seeds are usually exposed without covering the environment, whereas those of angiosperms (flowering plants) have a protective layer called fruits. In a planta s reproduction, the egg that is there inside the ovule gets fertilized with the help of a male nucleus via pollen grain. This process is termed pollination. Hence, many describe seeds to be the primary sources of various kinds of foods like beans, wheat, peas, corn, rice, peanuts, and so on. Even the cooking oil which we are using is derived from soybean, flax seeds, sunflower, mustard seed, cotton, coconut, and many others.
Types of Seeds
Before going further let us take a look at the various types of seeds along with their unique structures and characteristics. There are mainly two types and these two types are:
- Monocotyledonous Seed
- Dicotyledonous Seed
Monocotyledonous Seed
This is one type of seed that derived its name from its characteristic of having one cotyledon. The seed coat is there which protects them, and this type of seed contains only one cotyledon. The main parts of the Monocotyledonous seed are given below:
- Seed Coat: This type of seed is mainly present in cereals such as maize and wheat. The seed consists of a seed coat that is membranous. This membranous seed coat is fused with the wall of the fruit and is known as the Hull.
- Endosperm: Another part is the endosperm which is somewhat huge, and this is where it stores food. These seeds are mainly endospermic however there are some that are non-endospermic e.g., orchids.
- Aleurone layer: The endosperm has an outer covering that separates the seeda s embryo. This is a proteinous layer which is known to be the aleurone layer.
- Embryo: Embryo is a part of the seed located at one end of the endosperm and is kept in a groove and is small in nature.
- Scutellum: This is a cotyledon that is large and shield-shaped.
- Embryonal axis: Radicle and plumule are two ends of a seed.
- Coleoptile and coleorhiza: They are plumule and radicle (coleoptile and coleorhiza) enclosed in sheaths
Dicotyledonous Seed
This type of seed unlike the monocotyledonous has two cotyledons and the main parts of the seed are:
- Seed coat: The outermost covering is called the seed coat of a seed. It generally consists of two layers,
- Testa (outer) and
- the tegmen (inner).
- Embryo: This part has two cotyledons and the embryonal axis.
- Hilum: This is said to be a scar present on the seed coat. It is via this, that the seed is attached to the fruit.
- Micropyle: This is situated above the hilum.
- Cotyledons: The cotyledons are the fleshy part and are reserved with stored food materials.
- Radicle and plumule: Just like in the Monocotyledonous Seed, the Radicle and plumule are seen to be there at the two ends of the embryonal axis.
- Endosperm: the endosperm in the case of castor seed is formed due to double fertilization and it also stores food. Hence, it is a food storing tissue. However, in other plants like gram, bean, and pea, the endosperm is absent in the well-matured seed. These types of seeds are non-endospermic.
Seed Structure and Development
The structure of the seed can be attributed to the presence of three parts: the embryo, the outer seed coat, and the endosperm. The embryo is a part of the plant where it is the young plant itself, the outer seed coat is the part that protects the seed whereas the endosperm on the other hand reserves food. The germination process starts when the seed becomes mature and is present in a favorable condition or environment. By germination, it means that the plant begins active growth.
What happens during seed development?
Seed development means the germination of the seed starts and in this process of germination, the embryo absorbs the water leading to the rehydration of the new plant and this, in turn, expands the plant cells. After some time from the beginning of the process of water uptake, popularly called the imbibition process, all the steps that lead to the growth of plants start like there is an increase in the rate of respiration, an increase in several metabolic processes, reduce during dormancy, and many others.
Export and Import of Seeds in India
For the import and export of seed, the importer or exporter or his/her agent needs to apply for a permit to do so. There is a separate permit for importing seeds or plant materials that need to be imported with the motive of sowing, planting, and propagating and this needs to be done seven days prior to the date of permission from the permit issuing authority of the particular or specific designated port. This should be in accordance with the regulation imposed on importing seeds into India that is notified as vide clause of the Plant Quarantine Order of 2003. According to this, it is said that it is only through the Regional stations of Mumbai, Chennai, New Delhi, Kolkata, and Amritsar as per Schedule-I that consignments of all plants or seeds for propagation shall be imported through such scheduled places. However, for consumption, the importer has to make an application for importing seeds or plant materials along with a DD or pay the order for Rs.150. One can check these permissions online. Exporters have to submit around 20 copies of their applications for the export of seeds.
FAQs: Seeds
1. Why are seeds of different sizes and shapes?
Answer: During germination, it happens that the germination is uneven leading to different sizes of seeds. The reason for this is because of slow growth, and differences in the growing environment like the difference in moisture, temperatures, or soil. The planting depth also matters in the planting of the seed, leading to seedlings of several sizes. Also, the size and weight of the seed depend directly on the nutritional reserves that it needs, and the amount of nutritional food allocated is usually more for the initial seedling growth. The plants they produce might be looked very much alike however, the seeds are not alike. One seed is different from another as nature has not only given them different shapes, sizes, and colors, but the packaging of each seed is also unique in various ways. For example, some seeds are found to be soft inside, some have fleshy coverings, and so on. The seeds that are larger in size always tend to produce more vigorous or faster seedlings compared to smaller ones.
2. Which seeds are exported from India?
Answer: Currently, India is custom producing vegetable seeds and has the capability of becoming a global leader in this for many countries and exporting them to China and other Asian countries and the world.
3. Which seeds are imported into India?
Answer: In India, the import of seeds happens only via proper permission that can be taken from the concerned authority, and they need to import only through selected entry ports like New Delhi, Chennai, Amritsar, Mumbai, and Kolkata. The imports can be seeds, budwood, rhizomes, bulbs, cuttings, and tubers, for sowing, propagation, and even consumption. However, there are imports of certain seeds that do not require a license in accordance with the New Policy on Seed Development. These include import of seeds of bajra, ragi, barley, rye, millet, oat, jowar, maize and many other kinds of cereal, cotton, groundnut, sesamum, soybean, palm nut, castor, linseed, jojoba, safflower, clover, mustard, etc.
4. Which is the largest seed producer in the world?
Answer: North America along with Europe constitutes about 55% of the seed market globally. North America occupies a large market share in the seed market. Then this is followed by the Asia-Pacific with a fast-growing curve having a CAGR of 7.9%. Next to this is South America during 2015-2020. Companies like Monsanto and Dupont have gained popularity in producing and providing seeds around 50% worldwide. The top ten producers of seeds are from Japan, the U.S.A, and Europe.