Difference Between Epicotyl and Hypocotyl
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Difference Between Epicotyl and Hypocotyl

Difference Between Epicotyl and Hypocotyl

Epicotyl

An epicotyl is the first part of a seedling, from which emerge the cotyledons and plumule. This organ is responsible for converting the nutrients and water absorbed by the seed into energy, which will be used to support the growth of the seedling.

Epicotyl Functions

An epicotyl functions primarily because it contains meristematic cells, which are capable of producing new cells. Meristematic cells are found in regions that allow rapid cell division in early development, such as a plant’s shoot tip or root apex.

In an epicotyl, these kinds of cells form at the embryo’s junction with a radicle (primary root). These cells continue to produce new cells, which are necessary for the expansion of the epicotyl. The production of these cells in the epicotyl is the main function of that structure. These cells are capable of dividing symmetrically or asymmetrically.

In other words, some can divide into two equal daughter cells or into unequal daughter cells that will differentiate as a new cell type. This ability allows for the rapid expansion of the epicotyl.

When a radicle starts to emerge from the soil, a new layer of epidermal cells is created. These cells become the root cap, and their function is to protect the epidermis against mechanical damage. The growing tip of an epicotyl forms lateral meristems that produce extra cell layers, or periclinal divisions, and expand at the apex by the basipetal formation of new layers (cells).

Lateral meristems produce intra- and inter-clonal layers, while the apex produces anticlinal divisions. The result is a structure that elongates faster than the rate of cell division within it. A phenomenon is known as disproportionate growth.

The production of cells in an epicotyl’s meristematic layer helps the epicotyl to push through the soil. This process generates friction which limits expansion unless a way is found to reduce friction. Two different types of cells found in the epicotyl’s meristematic layer are responsible for reducing friction.

The second function of an epicotyl is to provide a source of food for the developing seedling. The epicotyl contains starch grains converted into sugars by enzymes that the new tissue can use to synthesize proteins. This process is known as translocation. At the same time, tannins are translocated from the endosperm to the epicotyl. This helps to protect the meristematic cells from damage to the soil. These tannins are later re-concentrated in the cotyledons.

Epicotyl Formation

The shape of an epicotyl varies depending on its species and tissue. The structure is often curved because the growing tip wants to keep its distance from the root cap. The growing tip is composed of an apical dome, which is a cap of cells at the end of an epicotyl. The cells are covered with a waxy cuticle that protects the tip of the epicotyl.

In most monocots, an epicotyl is one cell thick and is covered by a waxy cuticle. A single epidermis covers the epicotyl and can be composed of one or more layers of cells, depending on species. The epidermal cells are similar in structure to root cap cells because they both cover the growing tip of an organ.

The epidermal cells are involved in the passage of water and minerals, which are absorbed from the surrounding soil. As the epicotyl grows through the soil, these cells increase in length by adding new segments.

Epidermal cells also contain small pores called stomata, which allow air into the leaf tissue to facilitate gas exchange.

Epidermal cells can divide to form a new layer of epidermal tissue or added segments of the existing tissue. The former is called intra-clonal division, and the latter inter-clonal division.

In vascular plants, and epicotyl is usually connected to the radicle through a flat stem called a hypocotyl. In fruiting plants, and epicotyl can also be connected to some kind of fruiting body, such as a fruit or flower that attracts animals that disperse the seed.

Cotyledons

Another important part of a seed is the cotyledons. Cotyledons are the first major organs in a seed that emerge from the seed’s dormant state. They contain most of the seed’s stored food, located in its endosperm.

The same cotyledons that contain food also serve as the starting point for a new shoot or root when they are ready to produce new roots and leaves. During germination, cotyledons take up water and nutrients from the surrounding soil and pass them on as food to growing tissues. The stored food in cotyledons is often used to nourish the seedling’s first leaves.

Epicotyl photosynthesis allows the new plants to begin fueling themselves. It is also thought that epicotyl photosynthesis enables the new root and shoot system to make a gas called ethylene, regulating growth, water uptake, and other plant growth processes.

Epicotyls are subject to herbivory by plant-eating animals such as snails and grasshoppers. The epicotyl and the rest of the seed must be protected from these herbivores, particularly in species that produce hard fruit, because they can damage or destroy a new plant before it has a chance to grow and reproduce.

To help protect against herbivory, plants have evolved two different types of specialized epicotyl tissue.

Epicuticular wax

Epicotyl cells produce a waxy cuticle that covers them. This cuticle may be more or less thick, depending on the species. The cuticle may be a single layer, or it may have several layers.

Epidermal trichomes

Some species produce cutin and suberin on the epicotyl’s epidermis and other cells of the seed. This layer protects the epicotyl from animals that eat seeds and aids in absorbing water and minerals from the soil. In some species, epicotyls are completely covered with trichomes.

In others, the epicotyl is mostly covered with trichomes but has a few openings for air and water.

The colonization of a new location is accomplished by first haustoria, which are specialized structures that allow the plant to attach to and colonize a location. As the plant grows, it forms root hairs that grow out from its epicotyl tissue.

These root hairs anchor in the soil, where they will grow new roots and leaves for continued growth. As the plant grows, it also forms shoots. These new shoots grow from the root and shoot tissues in the epicotyl.

When plant parts mature, they continue to produce new cells that help them function and survive in their new locations. The senescence of a plant means that its body is losing efficiency and vitality as it nears death.

Senescence causes leaves and other parts that make up a plant’s structure to dry out, lose color, fall off or decompose (biodegrade). The process of senescence usually begins in the leaf tips and ends in the roots.

Summary

The epicotyl is responsible for, among other things, storing food and growing new leaves and shoots for possible later use. It also allows the plant to begin searching for a suitable environment and then grow there. The epicotyl contains some of the same vascular tissue that makes up its roots, but it differs from the root in important ways.

The epicotyl and its associated leaves are always green, unlike the root system, which is made up of older tissues that have dried up and are often brown. The epicotyl is much longer than the main root but has fewer branches than its main root.

Hypocotyl

The hypocotyl is the first and lowest part of a seedling’s stem, or in other words, it is the area between the cotyledons and root. It can be described as the junction between the shoot and root.

What is the Hypocotyl Function?

The hypocotyl functions as a nutrient delivery system to the cotyledons, store nitrogen and produces important hormones for germination. It also changes its structure as it goes through different growth phases – from seedling to the embryo.

The upper part of the hypocotyl is known as coleoptile. In this phase, the hypocotyl elongates rapidly and develops during the early stages of germination.

Coiling is a key step in development, and the coleoptile stage “may be as important for embryo development as the cotyledonary phase. For example, coleoptile abscission is essential for the proper development of the adult plant.

The hypocotyl morphology depends on the plant’s internal and external environment and has changed as new species and varieties evolved.

Take, for example, “Arabidopsis thaliana,” a member of the Brassicaceae family. This plant has a narrow hypocotyl coleoptile that is inclined to form a helix. The formation of helical structures in the Arabidopsis was possibly related to leaf initiation (Lahaye et al., 2001).

In another species, “Triticum aestivum,” which is the important cultivated wheat plant, the hypocotyl forms a straight, spiral-like protrusion due to a leaf initiation process. This may be useful for the identification of plants.

In angiosperms, the coleoptile is an evagination of the hypocotyl containing a bundle of elongated cells, which develop into two or three layers of epidermal tissue and numerous mesophyll cells. This structure is termed a “towel cylinder.” In the case of grasses, this structure develops into a leaf blade.

Hypocotyl elongation is important in germination. The hypocotyl elongates to absorb nutrients and water through its lower part and then leads that supply upwards to the cotyledons in order to aid in germinating.

While the seed stays dormant, certain parts of the plant must change their functions. Cells change shape and organize to aid in the process of germination.

The hypocotyl is called into action once the seed begins to germinate. Once the cotyledon begins to grow above ground, other parts of the plant must begin growing to aid in its continued development.

The cotylisae cells change shape and organize into filaments that grow up through and above the root cap, where they are a source of water and nutrition for the tiny plant growing under it.

The hypocotyl is also an important area in the developmental stage of the seedling. As the hypocotyl grows, other cells in the cotyledons need to be able to tell each other up which direction they should grow.

The cotyledons send signals from their apical receptors (border cells) and their basal buds (xylem) to their neighbors, which allow them to grow similarly. This allows the cotyledons to grow together and above the root.

This is a critical system that must be working for the seedling to survive when first exposed to air and soil after germinating. The leaves of grasses also grow at an oblique angle relative to their attachment point on the stem (the sheath base).  This is an important part of the plant’s development as it helps gather sunlight from all areas.

Difference Between Epicotyl and Hypocotyl

The difference between Epicotyl and Hypocotyl is the part of the embryo that will become the stem. The epicotyl (the shoot) will grow into a seedling’s stems and leaves. The hypocotyl (the root) will grow into a seedling’s roots.

Differences in Structure (Epicotyl and Hypocotyl):

An epicotyl is much more like a leaf than a root, while a hypocotyl has some resemblance to roots and little resemblance to leaves or shoots.

The Epicotyl

The epicotyl connects the embryo to the placenta. It is a non-photosynthetic structure that grows into the seedling’s stem.

The Hypocotyl

The hypocotyl connects the embryo to the placenta. It is a non-photosynthetic structure that grows into the seedling’s roots and lower stems.

Epicotyl and Hypocotyl Fact:

Some plants have two epicotyls instead of one, which is uncommon in nature. These are some examples of plants with two epicotyls: lettuce, most root crops, tomato, celery, and cucumber.

Difference Between Epicotyl and Hypocotyl

The difference between Epicotyl and Hypocotyl is that epicotyl is the shoot of a seedling while hypocotyl is the root of a seedling. To understand this better, we must see them from both ends.

Epicotyl can be broken into two parts – the apical meristem and the basal part.

The apical meristem is found at the tip of the epicotyl and is responsible for all the plant’s above-ground parts. The apical meristem grows and develops into the stem, leaves, flowers, etc.

The basal part forms roots in certain plants, but it does not develop into roots in some plants. In such a case, it becomes a storage organ for starch or fats like potatoes. In other plants, it can become a shoot if conditions are favorable for shoot formation.

Hypocotyl, on the other hand, is present between the cotyledons of a seed. The hypocotyl is generally replaced by the radicle. The radicle is responsible for the formation of roots, which in turn helps in the absorption of water and nutrients from the soil.

In the case of monocots, the cotyledons are partly absorbed.

It is interesting to note that both epicotyl and hypocotyl can become roots in some plants, like in yams and dahlias. However, it is quite possible that you might encounter these terms as tops in your garden.

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