- This article is all about plant tissues.
- We’ll start defining what a plant tissue is.Then, we’ll classify the types of plant tissues.
- We’ll continue with the description of the three types of permanent tissues: dermal, ground and vascular tissue.
- We’ll also see the types of ground tissue in more detail, as plant tissue examples.
What is plant tissue?
A plant tissue is a group of cells working together in one or more functions and form part of the plant organs.
Tissues in general are a group of cells that work together to perform a function. So, when tissues work together, organs are formed. Plant tissues make up the organs of plants, including the leaves, the stem, and the roots.
Types of plant tissue
There are typically two types of plant tissue groups to start with: meristematic tissue and permanent tissue.
Meristematic tissue is plant growth tissue that contains cells that are undifferentiated meaning they have no specialized shape, function, or size yet. Meristematic tissue cells differentiate to become a certain type of tissue with certain qualities.
When it differentiates, it becomes permanent tissue, which makes up the three main classifications of plant tissue we are concerned with.
Compare the tissues in this micrograph to the ones in the diagram in Fig. 6 at the end of the article.
Meristematic tissue in plants is undifferentiated tissue with no specialized function yet (like stem cells in animals). When it differentiates it becomes permanent tissue.
Permanent plant tissue is divided into three groups: dermal, vascular, and ground.
Dermal tissue is the outermost layer or layers of tissue that surrounds the plants,
the vascular tissue is the tissue associated with the vascular system,
and ground tissue is the tissue that is not epidermal or vascular and makes up a large percentage of the plant tissue.
Primary versus secondary growth
All vascular plants undergo the primary growth of stems and roots. Primary growth is characterized by cell division and cell growth that will increase the length of the plant. Typically, plants that are considered herbaceous will only undergo primary growth.
Woody plants may undergo another round of growth known as secondary growth. Secondary growth is lateral growth that increases the width of a root or stem. This occurs through the production of new vascular tissue (secondary xylem and phloem) which is produced from the lateral meristem (cork cambium and vascular cambium). The older xylem does not function for transport but continues to support the plant, allowing plants exhibiting secondary growth to grow larger.
Dermal tissue in plants
The dermal tissue in plants has a similar function to your own skin, protecting the plant organs and helping to prevent water loss!
Did you know that "dermis" means skin?
Dermal tissue in plants is made up of epidermal cells that are usually small, round, and may or may not have a vacuole. These epidermal cells make up the outer cell layer(s) of plant organs and their main function is to protect the plant organs from the climate or pathogens. Epidermal cells also secrete a cuticle, which is a waxy layer that provides extra protection against water loss and UV rays from the sun.
Epidermal cells may become specialized in their later development, depending on the organ they protect, and may become trichomes, stomatal guard cells, or root hairs.
Trichomes are protective projections on stems and leaves,
the stomatal guard cells control gas exchange in leaves,
and root hairs help increase root surface area.
Ground tissue in plants
Ground tissue in plants includes all of the tissue that is not vascular or dermal. This means a lot of the plant tissue is actually ground tissue. Ground tissue in itself is diverse and has various functions, including:
Storage
And structural support.
The three types of cells associated with the ground tissue, which we describe in the next section, are the collenchyma, the parenchyma, and the sclerenchyma.
Examples of plant tissues
There are many examples that we can delve into showcasing tissue in plants, here we focus on examples of ground tissue in plants: collenchyma, parenchyma and sclerenchyma.
Collenchyma
The collenchyma cells are typically long and fibrous and they provide support for the non-woody parts of the plant including the stems of herbaceous plants and petioles (the part that attaches the leaf to the branch). Unlike the other ground tissue cell types, the collenchyma cells do not have a secondary cell wall, making them more flexible.
Collenchyma tissue may be more noticeable than you think. Have you ever eaten celery (the stem) and realized if you rip a piece in half, stringy, strong hair-like fibers remain? Well, those fibers would be collenchyma tissue.
Parenchyma
The parenchyma is the plant tissue mostly involved in photosynthesis. In fact, the mesophyll tissue in leaves is made up of parenchyma cells, where photosynthesis occurs, thus some parenchyma cells contain chloroplasts (Fig. 3). The parenchyma cells can also act as storage sites, especially in the cortex and pith of certain roots.
For example, the cortex of carrots is parenchyma tissue for storage.
Parenchyma cells help in the wound healing process for plants because, unlike other cells after differentiation, this is a plant tissue that retain the ability to divide.
Sclerenchyma
The sclerenchyma cells are mainly for support. They have a thick secondary cell wall and are fortified with lignin. Lignin is a rigid polymer that helps provide support in woody plants and in some nuts and seeds. Oftentimes, these cells will undergo programmed cell death (apoptosis) and exist merely as structural support. The two types of sclerenchyma cells are fibers (support for woody stems) and sclereids (protection in nuts and seeds).
Biting into a stone fruit like a peach, cherry, or a plum, you might be aware of those pesky central pits. Those pits are tooth-breakers because they are made up of hardy sclereids (sclerenchyma tissue).
Vascular tissue in plants
The vascular tissue in plants consists of the xylem and the phloem, which transport water and food/nutrients respectively.
Vascular tissue exists in the roots, stems, and leaves, connecting them to ensure that each plant organ can get the necessary nutrients and water it needs for survival. Water and minerals only flow through xylem tissue in one direction, and food and nutrients flow in both directions through the phloem.
The xylem tissue of most plants is made up of:
Tracheids: Tracheids are long cells that are fortified with a strong polymer called lignin and are typically dead at maturity (they undergo apoptosis). Tracheids are thought to be the earliest conductive cell in the vascular system.
Vessel elements: Vessel elements are shorter and wider than tracheids, and are not fortified with lignin. They are specific to flowering plants (angiosperms).
The apoptosis that the xylem tissue cells undergo allows the cells to have holes in their cell walls so that water and minerals can pass through easily.
The phloem tissue of most plants is made up of:
Sieve elements: In flowering plants, the sieve tube elements are long cells connecting at the end that have cytoplasm but few organelles. The ends have plasmodesmata which become bigger to allow for nutrient transport, these ends are known as sieve plates. Unlike in cells of the xylem tissue, these cells do not undergo apoptosis when they mature.
Plant vascular tissue: monocots versus dicots
The arrangement of tissues in plant organs may vary depending on the group of plants. The monocots and dicots, the two main groups of flowering plants, have different arrangements of vascular tissue throughout their roots, stems (fig. 5), and leaves.
- In the stem, the vascular tissue of monocots is spread out, with vascular bundles (xylem and phloem tissue) being dispersed throughout the stem. In dicots, the vascular bundles are organized in a circular pattern around the stem.
- In the leaves, the vascular issue of dicots is often branched (think of a maple leaf), and in monocots, it is often unbranched and in parallel lines (think of a grass leaf).
Plant tissue diagram
A plant tissue diagram illustrating the various permanent tissue types found in vascular plants. Once the plant differentiates, three main tissue types present themselves: dermal, ground and vascular. Each organ of a plant - roots, stems or leaves - contains these tissues for specific reasons as laid out in the sections above.
Plant Tissues - Key takeaways
- Plant organs are composed of different plant tissues with a variety of functions. Tissues are groups of cells that work together to perform certain functions.
- Plants have two types of tissue overall: meristematic tissue (undifferentiated) and permanent tissue (specialized).
- Dermal tissue is made up of epidermal cells, that help protect the plant from drying out and pathogens, and also secrete a waxy cuticle to further prevent drying out.
- Ground tissue offers support, serves as the site of photosynthesis, and provides storage.
- Vascular tissue is the transport tissue made up of water-conducting tissue (xylem) and food-conducting tissue (phloem).
References
- Fig. 1: Modified from Fayette A. Reynolds, Bioscience Image Library Berkshire Community College, public domain, via flickr.com.
- Fig. 4: Edited from Image of carrot pieces (https://pixabay.com/photos/carrot-cut-daucus-carota-2523953/) by anaterate (https://pixabay.com/users/anaterate-2348028/); Plum stone (https://pixabay.com/photos/plum-plum-stone-fruit-food-1690579/ ) by Couleur (https://pixabay.com/users/couleur-1195798/); celery (https://pixabay.com/photos/vegetables-celery-green-vitamins-5040035/) by pasja1000 (https://pixabay.com/users/pasja1000-6355831/); all images free to use under the Pixabay Content License (https://pixabay.com/service/terms/);
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Frequently Asked Questions about Plant Tissues
What are the types of tissue in a plant?
The main types of tissues in a plant are:
- dermal tissue
- vascular tissue and,
- ground tissue.
What is the function of each plant tissue?
The function of each plant tissue is:
- Dermal tissue: mainly protective, help to prevent water loss and UV damage through secretion of the waxy cuticle and a barrier between the internal tissues and climate and pathogens. Epidermal cells can also specialize to perform other defensive functions like deterring herbivory (trichomes).
- Vascular tissue: transportation of water, minerals, nutrients, and food from the roots to the leaves and other organs or from sources (food-producing sites) to sinks (food storing, growth sites).
- Ground tissue: has a plethora of functions, mainly for photosynthesis, storage, and structural support.
What is vascular tissue in plants?
Vascular tissue in plants is the tissue associated with the plant's vascular system. The vascular system transports water and minerals from the roots to other plant parts and food from where it is produced to where it is needed or stored.
The two types of vascular tissue in plants are the xylem, which transports water and minerals, and the phloem, which transports food (sugars).
What is plant tissue?
A tissue is a group of cells that works together to perform a specific function. In plants, these groups of cells are called plant tissues. For example, the epidermal cells of plants work together to cover and protect the plant and form the dermal tissue. Plant tissues work together to form plant organs, which are the stems, roots, and leaves.
Where is ground tissue found in plants?
The ground tissue is found all throughout the plant, in the leaves, roots, stems, and even reproductive structures.
In the leaves, the ground tissue is called the mesophyll tissue and is where photosynthesis takes place. In the roots, ground tissue is largely used for storage. In the stem, it helps to provide structural support and acts as storage as well.
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