Root Hair Cells

Introduction

Root hair cell is an offshoot of a hair-forming cell of the epidermis. It is mainly considered an exclusive feature of plants, but its contemporary is also found in animal species. The functional unit of root hair cells is recognized as” root hair.”

Root hairs are essentially the lateral extensions formed by the divisions in the basal root hair cells, visible to the naked eye. They go by the names of rhizoids as well as absorbent hairs.

Occurrence

  • In plants, the root hair cells are present in roots, as the name suggests.
  • In animals, the contemporary is called” the hair follicle,” which is present all over the body as most animals have fur coats, and those not having fur coats have body hair (like animals), distributed unevenly. In places, hair growth is scarce, which represents lesser hair follicles (e.g., Facial hair in women) while other places have an abundance of hair follicles (e.g., Facial hair in man, the hair on the head, etc.)  

Dimensions

The root hair cells vary between 15-17 micrometers in diameter and 80-1500 micrometers in length.

Structure

The root hair cell is roughly rectangular in shape with a cytoplasmic extension on its lateral end (the root hair). It has the following cellular components:

  • A cell wall with intercellular spaces
  • A semi-permeable cell membrane
  • A large central vacuous for maximum water and salt retention
  • A cornered nucleus
  • Cytoplasm
  • Mitochondria for energy production for active transport of nutrients.

Development of Root Hair Cells 

As mentioned earlier, root hair cells are present at the spices/tips of roots and not all over the root. This is because they aid in expanding the reach of plants underground.

To understand the developmental occurrence of root hair cells (which occurs on roots), we need a deep insight into the four zones of roots specified for various purposes. Starting from the tip upwards, the zones are as follows:

Root cap

Which serves to protect the meristematic region of roots from environmental changes (i.e., drought, flood, low nutrient conditions, over-fertilization, etc.)

Meristematic region

This region characterizes high metabolic function and is involved solely in the mitotic activity of undifferentiated meristems.

Zone of elongation

As the name suggests, this zone helps in the lengthening of roots to get a deeper grasp of the soil. No root hair cells are present in this region because any cell will be swept off during root elongation.

Zone of maturation

Undifferentiated cells undergo maturation and are specified for various functions. This zone is where all the root hair cells are located.

Root hair cells alternate with non-hair cells on the surface of roots. So, the development begins with the” specification” of these two groups of cells.

Then occurs” initiation,” which is characterized by forming a primordium for the cell formation.

Lastly comes the” outgrowth/extension phase” in which the root hair cell decides the length of the root hair according to specific chemical stimuli from plants and the species of plants.

Modifications of Root Hair Cells 

Root hair cells have various modifications which help them efficiently execute their task. They are as follows:

Large surface expanse

Numerous root hairs ultimately upswing the plant’s total surface area because bends and loops in an otherwise plain surface serve to spread out the surface. This is especially beneficial in water and nutrient absorption from the soil. The plant with a tremendous root system is bound to survive in the long run or when the nutrients run out.

Lack of cutin

Cutin is a waxy layer that prevents water and water-soluble material exchange across as it is lipid soluble. So, the presence of a cuticle layer would hinder water transport and absorption. For these reasons, root hairs lack cut in.

Lack of chloroplasts

Root hair cells lack the green pigment, which is responsible for photosynthesis rendering them incapable of making their food. Hence, they are dependent on surrounding cells for survival. At the same time, they do not require sunlight to function. So, their activity is undisturbed regardless of the time of the day.

Growth rate

They have an exceptionally rapid growth rate, which has been a considerable assistance for botanists experimenting with growth and developmental changes in cells. Their growth rate is 1 micrometer per minute.

Vacuolar adaptations

The vacuoles are large and central, like in all other plant cells. They are involved in maximum fluid and nutrient storage and retention.

Salt reserves

The vacuoles of root cells have large amounts of salts to create a concentration difference between soil and plant interior. Though the soil has extra nutrients, but the salts accumulated inside root cell vacuoles comparatively win. The root hair vacuous becomes the” sink” or higher salt concentration, while soil becomes the” sink” or the place of low salt concentration. The osmosis principle states that water movement will occur from a state of high concentration to a state of low concentration or along the concentration gradient.

In this way, water moves inside the root hairs from surroundings carrying with it some of the essential nutrients as well.

Transport mechanisms utilizing root hairs

Water absorption occurs via specific pathways. Since the onset of water absorption occurs through root hair cells, it is crucial to discuss the routes.

Apoplast pathway

Apoplast means the nonliving space surrounding cells i.e. cell membrane and beyond. Though it is faster but is an accessory pathway as it is discontinued and always requires the assistance of either vacuolar or symplast pathway for the completion of its function. The water moves from the cell wall of one root hair cell to another as cell walls are permeable. But the movement is hindered at sites of casparian strips present in endodermal cells.

Symplast pathway

Symplast means the living matter or protoplasm of cell. This is the major but slightly slow pathway. The water moves from cytoplasm to cytoplasm of adjacent cells. Plasmodesmata are the connecting junctions.

Vacuolar pathway

As the name suggests, the movement occurs through vacuoles. 

Functions of root hair cells

Root hair cells are specialized structures necessary for the maintenance, growth, and development of plants. They are responsible for the nutritional uptake within plants.

Absorption

Their elongated, tubular, and pointy structures precisely aid in increasing the exchange of nutrients between the soil and plants’ root systems. To up take mineral ions and water molecules from the soil, root hair cells have special protein carriers located in their outer membrane. 

These cells primarily perform the absorption function. These small rectangular structures digest the water and nutrients that are already present in the soil. Furthermore, the absorbed matter is retained and supplied to the plant’s essential parts for the development, growth, and sustenance of healthy plant life.

Storage

The components of food and water taken up by the root hair cells are then stored in vacuoles. These cells have large vacuoles for the sake of maximum storage. 

For those who do not know what are vacuoles? Vacuoles are organelles or vessels present in a cell that is surrounded by cytoplasm. 

Preservation

At times of flood or when water or nutrients are present in abundance in the soil, they retain the internal storage and strive to strike an optimal balance within and outside the cells. 

Often due to change in weather conditions, the soil gets either too concentrated when it drizzles or dry out completely; these cells protect the root system by maintaining and taking care of the water and nutrient levels in the plant. 

Supplement the surface area

Having a small diameter and greater length, root hair cells have a larger surface area for maximum storage of nutrients and essential fluids. Since they are present at the outer side of the plant roots in the form of small projections, they necessarily increase the surface area of plants to maximize the efficiency of the process of osmosis.

Facilitate Transport

Apart from sucking up the essential nutrients from within the soil, root hair cells also transfer or transport these to different parts of plants. 

Having adjacent cell walls, root hair cells are present in abundance with no intercellular space, therefore encouraging and assisting in the deposition of nutrients to the various parts.

Turgidity vs. flaccidity

This is solely a vacuolar mechanism. The cell’s internal environment changes in response to the conditions of the soil. In floods, the root hair cell vacuole becomes turgid and does not allow much water to enter or leave the cell. 

In this way, it saves the plant from excess water while also not allowing much water to enter the roots. On the other hand, the vacuole loses its content and turns flaccid in conditions of drought. Thereby allowing more water to enter and leave the cell whilst also maintaining the concentration gradient. 

Enhance the root diameter

Since root hair cells are cylindrical in shape and are delicate extensions of epidermal cells, they elongate over time but maintain their small diameter. 

They are the cytoplasmic outgrowth of root cells. They increase the overall root diameter and extend root surfaces within the soil.

Anchorage

Roots substantially perform the anchorage function, and Anchorage itself aids in root penetration. Whereby Root hair cells play an essential part in the roots to carry out this leading role. 

They create channels for the root tips to grow deeper into the soil and soil pores to absorb minerals and water better. All in all, keeping a firm hold on a portion of the soil.

Nitrogen Fixation

They form interactions with the soil bacteria or microbes present in the soil because they are the outermost components of roots exposed to the soil. 

The bacteria aids in converting the available nitrogen (in air or soil) into nitrate or nitrites for the plants to use readily for developmental purposes. In return, root hair cells allow the microbes to share the nutrients stored within them. They are thereby laying the basis for a mutualistic interaction.

Sustainability

Even though root hair cells are diaphanous in nature, they provide strength and flexibility for the intense growth of roots through and into the tightly packed grains of soils. 

Therefore, it can be easily said that these ensure plants’ optimal strength to grow and healthily sustain life while keeping the nutrient supply in check.

Regulation of food supply

They take in or store the water or mineral nutrients according to the needs of the plant. For instance, the intake of phosphorus, potassium, and the formation of nitrates from nitrogen increases during the flowering season to provide the plant with the maximum needed supply for the execution of processes that concern blooming and flowering. Therefore, based on the demand for a specific nutrient, the supply is increased or decreased.

Life Span of Root Hair Cells 

Root hair cells have an average life of 2 to 3 weeks, after which they die and are sloughed off. But they are constantly being replaced as new ones are formed at the tip of roots so that the plant does not take a toll on such small changes. 

Another mechanism for the renewal of root hair cells is releasing certain cellular toxins by the newly produced root hair cells, which prove hazardous for the old ones. 

Summary

The acquisition of food that includes a variety of chemicals, water, minerals, etc. in small or large proportions accurately for plants is regulated by root hair cells. They provide a gateway for the nutrients, good bacteria, and other essential things to enter and leave the plant. 

Besides, they are the mechanisms for absorption and keep a check on the quantities of necessary elements required by various parts of plants to grow, develop, fight diseases, sustain against critical weather and soil conditions, etc. They are involved and responsible for the active uptake of nutrients from the soil and work efficiently to support plants’ essential parts in executing supreme functions such as photosynthesis. 

Apart from this, they are sensitive to environmental changes and respond accordingly depending on the moisture or concentration level of salts and minerals in the soil as well as concerning the plant’s requirements. 

The discussion regarding these essential cells explains their importance, function, structure, and other vital aspects in order to provide a detailed analysis of root hair cells to the readers and students out there who find botany an interesting subject. Though not much research is carried out on these cells, this topic is under scientists and researchers’ speculation for decades to find out more about them. 

References

  1. Grierson, Claire; Schiefelbein, John (2002-04-04). “Root Hairs”. The Arabidopsis Book / American Society of Plant Biologists. 1: e0060. doi:10.1199/tab.0060ISSN 1543-8120PMC 3243358PMID 22303213.
  2. Dosier, Larry W.; Riopel, J. L. (1977). “Differential Enzyme Activity During Trichoblast Differentiation in Elodea Canadensis”. American Journal of Botany. 64 (9): 1049–1056. doi:10.1002/j.1537-2197.1977.tb10794.x.

Grierson, C.; Schiefelbein, J. (2002). “Root Hairs”. The Arabidopsis Book. 1: e0060. doi:10.1199/tab.0060PMC 3243358PMID 22303213.