_Internal and external Root structure .pptx

Aimed for students studying RHS level 2 Priciples and development

1. Internal and external Root structure

2. Identify and describe the primary components of root structure and their respective functions. Analyse the role of roots in plant growth, development, and nutrient uptake. Evaluate the impact of environmental factors on root health and development in horticultural practices. Lesson Aims

3. Primary Functions of Roots The primary functions of a root are: Respiration To absorb and transport water with dissolved nutrients Mechanical support Anchorage Storage of the sugars (starch) that have been manufactured in the leaves Associating with soil microbes in a symbiotic relationship Grow by extension Together, these functions enable plants to remain stable, access vital resources, and interact beneficially with their environment. Plant Biology

4. Moss Liverwort Bryophytes do not have true roots. Instead, they have rhizoids, which are root-like structures. Rhizoids function is to anchor the plant to the substrate and absorb water and minerals to a limited extent Hornwort Rhizoids perform basic functions of roots but lack the complexity and vascular structure of true roots. Bryophytes: First Land Plants in Moist Environments Bryophytes absorb water mainly through their surface

5. Tap root Fibrous root A tap root is a single, thick primary root that grows deep into the soil, with smaller lateral roots branching off. Example: carrot. Fibrous roots consist of many thin, branching roots emerging from the base of the stem, forming a dense network. Example: grass. Adventitious root Adventitious roots arise from non-root parts of the plant, such as stems or leaves, helping in support and propagation. Example: banyan tree aerial roots. Root Types We classify roots into three different types

6. Seed Germination: Root System Development When a seed germinates it produces either a fibrous root system or a tap root system. A fibrous root system is made up of many thin roots that spread out in all directions, commonly found in grasses and cereals. A tap root system consists of one main thick root that grows downward with smaller lateral roots, typical in plants like carrots and dandelions. The type of root system influences how a plant absorbs water and nutrients from the soil. Roots

7. The Role of the Radicle in Seed Germination The radicle is the embryonic root found in the seed. It is the first organ to emerge when a seed germinates. It grows downward into the soil and starts absorbing water and minerals. It anchors the young plant and gives rise to the primary root system. Key Facts about the Radicle Seed Anatomy The radicle is the first root to appear during germination and plays a key role in early nutrient and water uptake.

8. Monocots : Radicle may die early and is replaced by fibrous adventitious roots from the stem base Eudicots : Becomes the taproot, which grows deep and gives rise to lateral roots

9. Zone of elongation The cells in this zone grow longer, which pushes the root tip forward through the soil. A B C D E F G H Zone of differentiation Zone where root cells differentiate and become specialised in their function. This zone has many root hairs and plays a key role in absorption of water and minerals. There is no waxy cuticle so water can be absorbed freely. Root tip A: Epidermis B: Root hair C: Cortex D: Endodermis E: Pericycle F:Stele/vascular cylinder G: Root tip Apical meristem H: Root cap

10. A. Epidermis: The outermost layer of cells forming a protective barrier that shields underlying tissues from mechanical injury, pathogens, and water loss. It also plays a role in gas exchange and secretion of metabolic compounds. B. Root Hair: These are specialised extensions of individual epidermal cells located near the root tip. Root hairs significantly increase the root's surface area, enhancing the plant's ability to absorb water and mineral nutrients from the soil efficiently. They are vital for nutrient uptake and overall plant growth.

11. Root tip: produces new root cells for elongation and differentiation contains the apical meristem Responsible for primary growth (lengthening of the root) Root cap : Protection, shields the growing tip and helps the root navigate soil.The outer cells of the root cap are regularly worn away and replaced, protecting the sensitive root tip during growth.

12. Cortex The cortex is a large region of ground tissue that lies between the epidermis and the stele. Composition: It consists mostly of large, thin-walled parenchyma cells, with significant intercellular spaces. Some cortical cells may also contain chloroplasts and perform photosynthesis. Functions: Storage: A major function, particularly in roots, is the storage of reserve foods, such as starch. Transport: It facilitates the transport of water and nutrients from the epidermis to the endodermis. Protection: It helps protect the internal vascular tissues.

13. Endodermis The endodermis is a specialized, single layer of tightly packed cells that forms the innermost boundary of the cortex. Composition: The key feature of the endodermis is the Casparian strip , a waxy, waterproof band of suberin embedded in the radial and transverse cell walls. Functions: Selective Barrier: The Casparian strip forces water and dissolved minerals to pass through the cytoplasm of the endodermal cells rather than between them (the apoplastic pathway). This gives the plant precise control over which substances enter the vascular tissue. Regulation of Water Flow: By controlling the movement of water, the endodermis helps prevent excessive water loss from the stele and protects the plant from toxic ions in the soil, such as sodium. Protection: It protects the delicate central vascular tissue from pathogens and other harmful substances

14. Pericycle Location: As the outermost part of the stele, the pericycle is situated between the endodermis (the innermost layer of the cortex) and the vascular bundles (xylem and phloem). Composition: It is composed of parenchyma or sclerenchyma cells that can be one or more cell layers thick. Functions: Initiates lateral roots Aids in secondary growth: In eudicot plants Protects vascular bundles:

15. Vascular Cylinder Definition: The stele is the central cylinder of vascular tissues in the roots and stems of vascular plants. It is also known as the vascular cylinder. Composition: The stele is primarily composed of the pericycle, xylem, and phloem. In some plants, it also contains a central region of ground tissue called the pith. Functions: Transport system: It contains the vascular tissues responsible for transporting water and nutrients throughout the plant. Anchoring and support: It helps strengthen the plant's roots and stems, providing structural support.

16. Video: internal root structures

17. Plant Anatomy Epidermis & Root Hair Cortex Endodermis Pericycle Epidermis: Outer layers of cells for protection. Root Hair: Specialised root epidermal cells increasing surface area for absorption of water and minerals. Region between epidermis and vascular cylinder. Supports plant parts and stores food, serving as a buffer and storage area. Layer of cells just outside the vascular cylinder containing the caspian strip. Regulates the flow of water and nutrients into the vascular system. Layer of cells containing meristematic tissue that produces lateral roots, contributing to root branching and growth. Key Structures in Root Anatomy Stele/Vascular Cylinder Vascular tissues as a central cylinder in roots. Xylem: non-living (outer) vascular system carrying water & minerals. Phloem: living (inner) vascular system carrying dissolved sugars and organic compounds.

18. Key Metrics: Pith in Monocot Roots Anatomy Pith In monocot roots, the vascular bundles (xylem and phloem) form a organised ring near the edge of the stele The pith in monocots is often large and well-developed, helping in: Storage of nutrients and water Structural support for the root Monocot roots have a pith eudicots don’t

19. Key Metrics: Pith in Eudicot Roots Anatomy In eudicot roots, vascular bundles are arranged in a radial pattern, and they are not in bundles like in stems, instead, the xylem and phloem are organised separately around the central core. Xylem:Arranged in a star-shaped or cross-shaped pattern in the center of the root Phloem:Found in small groups between the arms of the xylem. The vascular cambium develops between the xylem and phloem, forming a continuous ring. Once this ring is active as roots mature, it starts dividing, producing: Secondary xylem (inside) (adds to root thickness and conducts water) Secondary phloem (outside) (transports sugars) and increases the girth (diameter) of the root

20. Understanding Root Tips Plant Biology Function of the root tip Anchorage and growth Absorption Environmental sensing Gravitropism Hydrotropism Interaction with the soil Root tips are lighter in colour than older roots.

21. Within the root cap are also other specialist cells and hormones that can allow the plant to detect gravity and help guide the roots downward; an effect known as gravitropism or geotropism . Even when the plant is turned on its side, the gravitropic response is so strong that the shoot bends upwards towards the light Phototropism and the roots grow downwards Plant stems normally grow upward, so they are negatively gravitropic Plant roots normally grow downwards, so they are positively geotropic

22. Symplastic movement- Through the cells following up take by osmosis Apoplastic movement- through cell walls between cells Casparian strip -An impermeable layer that forces water to enter the root cells via osmosis and continue via the symplastic route. Water movement- Roots

23. Video: Water movement across the root

24. A Fibrous Root System Grown by monocotyledons. All the roots that emerge from the seed are similar in size and thickness. Roots may or may not branch, usually only once or twice. New roots continue to grow from the base of the plant stem or crown all its life; old roots die. Palm roots may live for around 3 years. Fibrous roots do not become thicker and woody. Root Types Fibrous root system of a palm.

25. Fibrous Roots Shallow roots cover a large area​ More efficient absorption of water & minerals​ Roots hold the soil to prevent erosion Root Types

26. Monocots with fibrous root systems are always producing new roots from the base of the stem. This makes them easy to transplant. Washington palms being transplanted

27. A Tap Root System Is grown by Eudicotyledons and conifers Produces one primary (tap) root from the seed. Lateral roots branch from the tap root. The tap root may grow deep, but usually it doesn’t. Roots may become thicker and woody, unlike a fibrous root system. Root Types Lateral root Primary root Ground level

28. Tap Roots Eudicots and conifers only​ One main root, no nodes​ Ideal for anchorage​ Penetration is greater for water and food storage

29. The tap root system of a tree is much wider than it is deep. This is because the upper soil is warmer, more fertile and has more air than subsoil.

30. You can see how shallow most roots are if a tree blows over. This is called a ‘root plate’

31. Eudicot transplanting is limited mainly by their taproot sensitivity and reduced ability to regenerate damaged roots. Careful handling and timing are key to successful transplanting. Transplant shock can have negative affects on our plant like: Stunted growth Reduce nutrient/water uptake Lead to wilting or death Transplant when tree is dormant Keep soil intact around roots during transplanting. Water thoroughly before and after transplant. Choose a cool, moist time of day to transplant (early morning or late afternoon).

32. Tree Selection What to Look for in Balled and Burlapped Trees

33. If a root is bent or distorted when a plant is potted up or planted out it may function well at first, but as it gets thicker and woodier the plant will lose vigour and may die or fall causing hazards These roots are called kinked or girdling roots

34. Roots of dicotyledons can become woody, but they do not grow as thick as trunks and main branches. This is because they do not need to resist gravity. These woody roots have been used ornamentally to create a rootery (also called a stumpery), a very Victorian era garden feature. Highgrove House

35. National trust biddulph grange garden

36. Adventitious Root System Both monocots and dicots can produce adventitious roots. Adventitious roots do not grow from a seed. They grow from other parts of the plant, such as stems. Adventitious roots can develop above or below ground. and are produced both during normal development and in response to stress conditions, such as flooding, nutrient deprivation, and wounding. . Root Types

37. Adventitious Foraging Root Foraging Stems and Tropism Foraging stems, such as stolons and runners, are horizontal stems that explore the environment to find optimal spots for new growth. Their direction and placement are guided by tropism, or growth responses to external stimuli. Types of Tropism in Roots Foraging roots are guided by several types of tropism: Light (Phototropism), Gravity (Gravitropism), Moisture (Hydrotropism), Touch (Thigmotropism), and Oxygen (Aerotropism). Root Function and Microbial Support These shoots are found behind the growing tip in younger roots, which are long and white. Foraging roots produce exudates that supply bacteria and fungi in the rhizosphere. Plant Physiology

38. 1900s: Early Propagation 1950s: Cloning Advances Adventitious roots were used to propagate plants like ficus and ivy, helping gardeners multiply plants easily. Cuttings and tissue culture used adventitious roots for mass propagation, boosting crop uniformity and yield. 2000s: Modern Challenges Cloning allows rapid, large-scale production of plants with desirable traits, but reduces genetic diversity and increases susceptibility to disease. Propagation Adventitious Roots in Propagation & Cloning

39. Propagation Methods of Adventitious Root Formation Most common method for adventitious root propagation. A piece of stem (with or without leaves) is cut from the parent plant and placed in soil or water. Adventitious roots grow from the cut surface. Examples: Rose, money plant, coleus, and hibiscus. A stem is bent down while still attached to the parent plant and covered with soil. Adventitious roots grow at the covered part; once rooted, it’s cut and planted separately. Types: Simple layering, air layering, mound layering. Examples: Jasmine, rose, strawberry, Ficus (via aerial roots). Stem Cuttings Layering In some species, new shoots and adventitious roots grow from pieces of existing roots. Examples: Blackberries, poppies, and sweet potatoes. Root Cuttings In some plants, leaves or leaf sections can grow roots and form new plants. Roots develop from the veins or edges of the leaf. Examples: Begonia, African violet. Leaf Cuttings Small plant tissues (explants) are grown in a nutrient-rich, sterile medium. Adventitious roots form from cells, producing many identical plantlets. Used for: Orchids, banana, and many ornamental plants. Tissue Culture (Micropropagation)

40. Aerobic Respiration in Roots Roots perform aerobic respiration using glucose and oxygen to produce energy (ATP), carbon dioxide, and water. Energy produced powers active transport of nutrients like nitrates and potassium into root cells. Aerobic respiration supports cell division and elongation at the root tip for growth. Respiration provides energy for forming symbiotic relationships with beneficial soil microbes, enhancing nutrient uptake. Roots also use energy to repair and regenerate after injury, maintaining root health and function. Respiration Roots, like all living plant parts, perform aerobic respiration: Glucose (C₆H₁₂O₆) + Oxygen (O₂)→Carbon dioxide (CO₂) + Water (H₂O) + Energy (ATP)

41. Soil that has been compacted and has less air spaces Deep soil -when soil levels around a tree have been raised there is less available oxygen. Soil that is flooded, filling air spaces with water Urban environments On building sites, the root zones of existing trees should be protected. Tree Protection Zone radius = at least 12 x the trunk diameter at 1.4m. Oxygen is less available in: Tree Health

42. Best Practice for Mowing and Soil Management Under Tree Canopies Avoid regular mowing or foot traffic directly under the canopy (the drip line) to prevent soil compaction, No-Dig Approach Do not mow over roots Apply organic mulch, keep mulch 5–10 cm deep and away from the trunk base to prevent rot. Limit Grass Competition Avoid growing turf grass under trees, as it competes with roots for water and nutrients. Avoid Heavy Equipment Recommended Practices Maintenance

43. In compacted soil, tree roots will follow cracks in soil or rocks or paving to get oxygen and water. Roots follow cracks in compacted soil They may be attracted to pipes for the same reasons. Roots attracted to pipes Root Behaviour Tree Roots Seeking Water and Oxygen

44. Raising the soil level over tree roots will reduce available oxygen and weaken the tree. Mature Golden Robinia, now almost dead New additional landscaping Raised soil level – changed one year ago Original soil level

45. The whole root zone should be protected from changed soil levels. We used to believe that protecting the trunk from soil would save the tree The tree dies from lack of oxygen to the roots, not rot around the trunk.

46. The rhizosphere soil is the thin layer clinging to roots after loose soil is shaken off. This area is rich in bacteria, nutrient cycling, & disease suppression, all occurring right next to the roots. The rhizosphere is the region of soil directly influenced by roots. Soil Biology

47. Key Concepts of the Soil Food Web Plants Fuel the System Root Exudates: Plants use energy from photosynthesis to secrete carbohydrates (sugars) and proteins , called exudates , through their roots. Rhizosphere: This secretion happens in the rhizosphere , the immediate zone around the roots. Controlling the Web: Plants are the central organisers, controlling the types and numbers of bacteria and fungi attracted to the rhizosphere based on the specific exudates they produce, which change with the plant's nutrient needs.

48. Rhizobia and Nitrogen Fixation in Legumes Rhizobia are soil bacteria which become established inside root nodules of legumes (the pea family: Fabaceae). They fix nitrogen in a form the plant can use. Rhizobia require a plant host; they cannot independently fix nitrogen. The relationship is a classic example of symbiosis and mutualism. This process is vital in agriculture, as it naturally enriches the soil with nitrogen, reducing the need for synthetic fertilisers. Legumes, such as peas, beans, and clover, benefit from this partnership, growing more vigorously and improving soil health for future crops. Symbiosis

49. How Beneficial Bacteria Help Plants Beneficial bacteria support plant growth in several ways. They make nutrients available for root absorption and produce growth hormones to boost development. These bacteria protect roots by blocking pathogens and triggering plant defences. They also clean soil by filtering out heavy metals and toxins. When beneficial bacteria die, they act as fertiliser, releasing nutrients back into the soil to support further plant growth.

50. Absorb water and nutrients (e.g., nitrates, potassium) using passive and active transport. Form symbiotic relationships (e.g., with fungi or nitrogen-fixing bacteria). Grow and divide cells in the root tip. Heal and regenerate after injury or pruning Roots are not just passive straws; they actively: Mechanical support Respire

51. Quizlet root-structures-flash-cards Plenary activity