Plant-Tissues-Roots

Plant Tissues Overview

  • Multicellular organisms have cells organized into tissues that function collectively.

  • In plants, tissues are crucial for the functioning of organs and organ systems.

  • Classification of plant tissues can be based on origin, structure, and function.

Types of Plant Tissues

1. Meristematic Tissues

  • Definition: Tissues where cells actively divide to produce more cells.

    • Characteristics: Small size, large nucleus, and tiny/absent vacuoles in new cells.

    • As they mature, they assume various shapes and functions.

  • Types based on location:

    • Apical Meristems:

      • Found at tips of shoots and roots; increase length.

      • Produce primary meristems: protoderm, ground meristem, procambium.

    • Lateral Meristems:

      • Increase girth of the plant, located along roots and stems.

      • Include vascular cambium and cork cambium in dicots.

    • Intercalary Meristems:

      • Found near nodes, increase stem length, short-lived.

2. Permanent Tissues

  • Definition: Tissues derived from meristems that have matured into structurally and functionally specific cells.

  • Types based on cell type:

    • Simple Permanent Tissues: Composed of one kind of cell.

    • Complex Permanent Tissues: Composed of different cells working together.

Simple Permanent Tissues

  1. Parenchyma:

    • Most abundant tissue; spherical in young, various shapes upon maturation.

    • Thin-walled, large vacuoles; functions include storage of food and waste.

    • Variants include: aerenchyma (air spaces) and chlorenchyma (chloroplasts).

  2. Collenchyma:

    • Thick-walled, unevenly thickened cells; occur beneath epidermis.

    • Provide flexible support; longer than they are wide.

  3. Sclerenchyma:

    • Thick-walled, tough, often dead at maturity; provide support.

    • Types include sclereids (short, irregular) and fibers (longer, with tiny lumen).

  4. Epidermis:

    • Outermost cell layer of young plant organs;

    • Secretes cutin (protective cuticle), may have trichomes and stomata.

  5. Cork:

    • Protective layer of old stems and roots; dead cells with suberin.

  6. Secretory Tissues:

    • Cells that produce hormones or waste products.

    • Examples: nectar, oils, mucilage, latex, resin.

Complex Permanent Tissues

1. Xylem

  • Responsible for water and minerals transport from soil to plant.

  • Composed of:

    • Xylem Fibers: Provide support.

    • Xylem Parenchyma: For nutrient storage.

    • Vessels: Long tubes for water transport.

    • Tracheids: Elongated cells aiding in water movement.

  • Types of tracheary elements:

    • Spiral, Scalariform, Pitted, Reticulate, Annular – differentiate by wall thickening types.

2. Phloem

  • Transports food produced in leaves.

  • Composed of:

    • Companion Cells: Support sieve tubes.

    • Phloem Fibers: Provide structural support.

    • Phloem Parenchyma: For nutrient storage.

    • Sieve Tube Elements: Live cells, do not have nuclei, facilitate metabolic functions.

Roots

External Morphology

  • Functions of roots:

    • Anchorage: Stabilize the plant.

    • Absorption: Water and minerals uptake.

    • Conduction: Transport water and nutrients.

    • Storage: Store energy in forms like starch.

    • Reproduction & Photosynthesis.

  • Types of Root Systems:

    • Taproot System: One main root, common in dicots.

    • Fibrous Root System: Numerous small roots, typical in monocots.

    • Adventitious Root System: Roots from non-radicle parts like stems and leaves.

Internal Morphology

  • In young dicot root cross-section, regions include:

    1. Epidermal Region: Single-layer outer cells with root hairs.

    2. Cortex Region: Layer of parenchyma for storage.

    3. Endodermis: Innermost cortex layer, suberin bands (Casparian strips).

    4. Stele or Vascular Cylinder: Central portion with pericycle and vascular tissues; xylem is often star-shaped.

Anatomy of Monocot Roots

  • Similar regions (epidermis, cortex, stele) as dicots but differ in protoxylem and pith presence.

Regions in Dicot Roots

  1. Region of Cell Division (Meristematic): Actively dividing cells.

  2. Region of Elongation: Cells elongate, push root into soil.

  3. Region of Maturation: Specialization of cells, forms root hairs for absorption.

Specialized Roots

  • Types of Specialized Roots:

    1. Food Storage: Enlarged roots with starch.

    2. Water Storage: Fleshy roots.

    3. Reproduction: Adventitious root buds.

    4. Gas Exchange: Pneumatophores in mangroves.

    5. Support: Buttress roots, prop roots.

    6. Protection: Spines/thorns.

    7. Photosynthesis: Green aerial roots.