BOTA 205 Lecture 7 Vascular Tissue Systems

Vascular and Dermal Tissue Systems

Plant systems responsible for transport, support, and protection; present throughout all plant organs.

Vascular Tissue System

Facilitates long-distance transport of materials and provides mechanical support.

Vascular Tissues

Xylem and Phloem.

Xylem

Transports water and dissolved minerals upward from roots; provides structural support.

Phloem

Transports sugars and other organic nutrients from sources (leaves) to sinks (roots, fruits, etc.).

Xylem Conducting Cells

Tracheids and vessel elements; dead at maturity, form hollow tubes for water flow.

Phloem Conducting Cells

Sieve-tube elements; alive but lack a nucleus and depend on companion cells for metabolism.

Lignin Reinforcement

Hardens xylem secondary walls to prevent collapse during water transport and add strength.

Pits

Thin wall regions in xylem that allow lateral water movement between adjacent cells.

Tracheids

Long, thin, tapered xylem cells; found mainly in gymnosperms and seedless vascular plants.

Vessel Elements

Wider, shorter xylem cells stacked end-to-end to form vessels; main water conduits in angiosperms.

Perforation Plates

Holes in end walls of vessel elements allowing free water flow through vessels.

Xylem Parenchyma

Cells within xylem that store materials.

Xylem Fibers

Supportive, lignified cells that add structural strength.

Phloem Composition

Sieve-tube elements, companion cells, phloem fibers, and phloem parenchyma.

Sieve-Tube Elements

Long, thin living cells joined end-to-end for sugar transport; lack nucleus and most organelles.

Sieve Plates

Porous end walls between sieve-tube elements enabling nutrient flow.

Companion Cells

Metabolically active cells that regulate and maintain adjacent sieve-tube elements.

Plasmodesmata

Cytoplasmic channels connecting sieve-tube elements and companion cells for communication.

Sieve Cells

Long, narrow sugar-conducting cells in gymnosperms and seedless vascular plants (instead of sieve tubes).

Photosynthate

Transported mixture of sugars, water, amino acids, hormones, and minerals in phloem sap.

Dermal Tissue System

Outer protective covering of plants; includes epidermis and periderm.

Epidermis

Single-cell-thick outer layer on primary plant body (herbaceous and young woody plants).

Cuticle

Waxy layer secreted by epidermal cells on aerial organs to prevent water loss.

Stomata

Pores in the epidermis for gas exchange; each surrounded by two guard cells.

Guard Cells

Control opening and closing of stomata to balance CO₂ intake and water loss.

Stomatal Regulation

Open during day for photosynthesis; close at night or during drought to conserve water.

Trichomes

Hairlike outgrowths of the epidermis with diverse roles such as absorption, defense, reflection, and secretion.

Root Hairs

Simple trichomes that increase root surface area for water and mineral absorption.

Defensive Trichomes

Contain irritating or toxic substances (e.g., stinging nettle).

Reflective Trichomes

Help desert plants reflect sunlight, keep cooler, and reduce water loss.

Salt-Excreting Trichomes

Remove excess salts in plants from saline environments.

Cotton Fibers

Commercially valuable trichomes attached to seeds.

Periderm

Secondary protective tissue replacing the epidermis in older woody plants; forms outer bark.

Cork Cambium

Meristematic tissue that produces periderm.

Cork Cells

Dead at maturity; walls impregnated with suberin for waterproofing and protection.

Suberin

A waxy substance in cork cell walls that prevents water loss.

Cork Parenchyma (Phelloderm)

Living storage cells within the periderm.

Function of Periderm

Protects woody plants, prevents water loss, and replaces the sloughed-off epidermis.