Today: -Introduction to Plant Anatomy

Plant Morphology Reflects the demands of two very different environments: Soil and Air Intro to Plant Anatomy

The Root System Functions:???

Root Systems Monocots: typically have fibrous root systems (mats of thin roots below the soil surface) Dicots: typically have a taproot system (one large vertical root with smaller lateral roots)

Root Modifications Both Monocots and Dicots use root hairs at the root tips. Why??

Both may have adventitious roots arising from stems or leaves Root Modifications

Many Modified Shoots Look Like Roots! Roots StemLeaves Axillary buds Swollen Ends of Rhizomes!

Plant Organs are Composed of 3 Tissues: 1. Dermal Tissue 2. Vascular Tissue 2. Vascular Tissue 3. Ground Tissue

1. Dermal Tissue (Epidermis) Single layer of tightly-packed cells Single layer of tightly-packed cells Covers and protects young plant parts Covers and protects young plant parts May have other specialized functions: May have other specialized functions: Example: Root hairs or the Cuticle secreted by leaves and stems

2. Vascular Tissue Transports materials between roots and shoots Transports materials between roots and shoots Composed of xylem and phloem Composed of xylem and phloem

2. Vascular Tissue Wood is composed primarily of vessels and tracheids

Plant Cell Walls: A Quick Review Note the thick, secondary wall!

2. Vascular Tissue: Xylem Tracheids have secondary walls hardened with lignin, allowing them to function in support Tracheids have secondary walls hardened with lignin, allowing them to function in support Water is transported through pits in the secondary cell wall. Water is transported through pits in the secondary cell wall. Vessel elements are wider, shorter, and have thinner walls. They align end to end to form “pipes” or xylem vessels. Vessel elements are wider, shorter, and have thinner walls. They align end to end to form “pipes” or xylem vessels.

2. Vascular Tissue: Phloem Sugars and other organic molecules and ions are transported through chains of specialized cells- the sieve tube members.

Sieve-tube members are alive, but have no nucleus or ribosomes! Each sieve-tube has a nonconducting companion cell connected by plasmodesmata 2. Vascular Tissue: Phloem

3. Ground Tissue Ground tissue is tissue that is neither dermal or vascular! Functions include photosynthesis, storage and support. In dicot stems (above), ground tissue is divided into pith (C) inside the vascular tissue and cortex (D), outside the vascular tissue

Cell Types All plant tissues are composed of three basic cell types: 1. Parenchyma Cells 2. Collenchyma Cells 3. Sclerenchyma Cells

Cell Types: Parenchyma Cells Thin, flexible primary walls Thin, flexible primary walls Typically no secondary wall Typically no secondary wall Large central vacuole Large central vacuole Typically generalists! But sieve-tube members (phloem) are also parenchyma cells Typically generalists! But sieve-tube members (phloem) are also parenchyma cells

Developmentally important, and used in repair and replacement! Can generate an entire plant from a parenchyma cell! Cell Types: Parenchyma Cells

Collenchyma Cells Thicker (but uneven) primary walls Thicker (but uneven) primary walls Grouped in strands or cylinders to support young plant shoots Grouped in strands or cylinders to support young plant shoots Provide support without restraining growth (no lignin!) Provide support without restraining growth (no lignin!)

Sclerenchyma Cells Thick secondary walls (with lignin) Thick secondary walls (with lignin) Many are dead at functional maturity Many are dead at functional maturity Example: vessel elements and tracheids Fibers and sclereids are sclerenchyma cells specialized entirely for support. Fibers and sclereids are sclerenchyma cells specialized entirely for support.

Shoot Anatomy Shoots are composed of stems and leaves, and may be vegetative or reproductive Stems are alternating nodes (where leaves are attached) and internodes (stem segments between nodes)

At the intersection of each leaf and the stem is an axillary bud with the potential to form a vegetative branch. Most axillary buds of a young shoot are dormant. Shoot Anatomy

Growth of a young shoot is typically concentrated at the terminal bud (apex) Presence of the terminal bud helps inhibit growth of axillary buds ( apical dominance ) Shoot Anatomy

Leaves Most leaves are composed of a flattened bladeand a stalk, the petiole Most leaves are composed of a flattened blade and a stalk, the petiole

So what’s this? One petiole…. No axillary buds…

Many leaves are specialized for functions besides photosynthesis! Leaves

Plant Anatomy: A Quick Review

Tissue Systems in a Leaf

In dicots, two distinct regions of mesophyll: 1. Palisade Parenchyma- columnar cells 1. Palisade Parenchyma- columnar cells 2. Spongy Parenchyma- multiple air spaces (esp. near stomata) 2. Spongy Parenchyma- multiple air spaces (esp. near stomata) The Leaf Ground Tissue Lots of surface area! Hmm….

Plant Growth Most plants have indeterminate growth Most plants have indeterminate growth May be annual, biennial, or perennial May be annual, biennial, or perennial CREDIT: "Falling an old-growth redwood, 1985." Photo by Karen Tillson for "Timber and Forests: Post war to Present," a California Local Legacies project.

Indeterminate growth is possible because of meristems, regions of perpetually embryonic tissues Plant Growth 1.Growth in Roots 2.Growth in Shoots

Elongation of roots and shoots from the apical meristems is called primary growth Progressive thickening of roots and shoots as a product of lateral meristems is called secondary growth Both occur simultaneously in woody plants! Plant Growth

Revisiting Roots What did you notice when you drew the root tip??

Primary Growth in Roots

A Typical Dicot Root

A Typical Monocot Root

Lateral roots form from the outermost layer of the stele, the pericycle Primary Growth in Roots

Secondary Growth of Roots Two lateral meristems create secondary growth: 1. The Vascular Cambium- produces secondary xlyem (wood) and phloem 2. The Cork Cambium- produces a tough thick covering, the periderm, that replaces the epidermis (and is impermeable to water!!)

Primary Growth in Shoots Apical Meristem Leaf Primordia Axillary bud meristems

Primary Growth in Shoots Apical meristem gives rise to protoderm, procambium and ground meristem

Primary Tissues In Stems Vascular tissue is packed in vascular bundles

Primary Tissues In Stems Vascular tissue is packed in vascular bundles

Secondary Growth in Shoots Vascular cambium = cylinder of meristematic cells Originates from parenchyma cells that regain the capacity to divide

Secondary Growth in Shoots

Each time a cambium cell divides (C), one daughter cells continues as an initial, the other becomes the derivative (D)

Secondary Growth in Shoots As the diameter increases, a second lateral meristem, the cork cambium, develops from parenchyma cells in the cortex

Dead cork cells (from the cork cambium) provide a barrier to water loss, physical damage, and pathogens Secondary Growth in Shoots

Original cork cambium is a fixed size! New cork cambium must continually form deeper in the cortex, and eventually from the secondary phloem. (So only the youngest secondary phloem functions in sugar transport!)

Bark Bark = all tissues external to the vascular cambium (secondary phloem, cork cambium, and cork)

Bark The periderm (cork + cork cambium) may split open. The openings ( lenticels ) allow for gas exchange for cellular respiration This species of Jatropha (Family Euphorbiaceae) of western Mexico has conspicuous horizontal lenticels on its smooth, peelable red-brown bark. Photo: Ontario Ministry of Agriculture and Food

Growth Rings In temperate regions, secondary growth is interrupted each winter (vascular cambium becomes dormant) Early wood (spring) has larger tracheids and vessels with thinner walls Late wood (summer) has thicker cell walls

Heartwood- older, no longer functions in water transport (support), cell cavities typically clogged with resins Sapwood- secondary xylem still functional

Generating a Stem Diagram: Primary xylem, secondary xylem, primary phloem, secondary phloem, pith, periderm, cortex, vascular cambium, cork cambium, cork, heartwood, sapwood