Plant kindom

Plant Morphology
& Anatomy
Plant Organs
Types of Plant Organs
Vegetative organs:
Roots
Leaves
Stems

Reproductive organs:
Flowers
Fruits
Plant Body Systems
The plant body is organized into a root system and a shoot system:
Root system is generally below ground.
Shoot system consists of vertical stems, leaves, flowers, & fruit s that contain seeds.

Root System
“absorbtion” and “anchorage” …
The Root System
Although we do not see much of roots, they are equally important to plant growth as stems and leaves …
Leaves collect light and CO2 to produce sugar for growth as long as the plant can get enough water and nutrients from its roots!
Types of Root Systems
A true root system consists of both primary & secondary roots (lateral roots)
Primary root system:
Taproot System*
Fibrous Root System**
Adventitious Roots**


*Found in most dicots
**Found in most monocots
Primary Root System
The 1st root to emerge from a seed is the radicle (primary root), which emerges to form a taproot that persists throughout the life of the plant.
Many progressively smaller branch roots (lateral roots) grow from the taproot.

Taproot System
Definition: the root system consisting of a thick, central primary root, which forms many smaller lateral roots.
Common in dicots and conifers.
In some plants such as carrots and beets, fleshy taproots are the plant’s “food pantry”.
In other plants the long taproots are modified for reaching water deep in the ground.
Fibrous Root System
Definition: root system that consists of several to many roots of the same size that develop from the end of the stem with smaller, lateral roots branching off of them.
Typically slender, small roots
Found in monocots like onion, sweet potatoes, etc…
Form in plants in which the embryonic root is short-lived.
Fibrous Root System
Most fibrous roots are very extensive and cling to soil particles, >>> can be used for preventing erosion.

Fibrous roots do not arise from preexisting roots but rather from the stem.
Adventitious Roots
Definition: roots that arise on organs other than roots

Usually begin growing after the seed germinates

They form in all sorts of places on plants including leaves, petioles, and stems.
Adventitious Roots
Why Different Root Types?
Help plants compete for water and minerals …
- Shallow, wide-spreading fibrous roots: <15 cm deep

- Medium-depth, evenly distributed fibrous roots (<1.5 m deep)

- Deep taproots (lack width, but go deeply)
Root Functions
Primary & Specialized
Primary Root Functions
Roots perform 4 main functions:
Absorption/Conduction of water and dissolved minerals
Anchorage
Storage (carbohydrates)
Production of hormones (e.g., gibberellins) & secondary plant compounds (e.g., nicotine in tobacco plants)
Some specialized roots are modified for other functions ….
Specialized Roots
Prop/Stilt roots
Aerial roots
Strangling roots
Contractile roots
Parasitic roots (haustoria)
Storage roots
Buttress roots
Pneumatophores
Prop or Stilt Roots
Help to stabilize and support the plant.

Examples:
Ficus
Corn

Aerial Roots
Absorb water from the air; may also be photosynthetic
Examples:
Orchids

Anchor plant to the soil and support the tree

Strangling Roots
Help the plants to “climb” up another tree to get to sunlight; eventually will “strangle” the host plant (parasitic)

Example: Fig
Contractile Roots
Pull the plant shoot closer to the ground or deeper into the soil where the soil is relatively warm, helping plants survive variable early spring weather

Example: Dandelion
Parasitic Roots (Haustoria)
Penetrate the stems & roots of host plant to obtain water, minerals, and organic molecules


Storage Roots
Store water & food

Examples:
Carrot
Beet

Buttress Roots


Stabilize plants in thin soil & prevent uprooting.


Pneumatophores (air roots)
Supply oxygen to plants growing in swamps where water may be deoxygenated

Examples:
Mangrove trees
Root Structure
Intimately related to root function …
Primary Structure of a Root
Relates to obtaining water and dissolved minerals
Cross-section shows that roots consist of cylinders:
Epidermis--protection
Cortex--storage of starch
Vascular tissue —transport of water & food
Monocot vs. Dicot Root
External Root Structure
Branch roots
Root hairs
Root tip (root cap and apical meristem)
Branch Roots
Also known as lateral roots or feeder roots when they are young
Decrease in age from the soil surface to the root tip
Youngest roots occur closer to the root tip
Soil texture influences root branching:
Plants that must grow through hard, dry soil have fewer branch roots than those in moist, loose soil.
Root hairs
Definition: short-lived, single-celled extensions of epidermal cells near the growing root tip.
Form in the region of maturation
Short, but numerous
Function: raise absorptive capacity of the root by increasing surface area of the root that is in contact with moist soil.
Root cap
Definition: a protective thimble-like layer many cells thick that covers the delicate root apical meristem
As the root grows and pushes its way through the soil, parenchyma cells of the root cap slough off and are replaced by new cells
Root cap
The root cap consists of two types of cells:
Columella cells
Peripheral cells
Peripheral cells
Columella cells
Root apical Meristem
Regions of growth and development
Located in the cone-shaped root tip
Divided into 3 regions:
Region of division (grow & divide)
Zone of elongation (enlarge & specialize)
Zone of maturation (differentiation)
Mucigel
A hydrated polysaccharide containing sugars, organic acids, vitamins, enzymes, and amino acids.
Functions:
Protection – from other plant’s roots
Lubrication – lubricates roots as they move through the ground
Water absorption – help maintain the connection between roots and water for a continuous flow
Nutrient absorption – helps take in nutrients through intake of water
Roots Have Cooperative Relationships with Others …
Roots often form mutualistic (beneficial) relationships with other organisms:
Mycorrhizae: mutualistic associations between plant roots and soil fungi;
Plants gain increased absorption of minerals and don’t need to produce as many root hairs; also fungi may protect against disease-causing fungi & worms. (Fungus gets “food”.)
Occurs in 80% of plants.
Roots Have Cooperative Relationships with Others …
Nitrogen-fixing Bacteria: Bacteria can convert nitrogen gas from the air into ammonium, which is incorporated into various organic molecules, which plants can take up.
Only way for plants to get “useable” nitrogen.
Root nodules (see pictures to the right) are the “homes” of bacteria in the plants.
The End
Columella cells
Elongate cells that contain 15-30 amyloplasts that sediment in response to gravity to the lower side of the cell.
This is how plant roots perceive gravity.
Peripheral cells
Columella cells differentiate into peripheral cells within 2-3 days, which surround the columella cells.
Thousands of these cells are shed from the cap as the plant pushes through the soil.
Peripheral cells secrete large amounts of mucigel—a slimy substance with many functions …

Peripheral cells
Mucigel