Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 7: Roots (Other Types of Roots and Root Modifications (Mycorrhizae…
Chapter 7: Roots
Other Types of Roots and Root Modifications
Prop Roots
Buttress Roots - Their upper side grows more rapidly than other parts of the root
Prop Roots - Makes contact with the soil
Aerial Roots of Orchids
Storage Roots
Root Nodules and Nitrogen Fixation
#
Infection Thread - In the formation of root nodules
Root Nodules -A small swelling or aggregation of cells in the body
Nitrogen Fixation - The chemical conversion of atmospheric nitrogen into useable compounds
Mycorrhizae
Ectomycorhizal relationships - Exists in which fungal hyphae penetrate between outermost root cortex cells
Endomycorrhizal relationships - In which the hyphae penetrate the root cortex as far as the endodermis
Mycorrhizae - Roots of most species of seed plants (at least 80%) have a symbiotic relationship with soil fungi in which both organisms benefit
Contractile Roots
Gladiolus
Crinum
Oxalis
Haustorial Roots of Parasitic Flowering Plants
Haustoria - A slender projection from the root of a parasitic plant
Parasitic plant - Tristerix
Roots of Strangler Figs
Origin and Development of Lateral Roots
Lateral roots are initiated by cell divisions in the pericycle
The activity is localized to just a few cells
Creating a small root primordium that organizes itself into a root apical meristem and pushes outward
As the root primordium swells into the cortex
The new lateral root destroys cells of the cortex and epidermis that lie in its path
Forms a root cap and establishes a connection to the vascular tissues of the parent root
Internal Structure of Roots
Zone of Elongation
#
Cells expand greatly
Similar to the shoot's subapical meristem region
Just behind the root apical meristem
Outermost cells are protoderm and differentiate into epidermis
Center is composed of provascular tissue
Primary xylem
Primary phloem
Tissues are all quite permeable
Minerals penetrate deep into the root through apoplast
Little absorption actually occurs
Zone of Maturation/Root Hair Zone
Root hairs grow outward, greatly increasing absorption of water and minerals
Zone of elongation merges gradually with the zone of maturation
Cells differentiate into different types of cells
Minerals don't have free access to the vascular tissues
Casparian Strips - Are involved in controlling the types of minerals that enter the xylem water streams
Pericycle - Between the vascular tissue and the endodermis are parenchyma cells that constitute an irregular region
Root Apical Meristem
Examined in relationship to the root tissues it produces, regular files of cells can be seen to originate in the meristem
Extends into the regions of mature root tissues
Is the region within the growing root containing meristematic cells
Their nuclei do not take up the thymidine and thus does not become radioactive
Quiescent Center
Mature Portions of the Root
Root pressure - The absorption of minerals in the root hair zone causes a powerful absorption of water, and a water pressure
Could force the water to leak out into the cortex
The large fibrous roots of many monocots are strictly annual
Passage cells - Enables an individual to keep cells alive and growing
Root Cap
Root is growing through the edges of the root cap
Develop dense starch grains and their endoplasmic reticulum becomes displaced to the forward end of the cell
Provide effective protection, structure, and growth
Cells pushed closer to the edge - causes dramatic structure and metabolism
Approximately 4 or 5 days pass from cell formation in the root cap to its sloughing off
External Structure of Roots
Structure of Individual Roots
Root tips is the region where growth in length occurs
With apical growth, only the extreme tip pushes through the soil
An individual root is fairly simple
Root cap - is a type of tissue at the tip of a plant root.
#
Whereas the shoot apical meristem is protected by either bud scales or young, unexpanded foliage leaves, the root apical meristem is protected by the root cap
Sand grains, crystals, and other components
Dictyosomes secrete a complex polysaccharide called mucigel, which lubricates passage of the root through the soil
Mucigel is rich in carbohydrates and amino acids
Zone of Elongation
Only a few milliters long within which the cells undergo and division and expansion
Just behind the root cap and root apical meristem
Root Hair Zone
Region in which many of the epidermal cells extend out as narrow trichomes
Root hairs
Form only in a part of the root that is not elongating
A hairlike outgrowth of a plant root
Behind the zone elongation
Organization of Root Systems
Most seed plants have a single prominent taproot that is larger than all of the rest
Have lateral and branch roots
Highly ramified set of roots analogous to the branched shoot system of most plants
Lateral roots can become swollen like a taproot
Sweet potatoes
Tropical vegetable manioc (cassava)
Lateral roots may also produce more lateral roots
Perennial and woody - roots also undergo secondary growth
Produces wood and bark
Roots have an enormous adaptive surface
Carrots, beets, turnips, and other taproots sold in stores have dozens of lateral roots
Taproot develops from the embryonic root (radicle)
Fibrous root system
This arises because the radicle dies during or immediately after germination
As the plant ages, more root primordia are initiated in the stem tissue
Most monocots and some eudicots have this
Adventitious roots - Roots that do not arise from preexisting roots and are not radicles
Eudicots and Monocots
#
Most monocots cannot undergo secondary growth
After stem is formed - number of vascular bundles, tracheary elements, and sieve tubes are set
The ability to form adventitious roots is not limited to monocots
Many eudicots are perennial and undergo secondary growth
Results in an increased quantity of healthy, functional wood (xylem) in both the trunk and roots
Seed plants - conifers and cyads
