Roots Flashcards
Roots Functions
- Support (anchoring)
- Absorb water and minerals
- Conduct water and minerals to and from the shoots
- Store water or food
How roots develop ?
Embryo contains a radicle
- Radicle –> is the embryonic root of the plant. May develop into:
* A long taproot
* Many adventitious roots (do not develop from another root, but develop from a stem or leaf)
* Fibrous roots system
Root Structures
- The root cap
- The region of cell division
- The region of elongation
- The region of maturation
Root Cap
- Composed of a thimble-shaped mass of parenchyma cells covering the tip of each root.
- Functions :Protect the delicate tissues behind it from damage as it pushes through soil particles, perception of gravity.
(Root cap) Movement through soil
- Dictyosomes in the root cap’s outer cells
secrete a slimy substance that moves
into the cell walls and eventually exits
Root Cap. - Outer cells of the root cap constantly slough off and are replaced from
the inside, forming a slimy lubricant, aids root tip movement through the soil.
(Root Cap) Perception of Gravity
- Amyloplasts (a plastid) act as gravity sensors, collecting on the
bottom of the root-cap cells. - When a root that has been growing vertically is tipped horizontally, the amyloplasts tumble or float down to
the new bottom of the cells in which they occur.
Region of Cell Division
- Composed of an apical meristem in the center of the root tip
- Produce the surrounding root cap
- Most cell divisions take place next
to the root cap
(Region of Cell Division)
In both roots and stems, the apical meristem soon subdivides into three meristematic areas:
What are they ?
- Protoderm (Gives rise to an outer layer of cells, the epidermis)
- Ground meristem (Produces parenchyma cells of the cortex)
- Procambium (Produces primary xylem and primary phloem)
Pith
- Parenchyma tissue originates from the
ground meristem - Generally present in stems but is absent in most dicot roots
- Present in grass roots and those of most other monocots
Region of Elongation
- Merges with the apical meristem
- The cells become several times their
original length and wider - Couse the root to lengthen
- Tiny vacuoles merge and grow until
one or two large vacuoles have been
formed - Occupy up to 90% or more of the
volume of each cell. - Only root cap and apical meristem push through the soil
- Remainder of each root remains stationary for the life of the plant.
- If cambium is present, there is a gradual increase in girth through the addition of secondary tissues.
Region of Maturation
- Most cells mature (or differentiate) into various distinctive types of the
primary tissues in this regions. - Region of differentiation
- Root-hair zone
Cortex
- Tissue composed by parenchyma. May
be many cells thick. - Loosely packed to allow for water and
minerals to move through the cortex
without entering the cells. - Mostly store food
- Similar to cortex of stems, except for
the presence of an endodermis at its
inner boundary.
Endodermis
- Consists of a single-layered cylinder of compactly arranged cells whose primary walls are impregnated with suberin.
- The suberin bands, called Casparian strips, are on the radial and transverse walls
- The plasma membranes of the endodermal cells are fused to the
Casparian strips.
Vascular Cylinder
- Lies to the inside of the endodermis
- Most of the cells of the vascular
cylinder conduct water or food in
solution.
- Lying directly against the inner boundary of the endodermis is an important layer
of parenchyma tissue known as… - Usually one cell wide, may in some plants
be a little wider. - The cells of the…..may continue to
divide even after they have matured. - Lateral (branch) roots and part of the
vascular cambium of dicots arise within
the….
Pericycle
Xylem in Roots
- In most dicot and conifer roots, the primary xylem consists of a solid central core of water-conducting cells (Tracheids; Vessels)
- Arms tend to taper toward their tips and
terminate just inside of the thin cylindrical
pericycle layer - There are usually four of these arms, with
some plants having two, three, or several - primary xylem surrounds pith parenchyma cells in monocot roots and those of a few dicots; in such plants, the arms may not be well defined
Phloem in Roots
- Primary phloem forms in discrete patches between the xylem arms of both dicot and monocot roots.
Movement of Water and Minerals
- There are two paths through which water and minerals can travel in a root.
What are they?
- Apoplastic – movement through cell walls and intercellular spaces. Resistance to flow is approx. 50 times less than resistance of
symplastic movement. - Symplastic – movement through living cells. Secondary route for water movement due to greater resistance to water flow.
Some plants have roots with modifications that adapt them for performing
specific functions as well as the absorption of water and minerals in
solution.
Those are ??
Specialized Roots:
- Food-Storage Roots
- Water-Storage Roots
- Propagative Roots
- Pneumatophores
- Aerial Roots
- Contractile Roots
- Buttress Roots
- Parasitic Roots
Food-Storage Roots
- Roots are enlarged and store large quantities of starch and other carbohydrates.
- CHOs may later be used for extensive
growth. - In carrots, beets, turnips, and radishes,
food storage tissues are a combination of
root and stem.
Water-Storage Roots
- Characteristic of plants that grow in arid
regions or in areas where there may be no
precipitation for several months of the year. - The water in the roots is apparently used by the plants when the supply in the soil is
inadequate.
Propagative Roots
- Many plants produce adventitious buds (buds appearing in places other.
than stems) along the roots that grow near the surface of the ground. - The buds develop into aerial stems called suckers, which have additional
rootlets at their bases. - The rooted suckers can be separated from the original root and grown individually.
- Cherries, apples, pears, and other fruit trees often produce suckers.
Pneumatophores
- Water contains less than one-thirtieth the amount of free oxygen found in the air
- Plants growing with their roots in water may not have enough O2 available for normal respiration in their root cells
- Spongy roots, which extend above the
water’s surface and enhance gas exchange between atmosphere and the subsurface roots to which they are connected
Aerial Roots
- Velamen roots of orchids (May function in preventing loss of moisture from the root)
- Prop roots of corn and banyan trees
(Support the plant in high wind) - Adventitious roots of ivies
(Helps in climbing) - Photosynthetic roots of certain orchids
Contractile Roots
Some herbaceous dicots and monocots
have contractile roots that pull the plant
deeper into the soil.
Buttress Roots
- Some tropical trees growing in shallow
soils produce huge, buttresslike roots
toward the base of the trunk, giving
them great stability - Except for their angular appearance,
these roots look like a part of the trunk
Parasitic Roots
- Some plants, including dodders, broomrapes, and pinedrops, have no chlorophyll and have become dependent on chlorophyll-bearing plants for their
nutrition (enable to do PS) - Parasitize their host plants via peglike projections called haustoria, which develop along the stem in contact with the host.
- The haustoria penetrate the outer tissues and establish connections with the xylem and phloem.
Mycorrhizae
- More than 95% of the plants have fungi associated with their roots.
- Mycorrhizae are fungi that have a symbiotic (mutualistic) relationship with the roots of many plants
- “mycorrhiza” means
fungal root
Mycorrhizae – Benefits to the plant
- The fungus can absorb and concentrate P much better than root hairs.
- The fungus also often forms a mantle of millions of threadlike strands that facilitate the absorption of water and nutrients
Mycorrhizae – Benefits to the fungus
- The plant furnishes sugars and amino acids without which the fungus cannot survive.
Ectomycorrhizae
- For some mycorrhizae, the fungal
hyphae penetrate the root cortex, but
the hyphae do not enter the cells - On the root surface, the hyphae form
a thin, encrusting layer called mantle - This type of mycorrhiza is termed
ectotrophic - Common in trees like pines and
oaks
Endomycorrhizae
- In another type of mycorrhiza, the hyphae invade the cells of the cortex, and a mantle is not present.
- This type of mycorrhiza is termed endotrophic.
- Found in the majority of woody and
herbaceous land plants.
Nature of the Association
Between Rhizobia and Legumes
- Symbiotic relationship, mutually
beneficial. - Plants provide energy for rhizobia
(sugars, carbohydrates, ATP) to fix N2. - Rhizobia in turn provide N for
production of proteins by the host.
Is Nitrogen (N) is an important nutrients?
Yes, it is in fact the most common nutrient in plant.