Root Structure and Function Flashcards
root function
- conduit of vascular cylinder (Stele): xylem/phloem
- absorption of water and nutrient minerals
- anchor plants
- water/food storage
- aide in asexual reproduction
- produce hormones and secondary metabolites, that regulate plant development and communication
root systems
embryo radicle emerges immediately upon germination
radicle -> primary root -> secondary roots form
root systems can be fibrous or taproot
root systems: fibrous
- found in monocots and some dicots
- made of large % fine roots of similar diameter
- adventitious roots form from stem or leaf
- lateral roots form from adventitious roots
- typically shallow, increased # root lead to improved water acquisition; not drought tolerant
- stabilize soil, decrease erosion
monocot root
- a core of parenchyma cells (pith) is surrounded by rings of xylem and phloem
- pith cells arise from procambium and not ground meristem
root systems: tap root
- found in dicots and gymnosperms
- thick tap root
- from tap root, thinner secondary roots (lateral roots) form
- dive deep into soil
- not as effective water absorption as fibrous root systems, but allow plants to survive under drought condiions
- in dicots, can be used for water/food storage
dicot and conifer roots
- dicots and conifer gymnosperms have “arms” of xylem with phloem patches in between, no pith
root specialization: water storage
- some members of pumpkin family Cucurbitaceae produce water storage roots
- help survive in arid environments
- roots function as water reserve
root specialization: food storage
- many plants (root vegetables) store starch in roots: sweet potatoes, dandelions
- storage cells are increased number of parenchyma, formed by anomalous secondary growth
external root structure
- lateral roots
- root hair
- root cap
lateral roots
form from pericycle in region of root that has completed primary growth
root hair
epidermal cell extensions; aide in water/nutrient absorption
root cap
mass of parenchyma cells that cover each root tip
- protect tissues from damage as root grows, first cell layer has waxy cuticle
- secretes mucilage that aides in growth through soil and provides medium for beneficial bacteria
- amyloplasts in tip act as gravity sensors
12 essential nutrient elements (minerals)
roots compete with negatively charged soil silicates (SiO4 -4) for minerals and water
macronutrients:
- primary: nitrogen, phosphorus, potassium
- intermediate: sulphur, calcium, magnesium
micronutrients:
- iron, zinc, manganese, molybdenum, copper, boron
root hairs functions/characteristics
- adhere tightly to soil to compete for water/nutrients
- increase total surface area of absorption
- in growing roots, near root hairs are continuously formed with older root hairs dying off; root hairs always in zone of maturation near root cap
root chemical protection
- woody gymnosperm roots have resin canals
- dicot taproots produce latex
- polyphenol flavonoids with anti-fungal, anti-viral, anti-microbial properties accumulate in root cell vacuoles
root absorption
- to aide absorption, epidermal root hairs do not have a cuticle
- permeable to water, solutes, and potentially invasive microorganisms
- reduce %infection, roots impregnate key cell layers of cortex with suberin and lignin to restrict water/solute movement
- Casparian strips are deposits of lignin and suberin in radial primary cell wall and middle lamella of endodermis and exodermis
casparian strips
deposits of lignin and suberin in the radial primary cell wall and middle lamella of endodermis and exodermis
what plants have endodermis and exodermis?
all vascular plants have an endodermis, and almost all seed vascular plants have an exodermis
endodermis and exodermis
- both part of root cortex and have casparian strips
- exodermis outermost cell layer of cortex
- endodermis innermost cell layer of cortex (layer above pericycle and vascular cylinder)
- passage cells of endodermis/exodermis lack casparian strips to allow passive transport of solutes into vascular cylinder; not always present
Mycorrhizae mutualistic relationships
- > 75% vascular plant species have funal associations with roots, mycorrhizae essential for development
- mutualistic as both fungus and root benefit and are dependent
- fungi facilitate water/nutrient absorption, esp phosphorus
- root provides protection, sugars, and amino acids to fungus
2 types of mutualistic fungi
ectomycorrhizae and endomycorrhizae
ectomycorrhizae
- fungi remain on surface (epidermis), forming a mantle around the root
- plant: increase mineral absorption that accumulate in mantle coated root hairs
- fungi: solid substrate to grow on
endomycorrhizae
- fungi penetrate root cortex (parenchyma cells)
- fungi form branching structures (arbuscules)
- plant: increased absorption of nutrients, esp phhosphorous
- fungi: food (carbohydrates) and protection
bacterial root nodules
some species of bacteria (rhizobia) form association with legumes (Fabaceae)
- rhizobia have enzymes that convert (fix) N from atmosphere into plant usable formes (nitrates and ammonia)
- root nodules contain large numbers of nitrogen-fixing bacteria
