1. Chapter 4:
Roots, stems & leaves

2. Root systems Tap root system- Tap root + lateral roots branch of tap
explore soil deeper
Fibrous root system- develops from adventitious rooting
soil exploration shallow
What are the advantages/disadvantages to exploring in
shallow vs. deep soil horizons
Root architecture

3. Root development Root apical meristem (quiecent center)- cell division
Root cap- protects root apical meristem
mucigel (polysaccharide)- soil lubricant
Zone of elongation- cell growth (through expansion)
Zone of maturation- cell differentiation
Root hairs- produced in zone of maturation
Increases cell surface area- high water & mineral absorption

4. Root anatomy and water movement
Water movement through root
Apoplastic transport: movement between cells
Symplastic transport: movement through cells
Endodermis- regulates water and mineral movement into vascular tissue
Casparian strip – suberin (waxy, hydrophobic compound)- forces water
and nutrients moving in apoplastic pathway to pass through plasma
membrane of the endodermis
Symplastic
Apoplastic

5. Lateral root initiation
Pericycle -ring of meristimatic cells that give rise to lateral roots
-located just inside of the endodermis

6. Specialized roots Aerial roots
attachment; water & nutrient acquisition in epiphytes
Pneumatophores
oxygen acquisition in mangrove and swamp plants
Haustoria
parasitic plant roots- suck
resources from other plants

7. Root symbiosis: root-microbe associations
Mycorrhizas
N and P acquisition in
exchange for fixed carbon
Biological nitrogen fixation
N acquisition

8. Stems- nodes and internodes
Node: point on stem where leaf and axillary meristems are located
Internode: stem sections between nodes- elongation results in primary growth

9. Specialized stems Types: Stolons, rhizomes, tubers, bulbs, corms
Function: asexual reproduction

10. Leaf development
Plant first had photosynthetic stems; leaves evolved from flattened stems that grew together.
Apical meristem
Leaf primordia
Cell expansion
Cell differentiation

11. Leaf anatomy Mesophyll– Internal leaf cells packed with chloroplasts
Number of palisade mesophyll layers varies with light environment
Spongy mesophyll loose for easy gas diffusion
Vascular bundle (vein) delivers water & nutrients, exports sugars
Epidermis with waxy cuticle- upper and lower surface
Stomata- pores in epidermis that regulated leaf gas exchange
Guard cells- determine stomatal aperature (openness)

12. Leaf responses to light

13. Leaf epidermis
Epidermis –provides protection from pathogens and prevents water loss
waxy cuticle (cutin)
Stomata – regulate leaf gas exchange (balance carbon gain with water loss)
Stomatal pore is flanked by guard cells

14. Leaf parts and arrangements
Leaf blade
Leaf petiole

15. Leaf characteristics

16. Leaves modified for other functions
Spines- protection
Tendrils- anchoring
Insect traps- Nitrogen acquisition

17. Chapter 4: Homework questions
(T) What are the two major microbial organisms that are symbiotic with plant roots and how do they benefit plants? What are the microbes seeking in return?
Draw and label a cross section (from a side angle-see chapter 4 PPT slide #11) of a leaf. What is the purpose of the leaf and how does each of of the structural components contribute to the leaf function?
Gives examples (two for each organ type) of specialized or modified roots, stems and leaves and explain how the modification aids the plant.