The document provides information about plant nutrition and nitrogen fixation. It discusses how sugars are transported within plants through phloem tissue. It also describes the six essential macronutrients for plants and their functions. Additionally, it explains how nitrogen-fixing bacteria are able to convert atmospheric nitrogen gas into ammonia through a mutualistic relationship with legume plants in root nodules. This process of biological nitrogen fixation is an important source of nitrogen for plants.

1. Study Tips: Quizzes and Test
• Heavily weighted towards lecture notes
• ~80/20
• Be able to identify structures and function
• Will be multiple choice
• Calculate Water potential

2. Sugars: Translocation
• How do sugars made in leaves end up in other parts
of the plant?

3. Translocation = phloem transport
• Energetically demanding process
Sieve tube elements
(+companion cells)
+ Minerals, amino acids, hormones..
Materials can go either up or down
SOURCE vs. SINK
(but only one direction per tube)

4. What are some sinks and sources?
SINK
SOURCE
Flowers
Mature leaves
Fruits
Apical Meristems
Root?
Newly growing leaves
Roots
Movement is predictable-- radioactive CO2 studies

5. Transport of SUgars
• Sugar manufactured in mesophyll cells is transported
to sieve-tube members.
• Sugars are actively pumped into companion cells and
sieve-tube members

6. Pressure Flow or Bulk Flow

7. Figure 35.13

9. Plant Nutrition
CHAPTER 36

10. The 6 Macronutrients
= Building blocks of nucleic acids, proteins,
phospholipids, etc.
Nitrogen
Phosphorus
Potassium
Sulfur
Calcium
Magnesium

11. Plus micronutrients: (Small amounts)
Cofactors for enzymes.
Cl, Fe, Mn, Zn, B, Cu, Ni, Mo. (Table 36.1)
How do researchers determine what is an essential
nutrient?
- Hydroponics

12. “What is wrong with my house plant”
Symptoms depend on:
Function (see table 36.1) There should be a
picture of different
Mobility leaves *
Yellow: N
Purple: P
Burnt edges: K

13. “What is wrong with my house plant”
Symptoms depend on:
Function (see table 36.1)
Mobility
MOBILITY in plant tissue
Nutrient not highly mobile, Nutrient highly mobile,
trapped in older tissues shunted in actively growing
eg. Fe,S parts
Symptoms mostly in young eg. N, K, Mg
leaves Symptoms mostly in old
leaves

14. The basics about: SOIL
Soils
• Provide support
• Mineral nutrients and water
• O2 respiration
Divided into 3 horizons
Fig 36.4

15. Soil Horizon: A, B, and C
Horizon A: Topsoil: Consists of
sand, silt, clay and organic
matter
Minerals can be leached by rain
or through irrigation and can be
made inaccessible by plants

16. Soil Horizon: A, B, and C
Horizon B: Subsoil; zone
of infiltration and
leached mineral
accumulation

17. Soil Horizon: A, B, and C
Horizon C: Parent rock
(bed rock); weathering
of this rock
determines the basic
structure and chemical
composition of soil.

18. What is special about clay particles?
SOIL: Gravel, sand, silt = breakdown of rocks
Clay= chemical recombination
Silicon Aluminum Oxygen
Special structures: layers Negative charges along the
outside

19. Ions with positive charges (CATIONS)
Interact with OM and clay particles
IONS
Ions with negative charges (ANIONS)
DISSOLVE in water
(Except Phosphate: sticks to clay particles)

20. Clay in soils provide a cation exchange system
for plants
Protons leaked by
roots. Promote
release of cations by
clay particles

21. Other types of plant nutrition: Parasitic plants or
Carnivorous plants
• Found in Boggy habitats
• Acidic, nutrient deficient habitats
• Capture insects, digest their proteins, and absorb their
amino acids

22. Two important mutualism relevant to plant nutrition.
• Mycorrhizal associations
• Nitrogen fixation Mutually beneficial relationship
Mycorrhizae
-> Fungi
Form associations with plant roots
Hyphae: very thin tubular filaments
Improve absorption of N, P, water

23. Two types of mychorrhizae:
Ectomycorrhizae - 10% of plant families (including pine
trees)
Arbuscular mycorrihzae - 85% plant families (including
corn, wheat, legumes)

24. Fig 36. 7 Formation of mycorrhizae -> Complex signaling
between plants & fungus

25. What is cool about strigolactones?
Strigolactones
• Plant hormones
• Derived form carotenoids
• Have a labile ether bond that hydrolyzes in soil. ->
this creates a strong concentration GRANDIENT away
form the root. (cool!)

26. Mycorrhizae
• Increase access to nutrient and root surface area
• Expand root surface area 10-1000 fold
• Primarily responsible for obtaining Phosphorus.
• Exchanges nutrients for Carbohydrates

27. Last part of plant nutrition:
Nitrogen Cycle

28. Two important mutualism relevant to plant nutrition.
• Mycorrhizal associations
• Nitrogen fixation
Why do we use clovers as cover clovers....something?
Answer: Clovers, beans, alfalfa, etc. are legumes and
legumes are NITROGEN FIXERS
Legumes exploit bacteria to get NH4+

29. Last part of plant nutrition:
Nitrogen
Where is most of the N? AIR.
Plant cannot use atmospheric nitrogen N2 directly
Requires enormous energy to break the N-N bond
Prokaryotes can “fix” nitrogen- converting it form
dinitrogen to ammonia: N2--> NH3

30. Nitrogen fixation: N2-> NH3
Nitrogenous
• Done by bacteria, not plants.
• Very energy intensive -16 ATP per N2
• Can only occur in anaerobic conditions

31. Nitrogen fixation, cont.
Legume-rhizobia interaction = species -specific!
Rhizobia NOT transported in or on the seed.
How do they find each other?
Requires complex signaling between the plant root and
the bacteria. (cool!)
1. Rhizobia are attracted by root surface compounds
2. Rhizobia produce Nod factors
3. Plant proteins on root surface bind Nod factors
4. Plant turns on ENOD genes
5. Root hairs curl, begin to produce nodule

32. Nodule Formation (fig. 36.9)

33. How does the plant maintain an anaerobic environment
for bacteria?
• Bacteroid cells packed into vesicles
• Thick lignified wall
• Leghemoglobin - iron-containing protein that binds O2-
lowers [O2] in nodule

34. Implication of N fixation
• Production of N-rich vegitation
• Good source of organic fertilizer
• Production of protein rich seeds