Reading Assignments:

1
Reading Assignments In Physiology of
Crop Plants (Gardner) Chapter 1
Photosynthesis In Principles of Ecology
and Plant Production (Sinclair) Chapter 1
Human Population, Plant Production and
Environmental Issues
Chapter 8 Radiant Energy Chapter 11-
Carbon Dioxide and Other Atmospheric Gases
2
CHAPTER 1 PHOTOSYNTHESIS
Two major purposes 1. To develop an
understanding of the important
principles underlying the practices
used in the culture of crop plants, and
2. To develop the ability to apply these
principles in production strategies.
AGRICULTURE is basically a system of exploiting
solar energy through photosynthesis.... The
yield of crop plants ultimately depends on the
size and efficiency of this photosynthetic
system.
3
m (1 m) cm (10-2 m) mm (10-3 m) um (10-6
m) nm (10-9 m) one-billionth of a meter
4
RADIATION
Radiant energy from the sun can be viewed as
moving through space as 1. A wave
(Electromagnetic Wave theory) or 2. Discreet
particles of energy (Quantum theory)
5

Number of waves passing a given point in a
certain time interval is a frequency (No. waves
per sec.)
V C/

V - Frequency (no./sec)
C - Speed of light (3 x 1010 cm/sec)
- Wavelength (nm)

6
II. Quantum Theory
1. Light travels as a series of particles
called PHOTONS
2. A QUANTUM is the amount of energy
present in one photon

E h V h C /

V
E - Energy of quantum
h - Plancks constant (6.626 x 10-27 erg
s-1)
V - Frequency
(Note Textbook did not mention h)
Therefore, based on the preceding equation
the shorter the , the greater the energy
content of one photon

For example Light with a of 400 nm has more
energy per particle (photon) than light of 700 nm

7
PAR
Photosynthetic Active Radiation (PAR)
8
1. PHOTON FLUX DENSITY is the number of
photons striking a given surface area per
unit of time.
2. PHOTOSYNTHETICALLY ACTIVE RADIATION
(PAR) or PHOTOSYNTHETIC PHOTON FLUX
DENSITY (PPFD) is the number of photons in the
400-700 nm wavelength range per unit
area per unit time.
3. EINSTEIN (E) is one mole (6.02 X 1023) of
photons.
PAR or PPFD is usually expressed as micro-
einsteins per square meter per second (µE m-2
s-1).
9
LIGHT USED FOR PHOTOSYNTHESIS
The first step necessary for photosynthesis is
the absorption of photons (light energy) by
pigments such as chlorophyll in the
leaf. Radiation wavelengths above ca. 700 nm do
not have enough energy to drive the
photosynthesis process and energy is too high at
wavelengths below 400 nm. Only photons with
wavelengths between ca. 400 and 700 nm (visible
light) are used for the photosynthetic process.
10
Sun directly overhead at 23 N on June 22

Gainesville (29 N), so in GNV the sun is
always to the south, to some extent
On December 22, sun is directly above the Tropic
of Capricorn. On June 22, directly above the
Tropic of Cancer.
11
Diurnal Fluctuations In Solar Radiation
Northern Hemisphere (42 degrees N)

• In January
• Shorter days
• Lower sun angle
• Both leading to less solar
• radiation

12
Annual Cycle

• Reductions in
• Length of day
• Sun angle
• (lowered intensity)

(Forage Production winter vs. summer ??? 40
less light available)
13
SOLAR RADIATION AT EARTHS SURFACE
14
Outside atmosphere
15-30 absorption
At earths surface
Solar constant 2.0 cal/cm2/min
550 nm is maximum output from sun (green) Recall
that photosynthesis is driven by wavelengths
between 400-700 nm.
15
How does radiation in Florida winters compare to
that during the summer months? Does the
difference in radiation (summer compared to
winter) impact potential crop production? How
and why?
16
(No Transcript)
17
(No Transcript)
18
Just a few notes from Chapter 8 (Sinclair) A
long term decrease by as little as 0.5 in
energy output from the sun would cause drastic
changes in climate, triggering another Ice
Age. Sufficient energy is emitted from the sun
every second to meet the energy use of the
Earths 5.9 billion people for roughly 50
thousand years! Radiation received at the top
of the earths atmosphere is about 35 higher
than radiation at the earths surface. What
component of the atmosphere absorbs (or reflects)
the most significant part of that radiation? The
highest annual solar input is actually at the
Tropics of Cancer and Capricorn, rather than at
the equator. Why? Biomass production by crops
is linearly related to the interception of solar
radiation. Why? Ultra violet radiation output
from the sun is relatively high, but much less at
the earths surface. Why? Photoperiodism
will be discussed later in the semester
19
Florida Automated Weather System (FAWN)
http//fawn.ifas.ufl.edu

20
(No Transcript)
21
S Stroma GL Grana lamella SL Stroma
lamella SG Starch Granule
22
PHOTOSYNTHESIS

• Photosynthetic process in leaves occurs in
  chloroplasts (1 to 10 )
• 1. Light Reactions (electron transport)
• Dark Reactions (incorporation of CO2 into plant
  constituents)

• m

23
CHLOROPLAST STRUCTURE
Sub-components 1. Lamellae (means
membranes) a. Stroma lamellae (double
membranes) b. Grana lamellae ( stacked
membranes) Most leaf pigments are in the
chloroplast membranes 2. Stroma - Fluid
area between membranes
24
CHLOROPLAST STRUCTURE (Contd)

• Light reaction (conversion of light energy
• into chemical energy) occurs in the
• membranes
• Dark reaction (reduction of CO2 into plant
• constituents) occurs in the stroma.

- Refer to Fig. 1.7 in book GL - Grana
lamellae SL - Stroma lamellae S -
Stroma SG - Starch granule
25
LIGHT REACTIONS
ELECTRON TRANSPORT (light reaction) provides the
pathway for converting light energy into
chemical energy. ELECTRON TRANSPORT (light
reaction) provides an energy source (ATP) and a
source of electrons (NADPH), both of which are
required for forming C-C bonds of plant
structures. NADPH and ATP serve as the chemical
carriers of light energy until their energy and
electrons are transferred into carbon bonds
(dark reaction reduction of CO2). ADP
Pi ATP (Photophosphorylation)
PHOTOPHOSPHORYLATION Formation of ATP in the
presence of light. Light energy is converted to
chemical energy.
26
(No Transcript)
27
PHOTOPHOSPHORYLATION conversion of light energy
to chemical energy. Energy is stored as ATP in
biological systems.
ATP adenosine triphosphate (energy
source) NADPH nicotinamide adenine
dinucleotide phosphate (reductant - donates
e) (CH2O)n carbohydrate (starch)
28
S Stroma GL Grana lamella SL Stroma
lamella SG Starch Granule
29
Mg at center of chlorophyll structure
Protein
Lipid

• Pigments
• 1. Chlorophylls (green) A B
• 2. Carotenoids (yellow, orange)
• Carotenes, xanthophylls

30
protein

• Location of light reactions
• (electron transport photophosphorylation)
  
• Pigments are in lipid layers
• Lipid layer, with protein layer on both upper
  and lower
• surfaces
• - Some proteins penetrate the entire width of
  membrane

31
(No Transcript)
32
AGR 5444 Graduate Students Term
Papers Tentative Topics are due Friday,
January 25 Submit topic of interest and
a very brief outline and summary of what
the paper might comprise Refer to Term
Paper Guidelines which were included in the
packets that were distributed on first day of
class
33
Z Scheme Electron Transport (in grana)
(680 nm)
(400-690 nm)
Electron Transport passing of electrons from
one compound to another occurs in grana of
leaf Hill Reaction splitting of water,
releasing protons, electrons, and
oxygen Photophosporylation formation of ATP
(energy) Reduction formation of the reductant
NADPH (electron donor)
34
Blue
Green
Red
Wavelength (um)
Moles CO2 per 100 photons
Field Bean
Quantum efficiency Moles CO2 reduced per
mole of photons
Low 8-12
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)
38
DARK REACTIONS
Yield of crops Dry matter production
Dry matter CO2 uptake - CO2 evolution
(photosynthesis)
(respiration)
Normally, respiration is 25-30 of total
photosynthesis, so dry matter increases over time.
In dark, photosynthesis 0, but respiration
continues, so dry weight decreases with time.
39
THREE GENERAL CATEGORIES OF PLANTS (Based on
mechanism of CO2 fixation)
40
(No Transcript)
41
C3 Most Dicots
Alfalfa Leaf
Vacular Bundle (major veins)
42
C3 - DARK REACTIONS
1. RuBP - Ribulose bisphosphate carboxylase -
Enzyme which adds (fixes) a CO2 molecule
to a 5-C compound (ribulose bisphosphate) to
form two molecules of a 3-C compound
(Phosphoglyceric acid).
3-phosphoglyceric acid
5C1C 2(3C)
3-C is first product of dark reaction in C3 plants
CO2
2. 3-C compounds are then combined to form 6-C
compounds (hexoses sugars).
3. 6-C hexoses are joined in long chain C
compounds to form starch.
4. ATP and NADPH (from light reactions) are used
for converting various structures in the
pathway.
5. C3 pathway is also known as the Calvin cycle,
after the scientist who described the
pathway in 1957.
43
CALVIN CYCLE
(Overlay)
Dark Reactions (C3) (CO2 Fixation)
Dark reactions occur in the stroma
chloroplast
Products of Calvin Cycle Sucrose and/or Starch
Calvin Cycle (C3 photosynthesis)-1957 RUBPribulo
se bis-phosphate carboxylase-enzyme that fixes
CO2 Into (2) 3-phospho glyceric acid (3 carbon
molecule), (C3)
44
Maize Leaf (C4)
C3 PS occurs in BS cells
C4 PS occurs in mesophyll cells
Kranz Anatomy
45
C4 - DARK REACTIONS
1. PEP Carboxylase - Phosphoenol
pyruvate carboxylase (in the mesophyll cells) is
the first enzyme to fix CO2. It adds a CO2
molecule to phosphoenol pyruvate (3-C compound)
to form a 4-C compound (oxaloacetate).
3C1C 4C
(oxaloacetate) 4-C is the first product of dark
reaction in C4 plants
CO2
2. 4-C oxaloacetate is rapidly converted to
either malate or aspartate (both 4-C) which
carries the fixed CO2 into the bundle sheath
cells. In the bundle sheath cells, a CO2 is
removed from malate (or aspartate) and dropped
at the site of RuBP carboxylase.
46
(No Transcript)
47
C4 Pathway
PEP Carboxylase
48
Dark Reactions (C4) CO2 Fixation
C4 pathway - also called Hatch-Slack
pathway (1966)

• See p. 17 for
• Mesophyll
• Bundle sheath
• Vascular tissue

CO2 concentration is high in bundle sheath cells
where Calvin cycle occurs. (CO2 pump)
PEP carboxylase phosphoenol pyruvate
carboxylase enzyme which fixes CO2 into 4C
acid (oxaloacetate), C4mesophyll and C3 in
bundle sheath (vascular sheath).
49
COMPARISON OF C3 vs C4 SPECIES

• Anatomical differences
• a. C4 - Kranz anatomy (mesophyll cells
  surrounding
• bundle sheath cells)
• b. C3 - Palisade and spongy mesophyll
• C3 (Calvin cycle)
  in bundle sheath
• In C4 plants
• C4 (Hatch -
  Slack) in mesophyll

50
COMPARISON OF C3 AND C4 (Contd)
51
PHOTORESPIRATION -
Photorespiration is a wasteful loss of CO2 in the
light. Loss of CO2 for no apparent reason. -
Photorespiration occurs in peroxisomes.
- RuBP can act as either a(n) 1.
Carboxylase (incorporation of CO2)
or 2. Oxygenase (incorporation
of O2)
2 RuBP 3 O2 2 ATP H2O
3 3-PGA 2 ADP CO2 (9C)
(1C)
(10C)
At high O2 levels, photosynthesis is dramatically
reduced in C3 plants.
52
PHOTORESPIRATION (Contd)
Why does photorespiration not occur in C4
plants? The CO2 is concentrated at the site of
the enzyme (RuBP carboxylase), causing it to
function exclusively as a carboxylase rather than
an oxygenase.
Absence of photorespiration causes C4 plants to
be more efficient at fixing CO2 than C3
plants. Photorespiration is a completely
separate process from Kreb cycle respiration
which occurs in mitochondria.
53
C3 SPECIES
54
C4 SPECIES
55
CRASSULATION ACID METABOLISM (CAM) 1.
Occurs primarily in succulent plants, which have
fleshy leaves or stems 2. Adapted to arid
conditions because a. They open stomata at
night to fix CO2 b. They close stomata during
day to reduce transpiration (water loss from
leaves) 3. Domestic CAM plants Pineapple,
Prickly pear (desert plants) 4. Fix CO2
into 4-C acids with PEP carboxylase at night
then C3 during day. Low growth rates, but very
resistant to drought.
56
(No Transcript)
57
Leaf Cross Sections
Gradients for CO2 (in) H2O (out)
C4-maize leaf
58
(No Transcript)
59
WATER USE EFFICIENCY
Water Use Efficiency (WUE) Amount of
carbon fixed per unit of
water transpired
Photosynthesis Transpiration
WUE
WUE is affected by the gradients of CO2 and
water vapor from the stomatal cavity to the air
above the leaf surface.
60
LEAF GAS EXCHANGE
- Most cultivated crops have stomata on
both leaf leaf surfaces. In general, for highly
productive food and feed crops, more stomata on
lower leaf surface Abaxial Lower
surface Adaxial Upper surface -
However, many other plants have stomata only on
the lower surface - Most gaseous exchange
(CO2 and water vapor) occurs through the stomata
61
Stomatal number and size of several crop species
Adaxial (upper) epidermis 169 0 40 141 64 52 25
51 85 12 33
Abaxial (lower) epidermis 138 294 281 226 176 68
23 161 156 130 14
Open stomatal size (µm) --- --- 7 X 3 --- 10 X
4 19 X 5 38 X 8 --- 22 X 8 13 X 6 38 X 7
Common name Alfalfa Apple Bean Cabbage Castor
Maize Oat Potato Sunflower Tomato Wheat
Scientific name Medicago sativa Pyrus
malus Phaseolus vulgaris Brassica
oleracea Ricinus communis Zea mays Avena
sativa Solanum tuberosum Helianthus
annus Lycopersicon esculentum Triticum astivum
- - no. / mm2 - -
62
Staggered or random arrangement of stomata
Clover (dicot) C3
Stomata in rows
Maize (grass) C4
63
ENVIRONMENTAL FACTORS AFFECTING
PHOTOSYNTHESIS 1. Light 2. CO2 3.
Temperature 4. Water 5. Nutrients
discussed in the following chapters
64
DEFINITIONS
Gross photosynthesis Total CO2 uptake (does not
consider CO2 from respiration)
Net photosynthesis Net flux of CO2 (Gross
Photosynthesis - Respiration)
Preferred term Carbon exchange rate
(CER) amount of CO2 per leaf area per second (mg
m-2 s-1 or µmol m-2 s-1)
65
C3 Light Response Curve
Single leaf response
(PS is max)

• CER Carbon Exchange Rate (PS-RS)
• At zero light, CO2 is evolved (respiration)
• Light compensation pointlight level where PSRS
• (no net CO2 uptake)
• CER (carbon exchange rate)0 at light
  compensation point

66
C4-higher light saturation (corn)
C4
For single leaves C3 -photosynthesis is
usually Light saturated at 50-75 of full Sun
light. C4 -photosynthesis is not light saturated
even under full Sunlight.
67
(No Transcript)
68
CARBON DIOXIDE IN ATMOSPHERE

• Data from Hawaii
• Use of fossil fuels, CO2
• Seasonal lows in CO2 are associated with
• warm season (high PS) in Northern
• hemisphere

69
CO2 Concentrations Measured at Mouna Loa, Hawaii
from 1958 to 2001 Showing Trends and Seasonal
Changes

• The Mauna Loa atmospheric CO2 measurements
  constitute the longest continuous record of
  atmospheric CO2 concentrations available in the
  world.
• This site is considered one of the most favorable
  locations for measuring undisturbed air because
  possible local influences of vegetation or human
  activities on atmospheric CO2 concentrations are
  minimal and any influences from volcanic vents
  may be excluded from the records.
• The methods and equipment used to obtain these
  measurements have remained essentially unchanged
  during the 44-year monitoring program.

70
A CO2 Data Set from the South Pole from 1957 to
2001

• Precise measurements of atmospheric CO2 at the
  South Pole have been obtained by Scripps
  Institution of Oceanography (SIO) researchers
  since 1957.
• This record is based primarily on biweekly flask
  sampling.
• The SIO CO2 record from the South Pole shows that
  annual averages of atmospheric CO2 concentrations
  rose from 315 ppmv in 1958 to 368 ppmv in
  2001(Keeling, 2002).

71
CO2 Record Going Back Before Modern Record Keeping
Period of Record 417,160 - 2,342 years before
present

• Major transitions from the lowest to the highest
  values are associated with glacial-interglacial
  transitions.
• The extension of the Vostok CO2 record shows the
  present-day levels of CO2 are unprecedented
  during the past 420 kyr.
• Pre-industrial Holocene levels (280 ppmv) are
  found during all interglacials, with the highest
  values (300 ppmv) found approximately 323
  thousand years before present.
• When the Vostok ice core data were compared with
  other ice core data (Neftel, 1982) for the past
  30,000 - 40,000 years, good agreement was found
  between the records all show low CO2 values
  (200 ppmv) during the Last Glacial Maximum and
  increased atmospheric CO2 concentrations
  associated with the glacial-Holocene transition
  (Barnola, 2003).

72
Response of Leaf PS to Increasing CO2

• enhanced Ps at high CO2
• Maize (C4) shows less response to gtCO2 compared
• to sunflower (C3)

73
(No Transcript)
74
(No Transcript)
75
(No Transcript)
76
(No Transcript)
77
RESISTANCES TO CO2 MOVEMENT
78
RESISTANCES TO CO2 MOVEMENT INTO THE LEAF
- CO2 moves into the leaf by diffusion
along concentration gradients
rCO2 ra rs rm
rCO2
ra rs rm
79
Effects of Temperature on Ps and Rs
Usually a fairly broad plateau of maximum gross
(true) PS, and also apparent
true Ps minus respiration
continues to increase as temp increases
PS and RS are enzymatically controlled, so
response to Temp is expected.
80
FACTORS AFFECTING PHOTOSYNTHESIS
Water Affects photosynthesis through its
effect on stomatal opening and closing
(rs). Severe water stress may increase rm
. Leaf Age Photosynthesis usually
declines with leaf age. Mineral Content
Declines with leaf age. Nitrogen depletion
with leaf age closely related to reductions in
photosynthesis (enzymes, chlorophyll).
Other nutrients are also depleted as leaves age.
81
(No Transcript)
82
C3 25-35 mg CO2 m-2 s-1 C4 40-60 mg CO2 m-2
s-1
C4 photosynthesis is generally 40-60 higher
than C3 photosynthesis
83
(No Transcript)
84
RESPIRATION AND GROWTH
85
RESPIRATION
2. KREBS CYCLE (mitochondria) Pyruvic acid
moves into the mitochondria, loses a CO2, forming
acetyl-CoA (2C) which is an intermediate of the
Krebs cycle.
86
RESPIRATION (Contd)
In Krebs cycle a. C compounds are combusted
(oxidized) to CO2 and H2O and NAD is
reduced to NADH
b. Intermediate C skeletons produced in
the Krebs cycle are removed from the cycle and
used in the formation of Amino acids
Proteins DNA RNA, etc.
87
RESPIRATION (Contd) - OXIDATIVE
PHOSPHORYLATION
3. Oxidative phosphorylation
electron transport via a cytochrome chain
(mitochondria membrane)
Oxidative Requires oxygen. O2 is the terminal
electron acceptor. O2 is consumed and CO2
is evolved in respiration
Phosphorylation ADP ATP
ATP
ADP
H2O
O2
NADH
NAD
From glycolysis and Kreb cycle
88
(No Transcript)
89
(No Transcript)
90
(No Transcript)
91
SUMMARY OF RESPIRATION
1. GLYCOLYSIS
ATP NADH
2(3C) Pyruvic acid
(C- skeletons)
(6C)
Hexoses
Acetyl CoA (2C)
2. KREBS CYCLE
4C
CO2
NADH ATP
C- skeletons
3. OXIDATIVE PHOSPHORYLATION O2 ATP
produced CO2
(released in Krebs cycle)
92
RESPIRATION EFFICIENCY
(30 steps)
C6H12O6 6O2 6CO2 6H2O 637 kcal
(energy potential)
But, only 456 kcal is generated, for 68
efficiency
Respiration consists of 1. Glycolysis 2.
Krebs cycle 3. Oxidative phosphorylation
93
(No Transcript)
94
Per day should be added to all units of measure
95
(No Transcript)