Background on Maize and Photosynthesis - PowerPoint Presentation

Slide1

Background on Maize and PhotosynthesisSlide2

Corn or Maize –

Zea maysSlide3
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Typical Corn GrowthSlide5

Typical ear of cornSlide6

Zea

mays

subsp.

mexicana

Zea

mays

subsp.

maysSlide7
Slide8

Teosinte vs. Corn Growth

Teosinte CornSlide9

Steps from Teosinte

to Maize

Maize cobs do not shatter (fall apart) whereas

teosinte

ears shatter when mature

Each

teosinte

grain is

nestled

in a hard, deep floral structure the

cupule

and covered by a hard sheath (the

glume

). The grains of corn are naked and held outside a collapsed

cupule

Each

teosinte

cupule

contains a single fertile spikelet; maize cupules have two fertile

spikelets

Teosinte

cupules are arranged in 2 ranks (rows) but maize are in 4 to 10 rows

Teosinte

has long primary branches that each ends in a male tassel and there are numerous tiny ears along each branch. Maize has short primary branches that end in a single ear – only a few ears per plant; male tassel at apex of

plant

It is hypothesized that 5 major genetic changes in 5 polygene complexes account for these changes from

teosinte

to maizeSlide10

Perennial

Teosinte

–

Zea

diploperennisSlide11

Ear of teosinte –

Zea diploperennisSlide12

Zea maysSlide13

Variation in ear size and kernel color from

Mexican landraces of cornSlide14

Corn TypesSlide15

PopcornSlide16
Slide17

Maize productivity

Maize is tremendously productive - a typical Iowa cornfield will produce 3500 - 4000 g of carbon per meter squared per year - The most productive tropical rainforest or coastal salt marsh produce about 3500 g of carbon per meter squared per year

US corn production worth $76.5 billion in 2011; worth $49 billion in 2015

Average American spends $267 per year on corn productsSlide18
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Global Maize ProductionSlide20

Maize productivity

Maize is so valuable because it is productive across a huge range of conditions – temperate to tropical (following adaptation to different day lengths)

Among modern cereal grains it is the most efficient in converting water and carbon dioxide into grains – i.e. food

However, it requires large amounts of nutrients and current high yields such as occur in farm land around here require the input of tremendous amounts of fertilizerSlide21
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The Most Important Equation in BiologySlide23

Light and Dark Reactions

We shall see that the first, light-dependent stage of photosynthesis uses light energy to form ATP from ADP and to reduce electron carrier molecules, especially NADP+ to NADPH – so here energy is captured

In the light-independent reaction, the energy from the ATP and NADPH is used to build organic carbon molecules - and this is the process of carbon fixationSlide24
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Light Spectrums

Absorption spectrum - the light absorption pattern of a pigment

Action spectrum - the relative effectiveness of different wavelengths for a specific light-requiring process - such as photosynthesis, flowering or phototropismSlide26
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When pigments absorb light, electrons are temporarily boosted to a higher energy level

One of three things may happen to that energy:

1. the energy may be dissipated as heat

2. the energy may be re-emitted almost instantly as light of a longer wavelength - this is called fluorescence

3. the energy may be captured by the formation of a chemical bond - as in photosynthesisSlide28

The Photosynthetic Pigments

Chlorophyll a - found in all photosynthetic eukaryotes and cyanobacteria - essential for photosynthesis in these organisms

Chlorophyll b - found in vascular plants, bryophytes, green algae and euglenoid algae - it is an accessory pigment

Carotenoids - red, orange or yellow fat-soluble accessory pigments found in all chloroplasts and cyanobacteria - caroteniods are embedded in thylakoids along with chlorophylls

Two types of carotenoids - carotenes and xanthophylls Slide29

Overview

Of

PhotosynthesisSlide30
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Slide34

Melvin Calvin 1940s

Worked out the carbon-fixation pathway – now named for him

Won Nobel Prize in 1961Slide35
Slide36

Calvin Cycle Summary

Each full turn of the Calvin cycle begins with entry of a CO

2

molecule and ends when RuBP is regenerated - it takes 6 full turns of the Calvin cycle to generate a 6 carbon sugar such as glucose

the equation to produce a molecule of glucose is:

6CO

2

+ 12NADPH + 12H+ + 18ATP => 1 Glucose + 12NADP + 6O

2

+ 18ADP + 18 Pi + 6H

2

OSlide37

C4 Pathway

In some plants the first carbon compound produced through the light-independent reactions is not the 3 carbon PGA, but rather is a 4 carbon molecule

oxaloacetate

Leaves of C4 plants typically have very orderly arrangement of

mesophyll

around a layer of bundle sheath cells – called

Kranz

architecture

Mesophyll

cell chloroplasts are small with lots of

grana

; bundle sheath cell chloroplasts are large with little

granaSlide38

Cross section of corn

leaf -

Kranz

architectureSlide39

Location of C4 PathwaySlide40

Why Use C4 Pathway?

Fixation of CO

2

has a higher energetic cost in C4 plants than in C3 plants – it takes 5 ATP to fix one molecule of CO

2

in C4 but only 3 ATP in C3

For all C3 plants photosynthesis is always accompanied by photorespiration which consumes and releases CO

2

in the presence of light - it wastes carbon fixed by photosynthesis - up to 50% of carbon fixed in photosynthesis may be used in photorespiration in C3 plants as fixed carbon is

reoxidized

to CO

2

Photorespiration is nearly absent in C4 plants - this is because a high CO

2

: low O

2

concentration limits photorespiration - C4 plants essentially pump CO

2

into bundle sheath cells thus maintaining high CO

2

concentration in cells where Calvin cycle will occur

Thus net photosynthetic rates for C4 plants (corn,

sorgham

, sugarcane) are higher than in C3 relatives (wheat, rice, rye, oats)

Found in 19 plant familiesSlide41

CAM – Crassulacean Acid Metabolism

Crassulacean

Acid Metabolism (CAM) has evolved independently in 23 flowering plant families including the

stoneworts

(

Crassulaceae

) and cacti (

Cactaceae

) – and some non-flowering plants – ferns,

quillworts

,

Welwitschia

Plants which carry out CAM have ability to fix CO

2

in the dark (night)

so CAM plants, like C4 plants, use both C4 and C3 pathways, but CAM plants separate the cycles temporally and C4 plants separate them spatially

CAM plants typically open stomata at night and take in CO

2

then, then close stomata during day and thus retard water lossSlide42
Slide43

Replication

Because nature is inherently variable and it is almost impossible to find identical individuals of a species, identical field locations, etc. it is vital that all studies have adequate replication – the more individuals measured, the more confident we are that we have accurately measured the average responseSlide44

Control

A 

scientific control

 is an

experiment

or

observation

designed to minimize the effects of variables other than the single

independent variable

.

.

This increases the reliability of the results, often through a comparison between control measurements and the other measurements.

Controls help eliminate alternate explanations of experimental results, especially experimental errors and experimenter bias. Many controls are specific to the type of experiment being performedSlide45

Rules of Thumb for Experiments

Replication - rule of thumb: If you have a 2-group experiment (1 control and 1 experimental sample), you should aim for 12 replicates within each sample group.

Control – typically the control is your treatment of no difference or nothing being changed from general conditions