Background on Maize and Photosynthesis Corn or Maize

Background on Maize and Photosynthesis

Corn or Maize – Zea mays

Typical Corn Growth

Typical ear of corn

Zea mays subsp. mexicana Zea mays subsp. mays

Teosinte vs. Corn Growth Teosinte Corn

Steps from Teosinte to Maize 1. 2. 3. 4. 5. 6. 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 maize

Perennial Teosinte – Zea diploperennis

Ear of teosinte – Zea diploperennis

Zea mays

Variation in ear size and kernel color from Mexican landraces of corn

Corn Types

Popcorn

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 products

Global Maize Production

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 fertilizer

The Most Important Equation in Biology

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 fixation

Light Spectrums • Absorption spectrum - the light absorption pattern of a pigment • Action spectrum - the relative effectiveness of different wavelengths for a specific lightrequiring process - such as photosynthesis, flowering or phototropism

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 photosynthesis

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

Overview Of Photosynthesis

Melvin Calvin 1940 s • Worked out the carbonfixation pathway – now named for him • Won Nobel Prize in 1961

Calvin Cycle Summary • Each full turn of the Calvin cycle begins with entry of a CO 2 molecule and ends when Ru. BP 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: • 6 CO 2 + 12 NADPH + 12 H+ + 18 ATP => 1 Glucose + 12 NADP + 6 O 2 + 18 ADP + 18 Pi + 6 H 2 O

C 4 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 C 4 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 grana

Cross section of corn leaf - Kranz architecture

Location of C 4 Pathway

Why Use C 4 Pathway? • Fixation of CO 2 has a higher energetic cost in C 4 plants than in C 3 plants – it takes 5 ATP to fix one molecule of CO 2 in C 4 but only 3 ATP in C 3 • For all C 3 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 C 3 plants as fixed carbon is reoxidized to CO 2 • Photorespiration is nearly absent in C 4 plants - this is because a high CO 2: low O 2 concentration limits photorespiration - C 4 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 C 4 plants (corn, sorgham, sugarcane) are higher than in C 3 relatives (wheat, rice, rye, oats) • Found in 19 plant families

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 C 4 plants, use both C 4 and C 3 pathways, but CAM plants separate the cycles temporally and C 4 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 loss

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 response

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 performed

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