PLANT PHYSIOLOGY

Az Agrármérnöki MSc szak tananyagfejlesztése

TÁMOP-4.1.2-08/1/A-2009-0010

The light reactions of the photosynthesis

Photosynthesis inhibiting herbicides

Overview1. Photosynthesis, general concepts

2. Organization of the photosynthetic apparatus

3. Organization of light-absorbing antenna systems

4. Mechanism of electron transport

5. Proton transport and ATP synthesis in the chloroplast

6. Inhibitors of electron transport are effective herbicides

1. Photosynthesis, general concepts

1.1. Light has both particle and wave characteristics

1.2. Photosynthetic pigments absorb the light

1.3. Absorption and action spectra

1.4. Oxygen-evolving organisms have two photosystems

1.5. Light drives the reduction of NADP and the formation of ATP

1.6. NADPH and ATP are used for CO2 fixation

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 164.

Light is a transverse electromagnetic wave, consisting of oscillating electric and magnetic fields

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 165.

The electromagnetic spectrum

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 165.

The solar spectrum and its relation to the absorption spectrum of chlorophyll

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 167.

Molecular structure of some photosynthetic pigments

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 166.

Light absorption and emission by chlorophyll

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 168.

Absorption spectra of some photosynthetic pigments

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 168.

Action spectrum compared with an absorption spectrum

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 169.

Basic concept of energy transfer during photosynthesis

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 172.

The rate of photosynthesis when red and far-red light are given together is greater than the sum of the rates when they are given apart

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 172.

Z scheme of photosynthesis

2. Organization of the photosynthetic apparatus

2.1. The chloroplast is the site of photosynthesis

2.2. Thylakoids contain integral membrane proteins

2.3. Photosystems I and II are spatially separated in the thylakoid membrane

2.4. Anoxygenic photosynthetic bacteria have a single reaction center

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 173.

Transmission electron micrograph of a chloroplast from pea (Pisum sativum)

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 173.

Schematic picture of the overall organization of the membranes in the chloroplast

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 175.

Organization of the protein complexes of the thylakoid membrane

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 175.

Structures of the four main protein complexes of the thylakoid membrane

3. Organization of light-absorbing antenna systems

3.1. Antenna systems contains chlorophyll and are membrane associated

3.2. The antenna funnels energy to the reaction center

3.3. Many antenna pigment-protein complexes have a common structural motif

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 177.

The excited-state energy of pigments increases with distance from the reaction center

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 177.

Some energy is lost as heat, but almost all the excitations absorbed in the antenna complexes can be delivered to the reaction center

4. Mechanism of electron transport

4.1. Electrons from chlorophyll travel through carriers

4.2. The reaction center chlorophylls of the two photosystems absorb at different wavelength

4.3. Water is oxidized to oxygen by photosystem II

4.4. There are several electron acceptors and donors between photosystem II and I

4.5. The photosystem I reaction center reduces NADP

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 179.

The transfer of electrons and protons in the thylakoid membrane is carried out vectorially by four protein complexes

Source: Salisbury F.B., Ross C.W. (1992): Plant Physiology. p. 217.

The water oxidizing clock

5. Proton transport and ATP synthesis in the chloroplast

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 187.

Chemiosmotic mechanism of photosynthetic ATP formation

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 188.

Subunit composition of chloroplast F1F0 ATP synthase

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 189.

Compiled crystal structure of chloroplast F1F0 ATP synthase

6. Inhibitors of electron transport are effective herbicides

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 186.

Chemical structure and mechanism of action of two important herbicides

SummaryPhotosynthesis in plants uses light energy for the synthesis of carbohydrates and generation of oxygen from carbon dioxide and water. Energy stored in carbohydrates is used to power cellular processes in the plant and serves as energy resources for all forms of life.

Light harvesting antenna proteins funnel energy to the reaction center. Electrons are transported through a special thylakoid complex containing four protein subunits. Proton transport and ATP synthesis are also key elements during photosynthetic ligh reactions.

Questions• What is the relation between the electromagnetic

spectrum of solar radiation and the absorption spectrum of chlorophyll?

• Describe the two photosystems and provide two lines of experimental evidence that led to their discovery.

• What is the role of electron transport in oxygen-evolving photosynthesis? Describe the path traveled by an electron in the electron transport process.

• Can ATP synthesis take place in thylakoid membranes kept in the dark? Explain your answer.

THANK YOU FOR YOUR ATTENTION

Next lecture:Carbon reactions of the photosynthesis

Photosynthetic activity and the environmental factors

• Compiled by:Prof. Vince ÖrdögDr. Zoltán Molnár