PLANT PHYSIOLOGY

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PLANT PHYSIOLOGY

Az Agrármérnöki MSc szak tananyagfejlesztése TÁMOP-4.1.2-08/1/A-2009-0010

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Carbon reactions of the photosynthesis

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Photosynthetic activity and

the environmental factors

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Overview

1. Carbon reactions of the photosynthesis

1.1. The Calvin-Benson cycle

1.2. The C₂ oxidative photosynthetic carbon cycle 1.3. Inorganic carbon concentrating mechanisms

1.4. Accumulation and partitioning of photosynthates _______________________________________________

2. Photosynthetic activity and the environmental factors

2.1. Photosynthetic responses to light by the intact leaf 2.2. Photosynthetic responses to temperature

2.3. Photosynthetic responses to carbon dioxide

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1.1. The Calvin-Benson cycle

 The Calvin-Benson cycle has three stages

 Regulation of Calvin-Benson cycle

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Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 200.

The light and carbon reactions of photosynthesis in chloroplasts of land plants

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The Calvin-Benson cycle proceeds in three stages: carboxylation, reduction, and regeneration

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The Calvin-Benson cycle

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CO₂ functions both as activator and as substrate in the reaction catalyzed by rubisco

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Light regulates the Calvin-Benson cycle via the ferredoxin–thioredoxin system

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1.2. The C₂ oxidative photosynthetic carbon cycle

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Source: Hopkins W.G., Hüner N.P.A. (2009): Introduction to Plant Physiology. p. 142.

Gas exchange observed in C₃ leaf in the dark (A) and in the light (B).

GP, gross photosynthesis; PR, photorespiration; R, mitochondrial respiration

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Operation of the C₂ oxidative photosynthetic cycle involves the cooperative interaction among three organelles

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Dependence of the C₂ oxidative photosynthetic cycle on chloroplast metabolism

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1.3. Inorganic carbon concentrating mechanisms

 The C₄ carbon cycle

 Crassulacean acid metabolism

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Kranz anatomy in a C₄ dicot plant

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The C₄ photosynthetic carbon cycle

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The C₄ photosynthetic pathway in leaves

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Inorganic carbon-concentrating mechanism:

crassulacean acid metabolism (CAM)

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1.4. Accumulation and partitioning of

photosynthates

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Accumulation and partitioning of photosynthates:

starch and sucrose

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The cytosolic interconversion of hexose phosphates governs the allocation of assimilated carbon

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2. Photosynthetic activity and the environmental factors

2.1. Photosynthetic responses to light by the intact leaf

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Scanning electron micrographs of the leaf anatomy from a legume (Thermopsis montana) grown in different light environments

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Optical properties of a bean leaf

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Leaf movement in sun-tracking plants: (A) initial orientation, and (B) orientation 4 hours after exposure to light

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Excess light energy in relation to a light–response curve of photosynthetic evolution

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Diurnal changes in xanthophyll content as a function of irradiance in sunflower

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2.2. Photosynthetic responses to temperature

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The absorption and dissipation of energy from sunlight by the leaf

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2.3. Photosynthetic responses to carbon dioxide

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Points of resistance to the diffusion of CO₂ from outside the leaf to the chloroplasts

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The combination of atmospheric carbon dioxide levels and daytime growing season temperatures

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Summary

The reduction of CO

₂

to carbohydrate via the carbon- linked reactions of photosynthesis is coupled to the consumption of NADPH and ATP synthesized by the light reactions of thylakoid membranes. The

carbohydrates synthesized by the Calvin-Benson

cycle are converted into storage forms of energy and carbon: sucrose and starch.

Photosynthetic activity in the intact leaf is an integral process that depends on many biochemical

reactions. Different environmental factors, such as

light, temperature, and water supply, can limit the

photosynthetic rates.

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PLANT PHYSIOLOGY

Carbon reactions of the photosynthesis

______________________

Photosynthetic activity and

the environmental factors

Overview

1. Carbon reactions of the photosynthesis

2. Photosynthetic activity and the environmental factors

1.1. The Calvin-Benson cycle

1.3. Inorganic carbon concentrating mechanisms

1.4. Accumulation and partitioning of

photosynthates

2. Photosynthetic activity and the environmental factors

Summary

The reduction of CO

to carbohydrate via the carbon- linked reactions of photosynthesis is coupled to the consumption of NADPH and ATP synthesized by the light reactions of thylakoid membranes. The

carbohydrates synthesized by the Calvin-Benson

cycle are converted into storage forms of energy and carbon: sucrose and starch.

Photosynthetic activity in the intact leaf is an integral process that depends on many biochemical

reactions. Different environmental factors, such as

light, temperature, and water supply, can limit the

photosynthetic rates.

Questions

• Describe the different types of carbon reactions of photosynthesis in higher plants.

• If the level of atmospheric CO

were to double, how would the photosynthesis be affected? Explain your answer.

• How many environmental factors can limit

photosynthesis at one time?

THANK YOU FOR YOUR ATTENTION

Next lecture:

Secondary metabolites in plant defense

• Compiled by:

Prof. Vince Ördög

Dr. Zoltán Molnár