Difference Between Photooxidation And Photorespiration

What Is Photooxidation?

Photooxidation is a process in plants where, due to excessive light intensity, the production of ROS takes place. These ROS are highly damaging to cellular components, including lipids, proteins, chloroplasts, and nucleic acids. The latter damage leads to impairment in photosynthesis and generally in plant health.

Photooxidation typically occurs if the intensity of light is higher than the protective mechanisms developed in the plant and antioxidant defences can cope with. Excessive light energy overexcites chlorophyll molecules in photosynthetic apparatus and leads to the formation of ROS, which may result in oxidative stress and cellular damage.

Photooxidation Mechanism

The mechanism includes the following:

Role Of Reactive Oxygen Species, (ROS)

• Singlet oxygen, superoxide anions, and hydrogen peroxide are examples of ROS formed during photooxidation.

• These ROS are highly reactive and can damage cellular structures and molecules.

Effect Of High Light Intensity

• High light intensity overexcites chlorophyll, and it transfers excess energy to oxygen molecules.

• This excess energy results in the generation of ROS and causes oxidative stress in plant cells.

Chemical Reactions Involved

• Chlorophyll absorbs excessive light energy.

• Transferring this energy to oxygen by excited chlorophyll forms singlet oxygen and other ROS.

• ROS react with lipids, proteins, and nucleic acids, causing cellular damage.

Effects On Plants

• Damage to Chloroplasts and Other Cellular Components:

• ROS can damage thylakoid membranes, hence affecting photosynthetic machinery.

• Peroxidation of lipids by ROS, oxidation of proteins, and DNA damage can take place.

Consequences For Plant Health And Growth

• Reduced photosynthetic efficiency and stunted growth.

• The plants become more susceptible to environmental stresses.

• Probable cell death and a reduced crop yield.

What Is Photorespiration?

Photorespiration is a process in plants whereby, instead of carboxylating RuBP, RuBISCO oxygenises ribulose-1,5-bisphosphate. The result is the formation of phosphoglycolate and eventually the release of CO2. This step consumes energy and reduces photosynthetic efficiency by competition with the Calvin cycle.

Photorespiration generally takes place when there is a high concentration of oxygen and a low concentration of carbon dioxide in the leaf, for instance, when stomata are closed to avoid loss of water. It is more pronounced in plants of the C3 category, whereby RuBisCO has a higher affinity for oxygen.

Mechanism Of Photorespiration

The mechanism of photorespiration is described below:

Role Of The Enzyme RuBisCO

• The enzyme RuBisCO catalyses the oxygenation of RuBP to give phosphoglycolate and 3-phosphoglycerate (3-PGA).

Steps Involved In Photorespiration

• RuBP is oxygenated by RuBisCo to yield phosphoglycolate.

• Phosphoglycolate is converted to glycolate and is transported to peroxisomes.

• Glycolate is converted to glyoxylate and then to glycine.

• Glycine is transported into the mitochondria and there converted to serine, releasing CO2 and NH3.

• The serine in turn goes back to the chloroplast and is converted back to 3-PGA.

Effects On Plants

The details are given below:

Loss Of Energy And Diminished Efficiency Of Photosynthesis

• The photorespiratory pathway uses up both ATP and NADPH without producing sugars.

• This process diminishes the net efficiency of photosynthesis.

Impact On Crop Yield And Productivity Of Plants

• Low net photosynthetic output.

• Lower crop yields and agricultural productivity.

Difference Between Photooxidation And Photorespiration

Importance Of Knowing Photooxidation And Photorespiration

Knowing photooxidation and photorespiration is quite important in improving the health of plants and crop yields and in finding ways of minimising their harmful effects.

Agricultural Applications

This includes:

Crop Management And Production Practices

• The understanding of these processes contributes to selecting and breeding crop lines that resist oxidative stress better.

• Optimisation of the light environment in controlled production systems to reduce adverse effects of photooxidation.

Control Measures

• Use of antioxidants to reduce ROS damage.

• Breeding and genetic manipulation to minimise photorespiration.

Ecological Relevance

The details are given below:

Impacts On Plant Ecosystems And Biodiversity

• Photooxidation and photorespiration impact the survival and adaptation of plants.

• Understanding these processes helps in predicting the responses of plants to climate change and other environmental stressors.