Part 2: Abiotic stressors in evironment

At low light intensities,photosynthesis is limited only by the amount of light available. Light is the limiting factor for photosynthesis. There are not enough photons to excite many electrons in PSII and PSI. Electron transport is slow. ATP and NADPH production is slow. The Calvin cycle can only work as fast as light allows.

At low light intensities, plants produce CO2 beacuse respiration continues. but photosynthesis is too weak to consume that co2. Plants always perform cellular respiration, respiration releases CO2 as it breaks down sugars for energy. Photosynthesis consumes CO2 but only when there is enough light to power it.

At high light, photosynthesis reaches a point of saturation beacuse rubisco and the enzymes of the calvin cycle can only work at a maximum speed. Even if more ATP and NADPH are available, the Calvin Cycle cannot fix CO2 any faster. All reaction centers are already open/working at maximum efficiency

Eustress is positive, beneficial stress that stimulates helpful responses ans increases performance or resilience. In plants, it can activate protective mechanisms and improve tolerance. -> reversible

• Readjustment metabolism

• Induction repair and protection resonses (ROS signalling, gene exprrssion change, accumulation phytochemicals and antioxidants, morphological ans developmental stages)

Distress is negative, harmful stress that exceeds the organism’s capacity to cope. It causes damage to cells, proteins, membranes, DNA and reduces growth or survival. -> irreversible

• Physiological destabilisation (oxidative damage, ROS signalling, DNA damage, Inactivation photosynthesis, production distress hormones, Cell death)

Stress is a deviation from the normal, non- stress condition

Non-stress: when a plant is at a thermodynamically optimal state

At low light intensities, photosynthesis is limited only by the amount of light available. At low light, there are not enough photons to excite many electrons in PSII and PSI. Electron transport is slow. ATP and NADPH production is low. The calvin cycle can only work as fast as light allows.