1. Reactive oxygen species (ROS): An Introduction -- 2. ROS generation in plant cells orchestrated bystress -- 3. Oxidative stress triggered damage to cellular biomolecules -- 4. Senescence and Apoptosis: ROS contribution to stress tolerance or cellular impairment -- 5. Photosynthetic apparatus: Major site of oxidative damage -- 6. Generation and fate of ROS in mitochondria -- 7. Peroxisomes and ROS under stress conditions -- 8. ROS production and function at plasma membrane and apoplast -- 9. Antioxidant defensive mechanisms to regulate cellular redox homeostatic balance -- 10. Role of osmolytes in alleviation of oxidative stress -- 11. ROS as signaling molecule under unfavorable conditions -- 12. Molecular mechanisms underpinning signaling function of ROS.