The data on water stress induced regulation of the activity of photosynthetic enzymes other than Rubisco are scarce. The activity of several photosynthetic enzymes under progressive water stress in two different cultivars of Morus Alba. Unlike Rubisco, which is highly stable and resistant to water stress, the activity of some enzymes involved in the regeneration of ribulose-1,5-bisphosphate (RuBP) are progressively impaired from very early stages of water stress. Drought stress is accompanied by the formation of ROS such as O2, H2O2, and OH, which damage membranes and macromolecules. Plants have developed several antioxidation strategies to scavenge these toxic compounds. Enhancement of antioxidant defense in plants can thus increase tolerance to different stress factors. Antioxidants (ROS scavengers) include enzymes such as catalase, superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase.