Plant response to drought is a complex phenomenon consisting of numerous metabolic pathways primarily based on water loss prevention and redox homeostasis maintenance. This study analyses the correlation of stomatal and non-stomatal carbon assimilation-limiting mechanisms with the strategies in antioxidant metabolism pathways and their connection with anatomical modifications in tomato leaves during long-term drought period lasting over 28 days. The results obtained in this research indicate that activation of stomatal closure was the first response to drought as stomatal pore was narrowed by 20% in day 15. The stomatal closing in early stress response was followed by decline in photosynthetic and transpiration rates even though the RUBISCO content has not been changed. Along with drought stress, both stomatal closure and RUBISCO content dramatically decreased leading to a decline in gas exchange parameters; thus, at the end of the experimental Queryperiod, the photosynthetic rate was reduced by 69% and transpiration rate by 80% in comparison with control plants. Superoxide dismutase and ascorbate peroxidase were induced in early stress response (as soon as after 15 days) with a constantly elevated activity during entire drought period. Terminal phase of drought induced the synthesis of new peroxidase isoform (MW ~ 49 kDa) which highly correlated with the phenolic acid contents. At the end of experimental period, the total phenol content of drought-treated plants was doubled as compared to control plants and this increase is correlated to elevated concentrations of hydroxybenzoic acid, ferulic acid, p-coumaric acid and caffeic acid. The progressive involvement of different antioxidant mechanisms over the drought period and their correlations with anatomical modifications and photosynthetic pigments protection was discussed in this paper.
