Rice is a vital cereal crop, coming after wheat in the most consuming crop list. Rice was considered to be one of the most water-consuming crops, so it was severely affected by drought stress. Drought stress is currently affecting more than 50% of agricultural land worldwide. Rice suffers from drought stress more than one time during its life cycle. Thus, we are dealing with a big problem that possesses a great risk to the crop. The present study was conducted on two rice cultivars that vary in their tolerance to drought stress, Giza 179 (Gz179) (tolerant cultivar) and Sakha 101 (Sk101) (sensitive one), to compare their responses to drought treatment (40% water holding capacity). Fifteen sugar types, seventeen phenolic acids, and fifteen flavonoid compounds and phytohormones (including indole acetic acid, indole butyric acid, gibberellic acid, abscisic acid, and salicylic acid) were analyzed and quantified using high-performance liquid chromatography to identify strategies behind stress tolerance. Tolerant cultivar (Gz179) was less affected by water deficit and oxidative stress resulting from drought stress than the sensitive cultivar (Sk101). This could be attributed to the metabolic changes detected in the tolerant cultivar, which showed an increased accumulation of osmoprotectants including proline, sugars (mannitol, stachyose, sucrose, and galacturonic), and organic acids (tartaric and glutaric) to maintain osmotic adjustment of the cell, as well as a significant increase in nonenzymatic antioxidants such as phenols (isoferulic, cinnamic, and pyrogallol) and flavonoids (kaempferol and quercetrin) compared to the sensitive cultivar.
Key words: Osmoprotectant, Oryza sativa, secondary metabolites, sugars, water deficit.