Antioxidant system is essential to increase drought tolerance of sugarcane

Drought is one of the main factors affecting the productivity of agricultural crops, and plants respond to such stress by activating various physiological and biochemical mechanisms against dehydration. The present study investigated two varieties of sugarcane (Saccharum spp.) with contrasting responses to drought (RB867515, more tolerant; and RB855536, less tolerant) and subjected them to progressive drought conditions (2, 4, 6 and 8 days) followed by rehydration. Drought caused a decrease in water potential (ψ_w) and osmotic potential (ψ_os) in the leaves, which recovered to normal levels after rehydration only up to the fourth day of drought. Water stress changed the carbon metabolism of leaves by reducing starch and sucrose contents and increasing glucose and fructose contents in both varieties. Water deficit caused a significant reduction in the maximum quantum efficiency of photosystem II (F_v/F_m) and effective quantum yield (Φ_PSII) in both varieties; however, RB867515 recovered faster after rehydration. Under water stress, the more tolerant variety RB867515 exhibited increased activity of the antioxidant enzymes catalase, ascorbate peroxidase and superoxide dismutase compared with the RB855536 variety. The results suggest that RB867515 is more tolerant to drought conditions because of a more efficient antioxidant system, which results in reduced photosynthesis photoinhibition during water stress, thus revealing itself as a potential physiological marker for drought tolerance studies.