Accumulation of Soluble Solids and Activation of Antioxidant Enzymes by Deficit Irrigation in Fresh Tomato Fruits

Abstract

The effects of deficit irrigation on the accumulation of soluble solids and activation of antioxidant enzymes in fresh tomato (Lycopersicon esculentum Mill) fruits were investigated. Although fruit weight was reduced by deficit irrigation, dry matter was significantly increased. Deficit irrigation significantly increased sugars and organic acids compared with the normal irrigation. Content of hexoses (glucose and fructose) in fruits of moderate deficit-irrigated (MDI, -30 kPa) and severe deficit-irrigated (SDI, 40 kPa) plants was higher as 127.6% and 157.8% than those in fruit of normal-irrigated (NI, -20 kPa) plants. Content of citric acid was significantly increased to 127.0% and 160.7% by MDI and SDI compared with the fruit of NI plants, respectively. Activation of antioxidant enzymes exhibited differential patterns in terms of specific and gel activity by irrigation levels through developmental stages. The specific and gel activities of SOD, POD,PPO and G6PDH in fruits of NI plants were activated 50 d at ripening stage after anthesis. However, both activities of these antioxidant enzymes are activated as early as 10 d and 20 d by MDI and SDI treatment, respectively. These results suggest that accumulation of soluble solids by deficit irrigation is associated with activation of antioxidant enzymes, and its activation seems to play a critical role in the restriction of fruit size and acceleration of ripening.