The determination of changes in antioxidant activities during the drought stress of three citrus

Drought stress annually causes billions of dollars loss by approximately 35% decreases in the yield and quality of agricultural crops around the world. Citrus, which constitute an economically important fruit group, is also adversely affected by drought stress. Use of rootstock is necessary for resistance to environmental stresses in agricultural production of many crops including citrus fruits. In this study, changes in the antioxidant levels during the drought stress were investigated in sour orange (Citrus aurantium) and Troyer and Carrizo citranges (Poncirus trifoliata x Citrus sinensis) which are commonly used as rootstocks in citrus cultivation. Seedlings were grown for each rootstock used in the study; then, control and stress groups containinin 10 seedlings were formed for each rootstock. The seedlings in the control groups were regularly watered, but seedlings in the stress groups were not watered for 14 days to apply drought stress. Leaf samples were collected separately from the control and stress groups of each rootstocks at 0, 7, 8, 9, 12 and 14 days of the drought stress and leaf samples were stored at -80 °C. The leaf samples were ground in liquid nitrogen and then extracted by appropriate methods. Then, soil moisture, stoma conductivity, lipid peroxidation (MDA) and hydrogen peroxide (H2O2), changes in protein content were investigated in samples from control and stressed plants as stress indicators. Moreover, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) enzyme activities were determined as enzymatic antioxidants and ascorbic acid and phenolic levels were determined as non-enzymatic antioxidants to determine antioxidative changes during drought stress. As a result of the statistical analysis, hydrogen peroxide (H2O2), malondialdehyde (MDA), ascorbic acid, phenolic amounts, CAT activity and APX activities increased in all stressed plants compared to the controls. While GR enzyme activity and protein amount decreased in stressed sour orange rootstock, it is increased in other rootstocks compared to control after drought stress. On the other hand, SOD enzyme activity decreased in all stressed treated rootstocks compared to the controls. As a result, it was determined that the stress indicators of Troyer and Carrizo rootstocks were higher than that of sour orange rootstocks. Therefore, these citrus rootstocks were more resistant to drought stress than sour orange rootstock. These results indicated that the use of Troyer and Carrizo citrange rootstocks can be more suitable than sour orange in citrus cultivation during drought condition.