Effect of foliar spray with putrescine and proline on some physiological characteristics of peel and pulp of two citrus species in response to low temperature stress

Different species of Citrus are sensitive to low temperature stress. Today plant growth regulators are used to reduce the negative effects of stress on plants. In this study, physiological and biochemical changes in the peel and pulp of Citrus fruits treated with different concentrations of putrescine and proline under low temperatures were investigated. The selected branches were sprayed with putrescine (0, 5 and 10 mM) and proline (0, 15 and 20 mM), 24 hours before exposure to low temperatures. Then, the treated bearing branches were exposed to temperatures of +1, -1 and -3 °C for three hours. Results of the study indicated that in control trees of both Citrus species, low temperature decreased the rate of reduction in sugars concentration, while the amounts of phenolic compounds, flavonoids and soluble solids in peel and pulp of both Citrus species were increased. The amount of phenolic compounds, flavonoids and soluble solids increased in fruits treated with proline and putrescin compared to control. The highest amounts of these parameters were observed in samples treated with proline at 20 mM and putrescine at 10 mM.