Effect of putrescine and proline on proflies of GABA, antioxidant activities in leaves of three Citrus species in response to low temperature stress

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This study was carried out to assess antioxidant activities and defense role of putrescine and proline in leaves of three Citrus species under low temperature stress. Branches of three Citrus species (C. reticulata L., C. sinensis L. and C. paradisi L.), sprayed with putrescine 0, 5, 10 mM and proline 0, 15, 20 mM. 24 h after application, containers containing treated shoots exposed to temperatures 1, − 1 and − 3 °C for six hours. The amount of hydrogen peroxide, flavonoids, phenolic compounds and antioxidant capacity increased with temperature reduction to − 3 °C. HPLC analysis showed that low temperature (− 3 °C) induces the levels of Gamma Aminobutyric Acid (GABA) in leaves of all species. The comparison of the HPLC patterns of the three species showed that GABA levels in treated leaves increased than control. The application of different concentrations of putrescine and proline decreased production of hydrogen peroxide but improved antioxidative activities of leaves under low temperatures. Putrescine 10 mM and proline 20 mM showed the highest effects than the other levels. The highest value of hydrogen peroxide was observed in leaves of control (putrescine and proline 0 mM) under − 3 °C but its lowest level was seen in leaves treated with proline 20 mM and putrescine 10 mM in all three species of Citrus. The highest level of phenolic compounds, flavonoids and antioxidant capacity were observed in leaves treated with putrescine 10 mM and proline 20 mM at − 3 °C. Putrescine 10 mM and proline 20 mM showed the highest impact on reduction of the damages caused by low temperature stress.