Abstract: [Objective] In order to reveal feasibility of different concentrations of BRs, BT and SA on Citrus aurantium under low temperature stress, the effects of BRs, BT and SA on physiological index were studied.[Method] Pot C. aurantium seedlings cultured under the same outdoor conditions were sprayed on the leaves with BRs, BT and SA separately, and then placed in the low incubator [0℃/4℃,(day/night),light intensity of 600 μmol·m^-2s^-1], and the seedlings sprayed with distilled water and set at 25℃ were served as control Ⅰ(CK₁), and the seedlings sprayed with distilled water and set at low temperature stress (0℃/4℃, day/night) were served as control Ⅱ(CK₂). The relative electric conductivity, contents of proline, malondialdehyde, soluble protein, chlorophyll, and activities of SOD, POD and CAT were measured.[Result] Compared with normal temperature CK₁, low temperature significantly inhibit the antioxidant enzyme activity of CK₂, enhanced the cell membrane damage and brought about loss of the normal functions of cell membrane. Thus, low temperature stress caused some increase in relative electric conductivity and MDA content of C. aurantium seedlings. Low temperature stress treatment also destroyed the structure of the chloroplast, causing the decomposition of photosynthetic pigment and reducing the content of chlorophyll and carotenoid. Compared with CK₂, 0.15 mg·L^-1 BRs, 10 mmol·L^-1 BT, 1 mmol·L^-1 SA enhanced the activities of POD, SOD, and CAT, increased the contents of proline and soluble protein, and effectively reduced the damage of low temperature stress on cell membrane. At the same time, the exogenous BRs, BT and SA increased the contents of chlorophyll and carotenoid, the efficiency of leaf photosynthesis and thus effectively resisted the oxidative stress caused by low temperatures. But with the increasing concentration of spraying, the ability of C. aurantium to resist low temperature stress decreased.[Conclusion] The foliage spraying with BRs, BT and SA could reduce the damage of low temperature stress on C. aurantium seedling leaves.

Key words: Citrus aurantium seedlings, low temperature stress, exogenous substances, stress resistance