Photosynthetic response and antioxidative activity of 'Hass' avocado cultivar treated with short-term low temperature

To investigate the effects of short-term low temperatures, three-year-old avocado (Persea americana cv. Hass) seedlings were treated with 1, - 2, or - 5 °C for 1 h and subsequently recovered in ambient condition for 24 h. Leaf color changes were investigated with chlorophyll, carotenoid, and phenolic contents. Photosynthetic responses were examined using gas exchange analysis. With H₂O₂ contents as oxidative stresses, enzymatic (ascorbate peroxidase, APX; glutathione reductase, GR; catalase, CAT; peroxidase, POD) and non-enzymatic antioxidant activities were determined using spectrophotometry. Leaves in the avocado seedlings started to be discolored with changes in the contents of chlorophyll a, carotenoids, and phenolics when treated with - 5 °C. However, the H₂O₂ content was not different in leaves treated with low temperatures. Photosynthetic activities decreased in leaves in the seedlings treated with - 5 °C. Of antioxidant enzymes, APX and GR have high activities in leaves in the seedlings treated with 1 and - 2 °C. In leaves in the seedlings treated with - 5 °C, the activities of all enzymes decreased. Non-enzymatic antioxidant activity was not different among leaves treated with low temperatures. These results indicated that APX and GR would play a critical role in withstanding chilling stress in 'Hass' avocado seedlings. However, under lethal temperature, even for a short time, the plants suffered irreversible damage with the breakdown of photosystem and antioxidant system.