Abstract
Two-year-old seedlings of trifoliate orange (Poncirus trifoliata (L.) Raf.) and lemon (Citrus limonia Osbeck.) were sprayed with 0.1 mmol.L-1 abscisic acid (ABA) and then their leaves were collected randomly to expose to freezing stress. Specifically, these detached leaves were treated at 0, -3, -6, -9 and -12°C for 1 h respectively.The concentration of malondialdehyde (MDA), percentage of electrolyte leakage (EL) and the activities of several antioxidant enzymes (superoxide dismutase, catalase and peroxidase) were determined spectrophotometrically. The results show that the percentage of electrolyte leakage in trifoliate orange was lower than that in lemon, while the MDA concentration and the antioxidant activities of antioxidant enzymes in trifoliate orange were higher than those in lemon. Pretreatment with the abscisic acid can significantly reduce the membrane damage caused by freezing stress. However, the lipid peroxidation damage caused by low temperature and the activities of antioxidant enzymes were irregularly influenced by ABA pretreatment. We were thus able to infer that exogenous ABA can enhance the cold tolerance of citrus by a process rather than by activating antioxidant enzymes. Keywords: Antioxidant enzyme, short-term freezing stress, citrus, abscisic acid (ABA).
Highlights
Freezing is one of abiotic stresses that can cause irreversible damage to plant cells due to the mechanical forces generated by the formation of extracellular ice crystals, cellular dehydration and increased concentration of intracellular salts (Thakur et al, 2010)
The percentages of electrolyte leakage occurred in trifoliate orange (P. trifoliata (L.) Raf.) and lemon (C. limonia Osbeck.), both increased with the growing intensity of freezing stress
An exogenous application of abscisic acid (ABA) has been found to substitute for cold acclimation (Monroy and Dhindsa, 1995; Xing and Rajashekar, 2001; Nayyar and Kaushal, 2002)
Summary
Freezing is one of abiotic stresses that can cause irreversible damage to plant cells due to the mechanical forces generated by the formation of extracellular ice crystals, cellular dehydration and increased concentration of intracellular salts (Thakur et al, 2010). ABA is thought to trigger large amounts of cellular responses in plants required by the development of freezing tolerance (Shilpi and Narendra, 2005). It has been reported that the application of exogenous ABA can improve the freezing tolerance in various plant species, including Arabidopsis (Mantyla et al, 1995), Abbreviations: ABA, Abscisic acid; POD, peroxidase; CAT, catalase; SOD, superoxide dismutase; EL, electrolyte leakage; MDA, malondialdehyde; ROS, reactive oxygen species. Patens (Minami et al, 2003; Nagao et al, 2005), chickpea (Nayyar et al, 2005) and wheat (Zabotin, 2009) These findings indicate that ABA may function in a common physiological process during the development of cold tolerance and freezing tolerance. Treatment of Populus cathayana Rehd with ABA can increase the antioxidant activities of its antioxidant enzymes and the antioxidant levels (Yanwei et al, 2009)
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