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Regulatory role of exogenous salicylic acid in the response of Zoysia japonica plants to freezing temperatures: a comparison with coldacclimatisation

Li, Yueying, Liu, Chang, Li, Tianchun, Wang, Chuanyin, Xiao, Yuehuan, Zhang, Lin, Jin, Dandan, Zhao, Yan, Wang, Zhu, Cao, Jun, Hao, Lin
Journal of horticultural science & biotechnology 2011 v.86 no.3 pp. 277-283
Zoysia japonica, biotechnology, chlorophyll, cold stress, electrolytes, freezing, frost, horticulture, hydrogen peroxide, leaves, malondialdehyde, peroxidase, protein content, proteins, salicylic acid, sugar content, superoxide dismutase, survival rate, temperature
This study investigated the roles of exogenous salicylic acid (SA) in the response of Zoysia japonica plants to freezing stress, with cold-acclimatisation as a positive control. Sixty-day-old plants were sprayed with a 1.0 mM SA solution and, after 24 h, frozen at a series of sub-zero temperatures. For cold-acclimatisation, plants were exposed, in sequence, to 14°C, 10°C, 6°C, and 2°C for 24 h each, then stressed under the same sub-zero conditions as the SA pre-treated plants. Plant survival rates showed that SA pre-treated plants exhibited an increased tolerance to freezing, similar to that of cold-acclimatised plants, when compared to control plants (i.e., plants grown continuously under 28°C/23°C day/night) or to de-acclimatised plants (i.e., those first acclimatised at lower temperatures, then left at a warmer temperature of 28°C/23°C). Accordingly, both SA pre-treated and cold-acclimatised plants exhibited less chlorophyll damage than did control or de-acclimatised plants under all sub-zero temperatures tested, when compared to control values obtained from plants grown continuously under 28°C/23°C day/night. Under sub-zero freezing stress, the levels of H2O2 in both SA pre-treated and cold-acclimatised plants were lower than those in control or de-acclimatised plants, which correlated with decreased levels of malondialdehyde and electrolyte leakage in the SA pre-treated and coldacclimatised plants. Furthermore, the application of SA, or a cold-acclimatisation, protected the activities of superoxide dismutase (SOD) and peroxidase (POD) against freezing stress. In comparison with the controls, cold-acclimatisation increased the SA contents of leaves to those levels found in SA pre-treated plants. Soluble protein contents increased in both SA pre-treated and cold-acclimatised plants, while increases in soluble sugar contents occurred in coldacclimatised plants, but not in SA pre-treated plants, relative to the controls. Based on these data, pre-treatment with SA is proposed to improve tolerance to freezing stress in Z. japonica plants.This may be associated with increased levels of soluble proteins and/or the activities of anti-oxidative enzymes. Cold-acclimatisation and SA pre-treatment may involve, at least in part, common regulatory mechanisms to improve the freezing-tolerance of Z. japonica plants.