Abstract: In order to investigate the effects of low temperature stress on the plant growth rate, turf quality, MDA content, F_v/F_m, photosynthesis [P_n (net photosynthetic rate); G_s (stomatal conductance); C_i (intercellular CO₂ concentration); T_r (transpiration rate)], H₂O₂ and O2·- content, antioxidant enzyme activities (SOD, POD, CAT, APX), gene expression levels of antioxidant enzymes and cold-tolerance related genes (CBF1, COR, LEA), three Bermudagrass cultivars with differential cold tolerance, Tifsport, Tifway and Baoding Bermuda grass were selected and treated under a range of temperatures: optimum (30 ℃/25 ℃, day/night), suboptimum (18 ℃/12 ℃), chilling (8 ℃/4 ℃) and freezing (4 ℃/-4 ℃) in growth chambers. It was found that plant growth rate, turf quality, F_v/F_m and photosynthesis decreased while H₂O₂, MDA content and O2·- production rate increased with reduction in temperature, but the three cultivars varied in their response, with more rapid changes in the less cold-tolerant Baoding Bermuda grass. Leaf antioxidant enzyme activities were significantly increased with reduction in temperature, especially in the more cold-tolerant Tifsport. Similarly, the expression levels of CBF1, COR and LEA cold-tolerance genes were also significantly enhanced with decline in temperature, with Tifsport again exhibiting the greatest response. In summary, low temperature stress induced up-regulation of antioxidant enzyme genes and cold tolerance-related genes resulting in more active antioxidant defense systems, which in turn contributed to improved cell membrane stability, maintenance of higher photosynthesis levels and delay of chlorosis in Bermuda grass. These changes collectively were the basis for the higher cold tolerance.

Key words: bermudagrass, low temperature stress, antioxidant enzyme, gene expression