Metabolic defense responses of seeded bermudagrass during acclimation to freezing stress

This study was conducted to examine the changes in the levels of carbohydrates and N-rich defense compounds during cold acclimation associated with freezing tolerance. Two bermudagrass [Cynodon dactylon (L.) Pets. var. dactylon] cultivars, Riviera (cold tolerant) and Princess-77 (cold sensitive), were selected and either subjected to cold acclimation at 8/4[degrees]C (day/night) with a light intensity of 200 [micro]mol [m.sup.-2] [s.sup.-1] over a 10-h photoperiod for 21 d or maintained at 25/23[degrees]C (day/night) with natural sunlight in a glasshouse. Cold acclimation induced accumulation of sugars and proline in both cultivars and also an increase in total nonstructural carbohydrates (TNC) and protein in Riviera, but not in Princess-77. Superoxide dismutase (SOD) increased during the first 7 d and then declined, while catalase (CAT) and ascotbate peroxidase (APX) activity decreased in response to cold acclimation in both cultivars. Electrolyte leakage (EL) was reduced in both cultivars following cold acclimation. The LT50 was reduced by 2.2[degrees]C (from -6.1[degrees]C to -8.3[degrees]C) in Riviera and 1.7[degrees]C (from -4.6[degrees]C to 6.3[degrees]C) for Princess-77 following cold acclimation. Riviera had more carbohydrates and N-rich compounds and less EL than Princess-77 at the end of cold acclimation. Significant correlations of LT50 with sugars, proline, protein, CAT, and APX were obtained in Riviera, but only with proline and the antioxidant enzymes in Princess-77. The results suggest selection and use of cultivars with rapid accumulation of C- and N-rich compounds during cold acclimation could improve bermudagrass persistence in transition zone climates.