Relationship of seasonal changes in antioxidative enzymes and cold-hardiness in strawberry plant

In this study, seasonal patterns of antioxidative enzymes and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (EC 1.6.3.1) activities and their relations to cold-hardiness of eight strawberry (Fragaria x ananassa) cultivars [Camarosa, Camino Real, Cal Giant 2 (CG 2), Cal Giant 4 (CG 4), Kabarla, Selva, Sweet Charlie and Ventana] were investigated. Fully expanded, uniformly sized leaves from about 1-year-old field plants of the cultivars were collected in cold-acclimated (CA, in January) and non-acclimated (NA, in July) stages. Leaf samples were exposed to low temperature at 5, -5, -10, -20 and -30 degrees C for 12 h to determine their cold-hardiness (LT50; assessed by electrolyte leakage). A remarkable increase in cold-hardiness was observed with decreasing temperature. Ventana was found to have the highest cold-hardiness among the eight cultivars investigated. This cultivar has followed by Camino Real and CG 2 cultivars. CG 4 and Sweet Charlie have moderate cold-hardiness, while Selva and Camarosa were more sensitive than these two cultivars. On the other hand, Kabarla has the lowest cold-hardiness among the eight cultivars tested. Activities of catalase (CAT: EC 1.11.1.6), ascorbate peroxidase (APX: EC 1.11.1.11), glutathion reductase (GR: EC 1.6.4.2) and NADPH oxidase were correlated to changes in cold-hardiness. Activities of these enzymes were higher in the CA stage than in the NA stage. Activities of A PX and OR significantly varied depending on the cold-acclimation stage and the cold-hardiness level of the cultivars. This study indicates that, elevated antioxidative enzymes especially APX and OR, may be determinants of cold-hardiness in strawberry plant.