Apoplastic Antioxidant Enzymes in the Leaves of Two Strawberry Cultivars and Their Relationship to Cold-Hardiness

In this study, apoplastic antioxidant enzymes in the leaves of two strawberry cultivars (‘Aromas’ and ‘Diamante’) and their relationshipto cold-hardiness were investigated. Fully expanded, uniformly sized leaves from 1-year-old field plants of the cultivars were collected atthe hardening (late autumn, in November and winter, in January) and de-hardening (summer, in July) stages. Leaf samples were exposedto low temperatures of 5, -5, -10, -20 and -30ºC for 12 h to determine their cold-hardiness (LT50; lethal temperature, where 50% of theplants were killed). Cold-acclimation produced a remarkable increase in cold-hardiness. It was found that ‘Diamante’ had higher coldhardinessthan ‘Aromas’. Moreover, malondialdehyde and total carotenoid content increased during the hardening stage and decreasedduring the de-hardening stage. The activities of catalase, peroxidase and ascorbate peroxidase in the leaf apoplast and nicotinamideadenine dinucleotide phosphate oxidase activity in the leaf tissue were correlated with changes in cold-hardiness. The activities of theseenzymes were higher in the hardening stage than in the de-hardening stage. The activities of apoplastic catalase, peroxidase and ascorbateperoxidase varied significantly depending on the cold-acclimation stage and the cold-hardiness level of the cultivars. This study indicatesthat elevated apoplastic antioxidative enzymes may be determinants of cold-hardiness in the strawberry plant. The lower malondialdehydecontent and higher total carotenoid and apoplastic enzyme activities in ‘Diamante’ indicated an enhanced cold-hardiness capacity of thiscultivar, serving to protect the plant from oxidative damage.

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