Study on the expression of dehydrin genes and activities of antioxidativeenzymes in floral buds of two sand pear (Pyrus pyrifolia Nakai) cultivarsrequiring different chilling hours for bud break

Abstract

Seasonal expression pattern of antioxidative genes (dehydrins), activities of antioxidant enzymes and H 2 O 2 contents, and their relations to dormancy phases in floral buds of sand pear (Pyrus pyrifolia Nakai 'Cuiguan' and 'Wonhwang') were documented in the present study. The results showed that the expression patterns of PpDHN1, PpDHN2, and PpDHN3 in the two cultivars were similar, but the expression peak time and quantity were different. In the floral buds of Cuiguan, expression of all three dehydrin genes (PpDHN1, PpDHN2, and PpDHN3) was detected during endodormancy, reached the highest levels in ecodormancy, and then declined during the bud break stage. In the floral buds of Wonhwang, the expression of all the dehydrin genes (PpDHN1, PpDHN2, and PpDHN3) were at their highest in endodormancy and declined in ecodormancy. High activities of superoxide dismutase (SOD) were detected in endodormancy and decreased during ecodormancy, then increased again during bud break stage. Peroxidase (POD) quantities were different between the two cultivars, but followed similar activity patterns: POD activities were low during endodormancy, reached their lowest point during ecodormancy, and then increased again at the bud break stage. Catalase (CAT) activities were increased during endodormancy and reached their peak level in ecodormancy before decreasing in the bud break stage in both cultivars on different sampling dates. Ascorbate peroxidase (APX) activities were decreased in endodormancy, increased in ecodormancy, and at their peak in the bud break stage, with different amounts of ascorbate in both cultivars. The highest level of H 2 O 2 content was detected during endodormancy release in floral buds of Cuiguan, while it was decreased during endodormancy in Wonhwang; their content decreased in bud break stage. During dormancy, the activities of SOD, POD, and APX decreased while CAT activity increased with the expression of dehydrin genes and H 2 O 2 content. Therefore, the changes in gene expression, enzyme activities, and H 2 O 2 content may be involved in the antioxidant defense mechanisms in floral buds of pear cultivars during dormancy.