Effects of gibberellins A4 on budbreak, antioxidant enzymes’ activity and proline content of flower buds in sweet cherry (Prunus avium)

Chilling accumulation is required for deciduous trees to maintain its normal growth and development. However, warm winters appeared more and more frequently, which hindered severely the normal growth and yield of fruit trees. To avoid these problems, artificial dormancy breaking agents are widely used. In our study, the effect of mineral oil, hydrogen cyanamide and gibberellins A4 (GA4) on budbreak were evaluated in sweet cherry (Prunus avium), which indicated that GA4 treatment hastened the date of flower budbreak and increased the percentage of budbreak compared with the other treatments. To better understand the mechanism of GA4-induced budbreak, the contents of antioxidant enzymes’ activity and proline in sweet cherry flower buds treated with GA4 and water were evaluated. There was a sharp decrease of catalase (CAT) activity after 5 days of GA4 treatment and then an increase of CAT activity after 10 days of GA4 treatment. However, there was a sharp increase of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) after 5 days of GA4 treatment and then a decrease of these enzyme activities after 10 days of GA4 treatment. There was a transient increase in hydrogen peroxide (H2O2) content and proline content after 5 days of GA4 treatment and a decrease after 10 days of GA4 treatment. However, there were only small fluctuations after water treatment, which indicated that temporary oxidative stress may contribute to the dormancy release of flower buds in the sweet cherry treated with GA4 through the regulation of H2O2 content coincided with the changes of antioxidant defense system.