Variation in antioxidant enzyme activity and key gene expression during fruit development of blackberry and blackberry–raspberry hybrids

Blackberry (Rubus spp.) belongs to the Rubus genus in the Rosaceae family, and its fruits are rich in nutrients and function in exerting antioxidant effects. Based on this, the fruits of 'Chester' blackberry, 'Hull' blackberry and the hybrid cultivars 'Boysen' and 'Young' at different developmental stages were selected to evaluate antioxidant-related indexes, antioxidant enzyme activity and the expression patterns of genes encoding antioxidant enzymes. The results showed that the total antioxidant capacity of the hybrid fruits was higher than that of the pure blackberry fruits. PCA (principal component analysis) and correlation analysis showed that the antioxidant capacity was related to anthocyanin, ASA (ascorbic acid), GSH (glutathione), MDA contents and O2- production rate. However, the correlations between antioxidant capacity and metabolites were different among the cultivars. The O2- production rate and MDA (malondialdehyde) content increased with fruit development. The activities of CAT (catalase) and POD (peroxidase) were maintained at a relatively low level, while SOD (superoxide) activity was maintained at a relatively high level. This study was the first to analyze the content of antioxidant substances in different developmental stages of blackberry fruits and blackberry-raspberry hybrids fruits, which provided some suggestion for the extraction of specific antioxidant substances in different developmental stages. Based on the transcriptome data, the role of antioxidant enzyme genes in antioxidant system was concerned, providing a practical basis for the expression characteristics of key genes.