Changes in Gene Expression and Activity Pattern of Some Antioxidant Enzymes in Olive Trees (Olea europaea L. cv. Conservalia) in Relation to Alternate Bearing

The alternate bearing, severe fluctuation in annual fruit yield, causes a type of abiotic stress in olive trees during ON-year, i.e. the year with high fruit load. Hence, one could assume a hypothesis in variation of leaves antioxidant capacity in this regard. The current study was conducted aimed at assaying this hypothesis through analyzing some antioxidant enzymes activities and their gene expression patterns. For this, leaves samples were collected from 12-year-old olive (cv. Conservalia) trees, both ON- and OFF-type, at flower bud induction phase during two successive years. Among studied criteria such as antioxidant capacity, phenol, flavonoid and total protein contents, the amount of phenol in OFF-trees was substantially higher than ON-trees. The activity of peroxidase (POD), superoxide dismutase (SOD) and phenylalanine ammonia-lyase (PAL) was considerably influenced by bearing status. In comparison to OFF-trees, the activity of the POD enzyme was higher in ON-trees, and the opposite trend was revealed in terms of SOD and PAL activities. The relative gene(s) expression of POD and polyphenol oxidase (PPO) in ON-trees, and SOD and PAL in OFF-trees was significantly high. While the SOD showed downward trends, the POD witnessed an upward pattern in terms of its activity and gene(s) expression profile in ON-trees. In general, the phenolic compounds synthesis and their consumption are the dominant metabolic process in OFF- and ON-trees, respectively.