Biochemical changes in kiwifruit buds during dormancy under controlled and natural chilling

Chilling accumulation is associated with many metabolic changes that lead to release of endodormancy of buds. The aim of the present research was to assess the impact of both natural and controlled chilling on proline, total phenol and radical scavenging (RSA), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities in the buds of kiwifruit cultivars during dormancy. This study was undertaken during 2015–16 in the North of Iran. The results indicated that Hayward and Tomuri had different enzyme activities during and after endodormancy. Hayward cultivar showed higher PAL, RSA, total phenol and proline contents and lower PPO than Tomuri cultivar. Under the natural chilling method, PAL activity, RSA and total phenol contents increased significantly at the first chilling. The effects of controlled chilling treatments on the pattern of biochemical changes in buds were similar to those of natural chilling during the endodormant period. However, the activities and contents of the mentioned biochemical compounds were lower under controlled chilling than natural chilling. Higher phenylpropanoid pathway activity as shown by higher PAL/PPO enzymes activities giving rise to higher phenols accumulation and higher DPPH scavenging capacity can be used as valuable biochemical indicator (marker) for timing of bud endodormancy releasing in kiwifruit under natural chilling.