Sugar Accumulation Profile during the Ripening Process in the Pollination-Constant Non-Astringent Japanese Persimmon ‘Akiou’

Abstract

We monitored sugar accumulation profiles and developmental changes in fruit traits during the ripening process in pollination-constant non-astringent (PCNA)-type persimmon cultivars of ‘Akiou’, ‘Fuyu’ and ‘Taishuu’. As the fruit ripened, transverse and longitudinal diameter, fruit weight, soluble solids content (SSC), and flesh juiciness increased significantly, with a constant varietal ranking throughout the ripening process. Color development of ‘Akiou’ and ‘Taishuu’ seemed to be faster than that of ‘Fuyu’ during the initial stages of fruit ripening, but there was little difference in color chart values toward the latter stage of fruit ripening. Flesh firmness decreased steadily over time, whilst varietal ranking remained constant. The varietal ranking of SSC in the latter stage of ripening was ‘Akiou’ ≥ ‘Taishuu’ > ‘Fuyu’. Significant varietal differences were observed in sucrose, glucose, and fructose contents. Based on sugar accumulation profiles, the cultivars could be classified into two types: hexose accumulators (‘Taishuu’) and sucrose accumulators (‘Akiou’ and ‘Fuyu’). The transcriptional profiles of key sugar accumulation-related genes: sucrose synthase (SuSy), vacuolar acid invertase (VAI), and sucrose phosphate synthase (SPS), were also examined. Transcriptional levels of SuSy and VAI in sucrose accumulators were lower than those in the hexose accumulator. Conversely, transcriptional levels of SPS were higher in the sucrose accumulators than in the hexose accumulator. In particular, the concomitant and rapid increase of both SPS expression and sucrose accumulation in mid-October, suggests that this period is crucial for ‘Akiou’ in terms of the SSC elevation.