Comparison of the sub-cellular compartmentation of sugars in mature apples of two cultivars susceptible to different types of watercore and grown in different climates

Abstract

SummaryThe cellular compartmentation of sugars was compared between mature ‘Orin’ and ‘Fuji’ apple fruit (Malus × domestica Borkh.) which are susceptible to early and late watercore, respectively. Fruit were grown in a warmer climate (Ehime) and in a cooler climate (Aomori). Slight watercore, with a score of 1.4 (i.e., a remaining trace of early watercore), was detected in ‘Orin’ at Ehime, whereas severe late watercore, with a score of 3.0, was observed in ‘Fuji’ at Aomori. Sorbitol contents were significantly higher in watercored fruit than in non-watercored apples, not only in the intercellular spaces, but also in the cytoplasm and vacuoles, irrespective of the type of watercore. The permeability of the tonoplast to sorbitol was higher in watercored fruit than in non-watercored fruit in both cultivars, while a lower permeability of the plasma membrane to sorbitol was observed in watercored apples. Late watercore, which affected ‘Fuji’ at Aomori, showed similar levels of sorbitol to early watercore in ‘Orin’ at Ehime, despite the significantly higher watercore score in ‘Fuji’, suggesting that sorbitol may play only a minor role as a causative agent in the development of late (or low temperature-promoted) watercore compared with early (or high temperature-induced) watercore.