Can organic acid and sugar compositions be used to predict cell death point limits? Receptacle and pistil organs of apricot (Prunus armeniaca L.)

Abstract

To boost our understanding of recent frost damage events in apricot trees, we focused on estimating the cell death point in the receptacle and pistil organs of apricots by simulating the unexpected temperature changes occurring in early spring under laboratory-based freezing experiments. The hypothesis also that organic acids (oxalic, propionic, tartaric, butyric, malonic, malic, lactic, citric, maleic, fumaric and succinic acids) and soluble sugar compositions (glucose, fructose, sucrose and total sugar) may directly stimulate the change of the frost tolerance in apricot receptacle and pistil organs was investigated using two apricot (Prunus armeniaca L.) cultivars, one tolerant to frost (‘Iğdır Şalak’) and the other sensitive to frost (‘Mihralibey’). Our results indicated that the mean the cell death point (CDP) of flower pistil (from −13.26 to −14.18 °C) was at lower temperatures than those of flower receptacle (from −6.28 to −8.65 °C) in both apricot cultivars during the full blooming stage. In both apricot cultivars, receptacle organs showed more sensitive changes to the frost tolerance in response to low temperatures compared with pistil organs. In terms of organic acid and soluble sugar contents, significant differences were determined for both apricot cultivars and between the pistil and the receptacle organs of the flowers. Organic acid content was higher in the freezing-tolerant apricot cultivar (‘Iğdır Şalak’) than the freezing-sensitive apricot cultivar (‘Mihralibey’), but it was lower in the freezing-tolerant organ (pistil) in comparison with the freezing-sensitive organ (receptacle). Moreover, fructose concentrations for both ‘Mihralibey’ and ‘Iğdır Şalak’ were significantly higher in the receptacle compared to the pistil. A significant negative correlation was also observed between the mean CDP values and both all organic acids and sucrose contents in the pistil and the receptacle organs for both apricot cultivars. There was a positive relationship between the CDP values and fructose content in ‘Iğdır Şalak’. Additionally, there was a negative correlation between the CDP values and sucrose in 'Mihralibey'. Overall, the data presented suggest that the high level of sucrose and organic acid content of receptacle and pistil organs contributes to support frost tolerance of organs. The results of this study could help in the understanding of how receptacle and pistil organs of two different apricot cultivars react to frost stress, and how they modulate their soluble sugar and organic acid metabolism.Graphic abstract