Daily Dynamics of Sugar and Phenol Contents in Apple Fruitlets during June Drop

Abstract

The occurrence of the abscission signal in young developing fruits on apple trees (Malus domestica) was studied. Apple has a natural system of fruitlet shedding, so called June drop. Although physiological fruit drop is unable to guarantee production of marketable apples and avoid alternate bearing, knowledge of this is a key background for successful fruit thinning. A study was carried out on apple trees cv. 'Golden Delicious' during June drop. On three dates (beginning, middle and end of June drop), the daily dynamics of HPLC detected individual sugar and spectrophotometrically detected total phenolic content was investigated in central (K) and lateral (L) fruitlets. The results of daily dynamics showed the highest sugar contents at 2 p.m. On the final sampling date, on 2 nd July 2015, we observed a significant difference between sugar contents at 2 p.m. and the morning and afternoon measurements. Contents of sugars in K and L fruitlets were not significantly different. Total phenolic content at the beginning of June drop was higher than at the end. There was no statistically significant difference between K and L in an individual time period, while there were statistically significant differences in total phenolic content among the sampling dates. Although sugar and phenolic content in K and L fruitlets were rarely statistically different, their contents changed during June drop. In general, sugar contents increased and phenolic content decreased during the process, while the daily dynamic depended on weather conditions.

Variation in Phenolic Compounds Content and Antioxidant Activity of Different Plant Organs from Rumex crispus L. and Rumex obtusifolius L. at Different Growth Stages

“…It should be noted that phenolic compounds are not, apparently, typical compounds for phloem transport. However, many authors indicate the presence of a small number of phenolic substances in phloem exudates [53]. One of the factors preventing the free flow of phenols through phloem channels is the alkaline reaction of the central cavity solution, in which these compounds are particularly sensitive to oxidation, forming aggressive quinones.…”

Modifications in Organic Acid Profiles During Fruit Development and Ripening: Correlation or Causation?

“…Both metabolic patterns and concentration are highly variable according to the species. In this vein, accumulation of sucrose, glucose, and fructose during ripening are especially observed in sweet fruits such as apples ( Jakopic et al, 2018 ; Williams and Benkeblia, 2018 ), litchi ( Yang Z. et al, 2013 ), melons ( Burger et al, 2000 ; Huang et al, 2017 ), peach ( Cirilli et al, 2016 ), strawberries ( Shanmugam et al, 2017 ), mango ( Cosme Silva et al, 2017 ), papaya ( Paull et al, 1999 ) and watermelons ( Liu et al, 2013 ) (Table 2 ). In general, sugar accumulation in fruit is directly controlled by increasing the activities of sucrose synthase (Suzy) and SPS ( Chen et al, 2004 ).…”