Vol. 82 No: 5

Title:
Effects of branch bending on the levels of carbohydrates and phenolic compounds in 'Conference' pear leaves

Authors:
M. COLARIC, F. STAMPAR and M. HUDINA

pp: 815-821

Abstract:
The effects of bending on carbohydrates and phenolic compounds were investigated in ‘Conference’ pear leaves during the growing seasons in 2004 and 2005. Leaves were sampled from tree branches bent in the late-Summer of 2003, in Spring 2004, and from unbent branches. Levels of carbohydrates (i.e., sucrose, glucose, fructose and sorbitol) and phenolic compounds (i.e., chlorogenic acid, sinapic acid, vanillic acid, (+)-catechin, (–)-epicatechin, rutin, quercetin-3-D-galactoside and quercetin-3-β-D-glucoside) were determined in pear leaves using high performance liquid chromatography. In the first sampling year, significantly higher contents of some of the phenolics measured (i.e., chlorogenic acid, vanillic acid, sinapic acid, and rutin) were observed in leaves from the Spring treatment. In the second year, a similar tendency among treatments was significant at the September and October sampling dates for chlorogenic acid and vanillic acid, and at one sampling date in October for catechin and one in September for quercetin-3-D-galactoside. In June and August 2004, epicatechin and catechin levels, respectively, were significantly higher in the controls. In May and June 2005, quercetin-3-D-galactoside and sinapic acid, respectively, exhibited significantly higher values in the controls. Quercetin-3-β-D-glucoside was highest in control leaves in May, June, July and October. In August 2004, significantly higher contents of epicatechin were found in leaves from the Summer treatment. Carbohydrate levels showed no clear tendency among treatments, as did some phenolics. During our research, the patterns of carbohydrates and phenolics were also ascertained over the growing season. In general, in 2004, the levels of phenolics increased, then decreased over the growing season. In 2005, however, the maximum levels of phenolics were reached earlier, then, after decreasing, another increase occurred from August to October. Moreover, it was found that sorbitol predominated among the carbohydrates, and chlorogenic acid predominated among the phenolics in both growing seasons. These are the first data on variations in carbohydrate and phenolic contents in pear leaves, as influenced by branch-bending over two successive years. These variations appear to result from the physiological response of pear trees and leaves to this cultural practice.

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