Variation in chemical compounds of walnut (Juglans regia L.) leaves with tree age

Abstract

In this present study, we investigated the chemical compounds in the fresh leaves of ancient walnut trees (Juglans regia L.) aged 25, 75, 100, and over 400 year. Under similar environmental conditions, the fresh leaves of walnut trees were collected and analysed for chlorophyll molecules as chlorophyll a, chlorophyll b and carotenoids, enzymatic compounds (ascorbate peroxidase (APX), catalase (CAT) and superoxide dismutase (SOD) activities) and non-enzymatic compounds (proline, total soluble protein, total phenolic compounds), flavonoid and reducing sugars (glucose, sucrose, total soluble sugar). In addition, the oxidative stress level was determined by measuring lipid peroxidation (MDA-malondialdehyde) and hydrogen peroxide (H2O2). Significant differences in the chemical composition of the fresh leaves were found between the 4 different tree age classes. In general, the results showed that mean chlorophyll pigments were increased with increasing the age. There was also a general trend that mean glucose and starch concentrations increased with the age, while mean sucrose concentration decreased, but no changes were noted for mean total soluble carbohydrate. On the other hand, mean SOD concentration decreased with increasing the age. Other chemical compounds (mean proline, total soluble protein, malondialdehyde, hydrogen peroxide, APX and CAT), however, did not show clear trends with the age. As a result, these pioneer study have provided valuable insight into the variation in the chemical constituents of walnut tree leaves in relation to the age, and it can be used to better understanding, managing and fighting against pathogens of walnut ecosystems in future studies.