Abstract
The wood of the common oak (Quercus robur L.) has high mechanical strength, elasticity and resistance to fracture. However, constitutional stability is not always able to provide the plants with reliable protection from wood-decay fungi, and the initial stages of biodegradation are difficult to determine. Therefore, this study concerns research on appropriate biochemical markers for early diagnostics of wood defects. The total content of phenolic compounds in leaves and wood was determined by a spectrophotometer Optizen Pop using Folin & Ciocalteu’s phenol reagent; the flavonoid content in leaves – by adding solutions of aluminum chloride and sodium acetate to methanolic extracts; catechins content – by the reaction with vanillin reagent; the concentration of phenolic antioxidants – by Brand Williams; chlorophyll and carotenoids’ contents in leaves – by the formula for methanol extracts; the qualitative composition of phenolic compounds – by high performance liquid chromatography and highly effective thin-layer chromatography. During the planned felling of oak trees on the territory of the Boyar Forest Research Station, trees were found with signs of brown streak and biodestruction of wood. Brown streak in wood is caused by a polycondensation of phenolic compounds, which are deposited on the internal surfaces of tracheal elements. In cases of an increase in the total amount of oxidized polyphenols, the cell walls are also stained. Active oxidation processes in wood have a systemic nature for the plants and affect the physiological state of the assimilation apparatus. We determined that in leaves of the trees with signs of brown streak the total phenol content increases in comparison with the control by 1.6 times, as well as flavonoid and catechin content. Our research has shown that the complex of plastid pigments in common oak leaves does not significantly change in the early stages of destructive processes. Increase of brown streak and appearance of rot in wood are associated with slight increase in chlorophyll a to b ratio in leaves. Chromatographic profiling of the leaves showed that the presence of brown streak changes the content of individual phenolic compounds. The trees with brown rot have more substances with UV spectrum characteristic for kaempferol glycosides compared to the control. The results have shown that the biochemical profiles of the trees with signs of brown streak and brown rot differ from the control by the composition of low and medium polar compounds. The absence or presence of some individual phenolic components and their ratio in the leaves are considered as biochemical markers of hidden wood defects.
Highlights
The wood of common oak (Quercus robur L.) is highly valued for its high mechanical strength, elasticity and resistance to destruction
Brownstreak in wood is caused by a polycondensation of phenolic compounds, usually catechins into phlobaphenes, which are deposited on the inner surfaces of xylem cells (Fig. 2)
During a detailed study of xylem tissues, signs of partial damage to cell walls’ integrity was revealed (Fig. 2b, d). Defects of this kind are usually typical for the vital activity of xylotrophs, which hydrolyze the components of cell walls by exogenous enzymes
Summary
The wood of common oak (Quercus robur L.) is highly valued for its high mechanical strength, elasticity and resistance to destruction These properties are mainly provided by the structure of xylem cells, as well as by a complex of chemical compounds that is a part of cell walls. Destruction of common oak wood,except for mechanical destruction, is accompanied by a biochemical transformation of tissues First of all, it is associated with ageing processes, oxidative degradation (Zaprometov, 1993), auto-fermentation with the formation of important biopolymers for the plant (Volynets, 2013), or as a result of its hydrolysis, which leads to the appearance of oligomeric ellagitannins from the products of prepolymerization, with enzymatic activity of wood-decay fungi (phenol heterosidase, etherase, depsidase) with the conversion of heterosidic phenolic structures such as coumarins and hydrolyzed tannic compounds
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