An Indicating Role of Antioxidant System Enzymes at the Stage of Active Structural Anomalies Formation in Karelian birch (Betula pendula Roth var. carelica (Mercl.) Hämet-Ahti)

INTRODUCTION

A complex study of the antioxidant system enzymes (AOS) is an important subject of biochemical research; changes in the activity of these enzymes can be used as a biochemical marker of various processes in plants. At the same time, practically little attention has been paid to describing the regularities of these enzymatic reactions in different wood formation processes, such as xylogenesis. This article discusses the outcomes of different behaviors of AOS enzymes, which are involved in both the redistribution of the ROS balance and phenolic compounds at the early stages of wood formation in young plants of silver birch (Betula pendula Roth) with straight-grained wood and Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hamet-Ahti) with non-figured and figured parts within the single trunk.

BACKGROUND

Spectrophotometric determination of AOS enzymes' activity can be used as a biochemical marker in the different wood formation processes, including xylogenesis. In this study, we studied structural anomalies of the woody plant trunk of Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hamet-Ahti).

OBJECTIVE

This study aimed to study AOS enzymes' activity in 12-year-old plants of silver birch (Betula pendula Roth) with straight-grained wood and Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hamet-Ahti) with non-figured and figured parts within the single trunk.

METHOD

Plant tissues were ground in liquid nitrogen to a uniform mass and homogenized at 4 °C in the buffer containing 50 mM HEPES (pH 7.5), 1 mM EDTA, 1 mM EGTA, 3 mM DTT, 5 mM MgCl2, and 0.5 mM PMSF. After 20 min extraction, the homogenate was centrifuged at 10000 g for 20 min (MPW-351R, Poland). The sediment was washed in the buffer thrice. The pooled supernatant and sediment were dialyzed at 4 °C for 18-20 h against a tenfold diluted homogenization buffer. The enzymes' activity was determined spectrophotometrically (Spectrophotometer SF-2000, OKB Spectr, Russia). Proteins in the extracts were quantified by the method of Bradford.

RESULTS

We observed different behaviors of the studied enzymes involved in both the redistribution of the ROS balance and phenolic compounds with subsequent lignification even at the early stages of wood formation in young plants and even in different trunk parts within a tree, which was consistent with results obtained earlier on adult plants. High SOD activity in the phloem compared to the activity in the xylem was accompanied by higher CAT activity. The POD/SOD ratio was significantly higher in the figured trunk parts in Karelian birch compared to other variants in the xylem and higher in Karelian birch plants compared to plants of common birch in the phloem. The CAT/POD ratio was significantly higher in plants with no signs of anomalies. The high POD and PPO activity in the xylem of figured trunk parts and in the phloem of figured and non-figured trunk parts of B. pendula var. carelica can be associated with the high activity of apoplast invertase.

CONCLUSION

The study showed that at the stage of active formation of structural anomalies in the figured trunk parts in young plants of Karelian birch, hydrogen peroxide utilization occurred mainly due to increased POD activity. An increase in PPO activity in the trunk of figured plants could also be considered an indicator of the formation of structural anomalies. At the same time, in areas with developing abnormal wood, the POD/SOD ratio increased, and the CAT/POD ratio decreased, indicating a fine-tuning of the balance between superoxide radical and hydrogen peroxide, which, when changed, might regulate the rearrangement of xylogenesis towards proliferation in relation to differentiation.

Biochemical Aspects of the Spiral Grain Formation in Scots Pine (Pinus Sylvestris L.) Wood. Some Differences and Similarities with Biochemical Indicators of Abnormal Xylogenesis in Karelian Birch (Betula Pendula Roth Var. Carelica (Mercl.) Hämet-Ahti)

BACKGROUND

AOS enzymes can be biochemical indicators of abnormal xylogenesis in Scots pine, and this mechanism has similar features with the metabolic base of abnormal xylogenesis in Karelian birch.

OBJECTIVE

AOS enzymes' activity in 150-300-year-old Pinus sylvestris L. wood with straight-- grained wood and right-twisted spiral-grained wood, expressed in varying degrees (5-20 angle), grew in three sample plots in lingonberry and blueberry pine forest stands of different ages (100-300 years) in the middle taiga subzone in the Republic of Karelia.

METHODS

Plant tissues were ground in liquid nitrogen in a uniform mass and homogenized at 4°C in the buffer containing 50 mM HEPES (pH 7.5), 1 mM EDTA, 1 mM EGTA, 3 mM DTT, 5 mM MgCl2 and 0.5 mM PMSF. After 20 min extraction, the homogenate was centrifuged at 10000 g for 20 min (MPW-351R, Poland). The sediment was washed in the buffer thrice. The pooled supernatant and sediment were dialyzed at 4°C for 18-20 h against a tenfold diluted homogenization buffer. The enzymes' activity was determined spectrophotometrically (Spectrophotometer SF-2000, OKB Spectr, Russia). Proteins in the extracts were quantified by the method of Bradford.

RESULTS

The study showed that the activity of SS, ApInv, CAT, POD and PPO in xylem and PPO in phloem were biochemical indicators for abnormal wood of P. sylvestris. We noticed an increase in sucrose metabolism in the apoplast and the activity of POD and PPO under spiral-grain wood formation like under figured wood formation earlier. We assume that the alternative pathway of sucrose metabolism (an indicator of abnormal xylogenesis in B. pendula var. carelica plants) that lead to restructuring of AOS enzymes have the same biochemical regularities in the spiral-grain wood formation in P. sylvestris.

CONCLUSION

The study showed that the differences in the AOS enzyme's activity in P. sylvestris during the formation of straight-grained and spiral-grained wood were revealed for the first time. The increased CAT, POD and PPO activities in xylem with a decrease in SS and an increase in Ap- Inv during spiral-grained wood formation can be biochemical markers of these structural anomalies. Metabolic regularities found in the AOS enzyme complex during spiral-grained wood formation do not contradict those found earlier during figured wood formation in B. pendula var. carelica. The identified patterns can form the base for diagnostics of P. sylvestris wood quality in forest seed plantations and in their natural growth, which is necessary both for fundamental science and in various industry areas while high-quality material harvesting.

Molecular Genetic Characteristics of Different Scenarios of Xylogenesis on the Example of Two Forms of Silver Birch Differing in the Ratio of Structural Elements in the Xylem

Silver birch (Betula pendula Roth) is an economically important species in Northern Europe. The current research focused on the molecular background of different xylogenesis scenarios in the birch trunks. The study objects were two forms of silver birch, silver birch trees, and Karelian birch trees; the latter form is characterized by the formation of two types of wood, non-figured (straight-grained) and figured, respectively, while it is currently not clear which factors cause this difference. We identified VND/NST/SND genes that regulate secondary cell wall biosynthesis in the birch genome and revealed differences in their expression in association with the formation of xylem with different ratios of structural elements. High expression levels of BpVND7 accompanied differentiation of the type of xylem which is characteristic of the species. At the same time, the appearance of figured wood was accompanied by the low expression levels of the VND genes and increased levels of expression of NST and SND genes. We identified BpARF5 as a crucial regulator of auxin-dependent vascular patterning and its direct target—BpHB8. A decrease in the BpARF5 level expression in differentiating xylem was a specific characteristic of both Karelian birch with figured and non-figured wood. Decreased BpARF5 level expression in non-figured trees accompanied by decreased BpHB8 and VND/NST/SND expression levels compared to figured Karelian birch trees. According to the results obtained, we suggested silver birch forms differing in wood anatomy as valuable objects in studying the regulation of xylogenesis.