The effect of soil fertility on antioxidant enzymes activity in a subarctic woody species

The influence of major nutrients’ reserves (available to plants) – nitrogen (N), phosphorus (P), potassium (K) – in the top 25-cm layer of soil on the Karelian birch (Betula pendula Roth var. carelica (Mercl.) Hämet-Ahti) with non-figured and figured wood via the antioxidant enzymes’ activity was investigated. The analysis of sites in area where Karelian birch trees with varying degree of figured wood intensity were growing was carried out. The cambial zone of the sample trees during active cambial growth period was studied for the activity of AOS enzyme complex (superoxide dismutase (SOD); catalase (CAT); peroxidase (POD); polyphenol oxidase (PPO)). Cellulose content and lignin content were studied. It was noticed that the availability of major nutrients in the investigated sites had influence on the degree of figured wood intensity in Karelian birch plants. Thus, non-figured and figured Karelian birch plants that grew on sites with various levels of major nutrients’ reserves differed in the AOS enzymes’ activity, which was a consequence of different xylogenesis scenarios in the studied birch forms. It was supposed, that the certain site conditions (N, P, K levels) formation could affect the degree of figured wood intensity, cellulose and lignin content. The N level and P/N ratio had the most effects under the adequate K level. So AOS enzymes’ complex activity could indicate differences in Karelian birch wood quality in sites that differ in soil fertility (N, P, K levels).

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.

Expression Analysis of Key Auxin Biosynthesis, Transport, and Metabolism Genes of Betula pendula with Special Emphasis on Figured Wood Formation in Karelian Birch

Auxin status in woody plants is believed to be a critical factor for the quantity and quality of the wood formed. It has been previously demonstrated that figured wood formation in Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hämet-Ahti) is associated with a reduced auxin level and elevated sugar content in the differentiating xylem, but the molecular mechanisms of the abnormal xylogenesis remained largely unclear. We have identified genes involved in auxin biosynthesis (Yucca), polar auxin transport (PIN) and the conjugation of auxin with amino acids (GH3) and UDP-glucose (UGT84B1) in the B. pendula genome, and analysed their expression in trunk tissues of trees differing in wood structure. Almost all the investigated genes were overexpressed in Karelian birch trunks. Although Yucca genes were overexpressed, trunk tissues in areas developing figured grain had traits of an auxin-deficient phenotype. Overexpression of GH3s and UGT84B1 appears to have a greater effect on figured wood formation. Analysis of promoters of the differentially expressed genes revealed a large number of binding sites with various transcription factors associated with auxin and sugar signalling. These data agree with the hypothesis that anomalous figured wood formation in Karelian birch may be associated with the sugar induction of auxin conjugation.

Effect of sucrose exposure on the xylem anatomy of three temperate species

ABSTRACTThis study is a continuation of research on the role of sucrose in figured wood formation in temperate trees. Different concentrations of sucrose solutions were administered for 7 weeks to trunk tissues ofBetula pendulaRoth, Alnus incana(L.) Moench andPopulus tremulaL. Then xylem anatomy was examined with particular emphasis to the number of vessels and the spatial orientation of xylem elements. InB. pendulaandA. incanaa high level of exogenous sucrose caused a reduction in the number and size of xylem vessels, even to the point of absence of vessels. Sucrose concentrations of 100 and 200 g l-1induced the formation of curly grain and anomalous club-shaped rays in xylem ofB. pendula.Populus tremulaxylem was not significantly altered by the experiment; the xylem anatomy was more seriously affected by wounding than by sucrose. InB. pendulaandA. incanathe wood formed during the experiment was similar to figured wood of these species. The decrease in the number and size of vessels in the xylem formed during the experiment possibly suggests that high concentrations of sucrose lead to a decline in the level of physiologically active auxin. Changes in the orientation of xylem elements points to a disruption of basipetal auxin transport. Further biochemical and physiological studies are needed to provide more comprehensive understanding of the relationship between sucrose and auxin during the development of figure in wood.

Simple inheritance of a complex trait: figured wood in curly birch is caused by one semi-dominant and lethal Mendelian factor?

Even though individuals with a deviant morphology have been elemental in genetics of model species, they have thus far been largely ignored in the studies of forest trees. Here we studied the inheritance of curly-grained and brown-figured wood phenotype in curly birch (Betula pendula var. carelica (Mercklin) Hämet-Ahti). In addition of the figured wood, curly birches display reduced and aberrant growth, indicating that the causative locus (loci) is (are) vital for normal tree development. To explore the genetic basis of this mutation, we studied the inheritance of the curly birch phenotype in a progeny trial (crosses between curly birch parent trees, between curly and normal phenotypes, and from selfings of curly trees). Based on the external morphology, the phenotypes of 11-year-old progeny trees were scored as either curly or wild. Based on the phenotypic segregation ratios, we postulate a simple Mendelian inheritance model for curliness: (i) a one-locus, two-allele model in which the allele coding for curly phenotype is dominant over the allele coding for normal phenotype and (ii) the semi-dominant curly allele is lethal when homozygous. We expect that further studies on the molecular genetic basis of the curly birch phenotype will provide valuable information on the developmental pathways involved in wood formation.