The Formation of Structural Abnormalities in Karelian Birch Wood is Associated with Auxin Inactivation and Disrupted Basipetal Auxin Transport

Figured wood of Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hamet-Ahti) is highly appraised for its ornamental properties. The reasons for its formation remain largely unclear; judging by available data, we are dealing here with auxin inactivation through its interaction with sugars. The aim of this study has been to reveal the correlations between abnormal wood formation in Karelian birch and auxin conjugation producing IAA-glucose. Karelian birch trees with figured and non-figured wood in the trunk were used. Figured plants had a much higher expression of the gene encoding for the enzyme IAA-glucose synthase, which catalyzes IAA-glucose synthesis. The data obtained suggest that auxin conjugation in Karelian birch via a chain of biochemical reactions may be associated with hexoses produced in the apoplast through sucrose cleavage by cell wall invertase. The activity of the enzyme in figured Karelian birch trees is several times higher than in non-figured plants. Vessel differentiation requires free auxin. We assume that a reduced number of vessels in figured wood may be caused by auxin conjugation in the zone of xylem cell growth and differentiation. Figured wood of Karelian birch was found to have an increased transcript level of the PIN3 gene, which encodes for the auxin efflux carrier protein PIN3 responsible for lateral transport of the hormone. In this regard, PIN3 may generate auxin fluxes with a complex configuration. Microscopic analysis provides evidence that PIN3 overexpression in trunk tissues of Karelian birch is associated with active differentiation of parenchyma cells and disruption of wood structure.