Apoplastic Invertase Activity Regulation in the Cambial Zone of Karelian Birch

Abstract

We found that the regulation of apoplastic invertase (ApInv) activity in the cambial growth period in Karelian birch (Betula pendula var. carelica) is provided by the expression of encoding genes. In Karelian birches with normal wood, the content of CWIN1, CWIN1.1, and CWIN4 gene transcripts in xylem is lower than in birches with patterned wood. The regulation of ApInv activity in common silver birch (B. pendula var. pendula) is mainly provided at the posttranslational level by protein inhibitors (cell-wall inhibitor of β-fructosidase, CIF). In the trunk tissues of common silver birch, the expression level of ApInv encoding genes is similar to that of Karelian birch, but the concentration of CIF gene transcripts is increased; high expression rate of the CIF gene is caused by increased sucrose concentration in the apoplast. High activity rate of ApInv in Karelian birch provides high acceptor capacity of the cambial zone; a large amount of formed hexoses is intensely used for the formation of starch, a reserve metabolite. An increase in the wood pattern intensity correlates with the sucrose metabolization rate in the apoplastic pathway. In the trunks of birches with patterned wood, there are only local changes in the ratio of ApInv and sucrose synthase activity rates (ApInv activity higher) in the cambial growth period.