Arabidopsis AtcwINV3 and 6 are not invertases but are fructan exohydrolases (FEHs) with different substrate specificities

The genome of Arabidopsis thaliana contains six putative cell-wall type invertase genes (AtcwINV1-6). Heterologous expression of AtcwINV1, 3 and 6 cDNAs in Pichia pastoris revealed that the enzymes encoded by AtcwINV3 and 6 did not show invertase activity. Instead, AtcwINV3 is a 6-FEH and AtcwINV6 is a fructan exohydrolase (FEH) that can degrade both inulin and levan-type fructans. For AtcwINV6 it is proposed to use the term (6&1) FEH. In contrast, AtcwINV1 is a typical invertase. FEH activity was also detected in crude extracts of different parts of Arabidopsis. To verify that the FEH activity of AtcwINV3 and 6 were not artefacts of the heterologous expression system, the protein corresponding to AtcwINV3 was isolated from whole Arabidopsis plants and indeed showed only 6-FEH activity and no invertase activity. Although no fructans can be detected in Arabidopsis plants, it is shown that kestoses (trimers) can be synthesized in crude leaf extracts. The putative physiological significance of FEH in so-called non-fructan plants is discussed.     

Ecological Application of 'Herbchronology': Comparative Stand Age Structure Analyses of the Invasive PlantBunias orientalisL.

The age structures of stands of the herbaceous perennial forbsBuniasorientalisandRumex crispuswere determined in different habitatsin the vicinity of Würzburg (Unterfranken, Germany). Plantage was determined by counting annual rings in the secondaryroot xylem (herbchronology). In rarely-disturbed (unmown, notdisrupted) habitats, stands ofB. orientalisshowed a high proportionof older (     

Age-determination of Dicotyledonous Herbaceous Perennials by Means of Annual Rings: Exception or Rule?

Thirty-five herbaceous dicotyledonous perennial plant species,with permanent root systems, from 16 families, were examinedfor the presence of growth rings in the secondary root xylem.Most of the species surveyed showed ring zonations in the roots,and these could be verified as annual growth rings in the tenspecies for which plants of known age were available. The potentialvalue of ‘herbchronology’ as a tool in ecologicalinvestigations of species and stands of perennial herbs of temperatezones is discussed. Annual rings; age-determination; dendroecology; herbaceous perennials; anatomical patterns; secondary root xylem