Umeå universitets logga

• The phytohormone ethylene impacts secondary stem growth in plants by stimulating cambial activity, xylem development and fiber over vessel formation.
• We report the effect of ethylene on secondary cell wall formation and the molecular connection between ethylene signaling and wood formation. We applied exogenous ethylene or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC) to wild-type and ethylene-insensitive hybrid aspen trees (Populus tremulaxtremuloides) and studied secondary cell wall anatomy, chemistry and ultrastructure. We furthermore analyzed the transcriptome (RNA Seq) after ACC application to wild-type and ethylene-insensitive trees.
• We demonstrate that ACC and ethylene induce gelatinous layers (G-layers) and alter the fiber cell wall cellulose microfibril angle. G-layers are tertiary wall layers rich in cellulose, typically found in tension wood of aspen trees. A vast majority of transcripts affected by ACC are downstream of ethylene perception and include a large number of transcription factors (TFs). Motif-analyses reveal potential connections between ethylene TFs (Ethylene Response Factors (ERFs), ETHYLENE INSENSITIVE 3/ETHYLENE INSENSITIVE3-LIKE1 (EIN3/EIL1)) and wood formation.
• G-layer formation upon ethylene application suggests that the increase in ethylene biosynthesis observed during tension wood formation is important for its formation. Ethylene-regulated TFs of the ERF and EIN3/EIL1 type could transmit the ethylene signal.

This paper presents a total survey of the characteristics and changes over time (1990–2010) within the entire population of Swedish non-industrial private forest owners (NIPF owners). By charting the changed demographic, socio-economic and geographic profile of the NIPF owners, it also provides a baseline for a discussion and analysis of potential implications for forest management, policy and values. NIPF owners differ in important ways from the general population of Sweden. However, the gap has narrowed over time with regard to, e.g., educational level and sex composition. The ongoing urbanization process is evident in the growing share of non-residential NIPF owners who live at a distance from their forest property and who differ from their residential (rural) peers through, e.g., higher education, higher income and a higher prevalence of co-ownership of their forest holdings. Although these changes might translate into updated views on forest values among NIPF owners, there could be a delay before this impacts on forest management practices and output.