Cell-wall fluorescence highlights the phases of xylogenesis

Abstract

The monitoring of xylogenesis makes it possible to follow tree growth responses to stress factors in real-time, by observing the course of wood cell division and differentiation. Proper microscopy techniques are of key importance to exactly identify the xylem cells during the different phases of differentiation. We aimed to apply epifluorescence microscopy to follow the lignification process during the different phases of xylogenesis in Mediterranean softwood and hardwood. Microcores from trees of Pinus halepensis Mill. and Arbutus unedo L. were collected at a site in southern Italy, during the period June-December. Fluorescence imaging of sections stained with a water solution of safranin and Astra blue clearly highlighted the contrast between lignified and un-lignified tissue. The proposed methodology is useful to quickly and unambiguously detect the different stages of cell differentiation, as well as the progress in the lignification process. Moreover, it proved to be easily applied to demanding wood materials, such as Mediterranean woods and can be helpful to better track stress responses and the development of anomalies during wood formation, such as intra-annual density fluctuations.