In planta localization of stilbenes within Picea abies phloem

Abstract

Phenolic stilbene glucosides (astringin, isorhapontin, and piceid) and their aglycons commonly accumulate in the phloem of Norway spruce (Picea abies). However, current knowledge about the localization and accumulation of stilbenes within plant tissues and cells remains limited. Here, we used an innovative combination of novel microanalytical techniques to evaluate stilbenes in a frozen-hydrated condition (i.e. in planta) and a freeze-dried condition across phloem tissues. Semiquantitative time-of-flight secondary ion-mass spectrometry imaging in planta revealed that stilbenes were localized in axial parenchyma cells. Quantitative gas chromatography analysis showed the highest stilbene content in the middle of collapsed phloem with decreases toward the outer phloem. The same trend was detected for soluble sugar and water contents. The specimen water content may affect stilbene composition; the glucoside-to-aglycon ratio decreased slightly with decreases in water content. Phloem chemistry was correlated with three-dimensional structures of phloem as analyzed by microtomography. The outer phloem was characterized by a high volume of empty parenchyma, reduced ray volume, and a large number of axial parenchyma with porous vacuolar contents. Increasing porosity from the inner to the outer phloem was related to decreasing compactness of stilbenes and possible secondary oxidation or polymerization. Our results indicate that aging-dependent changes in phloem may reduce cell functioning, which affects the capacity of the phloem to store water and sugar, and may reduce the defense potential of stilbenes in the axial parenchyma. Our results highlight the power of using a combination of techniques to evaluate tissue-and cell-level mechanisms involved in plant secondary metabolite formation and metabolism.

Fate of Antioxidative Compounds within Bark during Storage: A Case of Norway Spruce Logs

“…The reasons for the observed decline in the content of stilbene glycosides and aglycones in Norway spruce bark may include trans to cis - isomerization of the double bond and subsequent photocyclization reactions, as stilbenes are well-known for their reactivity and photosensitivity [ 9 , 17 ]. The stilbene compounds may also leach out, as they are water soluble and mostly located within the soft tissue layers of inner bark [ 18 , 19 , 20 ].…”

“…Evidence exists that the content and composition of bark metabolites varies within bark layers, between individual trees and forest stands, as well as among the geographical origins of tree populations [ 18 , 19 , 20 ]. These biological variations in bark quality may, however, be rapidly exceeded by the more pronounced property changes due to terminal and logistical operations, e.g., storage of biomass [ 21 ].…”

Regulation of stilbene biosynthesis in plants

“…Pan et al (2009) also noted that the STS protein localization did not considerably change during berry development. Recently, Jyske et al (2015Jyske et al ( , 2016) applied a combination of novel microanalytical techniques to analyze distribution and localization of stilbenes in a frozen-hydrated condition (i.e., in planta) across phloem tissues of Norway spruce Picea abies and found that stilbenes were localized in axial parenchyma cells.…”

Microscopic distribution of syringin in freeze‐fixed Syringa vulgaris stems

“…Previously, the role of syringin as a phenolic glucoside compound stored in the phloem region was discussed in connection with its defensive characteristics (Cis, Nowak, & Kisiel, 2006;Cipollini et al, 2011). Similar compounds such as stilbene glucosides were also reported as defensive compounds, and their distribution in the phloem region was studied in detail (Jyske et al, 2016).…”