Populusroot salicinoid phenolic glycosides are not mobilized to support metabolism and regrowth under carbon-limited conditions

Abstract

Remobilization of carbon storage compounds in trees is crucial for the resilience to disturbances, stress, and the requirements of their perennial lifestyle, all of which can impact photosynthetic carbon gain. Trees contain abundant non-structural carbohydrates (NSC) in the form of starch and sugars for long term carbon storage, yet questions remain about the ability of trees to remobilize non-conventional carbon compounds under stress. Aspens, like other members of the genus Populus, have abundant specialized metabolites called salicinoid phenolic glycosides, which contain a core glucose moiety. In this study, we hypothesized that the glucose-containing salicinoids could be remobilized as an additional carbon source during severe carbon limitation. We made use of genetically modified hybrid aspen (Populus tremula x P. alba) with minimal salicinoid content and compared these to control plants with high salicinoid content during resprouting (suckering) in dark (carbon limited) conditions. As salicinoids are abundant anti-herbivore compounds, identification of such a secondary function for salicinoids may provide insight to the evolutionary pressures that drive their accumulation. Our results show that salicinoid biosynthesis is maintained during carbon limitation and suggests that salicinoids are not remobilized as a carbon source for regenerating shoot tissue. However, we found that salicinoid-producing aspens had reduced resprouting capacity per available root biomass when compared to salicinoid-deficient aspens. Therefore, our work shows that the constitutive salicinoid production in aspens can reduce the capacity for resprouting and survival in carbon limited conditions.

Perturbation of tonoplast sucrose transport alters carbohydrate utilization for seasonal growth and defense metabolism in coppiced poplar

“…The present findings suggest a complex developmental dynamic influenced by light, temperature, nutrient and source:sink ratio in which SUT4 has a role. Populus species maintain constitutive levels of salicinoids even under severe carbon limitation (Fabisch et al 2019; Hillabrand et al 2023), and our results may suggest an environmentally conditioned impact of vacuolar sucrose sequestration on the competition between growth and this important phytochemical sink.…”

“…While epicormic bud emergence was similar in all lines following summer coppicing, defense metabolite levels were substantially lower and new sprout biomass was significantly higher in sut4 than control lines. Populus species maintain constitutive levels of salicinoids even under severe carbon limitation (Hillabrand et al, 2023, Fabisch et al ., 2019), but our results suggest that growth can be prioritized over defense under sufficiently carbon limiting conditions, at least when trafficking of vacuolar sucrose is impaired.…”

“…Under such conditions, trees may rely instead on alternative substrates such as lipids (Huang et al, 2021, Fischer et al ., 2015) and hemicelluloses (Schädel et al ., 2009) to sustain respiration and growth. It is worth noting that phenolic glycoside salicinoids, which are abundant defense compounds in Populus species, are turnover-resistant during severe carbon deprivation (Hillabrand et al ., 2023). This highlights the importance of chemical defense in relation to growth and storage as a carbon destination in these species.…”