UHPLC-ESI/TOFMS Determination of Salicylate-like Phenolic Gycosides in Populus tremula Leaves

Associations of salicylate-like phenolic glycosides (PGs) with biological activity have been reported in Salix and Populus trees, but only for a few compounds, and in relation to a limited number of herbivores. By considering the full diversity of PGs, we may improve our ability to recognize genotypes or chemotype groups and enhance our understanding of their ecological function. Here, we present a fast and efficient general method for salicylate determination in leaves of Eurasian aspen that uses ultra-high performance liquid chromatography-electrospray ionization/time-of-flight mass spectrometry (UHPLC-ESI/TOFMS). The time required for the liquid chromatography separations was 13.5 min per sample, compared to around 60 min per sample for most HPLC protocols. In leaf samples from identical P. tremula genotypes with diverse propagation and treatment histories, we identified nine PGs. We found the compound-specific mass chromatograms to be more informative than the UV-visible chromatograms for compound identification and when quantitating samples with large variability in PG content. Signature compounds previously reported for P. tremoloides (tremulacin, tremuloidin, salicin, and salicortin) always were present, and five PGs (2'-O-cinnamoyl-salicortin, 2'-O-acetyl-salicortin, 2'-O-acetyl-salicin, acetyl-tremulacin, and salicyloyl-salicin) were detected for the first time in P. tremula. By using information about the formic acid adduct that appeared for PGs in the LTQ-Orbitrap MS environment, novel compounds like acetyl-tremulacin could be tentatively identified without the use of standards. The novel PGs were consistently either present in genotypes regardless of propagation and damage treatment or were not detectable. In some genotypes, concentrations of 2'-O-acetyl-salicortin and 2'-O-cinnamoyl-salicortin were similar to levels of biologically active PGs in other Salicaceous trees. Our study suggests that we may expect a wide variation in PG content in aspen populations which is of interest both for studies of interactions with herbivores and for mapping population structure

Boron in forest trees and forest ecosystems

This review critically examines the role of boron (B) in forests in view of recent findings on B nutrition and the continuing occurrence of B deficiency. Many perceptions about the role of B in plants and its uptake and mobility have been altered since the last review on B in forest trees in 1990. Now there is evidence for a fundamental role of B in the formation of the pectic structure in primary cell walls in plants, and further roles in membrane function are being explored. In plants, channel-mediated B uptake, active B uptake and B uptake by mycorrhizas have been shown, B transporters have been identified, and B retranslocation has been shown. We explore these findings and their consequences on forest trees and on ecosystems that they dominate. Particular emphasis is placed on B retranslocation and B in mycorrhizal symbiosis, given their importance in trees.Following from impaired development of the primary cell wall in B-deficient trees, disorders in the structural development of organs and whole plants are manifested. This has consequences for tree form, affecting wood quality and productivity. At a stand level, at least part of the value of wood production is lost by the time the deficiency symptoms appear. As symptoms identifying deficiency in many tree species are too easily confused with many other effects, greater use should be made of foliar analysis but this requires establishing robust prognostic values for the trees of interest. There is still no explanation as to why root tip and mycorrhiza development are among the first phenomena to be affected as the B supply decreases. Whether B is required by, or whether it is useful for fungi, is still an open question.Boron remobilisation within trees may be a key factor in the occurrence of forests in areas with very low B availability, as most of the B in the whole stand can be in the standing biomass. The ability to remobilise B varies considerably between species, but we suggest that there is a continuum rather than a strict division to B-retranslocating and non-retranslocating species. Boron output from forest ecosystems with potential for leaching is controlled by adsorption in the soil, which is still poorly understood particularly in soils with abundant organic matter. Increased concentrations of phenolic compounds in B-deficient plants and possibly altered lignin concentration can affect plant defence systems to herbivory and pathogens, and nutrient and carbon release through decomposition. Hence, B nutrition and fertilisation of low-B stands can have implications both to the resistance of trees to biotic stress, as well as influence the cycles of other nutrients and carbon in forests