ABSTRACT

Salicylates are typical compounds in the family of Salicaceae, genus Salix and Populus. These are regarded as low-molecular-weight phenolic glucosides that are variable with conjugated β-d-glucosides of salicyl alcohol. Free salicyl alcohol is rare in in vivo plants, but is readily

4.1 Introduction ............................................................................................. 65 4.2 Composition and variation of salicylates ............................................ 67 4.3 Biosynthesis and turnover of salicylates ............................................. 72

4.3.1 Biosynthesis of salicylates ......................................................... 72 4.3.2 Turnover of salicylates ............................................................... 74

4.4 Biological roles of salicylates ................................................................. 75 4.4.1 Salicylates in human health ...................................................... 75 4.4.2 Salicylates effective to herbivores ............................................. 75 4.4.3 Salicylates as deterrents to rusts ............................................... 77

4.5 Conclusion ............................................................................................... 78 References .......................................................................................................... 78

produced under decomposition conditions due to, for example, improper preservation of plant tissues after harvesting for analyses (JulkunenTiitto and Sorsa 2001; Julkunen-Tiitto and Tahvanainen 1989). The number of salicylates detected thus far from the Salix and Populus species is more than 15 individual structures (Figure 4.1). Salicin, the simplest glucoside, is the most widespread, while usually found in low amounts in the species, it is the rst phenolic glucoside ever found and extracted from plants. Salicin, β-d-glucoside of 2-hydroxybenzylalcohol, the sugar bound with the phenolic hydroxyl group of aglycone, was detected by Buchner in 1828, in the bark of S. alba and S. incana (Thieme 1963). The nal structure of salicin was found by Irvine and Rose in 1906 (Thieme 1963). Reichardt et al. (1988) claimed that salicin is the most commonly found phenolic glucoside in plants; in addition to Salicaceae, it has been found in some members of the Rosaceae family. In the 1960s, during the most intensive research period of Salicaceae, a number of more abundant salicylates were discovered and dened (e.g., Pearl and Darling 1970, 1971; Thieme 1965a), such as salicortin and tremulacin, although these are only found thus far in the Salicaceae species. Later, other conjugated forms of salicylates, such as disalicortins, cinnamoyl-salicortins, and acetyl-tremulacins were identied (e.g., Abreu et al. 2011; Paajanen et al. 2011; Randriamanana et al. 2015a).