| Summary: | Alkylresorcinols (ARs) are bioactive compounds found in 11 plant families. Indirect evidence showed that they were likely near/at the surface of plant organs, suggesting their defensive role against biotic and abiotic stressors in the environment. However, neither the exact function nor the forming mechanisms are known. To assess whether their primary function is exerted at plant surface and to unravel their biosynthesis, the local distribution of ARs has to be determined first. Hence, the goals of the research were to analyze the ARs in the leaf waxes, to compare their amounts with interior concentrations, to determine AR distribution within the surface wax layers, and to monitor their accumulation as a function of leaf development. Rye (Secale cereale L.) was chosen for this investigation, since previous studies had indicated that it has high levels of ARs in various organs.
The total wax mixture firstly extracted consisted of primary alcohols (71%), alkyl esters (11%), aldehydes (5%), and small amounts of alkanes, steroids, secondary alcohols, fatty acids and unknown compounds. ARs were identified by GC-MS and comparison with nonadecylresorcinol (AR19:0). They contributed 3% of total wax, and comprised a homologous series with odd-numbered alkyl side chains from C19 to C27. Secondly, abaxial and adaxial waxes separately sampled, contained very similar relative quantities of all constituents. Thirdly, the epicuticular and intracuticular wax layers were selectively extracted. ARs comprised 2% of the intracuticular wax, yet none in the epicuticular wax. All other wax components were spread uniformly between both wax layers.
By analyzing various segments at four growth stages of rye leaves, the spatial distribution of waxes along the length of leaf blade and wax accumulation over time were assessed. All the major compound classes shared similar wax production zone, spatial distribution pattern and timing for wax production. Yet ARs were formed in a remarkably different spatial area and time periods. They were only detectable at later growth stages (IV and III) and not detected near POE in contrast to major wax constituents which were produced from each growth stage to its next adjacent stage and mainly within 2-cm segments beyond POE.
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