| Lignum Aquilariae Resinatum (agarwood) is a solid-state condensate with mixed with resin and lignin that forms in Aquilaria and Gyrinops trees of the family Thymelaeaceae. Aquilaria sinensis is the most important plant resource which produces agarwood and peculiar precious medicinal plant in China. According to Chinese Pharmacopoeias (2010edition), agarwood have many therapeutic properties, such as anti-emetic, carminative, sedative and so on. In this article, we systematically investigated the change of microstructure, quality evaluation, and chemical compositions of the agarwood with increasing treatment time, Main findings are as follows:1Structure characteristic of xylem in A. sinensisThe stem of A. sinensis was composed of five parts:piths, included phloems, xylem rays, vessels, and fibre tracheids; The included phloem, which was foraminate type, evenly distributed in the xylem on the transverse section; Xylem rays belonged to heterogeneous Ⅲ; Alignment of vessels pore were generally in radial pore cluster(two to four), pore multiple, pore chain (five to ten), and pore solitary; Vestured pits were alternately arranged in the vessels’lateral wall; Simple acclivitous vestured pits were present in the lateral wall of fibre tracheid; Trabeculas crossed through ten fibre tracheids neighboring pith. Embolisms were observed in the vessels and fibre tracheid. Trabeculas and embolisms were firstly observed in A. sinensis. The contents and storage tissues of the starch grains, reducing sugar, and volatile constituents existed significant difference in different aged stem.2Agarwood formation is physical blocks to damagesIn the process of agarwood formation from A. sinensis with partial-stem-breaking method, gels and tyloses in vessels both originated from xylem ray parenchyma cells and neighboring paratracheal parenchyma cells. Tyloses are outgrowths of parenchyma cells into the neighboring vessels, while gels are amorphous substances into the vessel from the parenchyma cells. Obvious four distinct layers including decomposed layer, agarwood layer, transition layer, and white-timber layer were observed below the wound surface days after wounded. The typical agarwood chemical components were detected on days after wounded. Among chemicals assayed, previous notable wound inducible constituents in other plant species were detected in different zones at different time points after wounded. Every layer has unique structural features and layer depth depended on the different treatment time. The stratified structure characteristics from wound surface to agarwood layer and gradual transition to normal layer showed formation of agarwood layer was to defense against expansion of microorganisms and external damage. Distribution of each region in the vertical axis was not horizontal, presented mutual interleaving phenomenon.3Agarwood formation is chemical defenses to damageChemical composition of A. sinensis being injured compared with that of healthy A. sinensis, the type and relative content of alkaness harply decline, while the type and relative content of aromatics and sesquiterpene compounds rapidly increased with the increasing wounding time, especially in the agarwood layer, and these substances generally have antibacterial and antimicrobial effect, agarwood layer prevented from the expansion of damage from the other side. A total of sixty-five compounds were identified from the three wood samples with different wounding time. Types of constituents were different in each layer of sample, the major constituents being alkanes, scsquiterpenes and aromatics in wounded sample, while all eleven components being alkanes in control samples. This suggested agarwood formation was chemical defenses to damage.4Chang of metabolic pathways in in the process of agarwood formationContent of starch, sugar content, and volatile component were examined through anthrone-sulfuric acid methods, I2-KI colorimetry and GC-MS analysis, respectively. The starch content decreased, while the sugar content increased gradually with the different treatment time. Twelve kinds alkane component were identified in the control and eight kinds sesquiterpene and aromatic compounds were identified in the treated sample. The relative content of alkanes was drastically reduced and the relative content of sesquitcrpene and aromatic component.was rapidly increased. This suggested metabolic pathway has took changes5Content change of signal molecules in the process of agarwood formationMethods such as antibody enzyme-linked immunosorbent assay (ELISA), physiological and biochemical analysis were used to examine the content of signal molecules such as H2O2, SA, JA, NO, etliylene, variations in physiological indexes, and interaction between signal molecules in the samples of A. sinensis with different treatment time. Response time of NO, ethylene, SA, H2O2, NO, and JA increased in turns.6Changes of protective Enzymes activity in the process of agarwood formationMethods such as assay kit, conventional methods of physiological and biochemical analysis were used to examine the protective Enzymes activity, such as SOD, CAT, PAL, and NOs in the samples of A. sinensis with different treatment time. The main results were shown as follows:Enzymes activity of CAT, NOs, PAL, and SOD reached peak value in a short period in turns, and activated defence response. While content of MDA changed greatly in a short period, keep high level all the while.7Value investigation of agarwood with different induction methodsAgarwood characteristics through Agar-wit were similar to those of high-grade wild agarwood in terms of texture, chemical constituents, essential oil and ethanol-soluble extract content, and superior to that of agarwood with partly-breaking stem method and inoculated-fungus method, with the lattermost quality far surpassing the requirement of traditional Chinese medicine agarwood, as indicated in Chinese Pharmacopoeia2010. The obvious boundary divided stem into some different compartments at the transverse section. Boundary layer and the area on both side of boundary have significant different characteristics. The area inside boundary characterized by decay of tissues where hyphae were observed in the vessels and parenchyma cell of included phloem, while the area outside boundary characterized by living tissues where a large number of starch grains were observed in the parenchyma cell of included phloem and xylem ray and occlusions was not in the vessels. Boundary layer, which formed an obvious barrier and separated the decay area and white wood, was filled with oily substance in the vessels, fiber tracheids, and parenchyma cell of included phloem and xylem ray at the cross and longitudinal section. At the mean time, boundary layer limited the development of agarwood layer and influenced the output of agarwood. |
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