| Plerocarpus macrocarpus Kurz (P. macrocarpus Kurz) is one kind of rosewood which belong to Papilionaceae padauk and P. macrocarpus Kurz is one kind of the most important exclusive furniture, sculpture and decorative hardwood specie, which present fine wood figure and homogeneous structure. As a kind of furniture material, it’s heartwood is always used in the manufacture process, during which a lot of residue is taken shape. Therefore, it is important to know the mechanism of it’s antimicrobial and insecticidal effects and the application of it’s extracts in wood preservatives. In order to reveal the mechanism of strong decay resistance of P. macrocarpus Kurz and provide references on the potential of it’s extracts as natural wood preservatives. In this study, the natural decay resistance of P. macrocarpus Kurz heartwood was conducted; Six different extracts were extracted from P. macrocarpus Kurz heartwood with methanol, ethyl acetate, chloroform, acetone, petroleum ether and hot water,the chemical composition of these extracts was analysised by gas chromatography-mass spectrometry (GC/MS) meanwhile; these six different extracts were used to inhibit two kind of wood-decaying fungi with the growth rate of poison medium culture method as well, physiological and biochemical mechanism of the extracts’antifungal activity was researched. Lastly, the decay resistance activity of the extracts was researched and samples were characterized by SEM(scanning electron microscope) and FTIR(fourier transform infrared reflection)analysis. The main results were obtained as following:(1) The natural decay resistance of Pterocarpus Macrocarpus Kurz heartwood met the demand of degree I and showed strong resistance to fungal decay.(2) The order of the EC50 values of different P. Macrocarpus Kurz extracts against G. trabeum was:methanol extracts, ethyl acetate extracts, acetone extracts, chloroform extracts, petroleum ether extracts and hot water extracts, the methanol extracts had the lowest EC50 values at 0.0178g/L among the six different extracts, indicating that methanol extracts have the strongest inhibition activity. All extracts have antifungal activity against C. versicolor except hot water extracts. The order of the EC50 values of different extracts on C. versicolor was:chloroform extracts> methanol exracts> ethyl acetate extracts> acetone extracts> petroleum ether extracts. Which show that chloroform extracts had the best antifungal effect on C. versicolor.(3) From the results of GC/MS analysis, the major components (matching rate>80%, content>1%)of pterocarpin; alpha-Eudesmol; medicarpin; 2-Naphthalen emethanol,1,2,3,4,4a,5,6,7-octahydro-alpha,alpha.,4a,8-tetramethyl-, (2R-cis)-; 5-Hydroxy-2’,3’,4’-trimethylac-etophenone, and 3,9-dimethoxy-6H-Benzofuro [3,2-c] [1]benzopyra were common to both methanol extracts and chloroform extracts. These five main components have antifungal activity. While these five main components does not exist in hot water and petroleum ether extracts, which is why these two kinds of extracts have little antifungal activity.(4) Physiological and biochemical mechanism of the extracts of P.macrocarpus Kurz heartwood was detected. The methanol and chloroform extracts with different concentration could improve the electric conductivity of the C. versicolor hyphae and G trabeum hyphae, and protein permeability rised with the the concentration of the extracts, proving that the methanol and chloroform extracts could destroy the cell wall of the wood-decaying fungi. Additionally, the extracts have oxygen consumption inhibition effect, leading to abnormal energy metabolism. As a result, the life activity of C. versicolor and G. trabeum became weak even stopped. The inhibition activity of cellulase which was secreted by G. trabeum was increased with the rise of the extracts’concentration. The inhibition effect of the methanol extracts was stronger than the chloroform extracts. Over all, as for the antifungal effect, the target site of the P. macrocarpus Kurz heartwood extracts is not just one.(5) The results of the decay resistance performance experiment as follows:As for G. trabeum, all extracts of P. Macrocarpus Kurz heartwood had corrosion resistance effect except the hot water extracts, among six extracts the methanol extracts had the best decay resistance performance, while thers was still a certain gap when comparing to ACQ’s corrosion resistance performance. As for C. versicolor, the decay resistance performance of chloroform extracts effect was markedly superior than other extracts. The observations from SEM indicated that treatment with 10% methanol extracts of P. Macrocarpus Kurzm heartwood conferred stronger resistance to the decay by G. trabeum compared with the samples treated with 10% hot water extracts because relatively little hyphae were observed within the cell walls. Similarly, sample treated with 10% chloroform extracts conferred stronger resistance to the decay by C. versicolor compared with the samples treated with 10% hot water extracts. As for G. trabeum, From the FTIR analysis results, the peak of hemicellulose and cellulose displayed decrease in different degrees, while that of lignin decreased not obviously compared to the untreated samples, which means that the t the degradation activity of cellulose and hemicelluloses is stronger than that of lignin by G.trabeum. The ratio of I1510/I1738,I1510/I1374, I1510/I1161of the samples treated with 1% ACQ and 8% methanol extracts was smallest, which proved that these two kinds of wood preservative were better than other extracts. As for C. versicolor the spectral peak of cellulose and hemicellulose (1460 cm-1,1160 cm-1 and 895 cm-1) decreased not obvious, proving cellulose and hemicellulose were not degraded obvious by C. versicolor. Degradation of samples treated with 8% hot water extracts and 8% petroleum ether extracts led to a bigger descend at 1650cm-1 compared to that treated with ethyl acetate extracts, ACQ, chloroform extracts, acetone extracts and methanol extracts, which indicated the decay resistance performance of hot water extracts and petroleum ether was worse. |
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