Bean cells that have been habituated to grow in a lethal concentration （12 μM） of 2,6-dichlorobenzonitrile （dichlobenil or DCB, a cellulose biosynthesis inhibitor） are known to have decreased cellulose content in...Bean cells that have been habituated to grow in a lethal concentration （12 μM） of 2,6-dichlorobenzonitrile （dichlobenil or DCB, a cellulose biosynthesis inhibitor） are known to have decreased cellulose content in their cell walls. Xyloglucan, which is bound to cellulose and together with it forms the main loading network of plant cell walls, has also been described to decrease in habituated cells, but whether the change on cellulose affects the xyloglucan structure besides its abundance has not been analyzed. Fragmentation analysis with xyloglucan-specific endoglucanase （XEG） and endocellulase revealed that habituation to DCB caused a change in the fine structure of xyloglucan, namely a decrease in fucosyl residues attached to the galactosyl-xylosyl residues along the glucan backbone. After the removal of herbicide from the medium （dehabituated cells）, xyloglucan recovered its fucosyl residues. In addition, some cello-oligosaccharides could be detected only in habituated cells＇ xyloglucan digested by XEG and endocellulase, corresponding to a glucan co- valently bound or co-precipitated with the hemicelluloses. These results show that structural flexibility of cell walls relies in part on the plasticity of xyloglucan composition and opens up new perspectives to further research in this field.展开更多
Background: We investigated the impact of human recreational disturbances on the distribution of birds along a popular nature trail in Sinhararja World Heritage Forest, Sri Lanka. It was hypothesized that visual and n...Background: We investigated the impact of human recreational disturbances on the distribution of birds along a popular nature trail in Sinhararja World Heritage Forest, Sri Lanka. It was hypothesized that visual and noise stimuli caused by the presence of humans affect the distribution of avifauna associated with this nature trail.Methods: Nine circular plots of 25 m fixed-radius laid along the trail(0 m), and 18 plots laid perpendicular to the trail at 75 and 150 m intervals, were studied from March 2013 to January 2014. The degree of human recreational disturbances was assessed in terms of visitor group size(visual disturbance) and their noise level(sound disturbance). These disturbances were categorized along a four-point scale(no human disturbance, low, medium and high disturbance). The relationship between disturbance levels and the abundance of birds was statistically tested.Results: ANOVA results revealed that the abundance of birds differed significantly under various intensities of recreational disturbances at each distance level. A significant negative correlation between abundance of birds and intensity of disturbance at 0 m distance suggests an avoidance of edge habitats by birds in the presence of humans. Abundance of birds increased at the 75 and 150 m distance levels with increasing disturbances occurring at the trail. Significant negative correlations were further observed between disturbance level and the abundance of birds in ground/understory and sub-canopy vertical strata of the forest at 0 m distance.Conclusions: Under high levels of recreational disturbance occurring at this trail, the abundance of birds near the trail declined significantly, while bird abundance in the interior of the forest increased. The sensitivity of individual bird species to visitor disturbances varied with the vertical stratum of the forest they usually occupy. Birds occupying the ground, understory and sub-canopy are particularly sensitive to recreational disturbances while bird species occupying the canopy and abov展开更多
文摘Bean cells that have been habituated to grow in a lethal concentration （12 μM） of 2,6-dichlorobenzonitrile （dichlobenil or DCB, a cellulose biosynthesis inhibitor） are known to have decreased cellulose content in their cell walls. Xyloglucan, which is bound to cellulose and together with it forms the main loading network of plant cell walls, has also been described to decrease in habituated cells, but whether the change on cellulose affects the xyloglucan structure besides its abundance has not been analyzed. Fragmentation analysis with xyloglucan-specific endoglucanase （XEG） and endocellulase revealed that habituation to DCB caused a change in the fine structure of xyloglucan, namely a decrease in fucosyl residues attached to the galactosyl-xylosyl residues along the glucan backbone. After the removal of herbicide from the medium （dehabituated cells）, xyloglucan recovered its fucosyl residues. In addition, some cello-oligosaccharides could be detected only in habituated cells＇ xyloglucan digested by XEG and endocellulase, corresponding to a glucan co- valently bound or co-precipitated with the hemicelluloses. These results show that structural flexibility of cell walls relies in part on the plasticity of xyloglucan composition and opens up new perspectives to further research in this field.
文摘Background: We investigated the impact of human recreational disturbances on the distribution of birds along a popular nature trail in Sinhararja World Heritage Forest, Sri Lanka. It was hypothesized that visual and noise stimuli caused by the presence of humans affect the distribution of avifauna associated with this nature trail.Methods: Nine circular plots of 25 m fixed-radius laid along the trail(0 m), and 18 plots laid perpendicular to the trail at 75 and 150 m intervals, were studied from March 2013 to January 2014. The degree of human recreational disturbances was assessed in terms of visitor group size(visual disturbance) and their noise level(sound disturbance). These disturbances were categorized along a four-point scale(no human disturbance, low, medium and high disturbance). The relationship between disturbance levels and the abundance of birds was statistically tested.Results: ANOVA results revealed that the abundance of birds differed significantly under various intensities of recreational disturbances at each distance level. A significant negative correlation between abundance of birds and intensity of disturbance at 0 m distance suggests an avoidance of edge habitats by birds in the presence of humans. Abundance of birds increased at the 75 and 150 m distance levels with increasing disturbances occurring at the trail. Significant negative correlations were further observed between disturbance level and the abundance of birds in ground/understory and sub-canopy vertical strata of the forest at 0 m distance.Conclusions: Under high levels of recreational disturbance occurring at this trail, the abundance of birds near the trail declined significantly, while bird abundance in the interior of the forest increased. The sensitivity of individual bird species to visitor disturbances varied with the vertical stratum of the forest they usually occupy. Birds occupying the ground, understory and sub-canopy are particularly sensitive to recreational disturbances while bird species occupying the canopy and abov
