Cytotoxic Tirucallane and Apotirucallane Triterpenoids from the Stems of Picrasma quassioides.

Phytochemical investigation on the stems of Picrasma quassioides led to the isolation of a novel compound, picraquassin A (1), with an unprecedented 21,24-cycloapotirucallane skeleton, and four new apotirucallane-type triterpenoids (2-5), together with 15 new tirucallane-type triterpenoids (6-20) and 10 known tirucallane-type triterpenoids (21-30). To our knowledge, this is the first report demonstrating the presence of apotirucallane-type triterpenoids in the genus Picrasma. The structures of the new compounds were determined based on spectroscopic data interpretation. Cytotoxicities of the isolated compounds were evaluated using three human cancer cell lines, MKN-28, A-549, and MCF-7. Compound 2 exhibited the most potent activity against MKN-28 cells with an IC50 value of 2.5 µM. Flow cytometry and Western blot analysis revealed that 2 induces the apoptosis of MKN-28 cells via activating caspase-3/-9, while increasing Bax and Bad and decreasing Bcl-2 expression levels.

[Effects of thinning intensities on population regeneration of natural Quercus variabilis forest on the south slope of Qinling Mountains].

Taking the natural Quercus variabilis forest in Shangluo, south slope of Qinling Mountains as the object in May 2006 and August 2011, which was under close-to-natural management of different thinning intensities (30%, 20%, 10%), and the un-thinned forest as the control, changes of the stand growth situation before and after thinning, population regeneration, species diversity and soil fertility after 5 years of thinning were analyzed, and the effects of thinning on forestland revegetation and community development were evaluated comprehensively. The results showed that the number of 1-6 years old Q. variabilis seedlings increased with increasing thinning intensity, while no significant difference was found for above 6 years old seedlings. The regeneration potentials of population under 10%, 20% and 30% thinning were respectively increased by 10.8%, 28.5% and 32.9% compared with the control. Thinning promoted the DBH and crown of the trees and shrubs, as well as the height of shrubs, especially for light-loving plants, and the effect of promotion increased with increasing thinning intensity. The species diversity and soil fertility were improved after thinning, in order of 30% > 20% > 10% > control. The thinning intensity of 30% (canopy density 0.6) was more conducive to the continuable development of the natural Q. variabilis forest in which canopy density was above 0.85.

[Regeneration mode of Xanthoceras sorbifolia population and its contribution to population regeneration].

Sexual and asexual propagation of Xanthoceras sorbifolia natural populations in different habitats and their importance in population regeneration were studied. The results showed that X. sorbifolia populations were capable of the sexual and asexual propagation in 3 slope aspects, but a balance between the two propagation modes was observed. In sunny and semi-shady slope habitats, seedling amount and space-occupying competence were relatively high, suggesting that the sexual propagation was dominant. In semi-sunny slope habitat, the populations were superior in sexual sprout amount and space-occupying competence, suggesting that the predominant propagation mode was asexual. In the same habitats, asexual sprouts grew better than seedlings, while the growth of seedlings was in the order of sunny slope > semi-sunny slope > semi-shady slope on the basis of the same origin. The bottleneck stage appeared from seeds to seedlings for sexual propagation and from seedling to ramet for asexual propagation. X. sorbifolia invaded and settled in a way of sexual propagation in new habitats, and then rapidly occupied habitat space in a way of asexual propagation.

[Effects of thinning intensity on Pinus tabulaeformis plantation in Huanglong Mountain, Northwest China: a comprehensive evaluation].

A sampling plot investigation was conducted on the seedling regeneration, stand growth, species diversity, and soil characteristics in a Pinus tabulaeformis plantation in Huanglong Mountain on the Loess Plateau of Northwest China after 7 years of close-to-natural management thinning 15% (light thinning), 30% (medium thinning), and 45% (heavy thinning), with the effect of different thinning intensities evaluated. With the increase of thinning intensity, the amount and growth indices of 1-7 years old P. tabulaeformis seedlings increased, but the mean annual increments of the growth indices decreased after an initial increase, with the maximum under medium thinning. As compared with the control (un-thinned plantation), the individual volume under light, medium, and heavy thinning was increased by 20.9%, 32.1% and 52.6%, the volume per hm2 decreased by 4.4%, 15.1%, and 25.3%, and the mean annual growth rate of volume increased by 28.6%, 46.2% and 82.0%, respectively. The species diversity and soil characteristics were improved under thinning, with the order of heavy thinning > medium thinning > light thinning > un-thinning. In this study, 45% thinning was most suitable to the management of P. tabulaeformis plantation in Huanglong Mountain.

[Effects of thinning intensity on the seed bank and seedling growth of Quercus variabilis on the south slope of Qinling Mountains, Northwest China].

In August-November 2010 and August 2011, and taking the pure Quercus variabilis forests under close-to-natural management of different thinning intensity (30%, 20%, and 10%) in Shangluo district of south slope of Qinling Mountains as the object, an investigation was conducted on the seed amount of seed bank, the survival rate and growth status of seedlings, and their relationships with environmental factors 4-5 years after thinning. As compared with the control, the seed amount in the seed bank of 10%, 20%, and 30% thinning plots increased by 2.0%, 21.1%, and 34.8%, respectively in the fourth year after thinning, and the 1-year-old seedlings amount increased by 28.5%, 99.7%, and 122.2%, respectively in the next year. The survival rate of the seedlings in the 10%, 20%, and 30% thinning plots was increased by 25.5%, 235.7%, and 480.0%, respectively in the fifth year after thinning. Thinning improved the light, temperature, soil moisture, and soil nutrient conditions in the forests, which promoted the height- and new shoot growth and the leaf area index of each age seedlings. The three growth indices also increased with increasing thinning intensity. In the Q. variabilis forest with a canopy density of > or = 0.85, the thinning intensity 30% (canopy density 0.6) was most conducive to the seed germination and seedling growth.

[Effects of thinning intensity on community stability of Quercus liaotungensis forest on Loess Plateau].

A sampling plot investigation was conducted on the Quercus liaotungensis forests on Loess Plateau, China under close-to-natural management thinning 13.4% (light thinning) and 30.0% (heavy thinning). Taking the un-thinned forest as the control, the population regeneration, woodland productivity, soil fertility, and species diversity of the forests after 5 years of thinning were studied, with the community stability evaluated by calculating the subordinate function values based on fuzzy comprehensive evaluation. Comparing with the control, the regeneration potential of the forests after light and heavy thinning promoted by 14.2% and 20.2%, arbor volume reduced by 9.0% and 23.8%, shrub biomass increased by 7.3% and 12.2%, and herb biomass increased by 10.5% and 31.6%, respectively. In addition, the soil fertility and species diversity indices were higher in thinning forests than in the control. The community stability showed the order of heavy thinning forest > light thinning forest > un-thinned forest, suggesting that the close-to-natural management thinning 30.0% was more suitable to the management of secondary Q. liaotungensis forest on Loess Plateau.