西双版纳热带雨林中两种生态型蕨类植物的光合特性比较研究

通过比较分布于西双版纳热带雨林林下生境中的附生鸟巢蕨（Neottopteris nidus）和地生网脉铁角蕨（Asplenium finlaysonianum）的光合特征和光合诱导特性,来研究不同生态型蕨类植物的光斑利用策略。研究结果表明,2种蕨类植物的最大净光合速率、暗呼吸速率、表观量子效率、光饱和点和光补偿点没有显著差异,但网脉铁角蕨的最大气孔导度远远高于鸟巢蕨,表明后者具有更强的光合水分利用效率。在暗处理3／J＇,时接着光照（光强为20I~mol-m-2,s。‘）30分钟后,网脉铁角蕨的初始气孔导度显著高于鸟巢蕨。连续照射饱和强光后,网脉铁角蕨达到最大净光合速率50％（T50％）和90％的时间（T90%）比鸟巢蕨短：网脉铁角蕨和鸟巢蕨的T50%分别为0．57和5．31分钟,T90％分别为5．85和26．33分钟。诱导过程中,气孔导度对强光的响应明显滞后于净光合速率。鸟巢蕨达到最大气孔导度的时间明显比网脉铁角蕨慢,但在光合诱导消失过程中2种蕨类植物的光合诱导维持能力却没有显著差异。上述结果表明,与大多数地生林下植物（如网脉铁角蕨）相比,附生鸟巢蕨的水分保护比碳获得更重要,但却限制了附生蕨对光斑的利用。     

Unisexual Reproduction of Cryptococcus gattii

Cryptococcus gattii is a basidiomycetous human fungal pathogen that typically causes infection in tropical and subtropical regions and is responsible for an ongoing outbreak in immunocompetent individuals on Vancouver Island and in the Pacific Northwest of the US. Pathogenesis of this species may be linked to its sexual cycle that generates infectious propagules called basidiospores. A marked predominance of only one mating type (α) in clinical and environmental isolates suggests that a-α opposite-sex reproduction may be infrequent or geographically restricted, raising the possibility of an alternative unisexual cycle involving cells of only α mating type, as discovered previously in the related pathogenic species Cryptococcus neoformans. Here we report observation of hallmark features of unisexual reproduction in a clinical isolate of C. gattii (isolate 97/433) and describe genetic and environmental factors conducive to this sexual cycle. Our results are consistent with population genetic evidence of recombination in the largely unisexual populations of C. gattii and provide a useful genetic model for understanding how novel modes of sexual reproduction may contribute to evolution and virulence in this species.     

Tracking Seed Fates of Tropical Tree Species: Evidence for Seed Caching in a Tropical Forest in North-East India

Rodents affect the post-dispersal fate of seeds by acting either as on-site seed predators or as secondary dispersers when they scatter-hoard seeds. The tropical forests of north-east India harbour a high diversity of little-studied terrestrial murid and hystricid rodents. We examined the role played by these rodents in determining the seed fates of tropical evergreen tree species in a forest site in north-east India. We selected ten tree species (3 mammal-dispersed and 7 bird-dispersed) that varied in seed size and followed the fates of 10,777 tagged seeds. We used camera traps to determine the identity of rodent visitors, visitation rates and their seed-handling behavior. Seeds of all tree species were handled by at least one rodent taxon. Overall rates of seed removal (44.5%) were much higher than direct on-site seed predation (9.9%), but seed-handling behavior differed between the terrestrial rodent groups: two species of murid rodents removed and cached seeds, and two species of porcupines were on-site seed predators. In addition, a true cricket, Brachytrupes sp., cached seeds of three species underground. We found 309 caches formed by the rodents and the cricket; most were single-seeded (79%) and seeds were moved up to 19 m. Over 40% of seeds were re-cached from primary cache locations, while about 12% germinated in the primary caches. Seed removal rates varied widely amongst tree species, from 3% in Beilschmiedia assamica to 97% in Actinodaphne obovata. Seed predation was observed in nine species. Chisocheton cumingianus (57%) and Prunus ceylanica (25%) had moderate levels of seed predation while the remaining species had less than 10% seed predation. We hypothesized that seed traits that provide information on resource quantity would influence rodent choice of a seed, while traits that determine resource accessibility would influence whether seeds are removed or eaten. Removal rates significantly decreased (p < 0.001) while predation rates increased (p = 0.06) with seed size. Removal rates were significantly lower for soft seeds (p = 0.002), whereas predation rates were significantly higher on soft seeds (p = 0.01). Our results show that murid rodents play a very important role in affecting the seed fates of tropical trees in the Eastern Himalayas. We also found that the different rodent groups differed in their seed handling behavior and responses to changes in seed characteristics.     

游弋在热带雨林里的旗舰

展现在您眼前的神态各异的亚洲象,是热带雨林里的“旗舰种”。西双版纳拥有这样一个显赫的标志种．是大自然赐予的福分和财富。     

PCR Amplification-Independent Methods for Detection of Microbial Communities by the High-Density Microarray PhyloChip

Environmental microbial community analysis typically involves amplification by PCR, despite well-documented biases. We have developed two methods of PCR-independent microbial community analysis using the high-density microarray PhyloChip: direct hybridization of 16S rRNA (dirRNA) or rRNA converted to double-stranded cDNA (dscDNA). We compared dirRNA and dscDNA communities to PCR-amplified DNA communities using a mock community of eight taxa, as well as experiments derived from three environmental sample types: chromium-contaminated aquifer groundwater, tropical forest soil, and secondary sewage in seawater. Community profiles by both direct hybridization methods showed differences that were expected based on accompanying data but that were missing in PCR-amplified communities. Taxon richness decreased in RNA compared to that in DNA communities, suggesting a subset of 20% in soil and 60% in groundwater that is active; secondary sewage showed no difference between active and inactive populations. Direct hybridization of dscDNA and RNA is thus a viable alternative to PCR-amplified microbial community analysis, providing identification of the active populations within microbial communities that attenuate pollutants, drive global biogeochemical cycles, or proliferate disease states.     

Tropical Plant Extracts Modulating the Growth of Mycobacterium ulcerans

Mycobacterium ulcerans, the etiologic agent of Buruli ulcer, has been detected on aquatic plants in endemic tropical regions. Here, we tested the effect of several tropical plant extracts on the growth of M. ulcerans and the closely related Mycobacterium marinum. M. ulcerans and M. marinum were inoculated on Middlebrook 7H11 medium with and without extracts from tropical aquatic plants, including Ammannia gracilis, Crinum calamistratum, Echinodorus africanus, Vallisneria nana and Vallisneria torta. Delay of detection of the first colony and the number of colonies at day 7 (M. marinum) or day 16 (M. ulcerans) were used as endpoints. The first M. ulcerans colonies were detected at 8 ± 0 days on control Middlebrook 7H11 medium, 6.34 ± 0.75 days on A. gracilis-enriched medium (p<0.01), 6 ± 1 days on E. africanus- and V. torta-enriched media (p<0.01), 6 ± 0 days on V. nana-enriched medium (p<0.01) and 5.67 ± 0.47 days on C. calamistratum-enriched medium (p<0.01). Furthermore, the number of detected colonies was significantly increased in C. calamistratum- and E. africanus-enriched media at each time point compared to Middlebrook 7H11 (p<0.05). V. nana- and V. torta-enriched media significantly increased the number of detected colonies starting from day 6 and day 10, respectively (p<0.001). At the opposite, A. gracilis-enriched medium significantly decreased the number of detected colonies starting from day 8 PI (p<0.05). In conclusion, some aquatic plant extracts, could be added as adjuvants to the Middlebrook 7H11 medium for the culturing of M. marinum and M. ulcerans.     

Daily and Seasonal Osmotic Changes in a Tropical Treeline Species

The influence of environmental factors on osmotic propertiesin leaf tissue of Polylepis sericea, a widespread tropical treelinespecies in the Venezuelan Andes was studied under field andlaboratory conditions. Daily osmotic changes were determined with thermocouple psychrometers,and the degree of seasonal adjustments was estimated by analysisof pressure-volume (P-V) curves. Measurement of diurnal variationsin water potential components and soluble carbohydrates revealedosmotic adjustment between 0.6 and 1.0 MPa during the predawnhours. A linear relationship was found between minimum osmoticpotential and leaf temperature indicating that temperature maysignificantly affect the magnitude of the predawn osmotic potentialdrop. Analysis of P-V relationships indicated that there wasa seasonal adjustment, from the end of the wet season (November)to the middle of the dry season (February), of approximately0.5 MPa due probably to a net increase in osmotically activesolutes. Laboratory experiments revealed that lowering the preconditioningplant temperature decreased both the leaf osmotic potentialand the supercooling point and increased the leaf soluble carbohydratecontent. The adaptive significance of these mechanisms for trees growingat high elevations in tropical regions where freezing temperaturesmay occur any night of the year is discussed. Key words: Polylepis sericea, Osmotic adjustment, Cold resistance mechanisms.     

Influence of Calonectria crotalariae on Reproduction of Heterodera glycines on Soybean

Calonectria crotalariae enhanced root penetration of Lee 74 (susceptible) and Centennial (resistant) soybeans by juveniles of race 3 of Heterodera glycines. Numbers of cysts in and on the roots of Lee 74 increased during the first 30 days in the presence of the fungus. Percentage of root infection by the fungus increased at 40 days in Lee 74 in the presence of the nematode. Numbers of cysts in soil at 80 and 120 days after inoculation with both organisms accounted for the significantly increased nematode population levels on Lee 74. In the presence of the fungus on the resistant cultivar, significantly increased levels of cysts were recovered from soil at 120 days. Fungus infection of Centennial roots also infected with the nematode increased from 58 to 86% at 120 days. An inoculum timing study in which Lee 74 was infested with the nematode and fungus individually, sequentially, and in combination at days 0 and 35 indicated that enhanced nematode reproduction was related more to early plant-fungus than to early plant-fungus-nematode interaction(s).     

Enhanced Production of Bovine Chymosin by Autophagy Deficiency in the Filamentous Fungus Aspergillus oryzae

Aspergillus oryzae has been utilized as a host for heterologous protein production because of its high protein secretory capacity and food-safety properties. However, A. oryzae often produces lower-than-expected yields of target heterologous proteins due to various underlying mechanisms, including degradation processes such as autophagy, which may be a significant bottleneck for protein production. In the present study, we examined the production of heterologous protein in several autophagy (Aoatg) gene disruptants of A. oryzae. We transformed A. oryzae gene disruptants of Aoatg1, Aoatg13, Aoatg4, Aoatg8, or Aoatg15, with a bovine chymosin (CHY) expression construct and found that the production levels of CHY increased up to three fold compared to the control strain. Notably, however, conidia formation by the Aoatg gene disruptants was significantly reduced. As large amounts of conidia are necessary for inoculating large-scale cultures, we also constructed Aoatg gene-conditional expression strains in which the promoter region of the Aoatg gene was replaced with the thiamine-controllable thiA promoter. Conidiation by the resultant transformants was clearly enhanced in the absence of thiamine, while autophagy remained repressed in the presence of thiamine. Moreover, these transformants displayed increased CHY productivity, which was comparable to that of the Aoatg gene disruptants. Consequently, we succeeded in the construction of A. oryzae strains capable of producing high levels of CHY due to defects in autophagy. Our finding suggests that the conditional regulation of autophagy is an effective method for increasing heterologous protein production in A. oryzae.