Sequential colonization by river periphyton analysed by microscopy and molecular fingerprinting

1. An artificial glass substratum was incubated in the River Danube for a period of 28 days in order to detect the sequential colonization of microorganisms.
2. Light and fluorescent microscopy showed that microalgae and the picoalgal fraction on the slides increased rapidly over the first 2 weeks of colonization. Diatoms were numerically the most abundant component of the periphyton and their species richness and diversity increased rapidly in the early phase of colonization whereas diversity subsequently increased moderately.
3. Evenness of the diatom community was initially high, lower in the intermediate phase and again higher later on. Succession involving early, intermediate and late colonizer species was observed. Community composition during the first 5 days of colonization was very different from later stages whereas there were only minor changes subsequently.
4. Molecular community analysis by means of terminal restriction fragment length polymorphism analysis of PCR amplified 16S rRNA and 18S rRNA genes pointed to even larger differences between the composition of samples obtained early and late in the period.
5. The number of 18S rRNA and 16S rRNA terminal restriction fragments (T-RF-s) was variable over the colonization period and the fragment patterns of both the bacterial and eukaryotic portion of the microbial community were variable, with most T-RF-s unique to a single sample, suggesting a wide diversity and dynamic properties of periphytic organisms.     

Concerted transpositions of mobile genetic elements coupled with fitness changes in Drosophila melanogaster

In an inbred low-activity (LA) strain of Drosophila melanogaster with a low level of fitness and a complex of inadaptive characters, in situ hybridization reveals an invariant pattern of distribution of three copia-like elements (mdg-1, mdg-3, and copia). Rare, spontaneous, multiple transpositions of mobile elements in the LA strain were shown to be coupled with a drastic increase of fitness. A changed pattern of various types of mobile elements was also observed on selecting the LA strain for higher fitness. High-fitness strains show transpositions of mobile elements to definite chromosomal sites ("hot spots"). Concerted changes in the location of three different mobile elements were found to be coupled with an increase of fitness. The mdg-1 distribution patterns were also examined in two low-fitness strains independently selected from the high-fitness ones. Fitness decrease was accompanied by mdg-1 excision from the hot spots of their location usually detected in the high-fitness strains. The results suggest the existence of a system of adaptive transpositions of mobile elements that takes part in fitness control.      

Strong coupling of plant and fungal community structure across western Amazonian rainforests

The Amazon basin harbors a diverse ecological community that has a critical role in the maintenance of the biosphere. Although plant and animal communities have received much attention, basic information is lacking for fungal or prokaryotic communities. This is despite the fact that recent ecological studies have suggested a prominent role for interactions with soil fungi in structuring the diversity and abundance of tropical rainforest trees. In this study, we characterize soil fungal communities across three major tropical forest types in the western Amazon basin (terra firme, seasonally flooded and white sand) using 454 pyrosequencing. Using these data, we examine the relationship between fungal diversity and tree species richness, and between fungal community composition and tree species composition, soil environment and spatial proximity. We find that the fungal community in these ecosystems is diverse, with high degrees of spatial variability related to forest type. We also find strong correlations between α- and β-diversity of soil fungi and trees. Both fungal and plant community β-diversity were also correlated with differences in environmental conditions. The correlation between plant and fungal richness was stronger in fungal lineages known for biotrophic strategies (for example, pathogens, mycorrhizas) compared with a lineage known primarily for saprotrophy (yeasts), suggesting that this coupling is, at least in part, due to direct plant–fungal interactions. These data provide a much-needed look at an understudied dimension of the biota in an important ecosystem and supports the hypothesis that fungal communities are involved in the regulation of tropical tree diversity.     

Photosynthetic generation of O2 and H2 by photosystem I-deficient chlamydomonas mutants

A comparative study of aerobic generation of O2 and anaerobic photoproduction of H2 in whole cells of a wild-type strain of Chlamydomonas reinhardtii and its photosystem I-deficient mutants B4 and F8 found no contribution of photosystem II to ferredoxin photoreduction, which is not consistent with data of recent studies by Greenbaum et al. (Nature, 1995, 376, 438-441; and Science, 1996, 273, 364-367) who reported that they had discovered such a capacity in these mutant strains. In the wild-type and mutant strains, action spectra showed that O2 was evolved by photosystem II, whereas photoinhibition of chlororespiration and evolution of H2 depended on the activity of photosystem I. Single-turnover flash measurements of H2 evolution showed that the contents of photosystem I in mutant strains amounted to 3-35% of that in the wild-type strain. This fraction of photosystem I in "leaky" mutants displayed abnormal kinetic features and was highly sensitive to photoinhibition.     

Repeat motions and backbone flexibility in designed proteins with different numbers of identical consensus tetratricopeptide repeats

The tetratricopeptide repeat (TPR) is a 34-residue helix-turn-helix motif that occurs as three or more tandem repeats in a wide variety of proteins. We have determined the repeat motions and backbone fluctuations of proteins containing two or three consensus TPR repeats (CTPR2 and CPTR3, respectively) using 15N NMR relaxation measurements. Rotational diffusion tensors calculated from these data for each repeat within each TPR protein indicate that there is a high degree of motional correlation between different repeats in the same protein. This is consistent with the prevailing view that repeat proteins, such as CTPR2 and CTPR3, behave as single cooperatively folded domains. The internal motions of backbone NH groups were determined using the Lipari-Szabo model-free formalism. For most residues, there was a clear separation between the influence of internal motion and the influence of global rotational tumbling on the observed magnetic relaxation. The local internal motions are highly restricted in most of the helical elements, with slightly greater flexibility in the linker elements. Comparisons between CTPR2 and CTPR3 indicate that an addition of a TPR repeat to the C-terminus (before the solvation helix) of CTPR2 slightly reduces the flexibility of the preceding helix.     

Comparison between the backbone dynamics of an 11-amino acid peptide sequence in alpha-helical and beta-hairpin structural contexts

To investigate the relationship between backbone motions and the structural environment of a peptide sequence, we have used (15)N NMR relaxation data to characterize the backbone motions of the "chameleon-alpha" (Chm-alpha) and "chameleon-beta" (Chm-beta) proteins designed previously by Minor and Kim [Minor, D. L., Jr., and Kim, P. S. (1996) Nature 380, 730-734]. These two proteins contain an identical 11-amino acid sequence (dubbed the "chameleon" peptide sequence) in alpha-helix and beta-hairpin conformations, respectively, within the B1 domain of protein G. When placed in an alpha-helical context, the chameleon peptide shows very limited backbone motions, but some remote regions of the protein are induced to undergo conformational exchange motions, apparently due to modification of packing interactions with the chameleon peptide. In contrast, within a beta-hairpin context, the chameleon peptide displays substantial motions on both picosecond and microsecond-to-millisecond time scales, suggesting that it cannot be readily accommodated within the native reverse turn structure. These observations are consistent with the relatively low stability of the Chm-beta protein and can be rationalized in terms of native turn-stabilizing interactions that may be disrupted in the Chm-beta protein.     

外源亚精胺和精胺对NaHCO3胁迫下南蛇藤抗氧化系统的影响

研究了叶面喷施亚精胺和精胺对NaHCO₃胁迫下南蛇藤叶片抗氧化系统的影响.结果表明：外源亚精胺和精胺处理使NaHCO₃胁迫下南蛇藤叶片O₂^-·产生速率、H₂O₂、丙二醛(MDA)含量和电解质外渗率显著降低(P<0.05).亚精胺处理明显提高了盐胁迫下超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX)等抗氧化酶的活性,以及还原型谷胱甘肽(GSH)、类胡萝卜素(CAR)和脯氨酸(Pro)等抗氧化剂的含量,但对还原型抗坏血酸(AsA)含量没有作用;精胺处理明显提高NaHCO₃胁迫下POD和APX的活性以及GSH、CAR和Pro的含量,但对SOD和AsA含量影响不显著,甚至引起CAT活性明显降低.亚精胺和精胺处理明显改善了NaHCO₃胁迫下南蛇藤的生长.外源亚精胺和精胺可以改善NaHCO₃胁迫下南蛇藤叶片的膜保护功能,减少叶片中活性氧的积累,从而提高南蛇藤对NaHCO₃胁迫的抗性.