Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

The auxin content (extractable and ‘diffusible’ auxin) of non-sterile corn plants is much more increased by a tryptophan application than the auxin content of sterile plants. This effect is independent of the mode of tryptophan application (spray or supply with the transpiration stream). The epiphytic bacteria settling the shoot surface are responsible for this effect, since in special experiments the rhizosphere was separated from the tryptophan treatment. Sterilized plants which were artificially reinfected with epiphytic IAA-producing bacteria strains behave like non-sterile plants. Non-sterile plants which were superinfected with these bacteria strains have a still higher capacity to convert tryptophan to auxin.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metaholism

During an ether extraction (20 h, 4°C), nonsterilc pea epicotyls deliver at least 5 times more auxin than sterile ones. A great part of the additional auxin originates from a bacterial auxin production during the extraction. Presence of chloramphenicol or streptomycin during the extraction lowers the auxin amount extractable from nonsterile epicotyls. In extraction conditions (i.e. covered with ether, 20 h, 4°C), epiphytic bacteria contained in homogenates of nonsterile plant parts produce IAA from added tryptophan. Furthermore, first results are presented underlining the fact that epiphytic bacteria already produce auxin at the surface of nonsterile plant parts (before an extraction).     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

Homogenates of epicotyls or roots of nonsterile pea plants incubated with tryptophan produce IAA within 1 to 4 hours, which was detected by means of the Avena curvature test and thin layer chromatography. Three results prove this short-term IAA production to be mainly caused by epiphytic bacteria: 1) Homogenates of sterile plant parts catalyze a conversion of tryptophan to IAA, a hundredfold lower. 2) Chloramphenicol or streptomycin very actively reduce the IAA gain obtained with nonsterile homogenates. 3) Washing solutions of nonsterile plant parts which do not contain plant enzymes but only epiphytic bacteria, produce IAA from tryptophan, too. IAA synthesis from tryptophan in vitro by enzymes of the pea plant occurs with lower intensity than hitherto known; possibly it is physiologically unimportant. It is discussed to what extent the hitherto existing research work about the IAA biogenesis in higher plants might be incriminated by disregarding tbe rôle of epiphytic bacteria.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

Epiphytic, IAA-producing bacteria strains were fed with ¹⁴C-tryptophan (Try). ¹⁴C-Try absorption and, after transfer to a Try-free medium, ¹⁴C-IAA output were stated. Using 4 different methods, the ¹⁴C-Try containing bacteria were applied to the tips of sterile corn coleoptiles and the ‘diffusible’ auxin collected at the coleoptile bases by means of agar blocks. ¹⁴C-IAA was detected in the agar blocks. Sterile coleoptiles the tips of which were wupplied with ¹⁴C-Try also deliver some ¹⁴C-IAA at their bases, but much less than both sterile coleoptiles supplied with ¹⁴C-Try-containing bacteria and nonsterile supplied with ¹⁴C-Try.     

Ecochemical Studies of Interrelationships between Epiphytic Bacteria and Host Plants via Secondary Metabolites

The plant surface, which is representative of the phylloplane and rhizoplane, is a characteristic habitat for microorganisms. In this review, the ecological roles of phytoepiphytic bacteria will be described. The phylloplane and rhizoplane, which are adjacent to the atmosphere and soil sphere respectively, accumulate topically and/or selectively release secondary metabolites that are specific to the plant genera and species which reside within these regions. Some epiphytes have abilities to decarboxylate xenobiotic phenolic acids that have accumulated in the plant tissues and surfaces as a majority of such secondary metabolites. In physicochemically stressed soil, rhizosphere microflora often remedy such microenvironments within the rhizosphere in order to assist in the survival of the host, and some of the microfloral compositions behave as if they were symbionts. Specifically, some Sphingomonas spp., which are frequently isolated from the rhizosphere of acidic soil-tolerant plants in tropical zones, make possible the development of a rhizo-biocomplex. In this review, the possibility of rhizosphere regulation utilizing such a rhizo-biocomplex is discussed.     

Comparison of Diversity and Functions of Epiphytic Bacteria from Cultivated and Weed Plants in Agrocenoses

Diversity of epiphytic bacterial complexes from cultivated and weed plants was compared according to the frequency of predominance of bacterial taxa in these communities and using the principal component method. The presence of both common dominants on cultivated and weed plants and distinct differences in the composition of the epiphytic bacterial complexes of these plants was revealed. The representatives of chemolithotrophic bacteria capable of tetrathionate and thiosulfate assimilation were found only on weed plants. The antibiotic activity of bacteria isolated from weed plants was almost twice as high as that found for bacteria from cultivated plants. The obtained data indicate the positive effect of bacterial communities of weed plants, which make it possible to protect cultivated plants from phytopathogens.     

Aerial Dispersal and Epiphytic Survival of Pseudomonas syringae during a Pretest for the Release of Genetically Engineered Strains into the Environment

Prospective experimental field evaluation of genetically engineered microorganisms, such as microbial pest control agents, raises issues of how to properly ascertain their fate and survival in the environment. Field trials with recombinant organisms must reflect requirements for sampling and monitoring. Field trials were conducted at Tulelake, Calif., to monitor the numbers of viable cells of a nonrecombinant strain of Pseudomonas syringae that entered the atmosphere and landed on plants and soil during and after an aerosol spray application. An exponential decrease in numbers of viable cells deposited at increasing distances from three sprayed plots was observed. The relative rate of survival of cells sprayed directly on plants was more than 10 times higher than that of cells dispersed through the air to similar adjacent plants. Results are being used to gain experience with the characteristics of a release site that influence containment or dispersal and to develop appropriate sampling methodologies for evaluating survival and dispersal characteristics of genetically engineered bacteria released into the environment. The ability to make predictions about microbial dispersal and survival will reduce the uncertainties associated with environmental releases of recombinant organisms.     

Aerial Dispersal and Multiple-Scale Spread of Epidemic Disease

Disease spread has traditionally been described as a traveling wave of constant velocity. However, aerially dispersed pathogens capable of long-distance dispersal often have dispersal gradients with extended tails that could result in acceleration of the epidemic front. We evaluated empirical data with a simple model of disease spread that incorporates logistic growth in time with an inverse power function for dispersal. The scale invariance of the power law dispersal function implies its applicability at any spatial scale; indeed, the model successfully described epidemics ranging over six orders of magnitude, from experimental field plots to continental-scale epidemics of both plant and animal diseases. The distance traveled by epidemic fronts approximately doubled per unit time, velocity increased linearly with distance (slope ~½), and the exponent of the inverse power law was approximately 2. We found that it also may be possible to scale epidemics to account for initial outbreak focus size and the frequency of susceptible hosts. These relationships improve understanding of the geographic spread of emerging diseases, and facilitate the development of methods for predicting and preventing epidemics of plants, animals, and humans caused by pathogens that are capable of long-distance dispersal.     

Toxicity of Smoke to Epiphytic Ice Nucleation-Active Bacteria

Wheat straw smoke aerosols and liquid smoke condensates reduced significantly both the viability and the ice-nucleating activity of Pseudomonas syringae pv. syringae and Erwinia herbicola in vitro and on leaf surfaces in vivo. Highly significant reductions in numbers of bacterial ice nuclei on the surface of both corn and almond were observed after exposure to smoke aerosols. At −5°C, frost injury to corn seedlings colonized by ice nucleation-active bacteria was reduced after exposure to smoke aerosols. Effects on −9°C ice nuclei, although significant, were less than on ice nuclei active at −5°C. These results suggest that smoke from wildfires or smudge pots may reduce plant frost susceptibility and sources of ice nuclei important in other natural processes under some conditions.     

A Note on the Enumeration of Epiphytic Bacteria by Microscopic Methods with Particular Reference to Two Freshwater Plants

Bacteria on plant surfaces were examined using epifluorescence, bright-field microscopy and an impression technique. Staining bacteria directly on the plant surface with phenolic aniline blue was found to be the best method to use for the determination of bacterial density. The effect on the estimation of population density of pretreatment of the plant with agents such as methanol and eosin yellowish was investigated. The average sizes of the bacterial populations on two freshwater plants, Rorippa and Lemna , estimated after staining by this method, were 5 times 10⁶ and 9 times 10⁶ bacteria cm-^z respectively.     

Interaction of Epiphytic Bacteria and Activated Carbon on Root Growth

The influence of activated carbon and aseptic conditions has been studied on the growth of the primary root of wheat seedlings in order to ascertain whether or not the growth effect of activated carbon is connected with the occurrence of epiphytic bacteria. Growth was measured as mitotic activity, rate of cell elongation and duration of cell elongation. The surface infection of the septic roots probably consisted of common airborn and waterborn bacteria. Aseptic conditions increased the rate of cell elongation by ca 70 % but had no effect on the meristem activity. Activated carbon increased mitoses in the meristem and slightly augmented the duration of cell elongation but had no effect on the rate of elongation. The effects of sepsis and carbon were independent and appeared additative. Activated carbon removed inhibitors produced by the root tip itself but not those formed by the bacteria. In these experiments neither group of inhibitors seemed to contain IAA-like substances.     

Intercontinental Dispersal of Bacteria and Archaea by Transpacific Winds

Microorganisms are abundant in the upper atmosphere, particularly downwind of arid regions, where winds can mobilize large amounts of topsoil and dust. However, the challenge of collecting samples from the upper atmosphere and reliance upon culture-based characterization methods have prevented a comprehensive understanding of globally dispersed airborne microbes. In spring 2011 at the Mt. Bachelor Observatory in North America (2.8 km above sea level), we captured enough microbial biomass in two transpacific air plumes to permit a microarray analysis using 16S rRNA genes. Thousands of distinct bacterial taxa spanning a wide range of phyla and surface environments were detected before, during, and after each Asian long-range transport event. Interestingly, the transpacific plumes delivered higher concentrations of taxa already in the background air (particularly Proteobacteria, Actinobacteria, and Firmicutes). While some bacterial families and a few marine archaea appeared for the first and only time during the plumes, the microbial community compositions were similar, despite the unique transport histories of the air masses. It seems plausible, when coupled with atmospheric modeling and chemical analysis, that microbial biogeography can be used to pinpoint the source of intercontinental dust plumes. Given the degree of richness measured in our study, the overall contribution of Asian aerosols to microbial species in North American air warrants additional investigation.     

空拍南极

几十年的记者生涯,我走遍了边疆海岛,乘过歼击机、伊尔-18、直升飞机,拍摄过战斗机飞行编队、祖国锦绣河山,但在南极洲那样复杂的条件下进行空拍尚属首次。 南极洲,位于地球的最南端,面积1400万平方公里。那里千里冰封,万古长寒,狂风怒吼,极光夺目,被称为世界上最神秘的地方;那里有丰富的资源,是一个“万宝之地”,大陆和大陆架上蕴藏着220多种矿物,尤以石油、天燃气、铁矿石和煤的蕴藏量最为丰富;还有诸如磷虾、企鹅、海豹、鲸等生物资源;那里污染少,基本处于自然状态,它给科学家提供了一个特殊的科学研究场地,是当今人类进行科学研究的天然实验室。1984年11月20     

Coli-aerogenes Bacteria on Plants

S ummary . Specimens of plant foliage and flowers collected in the region of Attica from various situations and geographical regions were examined over a period of 13 months for the presence of coli-aerogenes bacteria able to grow at 37°. Twenty-five (12.2%) of 204 specimens carried coli-aerogenes bacteria of which Escherichia coli type I was isolated from 12 (5.8%). Coli-aerogenes bacteria were seldom isolated from plants grown in uninhabited areas, and they occured more frequently during summer and autumn.
Vegetables and fruits sold in the central market of Athens are frequently contaminated with coli-aerogenes bacteria. Of 76 specimens of vegetables examined 66 (86.8%) were positive for coli-aerogenes bacteria, and 17 (22.3%) for E. coli type I. The figures from 41 specimens of fruits were 26 (65.8%) and 4 (9.7%), respectively.     

Wind and Water Dispersal of Wetland Plants Across Fragmented Landscapes

Biodiversity in wetlands is threatened by habitat loss and fragmentation, of which agricultural activities often are a cause. Dispersal of plant seeds via wind and ditches (water) may contribute to connecting remnant wetland plant populations in modern agricultural landscapes, and help to maintain and restore biodiversity. We developed a spatially explicit model to assess the relative importance of dispersal by wind and dispersal by water through drainage ditches for two wetland plant species in agricultural landscapes: a typical wind disperser and a typical water-disperser. Simulation results show that the typical wind disperser had a much higher capability to disperse by wind (90th percentile <30 m) than the typical water-disperser (90th percentile <2 m). Surprisingly, the capability to disperse via water was similar for the two species: 90th percentile dispersal distances following a combination of wind and water dispersal were between approximately 100 and 1000 m. Dispersal by water transported more seeds over long distances for both species. The main determinants for dispersal distance by water were roughness of the ditch (determined by, for example, bank vegetation) and the presence of obstructions (for example, culverts). Density or direction of the ditch network did not seem to affect water dispersal distances substantially. From a biodiversity conservation perspective, it would be most useful if areas with suitable riparian wetland habitat were intersected with a network of shallow ditches with a high roughness promoting seed deposition. These areas should then be connected to other suitable areas by a few regularly cleaned ditches with no obstructions and low seed trapping probability.     

Mechanism of Zinc Absorption by Intact Bean Plants

The time course of absorption of ⁶²Zn and ³²P by roots of intactbean plants (Phaseolus vulgaris L.), and the effects of azideand amytal have been studied. The evidence indicates that zincuptake occurs mainly by a non-metabolic process.