Molecular characterization of a FKBP-type immunophilin from higher plants.

Immunophilins are intracellular receptors for the immunosuppressants cyclosporin A, FK506, and rapamycin. In addition to their use in organ transplantation, these natural products have been used to investigate signaling pathways in yeast, plant, and mammalian cells. We have recently described the identification of an immunosuppressant-sensitive signaling pathway in and the purification of several immunophilins from Vicia faba plants. We now report the molecular characterization of a 15 kDa FK506- and rapamycin-binding protein from V. faba (VfFKBP15). The amino acid sequence deduced from the cDNA starts with a signal peptide of 22 hydrophobic amino acids. The core region of VfFKBP15 is most similar to yeast and mammalian FKBP13 localized in the endoplasmic reticulum (ER). In addition, VfFKBP15 has a carboxyl-terminal sequence that is ended with SSEL, a putative ER retention signal. These findings suggest that VfFKBP15 is a functional homolog of FKBP13 from other organisms. Interestingly, two distinct cDNAs corresponding to two isoforms of FKBP15 have been cloned from Arabidopsis and also identified from rice data base, suggesting that pFKBP15 (plant FKBP15) is encoded by a small gene family in plants. This adds to the diversity of plant FKBP members even with the same subcellular localization and is in contrast with the situation in mammalian and yeast systems in which only one FKBP13 gene has been found. Like the mammalian and yeast FKBP13, the recombinant VfFKBP15 protein has rotamase activity that is inhibited by both FK506 and rapamycin with a Ki value of 30 nM and 0.9 nM, respectively, illustrating that VfFKBP15 binds rapamycin in preference over FK506. The mRNA of VfFKBP15 is ubiquitously expressed in various plant tissues including leaves, stems, and roots, consistent with the ER localization of the protein. Levels of VfFKBP15 mRNA are elevated by heat shock, suggesting a possible role for this FKBP member under stress conditions.

Expression of a plant viral polycistronic mRNA in yeast, Saccharomyces cerevisiae, mediated by a plant virus translational transactivator.

We demonstrate that the cauliflower mosaic virus (CaMV) gene VI product can transactivate the expression of a reporter gene in bakers' yeast, Saccharomyces cerevisiae. The gene VI coding sequence was placed under the control of the galactose-inducible promoter GAL1, which is presented in the yeast shuttle vector pYES2, to create plasmid JS169. We also created a chloramphenicol acetyltransferase (CAT) reporter plasmid, JS161, by inserting the CAT reporter gene in-frame into CaMV gene II and subsequently cloning the entire CaMV genome into the yeast vector pRS314. When JS161 was transformed into yeast and subsequently assayed for CAT activity, only a very low level of CAT activity was detected in cellular extracts. To investigate whether the CaMV gene VI product would mediate an increase in CAT activity, we cotransformed yeast with JS169 and JS161. Upon induction with galactose, we found that CAT activity in yeast transformed with JS161 and JS169 was about 19 times higher than the level in the transformants that contained only JS161. CAT activity was dependent on the presence of the gene VI protein, because essentially no CAT activity was detected in yeast cells grown in the presence of glucose, which represses expression from the GAL1 promoter. RNase protection assays showed that the gene VI product had no effect on transcription from the 35S RNA promoter, demonstrating that regulation was occurring at the translation level. This yeast system will prove useful for understanding how the gene VI product of CaMV mediates the translation of genes present on a eukaryotic polycistronic mRNA.

Effects of mechanical signaling on plant cell cytosolic calcium.

Mechanical signals are important influences on the development and morphology of higher plants. Using tobacco transformed with the Ca(2+)-sensitive luminescent protein aequorin, we recently reported the effects of mechanical signals of touch and wind on the luminescence and thus intracellular calcium of young seedlings. When mesophyll protoplasts are isolated from these transgenic tobacco plants and mechanically stimulated by swirling them in solution, cytoplasmic Ca2+ increases immediately and transiently up to 10 microM, and these transients are unaffected by an excess of EGTA in the medium. The size of the transient effect is related to the strength of swirling. Epidermal strips isolated from transgenic tobacco leaves and containing only viable guard cells and trichomes also respond to the strength of swirling in solution and can increase their cytoplasmic Ca2+ transiently up to 10 microM. Finally, the moss Physcomitrella patens containing recombinant aequorin exhibits transient increases in cytoplasmic Ca2+ up to 5 microM when swirled in solution. This effect is strongly inhibited by ruthenium red. Our data indicate that the effect of mechanical stimulation can be found in a number of different cell types and in a lower plant as well as tobacco and suggest that mechanoperception and the resulting increase in cytoplasmic Ca2+ may be widespread.

Plant regeneration functional groups modulate the response to fire of soil enzyme activities in a Mediterranean shrubland

Soil enzymes are critical to soil nutrient cycling function but knowledge on the factors that control their response to major disturbances such as wildfires remains very limited. We evaluated the effect of fire-related plant functional traits (resprouting and seeding) on the resistance and resilience to fire of two soil enzyme activities involved in phosphorus and carbon cycling (acid phosphatase and β-glucosidase) in a Mediterranean shrublands in SE Spain. Using experimental fires, we compared four types of shrubland microsites: SS (vegetation patches dominated by seeder species), RR (patches dominated by resprouter species), SR (patches co-dominated by seeder and resprouter species), and IP (shrub interpatches). We assessed pre- and post-fire activities of the target soil enzymes, available P, soil organic C, and plant cover dynamics over three years after the fire. Post-fire regeneration functional groups (resprouter, seeder) modulated both pre- and post-fire activity of acid phosphatase and β-glucosidase, with higher activity in RR and SR patches than in SS patches and IP. However, we found no major differences in enzyme resistance and resilience between microsite types, except for a trend towards less resilience in SS patches. Fire similarly reduced the activity of both enzymes. However, acid phosphatase and β-glucosidase showed contrasting post-fire dynamics. While β-glucosidase proved to be rather resilient to fire, fully recovering three years after fire, acid phosphatase showed no signs of recovery in that period. Overall, the results indicate a positive influence of resprouter species on soil enzyme activity that is very resistant to fire. Long-lasting decrease in acid phosphatase activity probably resulted from the combined effect of P availability and post-fire drought. Our results provide insights on how plant functional traits modulate soil biochemical and microbiological response to fire in Mediterranean fire-prone shrublands.

Drought and grazing combined: Contrasting shifts in plant interactions at species pair and community level

The combined effects of drought stress and grazing pressure on shaping plant–plant interactions are still poorly understood, while this combination is common in arid ecosystems. In this study we assessed the relative effect of grazing pressure and slope aspect (drought stress) on vegetation cover and soil functioning in semi-arid Mediterranean grassland–shrublands in southeastern Spain. Moreover, we linked these two stress factors to plant co-occurrence patterns at species-pair and community levels, by performing C-score analyses. Vegetation cover and soil functioning decreased with higher grazing pressure and more south-facing (drier) slopes. At the community level, plants at south-facing slopes were negatively associated at no grazing but positively associated at low grazing pressure and randomly associated at high grazing pressure. At north-facing slopes, grazing did not result in a shift in the direction of the association. In contrast, analysis of pairwise species co-occurrence patterns showed that the dominant species Stipa tenacissima and Anthyllis cytisoides shifted from excluding each other to co-occurring with increasing grazing pressure at north-facing slopes. Our findings highlight that for improved understanding of plant interactions along stress gradients, interactions between species pairs and interactions at the community level should be assessed, as these may reveal contrasting results.

How can an invasive grass affect fire behavior in a tropical savanna? A community and individual plant level approach

Some invasive grasses have been reported to change fire behavior in invaded plant communities. Urochloa brizantha is an aggressive invasive grass in the Brazilian Cerrado, an ecosystem where fire is a common disturbance. We investigated the effects of U. brizantha on fire behavior in an open Cerrado physiognomy in Central Brazil. Using experimental burnings we compared fire behavior at both the community and the individual plant level in invaded (UJ) and non-invaded (NJ) areas burned in July. We also assessed the effect of fire season in invaded areas by comparing July (UJ) and October (UO) burnings. We evaluated the following variables: fuel load, fuel moisture, combustion efficiency, maximum fire temperature, flame height, and fire intensity. Additionally, we evaluated the temperatures reached under invasive and native grass tussocks in both seasons. Fuel load, combustion efficiency, and fire intensity were higher in NJ than in UJ, whilst flame height showed the opposite trend. Fuel amount and fire intensity were higher in October than in July. At the individual plant level, U. brizantha moisture was higher than that of native species, however, temperatures reaching ≥600 °C at ground level were more frequent under U. brizantha tussocks than under native grasses. At the community level, the invasive grass modified fire behavior towards lower intensity, lower burning efficiency, and higher flame height. These results provide essential information for the planning of prescribed burnings in invaded Cerrado areas.

SILVER NANOPARTICLES AND THE PLANT-ASSOCIATING ABILITIES OF RHIZOBIACEAE BACTERIA

The use of nanoparticle technology in consumer products has been increasing due to their broad-spectrum antimicrobial properties. Specifically, silver nanoparticles (AgNPs) can demonstrate distinct physiochemical properties compared to bulk silver, including a large surface area to volume ratio that allows for higher reactivity with bacterial cell surfaces. AgNPs are being released into the environment, including soil ecosystems through various pathways such as points of production or during disposal of silver-containing products. This raises the concern about the potential impact on beneficial soil bacteria and their surrounding ecosystems. Members of the Rhizobiaceae family play important roles in nutrient cycling and contribute to overall soil fertility and the experiments in this thesis address the potential for AgNP-mediated toxicity on these plant-associating bacteria. Respiration analysis of Bradyrhizobium japonicum, Azospirillum brasilense, and Agrobacterium tumefaciens has revealed that AgNPs can negatively impact the growth and survival of these bacterial species, with B. japonicum being the most susceptible. Additionally, swimming motility assays using B. japonicum showed a significant decrease in colony diameter when treated with AgNPs (50 ppm). A significant decrease in root colonization of Triticum aestivum roots by A. brasilense was observed as AgNP treatment concentrations increased. Although some of the experiments could not be completed, taken together, these experiments and the research reported herein highlights the potential toxicological effects of AgNPs on bacterial species vital to the growth and health of agriculturally important crops.

Enriching plant diversity in grasslands by large-scale experimental sward disturbance and seed addition along gradients of land-use intensity

Aims The relationship between biodiversity and ecosystem functioning is among the most active areas of ecological research. Furthermore, enhancing the diversity of degraded ecosystems is a major goal in applied restoration ecology. In grasslands, many species may be locally absent due to dispersal or microsite limitation and may therefore profit from mechanical disturbance of the resident vegetation. We established a seed addition and disturbance experiment across several grassland sites of different land use to test whether plant diversity can be increased in these grasslands. Additionally, the experiment will allow us testing the consequences of increased plant diversity for ecosystem processes and for the diversity of other taxa in real-world ecosystems. Here we present details of the experimental design and report results from the first vegetation survey one year after disturbance and seed addition. Moreover, we tested whether the effects of seed addition and disturbance varied among grassland depending on their land use or pre-disturbance plant diversity. Methods A full-factorial experiment was installed in 73 grasslands in three regions across Germany. Grasslands were under regular agricultural use, but varied in the type and the intensity of management, thereby representing the range of management typical for large parts of Central Europe. The disturbance treatment consisted of disturbing the top 10 cm of the sward using a rotavator or rotary harrow. Seed addition consisted of sowing a high-diversity seed mixture of regional plant species. These species were all regionally present, but often locally absent, depending on the resident vegetation composition and richness of each grassland. Important findings One year after sward disturbance it had significantly increased cover of bare soil, seedling species richness and numbers of seedlings. Seed addition had increased plant species richness, but only in combination with sward disturbance. The increase in species richness, when both seed addition and disturbance was applied, was higher at high land-use intensity and low resident diversity. Thus, we show that at least the early recruitment of many species is possible also at high land-use intensity, indicating the potential to restore and enhance biodiversity of species-poor agricultural grasslands. Our newly established experiment provides a unique platform for broad-scale research on the land-use dependence of future trajectories of vegetation diversity and composition and their effects on ecosystem functioning.

(Table 2) Presence of plant remains in sediment core GIK14973, northern Kattegat

For the first time detailed physical properties were measured in addition to sedimentological parameters of near surface sediments of Kattegat channel system. This study has been accomplished on two sediment cores of different waterdepth of each Alkor-deep and Littorina-deep. The sediments of Littorina-deep, which have been dated with 210Pb-method, turned out to be surprisingly recent, with sedimentation rates up to 3,2 cm/year. Differences in physical properties lead to the assumption of lower sedimentation rates in Alkor-deep, the velocities of bottom and deepwater currents could be the cause of these differences in sedimentation rates. In Alkor-deep, the morphology runs parallel to the main direction of the bottom current. Therefore higher current velocities can be reached, which favor the erosion of fine sediment particles. Littorina-deep is located rectangular to the main direction of bottom currents. This might lead to an 'overflow' situation instead of a 'flow through'.

Adventitious root formation in cuttings of Backhousia citriodora F. Muell 2. Seasonal influences of temperature, rainfall, flowering and auxins on the stock plant

A 2-year study was carried out on established trees at two sites in southeastern Queensland, Australia, to identify environmental factors that influenced rooting of Backhousia citriodora from cuttings. Complex interactions of rainfall events above 20 mm from the preceding month and mean maximum temperature on stock plants resulted in a correlation with rooting success of r = 0.81 and 0.74 for sites at The University Of Queensland, Gatton Campus, and Cedar Glen, respectively. A more detailed investigation under controlled environmental conditions showed that maintaining stock plants at temperatures between 10 and 30degreesC had no direct effect on rooting capacity. However, temperature was correlated with growth, which may have an indirect effect on root formation. In spring floral initiation was found to only delay rooting and had no effect on the final rooting percentage. A series of seasonal experiments demonstrated that application of the auxins indole-3-acetic acid, indole-3-butyric acid and napthaleneacetic acid over a range of concentrations (1000-8000 mug/ml) did not significantly increase rooting compared to the control and there is no practical advantage in applying auxins. Seasonal results and the temperature experiment also suggest that under a glasshouse environment with higher temperatures in winter and an adequate supply of water, B. citriodora cuttings can be successfully rooted over the whole year. (C) 2004 Elsevier B.V. All rights reserved.

Approaches to training practitioners in the art and science of plant disease diagnosis

Allowing plant pathology students to tackle fictitious or real crop problems during the course of their formal training not only teaches them the diagnostic process, but also provides for a better understanding of disease etiology. Such a problem-solving approach can also engage, motivate, and enthuse students about plant pathologgy in general. This paper presents examples of three problem-based approaches to diagnostic training utilizing freely available software. The first provides an adventure-game simulation where Students are asked to provide a diagnosis and recommendation after exploring a hypothetical scenario or case. Guidance is given oil how to create these scenarios. The second approach involves students creating their own scenarios. The third uses a diagnostic template combined with reporting software to both guide and capture students' results and reflections during a real diagnostic assignment.