bluuebunny/crossref_metadata_2025_split huggingface dataset:
Does temperature stress induce nectar secretion in Mediterranean plants?
Authors: PETANIDOU THEODORA , SMETS ERIK 
Published: April 2006

summaryWe studied the effect of temperature on nectar secretion in Thymus capitatus, a typical labiate of phrygana (i.e. the garrigue of the East Mediterranean Basin). Experiments were carried out at controlled temperatures in a climatic chamber. We measured the nectar standing crop of the flowers at the end of the first day of their anthesis. All nectar values (i.e. volume per flower, sugar content and concentration) increased with temperature up to 38° C, as long as the plants were not water stressed. However, in the open and under normal temperate conditions (i.e. at relatively low temperatures) nectar secretion depended more on changes in solar irradiance than on temperature.Under the same conditions, nectar secretion in Ballota acetabulosa, a species that is sympatric and coflowering with T. capitatus, was affected neither by light nor temperature. Since in the wild these two species are found in different microhabitats (full sun and shade, for T. capitatus and B. acetabulosa, respectively), we attribute the differences we observed to the differential natural adaptation of the plants to these factors. We conclude that T. capitatus is very well adapted to the Mediterranean conditions. By performing optimally as a nectar source at high temperatures, it can support a very large insect fauna that visits its flowers for nectar. It is in fact a temperature–induced cornucopian species.
Effects of pollutants in snowmelt onKiaeria starkei, a characteristic species of late snowbed bryophyte dominated vegetation
Authors: WOOLGROVE C. E. , WOODIN S. J. 
Published: April 2006

summaryAreas which experience prolonged snowlie and possess a distinctive bryophyte‐dominated vegetation are termed snowbeds. Snow is a very efficient scavenger of atmospheric pollution. Because of the dynamics of snowmelt, much of the pollutant load of a snowpack is released in a highly concentrated episode known as the ‘acid flush’. This flush is received by the underlying vegetation when it is covered by the snow and also when it has been exposed after snow cover. Concentrations of pollutants which are already occurring in the meltwater of Scottish snowbeds are shown to be causing damage to the underlying bryophytes. Damage is greatest when the pollutants are received by the plants when out of snow cover. Recovery from the damage is slow and in some cases the plants show no signs of recovery 4 wk after exposure to polluted snow meltwater. Given the very short growing season available to the plants, damage persisting for so long could impinge on the plants'potential for survival. The long‐term threat to these sensitive communities is a serious one.
Habitat differentiation in a narrow hybrid zone between diploid and tetraploid Anthoxanthum alpinum
Authors: FELBER‐GIRARD M. , FELBER F. , BUTTLER A. 
Published: April 2006

summaryPopulations of diploid and autotetraploid Anthoxanthum alpinum A. & D. Löve formed a narrow hybrid zone in a study area in the Swiss Prealps. Detailed vegetation analyses were performed along transects in several contact zones between the two cytotypes. The vegetation differed according to the position in the hybrid zone. When considering the hybrid zone as a whole, and for one transect that was analysed in detail, there was strong evidence for habitat segregation between the cytotypes. Vegetation transitions, habitat preference and segregation of the two cytotypes differed according to location in the hybrid zone. The origin and dynamics of the hybrid zone are discussed.
Effects of nitrogen limitation and starvation on Chroococcidiopsis sp. (Chroococcales)
Authors: BILLI DANIELA , CAIOLA MARIA GRILLI 
Published: April 2006

summary Chroococcidiopsis sp. cells from hot desert rock (Timna National Park, Israel) were grown in modified BG‐11 medium which was either N‐free or which contained different concentrations of nitrogen, provided as nitrate. The life cycle, ultrastructure and physiological activities of the cyanobacterium were investigated over a period of 4 months. No alterations were detected in cells grown in medium containing 250 or 125 μg N ml−1. In contrast, cells grown in medium with 62 μg N ml−1 or lacking nitrogen occurred only as isolated viable forms, after 3 months and 1 month of growth, respectively. In these cells a decrease in the content of cellular chlorophyll and phycocyanin paralleled undetectable O2 evolution and depressed O2 uptake. In addition, such isolated cells were characterized by a multilayered envelope, whereas, in the cytoplasm, vesiculated thylakoids and glycogen granules were observed. N‐limited and N‐starved cells recovered their cellular organization and physiological activities upon N repletion. These ‘survival’ cells had a spore‐like form, and were functionally comparable to akinetes.
Experimental studies of growth and regenerative capacity in the foliose lichen Xanthoria parietina
Authors: HONEGGER ROSMARIE 
Published: April 2006

summaryA series of outdoor culturing experiments on artificial ceramic substrata was set up to test the regenerative capacity of thallus fragments of the foliose lichen Xanthoria parietina (L.) Th. Fr. which had been dissected along an axis from the growing marginal pseudomeristem to the apothecia‐covered central areas. This dorsiventrally organized macrolichen (photobiont: Trebouxia arboricola De Puymaly) is capable of regenerating new lobes along wound margins or cut edges in any part of the thallus, including the thalline margin of apothecial disks. In semithin sections of central thalline areas of non‐disturbed thalli, where fungal and algal cells have reached their mature dimensions and where a high percentage of oversized Trebouxia cells imply an arrested cell cycle, small islets of actively growing and dividing fungal and algal cells were found within the algal layer. These are likely to be the sites where primordial stages of new lobes initiate after wounding. In nature, apothecia‐covered central thalline areas of X. parietina usually lose their contact with the substratum and break off along drought‐stress induced cracks. When landing on a suitable substratum, detached thallus fragments were found to regenerate new lobes in the same manner as artificially dissected samples, thus serving as propagules of the symbiotic state of this ecologically very successful lichen species.
Resource re‐allocation following fruit removal in cucurbits: patterns in two varieties of squash
Authors: EL‐KEBLAWY ALI , LOVETT‐DOUST J. 
Published: April 2006

summaryThe effects of removal of marketable‐sized fruits on investment toward male, female and vegetative activities were evaluated using two monoecious varieties of cultivated squash, Cucurbita pepo, cv. Striato d'Itaha o di Napoli, and cv. Zucchini Black. Leaf and flower demography were used to examine potential trade‐offs among these activities. Treated individuals produced more leaves, but individual leaf life expectancies were lower than those of controls. Fruit removal also significantly stimulated the production of male and female flowers, fruit and total above‐ground biomass. By contrast, permitting the extended process of fruit maturation in controls significantly decreased the overall production of both male and female flowers. There was no significant difference in total fruit mass between treated and control individuals. However, production of female and male flowers was labile, and responsive to the resource relationships operating within the plant. Treated plants produced more female (potentially fruit‐bearing) flowers as their fruits were harvested, and both groups of plants produced more male flowers at the end of the season. Overall, the squash cultivar produced almost twice as many male flowers as the zucchini cultivar; the harvesting treatment enhanced male flower production later in the season, and did so earlier in squash than in zucchini. Since reduced fruit production is achieved through reduced production of female flowers rather than through abortion of early fruits, and this precedes the period where resource limitation is anticipated, it is concluded that available resources do not directly prevent fruit development. The results are interpreted in the light of recent artificial selection for one to two large fruits per plant in the case of the squash cultivar and many smaller fruits in the case of the zucchini.
Growth response of grasses to elevated CO2: a physiological plurispecific analysis
Authors: ROUMET C. , BEL M. P. , SONIE L. , JARDON F. , ROY J. 
Published: April 2006

summaryThe effect of CO2 enrichment on the growth and the economy of carbon and nitrogen of 11 Mediterranean grass species was investigated in order to determine the underlying causes of the large variation observed between species in their responses to elevated CO2. Plants were grown for 26–43 d (depending on species growth rate) under productive conditions at ambient (350 μmol mol−1) and elevated (700 μmol mol−1) concentrations of CO2. Plant parameters were determined at a common biomass of 0.15 g to determine the CO2 effect independent of ontogenic effects.The effect of CO2 on RGR ranged from −6.7 to 22.5%, with a mean stimulation of 10.3%. Averaged over the 11 species, the growth enhancement resulted from an increase in net assimilation rate per unit leaf d. wt. (narw) of 10.6 %. This was the result of a large increase (18.7%) in nar per unit leaf area (NARa) associated with a 8.1% decrease in the specific leaf area (sla). This decrease in sla was due to a large increase of the non‐structural carbohydrates. The increase in shoot activity was balanced by a 70.6% increase in the specific absorption rate of nitrogen (sar). AS a result, plant nitrogen content was not modified. Leaf nitrogen productivity was significantly increased (14.9%). Shoot vs. root allocation of biomass and nitrogen was not modified.An analysis across the 11 species of the relationships between the stimulation of rgb and the alteration in rgr components showed a significant correlation only with increases in narw, sar and nitrogen productivity. The co‐ordinated increase in these three parameters constitutes a single response syndrome, whose intensity is responsible for most of the species variability.
Effects of elevated CO2 on stem growth, vessel area and hydraulic conductivity of oak and cherry seedlings
Authors: ATKINSON C. J. , TAYLOR J. M. 
Published: April 2006

summaryPlants of Quercus robur L. and Prunus avium L. ×P. pseudocerasus Lind, were grown in either ambient (350 vpm) or elevated (700 vpm) CO2. The intention was to examine the effects of elevated CO2 on the morphological and functional development of the stem. The relationships between stem longitudinal transport capacity and development were explored in several ways: stem hydraulic function was related to stem cross‐sectional area, supplied leaf area and total stem vessel lumen area.The mean total vessel number and the total vessel lumen area per stem, for both species, was determined from basal sections of the xylem. In Primus seedlings grown in different CO2 concentrations there was no significant change in the mean vessel size or number of vessels per stem. Quercus seedlings grown at elevated CO2 showed a significant increase in both vessel number and mean vessel size. When total stem vessel area was calculated it had increased twofold for Quercus plants grown at elevated CO2.Measured stem hydraulic conductivity was shown to increase linearly with supplied leaf area, except in Quercus seedlings grown at elevated CO2. Stem hydraulic conductivity for Quercus seedlings grown at elevated CO2 did not change with the increase in supplied leaf area. This absence of an increase in the stem hydraulic conductivity appeared to relate to changes in total stem vessel area. Despite total stem vessel area being greater at elevated CO2 than that at ambient, it similarly did not increase with supplied leaf area.The implications of this change in the relationship between leaf area and stem hydraulic conductivity are discussed with respect to the possible effects the change might have on the plant's water balance. The possible causes and significance of the changes in xylem anatomy are also considered in relation to direct effects caused by CO2 or indirect effects on changes in cambial maturity and tree growth.
The response of Plantago major ssp. pleiosperma to elevated CO2 is modulated by the formation of secondary shoots
Authors: FONSECA F. , DEN HERTOG J. , STULEN I. 
Published: April 2006

summaryThe effect of elevated CO2 on the relative growth rate (RGR) of Plantago major ssp. pleiosperma was studied during the vegetative stage, in relation to plant development, by growing plants at 350 μl 1−1 or at 700 μl 1−1 CO2 in non‐limiting nutrient solution with nitrate. To minimize interference by the accumulation of non‐structural carbohydrates in the interpretation of results, RGR was expressed on a f. wt basis (RGRFW), as were all plant weight ratios. Stimulation of the RGRFW of the whole plant by elevated CO2 was transient, and did not last longer than 8 d. At the same time a transient increase in root weight ratio (RWR) was observed.In order to investigate whether the transient effect of elevated CO2 on rgrfw was size‐dependent, the data were plotted versus total f. wt (loge, transformed). The transient period of stimulation of rgrfw and of rwr by elevated CO2 was still found, but in both CO2 treatments rgrfw decreased after a certain plant size had been reached. This size coincided with the stage at which secondary shoots started to develop, and was reached earlier in plants grown at elevated CO2. The rgr of these secondary shoots (rgrset.) was still increased when the period of whole plant stimulation of rgrfw had ended, indicating that the development of these new sinks took priority over a continuation of the stimulation of rwr. It is hypothesized that in this Plantago subspecies the response of the rgrfw of the whole plants to elevated CO2 is modulated by the formation of secondary shoots. Apparently, partitioning of the extra soluble carbohydrates at elevated CO2 to this tissue takes precedence over partitioning to the roots, resulting in a cessation of stimulation of plant rgrfw by elevated CO2.
Localizing an Ophiostoma piceae proteinase in sapwood of four tree species using polyclonal antibodies
Authors: GHARIBIAN S. , HOFFERT C. , ABRAHAM L. D. , BREUIL C. 
Published: April 2006

summaryThe growth and proteolytic activity of the sap‐staining fungus Ophiostoma piceae were characterized in the wood of four tree species: lodgepole pine (Pinus contorta var. latifolia Dougl.), aspen (Populus tremuloides Michx.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and Western hemlock (Tsuga heterophylla Sarg.). Proteolytic activity and growth were highest in aspen. Proteolytic activity was minimal in both Douglas fir and Western hemlock. Polyclonal antibodies raised against the major proteinase produced by O. picaea were used to immunolocalize the enzyme after fungal growth in lodgepole pine and aspen. Immunogold labelling revealed that the proteinase was localized mainly in the cell wall of O. piceae. Gold particles concentrated in a sheath which was well defined after 10 d. Labelling appeared greater in the inoculated aspen than in lodgepole pine.
Nod factor‐induced host responses and mechanisms of Nod factor perception
Authors: HEIDSTRA RENZE , BISSELING TON 
Published: April 2006

SUMMARYSoil bacteria belonging to the genera Rhizobium, Bradyrhizobium and Azorhizobium are able to invade the roots of their leguminous host plants, where they trigger the formation of a new organ, the root nodule. At least two steps of signal exchange between the bacterium and the host plant are involved in starting the interaction. In the first step, flavonoids excreted by the plant induce the transcription of bacterial nodulation genes (nod genes). The induction of these nod genes leads to the synthesis of specific lipooligosaccharides (called Nod factors) that can induce various root responses, e.g. root hair deformation, depolarization of the root hair membrane potential, induction of nodulin gene expression, and formation of nodule primordia.We will focus on the various nod factor‐induced plant responses. We will discuss the ways these responses can be used to improve our knowledge of the mechanism of Nod factor perception. Furthermore, plant genes, in particular the sym2 allele from Afghanistan pea, encoding proteins that probably are involved in Nod factor recognition, are discussed. Based on the Nod factor‐induced plant responses and the phenotype displayed by sym2 peas, a model will be presented of how Nod factors may be perceived.
Suppression of defence responses in mycorrhizal alfalfa and tobacco roots
Authors: KAPULNIK YORAM , VOLPIN HANNE , ITZHAKI HANNAN , GANON DANA , GALILI SHMUEL , DAVID RAKEFET , SHAUL ORNA , ELAD YIGAL , CHET ILAN , OKON YAACOV 
Published: April 2006

SUMMARYThe broad host range of arbuscular mycorrhizal (AM) fungi differs from the specificity encountered in biotrophic pathogens. We summarize here the basic plant strategies of defence plant responses to colonization with pathogenic micro‐organisms and evaluate their possible involvement in AM performance. Detailed evidence is presented that, during early colonization of plant roots by symbiotic Glomus, defence‐related root responses are induced and then subsequently suppressed. In AM interactions, the broad host‐range infection capacity and the induction of defence‐related genes suggests that the compatible interaction is dominant. These results are discussed in relation to the possible conclusion that AM fungi might lack avirulence homologues or alternatively, that the factor causing suppression of the host defence response might be dominant.
Analysis of factors involved in fungal recognition responses to host‐derived signals by arbuscular mycorrhizal fungi
Authors: GIOVANNETTI MANUELA , SBRANA CRISTIANA , CITERNESI ANNA SILVIA , AVIO LUCIANO 
Published: April 2006

SUMMARYAn experimental model for the study of recognition responses by arbuscular mycorrhizal symbionts to host roots was validated by analysing the main factors which might affect such responses. Results showed that fungal responses to host‐derived signals were unaffected by the degree of sterility of the system, host age and mycorrhizal status, symbiont age, or different chemical and physical characteristics of hydrophilic membranes. Use of dialysis membranes showed that the molecules putatively eliciting fungal responses weigh less than 500 Da. Utilization of the model for studies of developmental expression of proteins and genes in arbuscular mycorrhizal symbionts is examined.
Molecular analysis of cell wall proteins expressed during the early steps of ectomycorrhiza development
Authors: TAGU DENIS , MARTIN FRANCIS 
Published: April 2006

SUMMARYEctomycorrhiza morphogenesis involves the differentiation of structurally specialized fungal tissues, the mantle and the Hartig net, and interfaces between symbionts. Proteins whose biosynthesis is specifically up‐ or down‐regulated have been identified in several ectomycorrhizal associations. Their spatial and temporal expressions have been characterized by cell fractionation, two‐dimensional polyacrylamide gel electrophoresis and lmmunochemical assays in the Eucalyptus spp ‐Pisolithus tinctorius symbiosis. These biochemical investigations have revealed the drastic alterations experienced by fungal cell wall polypeptides during the early stages of the ectomycorrhizal interaction. These include the increased synthesis of 32 kDa acidic polypeptides, together with the decrease in content of a major 95 kDa‐mannoprotein, gp95. Differential screening of a mycorrhiza cDNA library and large‐scale cDNA sequencing have allowed the characterization of several symbiosis‐regulated fungal genes coding for cell wall proteins (e.g. hydrophobins). In P. tinctorius, the content of hydrophobin transcripts is up‐regulated in aerial hyphae and during the mantle formation. The cell wall of the fungal partner therefore presents a novel protein composition, characteristic of the symbiotic status. A convergence of biochemical and molecular results now allows formulation of molecular models for the key role of the cell wall compartment in the early developmental stages of ectomycorrhiza formation. Clearly, we are only beginning to understand the formation of the symbiotic cell walls, their regulation and topologic specificity. Definitive information should emerge from biochemical, cytological and molecular analyses of the appropriate models.
Phylogeny of the Glomales: deciphering the past to understand the present
Authors: SIMON L. 
Published: April 2006

SummaryThe Glomales comprise more than 130 described species, presently classified in three families and five genera. Previous analysis of the sequence of the nuclear genes coding for the ribosornal small subunit rRNA (SSU) obtained from 12 isolates representing as many species generally corroborated the taxonomy based on morphological characters. As part of an ongoing effort to understand better the relationship between glomalean species, four new glomalean SSU sequences obtained in our laboratory are described, along with partial sequences from other laboratories. Using this enlarged dataset, a current phylogenetic tree of the Glomales was reconstructed. The dataset was also analysed to locate informative regions of the glomalean SSU that could be targeted by molecular ecologists studying the taxonomy, identification and ecology of arbuscular mycorrhizal fungi.
Inter‐ and intraspecific variation within the morphologically‐similar arbuscular mycorrhizal fungi Glomus mosseae and Glomus coronatum
Authors: DODD J. C. , ROSENDAHL S. , GIOVANNETTI M. , BROOME A. , LANFRANCO L. , WALKER C. 
Published: April 2006

SUMMARYThis collaborative investigation was aimed at using morphological and molecular characters to study inter‐ and intraspecific variation within isolates of Glomus mosseae and Glomus coronatum from different parts of the world. A secondary aim was to assess whether any divergence found was genetically based and/or correlated with the biogeographic origin of isolates. Morphological evaluations of various possible taxonomic characters including spore colour, size, sporocarp architecture and hyphal attachment morphology, showed that only spore colour could discriminate the two groups. Isozyme analysis of malate dehydrogenase and esterase loci clearly confirmed this grouping of the two species complexes. SDS profiles and cluster analysis showed the same separation on a selection of isolates from the two groups. A comparison of a representative isolate from the G. coronatum group (BEG 49) with other arbuscular mycorrhizal fungi using G. mosseae‐specific primers also provided evidence for separation of the two species complexes. The data and methodology employed provide a blueprint for future multimodal and multidisciplinary approaches to the unravelling of taxonomic problems within this ancient group of symbiotic fungi.