Bromeliads provide shelter against fire to mutualistic spiders in a fire‐prone landscape

1. A key challenge in the study of mutualistic interactions is understanding sources of variation that strengthen or weaken these interactions. In spider–plant mutualisms, spiders benefit plants by improving plant nutrition and protecting plants from herbivory. Although the benefits of plants to spider growth and survival are often claimed, they are rarely demonstrated. 2. In this study, empirical evidence is provided that bromeliads (Bromelia balansae, Bromeliaceae) are essential for the resilience of the mutualistic bromeliad‐living jumping spider populations (Psecas chapoda, Salticidae) after a fire event, sheltering spiders from the heat of the flames. 3. Spider populations were compared before and after a natural fire event and it was shown that spiders of different ages survived the fire. The survival of such individuals allowed the population of P. chapoda spiders to recover rapidly, returning to pre‐fire levels in 5 months. 4. Bromeliads reduced the susceptibility of P. chapoda spiders to burning, and this mutualistic relationship contributed to the resilience of the spider population after a fire event. It is suggested that frequent fires in fire‐prone landscapes may have strengthened this spider–plant relationship, contributing to the maintenance and evolution of this association.     

The Association of Clover Proliferation Phytoplasma with Stolbur Disease of Pepper in Spain

A phytoplasma disease, `stolbur', affects pepper ( Capsicum annuum ) in Spain. Affected plants have short internodes, green flowers buds and other symptoms that are characteristic of phytoplasma-induced diseases. Herein the detection and classification of the phytoplasma that may cause the disease is reported. DNA amplification by polymerase chain reaction, sequencing and phylogenetic analysis indicate that this phytoplasma should be classified in the clover proliferation group 16SrVI, a group that is clearly distinct from the stolbur group 16SrXII.     

TRAINING, VALIDATION AND MAINTENANCE OF A PANEL TO EVALUATE THE TEXTURE OF DRY BEANS (PHASEOLUS VULGARIS L.)

The inclusion of dry beans in diets has clear health benefits. However, consumers in developed countries mainly choose beans for their sensory qualities, especially for their texture. This article describes the constitution, training and validation of a panel of judges to evaluate the texture of dry beans. The judges were trained in the perception of different textures, analyzed a wide range of beans and selected seed-coat roughness, seed-coat perceptibility and creaminess/mealiness of the cotyledon as the main attributes to be scored. After training, the panel was capable of discriminating between different varieties of beans and even between beans of the same variety grown at different locations. The analysis of the behavior of the panel in a standard tasting session 2 years after its formation showed that periodic inclusion of samples from the extremes of the scales for the attributes during tasting sessions was sufficient to keep the panel trained.

PRACTICAL APPLICATIONS

This article could serve as a guide for the training of sensory panels to evaluate the texture of dry beans. It describes the selection of the attributes on which the analysis is based, references for the extreme values of the attributes and how to train the panel. It also provides a practical example of the analysis of the behavior of the panel some time after training.     

Prolongation of Embryo Sac Viability in Pear (Pyrus communis) Following Pollination or Treatment with Gibberellic Acid

Embryo sac development has been investigated in unpollinated,cross pollinated and gibberellic acid (GA₂) treated flowersof Pyrus communis L. While pollination and GA₃ treatments donot alter embryo sac development, they prolong embryo sac viability.In untreated unpollinated flowers, ovules degenerate between12 and 21 d after anthesis, while in cross pollinated and GA₃treated flowers this degeneration is postponed by about 10 d.Thus, in a cross pollinated flower this extends the period overwhich a successful fertilization can take place. This increasedperiod of viability is accompanied by an elongation of the embryosac itself. Elongation takes place two weeks prior to fertilizationin cross pollinated flowers. The extension of life span of embryo sacs following pollinationand treatment with gibberellic acid indicates that a stimulusinduced by ‘pollination’ could be mediated by GA₃Whatever its mechanism of operation, the prolongation of embryosac viability by pollination represents a selective advantage,in that the period at which the ovules are receptive to fertilizationmust be significantly extended. Embryo sac, gibberellic acid, Pyrus communis, pear, pollination     

Mini-exon Gene Sequences Define Six Groups within the Genus Crithidia

ABSTRACT. To develop molecular markers for lower trypanosmatids, we have examined the mini-exon gene repeats of 17 isolates that were classified as Crithidia by traditional methods. Representative repeats were amplified by polymerase chain reaction and the amplification products were cloned and used as hybridization probes against genomic DNA. Six hybridization groups of Crithidia were defined on the basis of the DNA blotting experiments. The three endosymbiont-bearing species ( C. deanei, C. desouzai and C. oncopelti ) and C. acanthocephali each belonged to single-member hybridization groups, while the C. fasciculata group contained additional named and undesignated species. The Crithidia lucilae thermophila probe hybridized to multiple undesignated isolates. The DNA sequence of the cloned products revealed that the specificity of the hybridization probes was due to substantial differences in the intron and the non-transcribed spacer regions. These data indicate substantial heterogeneity within the mini-exon gene locus of the taxon Crithidia .     

Non-functional flowers in Cat as e turn orchids (Gatasetinae, Orchidaceae)

ROMERO, G. A., 1992. Non-functional flowers in Catasetum orchids (Catasetinae, Orchidaceae). Plants of the genus Catasetum generally produce unisexual, dimorphic flowers but occasionally bear intermediate, polymorphic flowers. Staminate (male) flowers are commonly produced both in cultivation and in nature. Within the genus, the morphology, texture, resupination, and colour of male flowers are extremely variable. Pistillate (female) flowers, in contrast, are rarely produced in cultivation and in nature and have relatively constant morphology, texture, resupination and colour. Intermediate, polymorphic flowers are extremely rare, ranging in morphology from male-like to female-like, often combining characters of both. Some are bilaterally half male and half female. Intermediate flowers have previously been regarded as functionally hermaphroditic but evidence presented here shows that in Catasetum male and female functions appear to be mutually exclusive. Intermediate flowers that approach the morphology of female flowers may bear seeds but do not have functional pollinaria; those that approach male flower morphology do not have functional stigmas and seldom have functional pollinaria. The vast majority of Catasetum intermediate flowers are sterile. The absence of truly hermaphroditic flowers in Catasetum is important in the interpretation of evidence for gender choice in this genus, as flowers and/or plants can be unequivocally scored as either functionally male or female.     

Microtubular Systems of Paramecium in Division: Pattern of Cytospindle Assembly

The pattern of cytospindle assembly and the modifications of the microtubular cytoplasmic network during division of Paramecium are studied by means of indirect immunofluorescence. The assembly of cytospindle starts at two independent areas placed respectively around the proter's and opisthe's buccal overture. The moment of the microtubule bundles’appearance depends on their distance from the buccal opening, with those closest appearing 1st. The existence of microtubule organizing centers that act transiently during division of Paramecium is discussed.     

Spatial and temporal variability of fires in relation to ecosystems,land tenure and rainfall in savannas of northern South America

Fire is a predominant factor forcing global terrestrial biomass dynamics, with more than 30% of the land surface showing frequent burning, particularly in the tropics, where it mostly affects savannas ecosystems annually. Savannas, which cover approximately 269 million ha in South America, play a major role in the global carbon cycle. They are affected by increasing human pressures and global climate change. Using satellite data, this study quantifies vegetation burning in the Colombian Llanos savannas for the period 2000–2008, and analyzes how fire spatial pattern, frequency and extent vary with ecosystem type, land tenure and rainfall. On average 2.75±0.5 million ha (24±4.2%) of the savannas burn each year. Burned area is highly variable, with 3.4 million ha burned in 2002–2003 and <1.9 million ha in 2005–2006. However, during the 2000–2008 period near of 3.7 million ha (33.5%) of the savannas never burned. Compared with the average 8–10 years of fire return time for the tropics and subtropics, these savannas burn twice as often. In addition, the average burn size figure for tropical and subtropical grassland savannas (with <5% trees) of 7000 ha (median 5000 ha), is about seven times the average burned patch size we found in our study. Fires predominate in the well‐drained high plain savannas, lowest figures occurring along the Andean foothills, in forested areas and in pasture and croplands. Annual proportion burned varies with land tenure, being highest in National Parks. This study is the first complete regional map of fire disturbance in a South American savanna. This detailed regional data provides a unique opportunity for increasing the accuracy of global carbon emission calculations.     

The long-term effect of artificial destratification on phytoplankton species composition in a subtropical reservoir

1. The response of phytoplankton to the installation of an artificial destratification system in North Pine Dam, Brisbane (Australia) was investigated over an 18 year period (1984–2002); 11 years before and 7 years after installation. 2. An overall increase in phytoplankton abundance was revealed for some groups (in particular, diatoms, cyanobacteria and chlorophytes), but not for others (chlorophytes). Changes in the abundance of chlorophyte functional groups was attributed to eutrophication. 3. A strong spatial gradient in phytoplankton abundance and chlorophyll a was observed, with low abundance in the downstream regions affected by the destratification system which was likely because of light limitation induced by vertical mixing. The upstream region acted as a surrogate for the unaltered state of the reservoir, particularly as an indicator of eutrophication without direct influence from the destratification system. Despite the continuous trend in eutrophication of the reservoir, there has been a definite decrease in the rate of eutrophication (approximately 30%) since the installation of the destratification system at the downstream locations. 4. Correlations of the dominant cyanobacteria Cylindrospermopsis raciborskii with other genera changed after destratification, indicating that prior to destratification the dominance of Cylindrospermopsis was because of its ability to compete for phosphorus, whereas after destratification its dominance was because of its ability to compete for light.     

Ultrastructural Organization of Leaves of Transgenic Tobacco Overexpressing Histone H1 from Arabidopsis thaliana

We investigated the anatomical and ultrastructural featuresof transgenic tobacco plants that overexpressed a gene of histoneH1 from Arabidopsis thaliana. The overexpression of the heterologousgene resulted in more than a 2.5-fold increase over the physiologicallevel of the histone H1:DNA ratio in chromatin. H1-overexpressingplants had a distinct mutant phenotype characterized by dwarfappearance and severely hampered flowering. These changes wereaccompanied by extensive and unusual heterochromatinizationof nuclei occurring in all leaf parenchymal cells but not inleaf epidermal cells. The observed anomalies in the growth rateand size of the cells and in nuclei/chloroplast proportionsin histone H1-overexpressing plants suggest that the H1:DNAratio can influence some specialized cellular functions involvingthe cytoskeleton, and nuclear/organellar interactions whichare of importance for the normal development of a plant. Copyright1999 Annals of Botany Company Transgenic tobacco plant, histone H1 overexpression, heterochromatinization.