What happened to plant caspases?

The extent of conservation in the programmed cell death pathways that are activated in species belonging to different kingdoms is not clear. Caspases are key components of animal apoptosis; caspase activities are detected in both animal and plant cells. Yet, while animals have caspase genes, plants do not have orthologous sequences in their genomes. It is 10 years since the first caspase activity was reported in plants, and there are now at least eight caspase activities that have been measured in plant extracts using caspase substrates. Various caspase inhibitors can block many forms of plant programmed cell death, suggesting that caspase-like activities are required for completion of the process. Since plant metacaspases do not have caspase activities, a major challenge is to identify the plant proteases that are responsible for the caspase-like activities and to understand how they relate, if at all, to animal caspases. The protease vacuolar processing enzyme, a legumain, is responsible for the cleavage of caspase-1 synthetic substrate in plant extracts. Saspase, a serine protease, cleaves caspase-8 and some caspase-6 synthetic substrates. Possible scenarios that could explain why plants have caspase activities without caspases are discussed.     

Do “antisense proteins” exist?

A DNA double helix consists of two complementary strands antiparallel with each other. One of them is the sense chain, while the other is an antisense chain which does not directly involve the protein-encoding process. The reason that an antisense chain cannot encode for a protein is generally attributed to the lack of certain preconditions such as a promotor and some necessary sequence segments. Suppose it were provided with all these preconditions, could an antisense chain encode for an antisense protein? To answer this question, an analysis has been performed based on the existing database. Nine proteins have been found that have a 100% sequence match with the hypothetical antisense proteins derived from the knownEscherichia coli antisense chains.On sabbatical leave from Department of Physics, Tianjin University, Tianjin, China.     

Do strigolactones contribute to plant defence?

Strigolactones are multifunctional molecules involved in several processes outside and within the plant. As signalling molecules in the rhizosphere, they favour the establishment of arbuscular mycorrhizal symbiosis, but they also act as host detection cues for root parasitic plants. As phytohormones, they are involved in the regulation of plant architecture, adventitious rooting, secondary growth and reproductive development, and novel roles are emerging continuously. In the present study, the possible involvement of strigolactones in plant defence responses was investigated. For this purpose, the resistance/susceptibility of the strigolactone‐deficient tomato mutant Slccd8 against the foliar fungal pathogens Botrytis cinerea and Alternaria alternata was assessed. Slccd8 was more susceptible to both pathogens, pointing to a new role for strigolactones in plant defence. A reduction in the content of the defence‐related hormones jasmonic acid, salicylic acid and abscisic acid was detected by high‐performance liquid chromatography coupled to tandem mass spectrometry in the Slccd8 mutant, suggesting that hormone homeostasis is altered in the mutant. Moreover, the expression level of the jasmonate‐dependent gene PinII, involved in the resistance of tomato to B. cinerea, was lower than in the corresponding wild‐type. We propose here that strigolactones play a role in the regulation of plant defences through their interaction with other defence‐related hormones, especially with the jasmonic acid signalling pathway.     

Do human ‘life history strategies’ exist?

Interest in incorporating life history research from evolutionary biology into the human sciences has grown rapidly in recent years. Two core features of this research have the potential to prove valuable in strengthening theoretical frameworks in the health and social sciences: the idea that there is a fundamental trade-off between reproduction and health; and that environmental influences are important in determining how life histories develop. However, the literature on human life histories has increasingly travelled away from its origins in biology, and become conceptually diverse. For example, there are differences of opinion between evolutionary researchers about the extent to which behavioural traits associate with life history traits to form ‘life history strategies’. Here, I review the different approaches to human life histories from evolutionary anthropologists, developmental psychologists and personality psychologists, in order to assess the evidence for human ‘life history strategies’. While there is precedent in biology for the argument that some behavioural traits, notably risk-taking behaviour, may be linked in predictable ways with life history traits, there is little theoretical or empirical justification for including a very wide range of behavioural traits in a ‘life history strategy’. Given the potential of life history approaches to provide a powerful theoretical framework for understanding human health and behaviour, I then recommend productive ways forward for the field: 1) greater focus on the life history trade-offs which underlie proposed strategies; 2) greater precision when using the language of life history theory and life history strategies; 3) collecting more empirical data, from a diverse range of populations, on linkages between life history traits, behavioural traits and the environment, including the underlying mechanisms which generate these linkages; and 4) greater integration with the social and health sciences.     

Are metacaspases caspases?

The identification of caspases as major regulators of apoptotic cell death in animals initiated a quest for homologous peptidases in other kingdoms. With the discovery of metacaspases in plants, fungi, and protozoa, this search had apparently reached its goal. However, there is compelling evidence that metacaspases lack caspase activity and that they are not responsible for the caspaselike activities detected during plant and fungal cell death. In this paper, we attempt to broaden the discussion of these peptidases to biological functions beyond apoptosis and cell death. We further suggest that metacaspases and paracaspases, although sharing structural and mechanistic features with the metazoan caspases, form a distinct family of clan CD cysteine peptidases.     

Do rivers function as corridors for plant dispersal?

Abstract. We evaluated the importance of dispersal for species frequencies and distribution by comparing dispersal properties of vascular plant species with their frequencies along river banks. We assumed that species with long-floating seeds would be more frequent than species with short-floating seeds. We compiled data on frequencies of vascular plants and their dispersal properties from ten rivers in northern Sweden and compared these with boreal forests and grasslands in the same region. In all rivers, but in none of the reference areas, there was a positive relationship between floating capacity and frequency of species. A comparison of floating capacity between species with and without certain dispersal devices showed that seeds of vegetatively dispersed species had higher floating capacities than other seeds. For other dispersal categories (animal and wind dispersal), floating time did not differ from contrast groups. The results indicate that water dispersal has a certain role in structuring the riparian flora, and provide a basis for explaining species distribution patterns from dispersal characteristics. They also suggest that continuous river corridors are important for maintaining regional biodiversity.     

Do forest-dwelling plant species disperse along landscape corridors?

Woody corridors in fragmented landscapes have been proposed as alternative habitats for forest plants, but the great variation in species-specific responses blurs the overall assessment. The aim of this study was to estimate the dispersal success of forest-dwelling plants from a stand into and along an attached woody corridor, and to explain the observed patterns from the point of view of species’ dispersal traits and corridor properties. We sampled 47 forest–corridor transects in the agricultural landscapes of southeastern Estonia. Regionally common forest-dwelling species (observed in at least 10 % of seed-source forests) were classified on the basis of their ecological response profile—forest-restricted species (F-type) and forest-dwelling generalists (G-type). Species richness and the proportion of F-type species decreased sharply from the seed-source forest core to the forest edge and to the first 10–15 m of the corridor, while G-type species richness remained constant throughout the transect. Corridor structure had a species-specific effect—F species were promoted by old (≥50 years) and wide (≥10 m) corridors, while G species were supported by young and narrow corridors with ditch-related soil disturbances. Moderate shade (canopy cover <75 %) was optimal for all forest-dwelling species. Large dispersule weight, and not seed weight, dispersal vector or Ellenberg’s indicator values, was the trait that differentiated F species from G species. We conclude that most woody corridors are only dispersal stepping-stone habitats for habitat generalist species, and not for specialists. Only century old corridors can relieve the dispersal limitation of forest-restricted species.     

Do plant communities exist? Evidence from scaling‐up local species‐area relations to the regional level

Abstract. One long tradition in ecology is that discrete communities exist, at least in the sense that there are areas of relatively uniform vegetation, with more rapid change in species composition between them. The alternative extreme view is the Self‐similarity concept – that similar community variation occurs at all spatial scales. We test between these two by calculating species‐area curves within areas of vegetation that are as uniform as can be found, and then extrapolating the within‐community variation to much larger areas, that will contain many ‘communities’. Using the Arrhenius species‐area model, the extrapolations are remarkably close to the observed number of species at the regional/country level. We conclude that the type of heterogeneity that occurs within ‘homogeneous’ communities is sufficient to explain species richness at much larger scales. Therefore, whilst we can speak of ‘communities’ for convenience, the variation that certainly exists at the ‘community’ level can be seen as only a larger‐scale manifestation of micro‐habitat variation.     

Do fever and anapyrexia exist? Analysis of set point-based definitions

Fever and anapyrexia are the most studied thermoregulatory responses. They are defined as a body temperature (T(b)) increase and decrease, respectively, occurring because of a shift in the set point (SP) and characterized by active defense of the new T(b). Although models of T(b) control with a single SP (whether obvious or hidden) have been criticized, the SP-based definitions have remained unchallenged. In this article, the SP-based definitions of fever and anapyrexia were subjected to two tests. In test 1, they were compared with experimental data on changes in thresholds for activation of different thermoeffectors. Changes in thresholds were found compatible with an SP increase in some (but not all) cases of fever. In all cases of what is called anapyrexia, its mechanism (dissociation of thresholds of different effectors) was found incompatible with a decrease in a single SP. In test 2, experimental data on the dependence of T(b) on ambient temperature (T(a)) were analyzed. It was found that the febrile level of T(b) is defended in some (but not all) cases. However, strong dependence on T(a) was found in all cases of anapyrexia, which agrees with threshold dissociation but not with a decrease of the SP. It is concluded that fever (as defined) has only limited experimental support, whereas anapyrexia (as defined) does not exist. Two solutions are offered. A palliative is to accept that SP-based terms (anapyrexia, cryexia, regulated hypothermia, and such) are inadequate and should be abandoned. A radical solution is to transform all definitions based on comparing T(b) with the SP into definitions based on balancing active and passive processes of T(b) control.     

Do endotoxins devoid of 3-deoxy-D-manno-2-octulosonic acid exist?

After treatment with aqueous, 50% hydrofluoric acid, a well-known dephosphorylating agent, the presence of 3-deoxy-D-manno-2-octulosonic acid (KDO), an essential and characteristic constituent of endotoxins, can be readily demonstrated in reportedly KDO-deficient bacterial lipopolysaccharides.     

Does the natriuretic peptide system exist throughout the animal and plant kingdom?

Natriuretic peptides (NPs) and their receptors have been identified in vertebrate species ranging from elasmobranchs to mammals. Atrial, brain and ventricular NP (ANP, BNP and VNP) are endocrine hormones secreted from the heart, while C-type NP (CNP) is principally a paracrine factor in the brain and periphery. In elasmobranchs, only CNP is present in the heart and brain and it functions as a circulating hormone as well as a paracrine factor. Four types of NP receptors are cloned in vertebrates. NPR-A and NPR-B are guanylyl cyclase-coupled receptors, whereas NPR-C and NPR-D have only a short cytoplasmic domain. NPs are hormones important for volume regulation in mammals, while they act more specifically for Na(+) regulation in fishes. The presence of NP and its receptor has also been suggested in the most primitive vertebrate group, cyclostomes, and its molecular identification is in progress. The presence of ANP or its mRNA has been reported in the hearts and ganglia of various invertebrate species such as mollusks and arthropods using either antisera raised against mammalian ANP or rat ANP cDNA as probes. Immunoreactive ANP has also been detected in the unicellular Paramecium and in various species of plants including Metasequoia. Furthermore, the N-terminal prosegments of ANP, whose sequences are scarcely conserved even in vertebrates, have also been detected by the radioimmunoassay for human ANP prosegments in all invertebrate and plant species examined including Paramecium. Although these data are highly attractive, the current evidence is too circumstantial to be convincing that the immunoreactivity truly originates from ANP and its prosegments in such diverse organisms. The caution that has to be exercised in identification of vertebrate hormones from phylogenetically distant organisms is discussed.     

Do endogeic earthworms change plant competition? A microcosm study

Plants compete for limited resources. Although nutrient availability for plants is affected by resource distribution and soil organisms, surprisingly few studies investigate their combined effects on plant growth and competition. Effects of endogeic earthworms (Aporrectodea jassyensis), root-knot nematodes (Meloidogyne incognita) and the spatial distribution of ¹⁵N labelled grass litter on the competition between a grass (Lolium perenne), a forb (Plantago lanceolata) and a legume (Trifolium repens) were investigated in the greenhouse. Earthworms promoted N uptake and growth of L. perenne. Contrastingly, shoot biomass and N uptake of T. repens decreased in the presence of earthworms. P. lanceolata was not affected by the earthworms. We suggest that earthworms enhanced the competitive ability of L. perenne against T. repens. Nematodes increased the proportion of litter N in each of the plant species. Litter distribution (homogeneous vs. patch) did not affect the biomass of any plant species. However, P. lanceolata took up more ¹⁵N, when the litter was homogeneously mixed into the soil. The results suggest that endogeic earthworms may affect plant competition by promoting individual plant species. More studies including decomposers are necessary to understand their role in determining plant community structure.     

Do Sebacinales commonly associate with plant roots as endophytes?

Sebacinales are basal Hymenomycetes with diverse mycorrhizal abilities, ranging from ectomycorrhizae to ericoid and orchid mycorrhizae. Several previous PCR or isolation works raised the possibility that Sebacinales are endophytes in plant roots. We tested this hypothesis in an isolation-independent approach by using specific PCR primers for ribosomal DNA of Sebacinales on AM mycorrhizal or non-mycorrhizal roots. Thirty-nine plant species were sampled on a Caribbean and two European sites (3 repetition per species and site), covering 25 families in monocots and eudicots. PCR signals were obtained from 40 samples (28.9 %) from 27 species (69.2 %) and all sites. Whenever sequencing was successful, a sequence belonging to Sebacinales was recovered. A phylogenetic approach revealed that 13 of them belonged to clade B (encompassing ericoid and orchid mycorrhizal species) and 4 to clade A (usually encompassing only ectomycorrhizal species). These data suggest that Sebacinales may be endophytic in many angiosperm roots, and that this condition is plesiomorphic in Sebacinales. They bridge the gap between physiological studies, inoculating Sebacinales (Piriformospora indica or Sebacina vermifera) on diverse plants and molecular ecology, hitherto restricting Sebacinales to mycorrhizal interactions. Structural and functional aspects of the interaction deserve further studies.     

Do plant parts compete for resources? An evolutionary viewpoint

Simultaneously growing sinks are thought to compete for plant resources. Negative correlations, for example between grain number and stem mass in cereals, indeed resemble competition; but is the notion of intra-plant competition evolutionarily justified? Here we review intra-plant competition in light of two aspects of evolutionary biology: (a) major transitions that led to the reorganization of evolutionary individuals (e.g. isolated DNA molecules and independent cells) into new units of adaptation (e.g. chromosomes and multicellular organisms) with associated constraints to intra-individual conflict; and (b) genomic conflicts within individual plants with implications for resource allocation. Against this background, we look at apparent competition among genetically identical plant parts, and conclude that plants might use competition-like mechanisms to allocate resources, but only to the extent that these proximate mechanisms enhance overall plant fitness. In dealing with apparent competition among genetically different plant structures, we emphasize developing seeds attached to the same maternal plant, and the determination of yield components in annual crops. We propose that competition-like mechanisms among genetically different plant parts have been strongly shaped by the evolution of genomic conflict between parent and offspring, between female and male parents, and among siblings. By defining the number and potential size of grain simultaneously and before fertilization, a strong maternal control of resource allocation is exerted that favours uniform offspring size and partially counteracts genomic conflict.     

Do tomatoes on the plant behave as climacteric fruits?

I considered the possibility that changes in fruit photosynthesis obscure the occurrence of the climacteric rise in respiration in tomato fruits attached to the plant. Internal CO₂ and ethylene concentrations in tomatoes ( Lycopersicon esculentum Mill. cv. OH 7814) were analyzed after direct sampling through polyethylene tubes implanted in the external pericarp. Fruits which were shaded with aluminium foil contained up to 60 ml 1⁻¹ CO₂, until the internal ethylene concentration exceeded 1 μl l⁻¹, when CO₂ concentration declined to below 40 ml l⁻¹; the CO₂ concentration in fruits exposed to light only occasionally exceeded 40 ml 1⁻¹. The internal CO₂ concentration of detached fruits first declined and then increased along with ethylene concentration, as expected for the climacteric. Detached green fruits under continuous low photosynthetic photon flux density (100 μmol m⁻² s⁻¹) contained almost no internal CO₂ and produced no CO₂. Changes in photosynthesis and an associated CO₂-generating system in green fruits are thought to obscure the climacteric rise in tomato fruits developing on the plant.     

Do plant mites commonly prefer the underside of leaves?

The adaxial (upper) and abaxial (lower) surfaces of a plant leaf provide heterogeneous habitats for small arthropods with different environmental conditions, such as light, humidity, and surface morphology. As for plant mites, some agricultural pest species and their natural enemies have been observed to favor the abaxial leaf surface, which is considered an adaptation to avoid rain or solar ultraviolet radiation. However, whether such a preference for the leaf underside is a common behavioral trait in mites on wild vegetation remains unknown. The authors conducted a 2-year survey on the foliar mite assemblage found on Viburnum erosum var. punctatum, a deciduous shrub on which several mite taxa occur throughout the seasons, and 14 sympatric tree or shrub species in secondary broadleaf-forest sites in Kyoto, west–central Japan. We compared adaxial–abaxial surface distributions of mites among mite taxa, seasons, and morphology of host leaves (presence/absence of hairs and domatia). On V. erosum var. punctatum, seven of 11 distinguished mite taxa were significantly distributed in favor of abaxial leaf surfaces and the trend was seasonally stable, except for Eriophyoidea. Mite assemblages on 15 plant species were significantly biased towards the abaxial leaf surfaces, regardless of surface morphology. Our data suggest that many mite taxa commonly prefer to stay on abaxial leaf surfaces in wild vegetation. Oribatida displayed a relatively neutral distribution, and in Tenuipalpidae, the ratio of eggs collected from the adaxial versus the abaxial side was significantly higher than the ratio of the motile individuals, implying that some mite taxa exploit adaxial leaf surfaces as habitat.     

Do different speed types of action potentials exist in higher plants?

The problem of paradoxically different values of speeds of the propagation of action potentials in conduction pathways of higher plants is considered. Possible causes of this phenomenon are discussed.