Allocation, plasticity and allometry in plants

Allocation is one of the central concepts in modern ecology, providing the basis for different strategies. Allocation in plants has been conceptualized as a proportional or ratio-driven process (‘partitioning’). In this view, a plant has a given amount of resources at any point in time and it allocates these resources to different structures. But many plant ecological processes are better understood in terms of growth and size than in terms of time. In an allometric perspective, allocation is seen as a size-dependent process: allometry is the quantitative relationship between growth and allocation. Therefore most questions of allocation should be posed allometrically, not as ratios or proportions. Plants evolve allometric patterns in response to numerous selection pressures and constraints, and these patterns explain many behaviours of plant populations.

In the allometric view, plasticity in allocation can be understood as a change in a plant's allometric trajectory in response to the environment. Some allocation patterns show relatively fixed allometric trajectories, varying in different environments primarily in the speed at which the trajectory is travelled, whereas other allocation patterns show great flexibility in their behaviour at a given size. Because plant growth is often indeterminate and its rate highly influenced by environmental conditions, ‘plasticity in size’ is not a meaningful concept. We need a new way to classify, describe and analyze plant allocation and plasticity because the concepts ‘trait’ and ‘plasticity’ are too broad. Three degrees of plasticity can be distinguished: (1) allometric growth (‘apparent plasticity’), (2) modular proliferation and local physiological adaptation, and (3) integrated plastic responses. Plasticity, which has evolved because it increases individual fitness, can be a disadvantage in plant production systems, where we want to optimize population, not individual, performance.     

C-terminal actin-binding sites of smooth muscle caldesmon switch actin between conformational states

Caldesmon is a component of the thin filaments of smooth muscles where it is believed to play an essential role in regulating the thin filaments’ interaction with myosin and hence contractility. We studied the effects of caldesmon and two recombinant fragments CaDH1 (residues 506–793) and CaDH2 (residues 683–767) on the structure of actin–tropomyosin by making measurements of the fluorescence polarisation of probes specifically attached to actin. CaDH1, like the parent molecule caldesmon, is an inhibitor of actin–tropomyosin interaction with myosin whilst CaDH2 is an activator. The F-actin in permeabilised and myosin free rabbit skeletal muscle ‘ghost’ fibres was labelled by tetramethyl rhodamine-isothiocyanate (TRITC)–phalloidin or fluorescein-5′-isothiocyanate (FITC) at lysine 61. Fluorescence polarisation measurements were made and the parameters Φ_A, Φ_E, Θ_1/2 and N were calculated. Φ_A and Φ_E are angles between the fiber axis and the absorption and emission dipoles, respectively; Θ_1/2 is the angle between the F-actin filament axis and the fiber axis; N is the relative number of randomly oriented fluorophores. Actin–tropomyosin interaction with myosin subfragment-1 induced changes in the parameters of the polarised fluorescence that are typical of strong binding of myosin to actin and of the ‘on’ conformational state of actin. Caldesmon and CaDH1 (as well as troponin in the absence of Ca²⁺) diminished the effect of S-1, whereas CaDH2 (as well as troponin in the presence of Ca²⁺) enhanced the effect of S1. Thus the structural evidence correlates with biochemical evidence that C-terminal actin-binding sites of caldesmon can modulate the structural transition of actin monomers between ‘off’ (caldesmon and CaDH1) and ‘on’ (S-1 and CaDH2) states in a manner analogous to troponin.     

Plant-parasite interactions: has the gene-for-gene model become outdated?

The detection of pathogens by plants is often described as a ‘gene-for-gene’ interaction.

However, recent work from several laboratories indicates that, in some instances, a single gene product in the plant can mediate the recognition of multiple pathogen signals, and that multiple plant genes are required for the recognition of, and response to, a single pathogen signal.     

Fibre type characteristics and function of the human paraspinal muscles: normal values and changes in association with low back pain

This review focuses on the role of the paraspinal muscles in relation to the development and existence of low back pain. It begins with a discussion of the deficits in paraspinal muscle strength and fatigue-resistance observed in low back pain patients and addresses the issue of ‘cause or effect’ with respect to muscle dysfunction and back pain. Our current knowledge regarding the ‘normal’ fibre type characteristics of the human erector spinae is then presented and the influence of these fibre type characteristics on the muscle's performance capacity is discussed. Alterations in the ‘microanatomy’ of the musculature in connection with low back pain, and the associated implications for the performance capacity of the patient, are then considered. Finally, a number of outstanding issues in relation to the clinical significance of back muscle dysfunction are identified, leading to the proposal of areas for future research.     

Universal inheritable barcodes for identifying organisms

The needs for recognition of novel conventional or transgenic organisms include protection of patented or Identity Preserved lines, detecting transgenics and tracing dispersal. We propose simple ‘Biobarcodes™’ using universal PCR primers to recognize the universal ‘nonsense’ recognition site of all biobarcodes, followed by a variable nonsense sequence. The proposed sequences are long enough to allow recognition in spite of mutations, have stop codons to prevent coding, and will not self anneal. Sequences of PCR-amplified biobarcodes can be compared to a universal database.     

Photoacoustic detection of photosynthetic activities in isolated broken chloroplasts

Methodology and demonstration how to utilize the photoacoustic technique in photosynthesis research are presented. Photoacoustic signals were obtained from suspensions of isolated broken chloroplasts. In the presence of strong, continuous (non-modulated) background light the signals were normally larger than without the background light. The effect of the background light was saturable and was absent when non-active (e.g. heat-treated) samples were used, showing that the normal smaller signal in the absence of background light is a genuine reflection of the loss of heat due to the competing photochemistry. The effect of the background light is to close the reaction-centers and hence to inhibit the photochemical process. The percent difference of the photoacoustic signal (± background light) is taken as a measure of the photochemical activity (‘photochemical loss’).

Initial results demonstrate the wavelength dependence of the ‘photochemical loss’. As expected there was a ‘red-drop’ decrease of the ‘photochemical loss’ for λ > 690 nm, when the cofactor methyl viologen was present. Surprisingly, however, there was a ‘red-rise’ increase for λ > 690 nm when no cofactor was present. These findings indicate that under the last conditions there is an unsuspected photoactivity of PS I which was not detected hitherto by the conventional techniques. The dependence on the background light intensity confirms this result. This photoactivity can be explained tentatively as a cyclic electron flow around PS I, present without any added cofactor.

Initial results on the modulation frequency dependence in the presence of electron acceptors are also demonstrated.     

Effect of epiphytes on the extent of necrotic injuries of resistant and susceptible poplar clones infected with Dothichiza populea.

Poplar cuttings of a resistant clone, Populus ‘Grandis’, and susceptible clones, Populus nigra ‘Italica’ and Populus ‘Robusta’, were infected with the pathogenic fungus Dothichiza populea alone, or with the pathogen and one of five strains of epiphytes antagonistic towards it (in vitro), isolated from poplar bark. The extent of injury was examined for 28 days after infection by determining the length of necrotic patches and their area as expressed in per cent of the total area of a cutting or the area of necrotic injuries caused by the pathogen alone.

All the poplar cuttings of both the resistant and susceptible clones became diseased when infected with the pathogen alone. Surprisingly enough, however, the least affected clone was the susceptible P. ‘Robusta’, in which necrotic injuries covered 28% of the total area, as against 40% and 70% in the resistant P. ‘Grandis’ and the susceptible P. nigra ‘Italica’, respectively.

When the cuttings were infected simultaneously with Dothichiza populea and its antagonistic epiphytes, the diseased area in the resistant clone diminished by as much as two-thirds, and in the susceptible P. nigra ‘Italica’, by one-third in comparison with the area affected by the pathogen alone. In turn, in the susceptible P. ‘Robusta’ the introduction of three out of five epiphytes stimulated the growth of the pathogenic fungus producing on average a double increase in the necrotic area. The differences in the response of the pathogen to the presence of epiphytes recorded in the susceptible clones indicate a marked influence of the plant on the nature of interactions between its epiphytic microflora and the pathogen.     

X-ray absorption fine structure study of the atomic and electronic structure of molybdenum disulfide intercalation compounds with transition metals

The local structures of ‘host’ and ‘guest’ layers of MoS₂ intercalated with M(OH)₂ (M=Mn, Co and Ni) prepared via interaction of single-layer MoS₂ dispersions and solutions of M²⁺ salts were studied by X-ray absorption spectroscopy. According to M K-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) results, the electronic structure and atomic environment of the M atoms in the intercalates are similar to that of the crystalline hydroxides M(OH)₂. In the Ni intercalate, Mo K-edge EXAFS revealed a structural change of the ‘host’ MoS₂ layers similar to that reported for water dispersions of MoS₂ single layers. S K-edge XANES data indicate that the change is associated with increased electron density on the S atoms in the matrix. SO₄²⁻ and Mo″⁻ (4 < n < 6) were detected in the intercalated materials exposed to air, suggesting that transition metal intercalation may increase the susceptibility of the MoS₂ layers to oxidation.     

'P' solubilization potential of plant growth promoting Pseudomonas mutants at low temperature

Pseudomonas fluorescens strain GRS₁, PRS₉ and their cold tolerant mutants were examined for their tricalcium phosphate (TCP) solubilizing activity in NBRIP (broth) media at 10°C and 25°C. Invariably, all the cold tolerant mutants of GRS₁ and PRS₉ were found more efficient than their respective wild type counterparts for ‘P’ solubilization activity at 10°C as compared to 25°C. ‘P’ solubilization potential of CRM was found maximum among all the strains followed by CRPF₆ and CRPF₄. To the best of out knowledge, this is the first report regarding low temperature ‘P’ solubilization activity.     

The two-step model of bacterial UV mutagenesis

Recent results are discussed which have led to a two-step model for UV mutagenesis in excision-deficient Escherichia coli. After exposure to UV, the replication fork is assumed to continue until immediately before certain photoproducts where it stops and leaves a gap which cannot be dealt with by recombination repair. In the first (misincorporation) step, bases (a proportion of which are ‘wrong’) are postulated to be inserted opposite the photoproduct under the direct influence of the recA gene product. These misincorporated bases can be revealed as mutations by delayed photoreversal in umuD, C and lexA (ind⁻) bacteria. Their level is determined by the particular allele of recA that is present (recA441 > recA⁺ > recA430) and their rate of formation by the amount of recA protein in the cell and the degree of enrichment of the medium. No other protein needs to be synthesized for this step to occur. The second (bypass) step requires induced levels of the products of the umuD and C genes which are postulated to facilitate continued DNA synthesis on the priming end opposite the photoproduct. In principle, further errors could be made at this stage which might appear as ‘hitch-hiking’ rather than ‘targeted’ mutations.