Is phylogeny driving tendon length in lizards?

Tulli, M.J., Herrel, A., Vanhooydonck, B. and Abdala, V. 2012. Is phylogeny driving tendon length in lizards?—Acta Zoologica (Stockholm) 93 : 319–329. Tendons transmit tensile forces generated by muscles and are a crucial part of the musculoskeletal system in vertebrates. Because tendons and tendon cells respond to altered mechanical load by increasing collagen synthesis, we hypothesized that a correlation between tendon morphology and the loading regime imposed by locomotor style or habitat use exists. This makes tendons an interesting model for studying the relationship between morphology and environment. In this study, we compare the general morphology of the palmar flexor plate, the length of the digital tendons, and the length of the flexor carpi ulnaris tendon in species of lizards that exploit a variety of structural habitats. The results from statistical analyses show that phylogenetic relatedness has a major impact on our ability to detect differences between habitat groups, and no differences in tendon length could be detected between iguanian species occupying different habitats when taking into account the relatedness between species. Our data for lizards diverge from the general mammalian paradigm where variation in tendon is often associated with habitat use or locomotor style.     

Concerning “long wave length” pigments in algae

Summary Chlorophyll complexes with absorption maxima at 710 m have been observed in certain mutant strains of Chlorella pyrenoidosa. Certain properties of these complexes are described, and some biological activities of far red light are discussed.Dedicated to Professor Dr. E. G. Pringsheim on the occasion of his 80th birthday.     

Structural deformations and bond length alternation in porphyrin π-cation radicals

This review discusses the structural changes that occur when the porphyrin ring of metalloporphyrin complexes is oxidized to form a pi-cation radical species. Although various differences in core conformation between the pi-cation derivative and the unoxidized homologue have been observed, there does not appear to be a general pattern of change. A frequently observed feature in pi-cation derivatives is the appearance of an alternating bond distance pattern in the inner ring of the porphyrin consistent with a localized structure rather the delocalized structure usually seen. The pattern, first seen in cofacial dimeric structures, has now been seen in monomeric systems as well. The nature and frequency of the observation and possible explanation are given.     

What drives activation-dependent shifts in the force–length curve?

Skeletal muscles are rarely recruited maximally during movement. However, much of our understanding of muscle properties is based on studies using maximal activation. The effect of activation level on skeletal muscle properties remains poorly understood. Muscle optimum length increases with decreased activation; however, the mechanism responsible is unclear. Here, we attempted to determine whether length-dependent calcium effects, or the effect of absolute force underpin this shift. Fixed-end contractions were performed in frog plantaris muscles at a range of lengths using maximal tetanic (high force, high calcium), submaximal tetanic (low force, high calcium) and twitch (low force, low calcium) stimulation conditions. Peak force and optimum length were determined in each condition. Optimum length increased with decreasing peak force, irrespective of stimulation condition. Assuming calcium concentration varied as predicted, this suggests that absolute force, rather than calcium concentration, underpins the effect of activation level on optimum length. We suggest that the effect of absolute force is due to the varying effect of the internal mechanics of the muscle at different activation levels. These findings have implications for our understanding of in vivo muscle function and suggest that mechanical interactions within muscle may be important determinants of force at lower levels of activation.     

The length–tension curve in muscle depends on lattice spacing

Classic interpretations of the striated muscle length–tension curve focus on how force varies with overlap of thin (actin) and thick (myosin) filaments. New models of sarcomere geometry and experiments with skinned synchronous insect flight muscle suggest that changes in the radial distance between the actin and myosin filaments, the filament lattice spacing, are responsible for between 20% and 50% of the change in force seen between sarcomere lengths of 1.4 and 3.4 µm. Thus, lattice spacing is a significant force regulator, increasing the slope of muscle''s force–length dependence.     

Increased thorn length in Acacia depranolobium —an induced response to browsing

Summary I report here longer thorns induced by large mammal herbivory on the tree Acacia depranolobium. I compared trees that had been browsed by domestic goats to trees protected from goat browsing. Thorns on browsed branches within the reach of goats (<125 cm above the ground) were significantly longer than thorns from higher branches on the same browsed trees, and significantly longer than branches at similar heights on unbrowsed trees. It appears that increased thorn length was an induced response to large mammal herbivory in Acacia depranolobium, both among and within individual trees.     

Sarcomere length nanometry in rat neonatal cardiomyocytes expressed with α-actinin–AcGFP in Z discs

Nanometry is widely used in biological sciences to analyze the movement of molecules or molecular assemblies in cells and in vivo. In cardiac muscle, a change in sarcomere length (SL) by a mere ∼100 nm causes a substantial change in contractility, indicating the need for the simultaneous measurement of SL and intracellular Ca²⁺ concentration ([Ca²⁺]_i) in cardiomyocytes at high spatial and temporal resolution. To accurately analyze the motion of individual sarcomeres with nanometer precision during excitation–contraction coupling, we applied nanometry techniques to primary-cultured rat neonatal cardiomyocytes. First, we developed an experimental system for simultaneous nanoscale analysis of single sarcomere dynamics and [Ca²⁺]_i changes via the expression of AcGFP in Z discs. We found that the averaging of the lengths of sarcomeres along the myocyte, a method generally used in today’s myocardial research, caused marked underestimation of sarcomere lengthening speed because of the superpositioning of different timings for lengthening between sequentially connected sarcomeres. Then, we found that after treatment with ionomycin, neonatal myocytes exhibited spontaneous sarcomeric oscillations (cell-SPOCs) at partial activation with blockage of sarcoplasmic reticulum functions, and the waveform properties were indistinguishable from those obtained in electric field stimulation. The myosin activator omecamtiv mecarbil markedly enhanced Z-disc displacement during cell-SPOC. Finally, we interpreted the present experimental findings in the framework of our mathematical model of SPOCs. The present experimental system has a broad range of application possibilities for unveiling single sarcomere dynamics during excitation–contraction coupling in cardiomyocytes under various settings.     

Does limb length predict the relative energetic cost of locomotion in mammals?

Do relatively longer limbs result in a lower energetic cost of locomotion? To determine whether or not cost is correlated with limb length in some way other than that due to their respective relationships to body mass, we have removed the effects of size by calculating the residuals of the relationship between each character and body size. We then regressed the pairs of residuals on one another. Because biological variables do not occur in a series of units that have evolved independently, the degree of divergence of two species is likely to be influenced by the length of time since they last shared a common ancestor. We therefore corrected for the phylogenetic relatedness of species. Data on the energetic cost of locomotion of a wide variety of species were taken from published sources. Data on limb lengths were taken from specimens in various museum collections which were similar in body mass (± 12%) to the specimens on which the cost measurements were made. None of the correlations between the residuals of either fore- or hindlimb length and neither of two estimates of the cost of locomotion was significant at P = 0.05. It is concluded that limb length does not importantly influence an animal's locomotor efficiency. These results do not imply the lack of a close relationship between cost and stride length.     

Probing solvation decay length in order to characterize hydrophobicity-induced bead–bead attractive interactions in polymer chains

In this paper, we quantitatively demonstrate that exponentially decaying attractive potentials can effectively mimic strong hydrophobic interactions between monomer units of a polymer chain dissolved in aqueous solvent. Classical approaches to modeling hydrophobic solvation interactions are based on invariant attractive length scales. However, we demonstrate here that the solvation interaction decay length may need to be posed as a function of the relative separation distances and the sizes of the interacting species (or beads or monomers) to replicate the necessary physical interactions. As an illustrative example, we derive a universal scaling relationship for a given solute–solvent combination between the solvation decay length, the bead radius, and the distance between the interacting beads. With our formalism, the hydrophobic component of the net attractive interaction between monomer units can be synergistically accounted for within the unified framework of a simple exponentially decaying potential law, where the characteristic decay length incorporates the distinctive and critical physical features of the underlying interaction. The present formalism, even in a mesoscopic computational framework, is capable of incorporating the essential physics of the appropriate solute-size dependence and solvent-interaction dependence in the hydrophobic force estimation, without explicitly resolving the underlying molecular level details.     

Is telomere length a molecular marker of past thermal stress in wild fish?

Telomeres protect eukaryotic chromosomes; variation in telomere length has been linked (primarily in homoeothermic animals) to variation in stress, cellular ageing and disease risk. Moreover, telomeres have been suggested to function as biomarker for quantifying past environmental stress, but studies in wild animals remain rare. Environmental stress, such as extreme environmental temperatures in poikilothermic animals, may result in oxidative stress that accelerates telomere attrition. However, growth, which may depend on temperature, can also contribute to telomere attrition. To test for associations between multitissue telomere length and past water temperature while accounting for the previous individual growth, we used quantitative PCR to analyse samples from 112 young‐of‐the‐year brown trout from 10 natural rivers with average water temperature differences of up to 6°C (and an absolute maximum of 23°C). We found negative associations between relative telomere length (RTL) and both average river temperature and individual body size. We found no indication of RTL–temperature association differences among six tissues, but we did find indications for differences among the tissues for associations between RTL and body size; size trends, albeit nonsignificant in their differences, were strongest in muscle and weakest in fin. Although causal relationships among temperature, growth, oxidative stress, and cross‐sectional telomere length remain largely unknown, our results indicate that telomere‐length variation in a poikilothermic wild animal is associated with both past temperature and growth.     

Experimental determination of sarcomere force–length relationship in type-I human skeletal muscle fibers

The objectives of this study were to measure the active and passive force–length (F–L) relationships in type-I human single muscle fibers and to compare the results to predictions from the sliding filament model (the “standard model”). We measured isometric forces in chemically skinned fibers at different sarcomere lengths (SLs) in separate maximal activations. The experimental tolerance interval for optimal SL was calculated to be (2.37, 2.95 μm), which included the prediction by the standard model (2.64, 2.81 μm). Average passive slack length was 2.22±0.08 μm, and the passive F–L relationship was well described by an exponential function. Best fit lines were used to estimate the ascending and descending limbs from the active F–L data using the average SL obtained from a digital image of the fiber. The experimental descending limb was also estimated using the shortest SL to address the possible effects of sarcomere inhomogeneity (SI). The experimental slopes of the ascending and descending limbs, 0.42 F_o/μm and ?0.52 F_o/μm (vs. ?0.55 F_o/μm with the shortest SL) respectively, F_o being the maximal isometric force, were significantly less in magnitude than those from the standard model. These results suggested that the difference between experimental and standard models was not fully explained by SI and other factors could be important. The broader experimental F–L curve compared to the standard model implies that human muscle has functionally a wider operating length range where its force-generating capacity is not compromised.     

Fish-induced variation in abdominal spine length of Leucorrhinia dubia (Odonata) larvae?

The lengths of dorsal and lateral spines on abdominal segments 4, 6 and 9 were measured on last-instar larvae of Leucorrhinia dubia (Odonata) from seven natural lentic systems containing fish and nine systems lacking fish. Larvae from systems with fish had significantly longer spines than larvae from systems without fish. In contrast, lake/pond area and pH had no effect on the length of spines. The length of the spines was not correlated with larval size, but there was a high correlation between the length of the three spines measured. Also, abundances of L. dubia larvae differed between systems, being significantly lower in systems with fish. Laboratory experiments showed that perch (Perca fluviatilis) handled long-spined larvae for significantly longer times than short-spined larvae. The results suggest that fish predators may induce morphological defences in insects.     

KL₄ peptide induces reversible collapse structures on multiple length scales in model lung surfactant

We investigated the effects of KL₄, a 21-residue amphipathic peptide approximating the overall ratio of positively charged to hydrophobic amino acids in surfactant protein B (SP-B), on the structure and collapse of dipalmitoylphosphatidylcholine and palmitoyl-oleoyl-phosphatidylglycerol monolayers. As reported in prior work on model lung surfactant phospholipid films containing SP-B and SP-B peptides, our experiments show that KL₄ improves surfactant film reversibility during repetitive interfacial cycling in association with the formation of reversible collapse structures on multiple length scales. Emphasis is on exploring a general mechanistic connection between peptide-induced nano- and microscale reversible collapse structures (silos and folds).     

Phytosulfokine-α controls hypocotyl length and cell expansion in Arabidopsis thaliana through phytosulfokine receptor 1

The disulfated peptide growth factor phytosulfokine-α (PSK-α) is perceived by LRR receptor kinases. In this study, a role for PSK signaling through PSK receptor PSKR1 in Arabidopsis thaliana hypocotyl cell elongation is established. Hypocotyls of etiolated pskr1-2 and pskr1-3 seedlings, but not of pskr2-1 seedlings were shorter than wt due to reduced cell elongation. Treatment with PSK-α did not promote hypocotyl growth indicating that PSK levels were saturating. Tyrosylprotein sulfotransferase (TPST) is responsible for sulfation and hence activation of the PSK precursor. The tpst-1 mutant displayed shorter hypocotyls with shorter cells than wt. Treatment of tpst-1 seedlings with PSK-α partially restored elongation growth in a dose-dependent manner. Hypocotyl elongation was significantly enhanced in tpst-1 seedlings at nanomolar PSK-α concentrations. Cell expansion was studied in hypocotyl protoplasts. WT and pskr2-1 protoplasts expanded in the presence of PSK-α in a dose-dependent manner. By contrast, pskr1-2 and pskr1-3 protoplasts were unresponsive to PSK-α. Protoplast swelling in response to PSK-α was unaffected by ortho-vanadate, which inhibits the plasma membrane H(+)-ATPase. In maize (Zea mays L.), coleoptile protoplast expansion was similarly induced by PSK-α in a dose-dependent manner and was dependent on the presence of K(+) in the media. In conclusion, PSK-α signaling of hypocotyl elongation and protoplast expansion occurs through PSKR1 and likely involves K(+) uptake, but does not require extracellular acidification by the plasma membrane H(+)-ATPase.     

Effect of oligogalacturonides on root length, extracellular alkalinization and O₂⁻-accumulation in alfalfa

The effects of an oligogalacturonic acid (OGA) pool on root length of intact alfalfa seedlings (Medicago sativa L.), on extracellular pH and on both extracellular and intracellular O₂⁻ dynamics were examined in this study. Lower OGA concentrations (25, 50 and 75 μg mL⁻¹) promoted root length, but 50 μg mL⁻¹ had a stronger effect in promoting growth, while the higher OGA concentration (100 μg mL⁻¹) had no significant effect. Extracellular alkalinization was tested only at concentrations higher than 50 μg mL⁻¹ OGA, showing that the response is determined not only by the specific size of OGA, but also by the concentration of OGA. The promoting effect of OGA on root growth at 25, 50 and 75 μg mL⁻¹ OGA concentrations in alfalfa root appeared to be unrelated to extracellular alkalinization. A possible explanation could be the induction of an O₂⁻ burst at non-toxic levels, which could drive directly or indirectly several processes associated with root elongation in 25, 50 and 75 μg mL⁻¹ OGA-treated seedlings. Analyses using confocal microscopy showed that the increase in the O₂⁻ generation, mainly in the epidermal cells, induced by 50 μg mL⁻¹ OGA could be related to the promoting effect on root growth. The combination of OGA with DPI allowed us to demonstrate that there are different O₂⁻-generating sources in the epidermal cells of the meristematic zone, likely NADPH oxidase and oxidases or oxido-reductase enzymes, insensitive to DPI, that maintain detectable O₂⁻ accumulation at 60 and 120 min of treatment. These results suggest that OGA induce an oxidative burst by several O₂⁻-generating sources in the active growth zones.