Mineral nutrient supply, cell wall adjustment and the control of leaf growth

The possibility that changes in the plasticity of expanding cell walls are involved in regulating early leaf growth responses to nutrient deficiencies in monocot plants was investigated. Intact maize seedlings (Zea mays L.) which were hydroponically grown with their roots in low-nutrient solution (1 mol m^?3 CaCl₂) showed early inhibition of first-leaf growth, as compared with seedlings on complete nutrient solution. This early inhibition of leaf growth was not associated with reduced cell production. However, segmental elongation along the cell expansion zone at the base of the leaf and the lengths of mature epidermal cells were reduced by the low-nutrient treatment. Solute (osmotic) potentials in the expanding leaf tissues were unchanged. In contrast, low-nutrient treatments significantly altered leaf plasticity, i.e. the irreversible extension caused by applying a small force in the direction of leaf growth. For example, in vivo plasticity decreased, along with leaf growth, after transfer of seedlings from complete nutrient solution to low-nutrient solution for 15 h. Conversely, in vivo plasticity increased, along with leaf growth, after transfer of plants previously grown on low-nutrient solution to complete nutrient solution for 15 h. The nutrient treatments also induced similar changes in the in vitro plasticity of the expanding leaf cell walls. There were no consistent changes in elasticity. Thus, reductions in the plasticity of expanding leaf cell walls appear to be involved in controlling the early inhibition of maize leaf growth by root imposition of nutrient stress.     

Comparison of the cardiac effects between quinazoline-based α<Subscript>1</Subscript>-adrenoceptor antagonists on occlusion–reperfusion injury

Quinazoline-based compounds such as prazosin and its congeners including doxazosin, bunazosin, and terazosin are widely used as antihypertensive agents. However, there were many clinical observations showing that using these agents may result in higher risk of cardiovascular accidents in recent years. In this study, we compared the effects of four α-adrenoceptor antagonists: prazosin, doxazosin, bunazosin, and terazosin on occlusion–reperfusion injury. Langendorff-perfused rat hearts were pretreated with these four antagonists, and then the left main coronary artery was occluded. After 30 min occlusion, the hearts were reperfused for 2 h and the infarct sizes were measured. Two of the compounds studied, prazosin and doxazosin, apparently increased infarct size, CK-MB, and LDH activities after 2 h reperfusion. In contrast, bunazosin decreased infarct size and those biochemical indicators of cellular damage compared to control hearts. Although infarct size after reperfusion was differently changed by these four α-adrenoceptor antagonists, TUNEL-positive nuclei and caspase-3 protein expressions of all the groups were not significantly different. We supposed that the different effects of these four agents on infarct size came from the difference in necrosis rather than apoptosis.     

STRUCTURE,LIFE HISTORY AND SYSTEMATICS OF RHOICOSPHENIA (BACILLARIOPHYTA). V. INITIAL CELL AND SIZE REDUCTION IN RH. CURVATA AND A DESCRIPTION OF THE RHOICOSPHENIACEAE FAM. NOV.1

The initial epivalve of Rhoicosphenia curvata (Kütz.) Grun. differs from vegetative valves in having a strongly arched section, a wide hyaline marginal strip, no pseudosepta, an unthickened margin, and a terminal raphe fissure at the head pole. The initial epivalve is of the D type, with short raphe fissures. The epicingulum consists of three bands as usual, but they are narrower and more delicate than those of vegetative cells. The initial hypovalve and hypocingulum are similar in every way to those of vegetative cells, except for the rounded section of the hypovalve. During size reduction the almost isopolar outline of the initial valves and their immediate descendants gives way to an increasingly strong heteropolarity, and this is accompanied by changes in the relative lengths of the raphe slits and the shape of the central area. Different populations have different gametangium and initial cell sizes, suggesting the presence of races within the species. The structure of the initial cell indicates that Rhoicosphenia is less closely related to the monoraphid genera than to the gomphocymbelloid genera, confirming conclusions reached from studies of the vegetative cell and auxospore formation. Rhoicosphenia should therefore be separated into a new family, the Rhoicospheniaceae, which is described.     

Effective/census population size ratio estimation: a compendium and appraisal

With an ecological-evolutionary perspective increasingly applied toward the conservation and management of endangered or exploited species, the genetic estimation of effective population size (N_e) has proliferated. Based on a comprehensive analysis of empirical literature from the past two decades, we asked: (i) how often do studies link N_e to the adult census population size (N)? (ii) To what extent is N_e correctly linked to N? (iii) How readily is uncertainty accounted for in both N_e and N when quantifying N_e/N ratios? and (iv) how frequently and to what degree might errors in the estimation of N_e or N affect inferences of N_e/N ratios? We found that only 20% of available N_e estimates (508 of 2617; 233 studies) explicitly attempted to link N_e and N; of these, only 31% (160 of 508) correctly linked N_e and N. Moreover, only 7% (41 of 508) of N_e/N ratios (correctly linked or not) reported confidence intervals for both N_e and N; for those cases where confidence intervals were reported for N_e only, 31% of N_e/N ratios overlapped with 1, of which more than half also reached below N_e/N = 0.01. Uncertainty in N_e/N ratios thus sometimes spanned at least two orders of magnitude. We conclude that the estimation of N_e/N ratios in natural populations could be significantly improved, discuss several options for doing so, and briefly outline some future research directions.     

Oxidative Stability of Polyunsaturated Fatty Acid in Phosphatidylcholine Liposomes

Synthesized PCs containing docosahexaenoic acid (DHA), arachidonic acid (AA), linoleic acid (LA), and palmitic acid (PA) at known positions in the glycerol moiety were oxidized in liposomes, bulk, and organic solvent. In bulk and organic solvent, the oxidative stability of PC decreased with increasing degrees of unsaturation. However, the degree of unsaturation had little effect on the stability of PC in liposomes. The oxidative stability of PC in liposomes would be affected by the chemical reactivity based on the degree of unsaturation and by the conformation of fatty acyl component in PC bilayers. When the oxidative stability of 1-PA-2-LA-PC or 1-PA-2-AA-PC was compared with that of a 1:1 (mol ratio) mixture of 1,2-diPA-PC+1,2-diLA-PC, or 1,2-diPA-PC+1,2-diAA-PC, respectively, the former PC was more oxidatively stable than that of the latter PC mixture in all oxidation systems, although the degree of unsaturation of 1-PA-2-PUFA-PC was the same as that of the corresponding mixture of diPA-PC+diPUFA-PC. The higher oxidative stability of 1-PA-2-PUFA-PC than that of a corresponding mixture of diPA-PC+diPUFA-PC in liposomes was suggested to be due to the different conformation of PC bilayers and the different rate of hydrogen abstraction by free radicals from intermolecular and intramolecular acyl groups.     

Ontogeny of tracheal system structure: a light and electron-microscopy study of the metathoracic femur of the American locust, Schistocerca americana

Does oxygen delivery become more challenging for insects as they increase in size? To partially test this hypothesis, we used quantitative light and electron microscopy to estimate the oxygen delivery capacity for two steps of tracheal oxygen delivery within the metathoracic femur (jumping leg) for 2nd instar (about 47 mg) and adult (about 1.7 g) locusts, Schistocerca americana. The fractional cross‐sectional areas of the major tracheae running longitudinally along the leg were similar in adults and 2nd instars; however, since the legs of adults are longer, the mass‐specific diffusive conductances of these tracheae were 4‐fold greater in 2nd instars. Diffusive gas exchange longitudinally along the leg is easily possible for 2nd instars but not adults, who have many air sacs within the femur. Mitochondrial content fell proximally to distally within the femur in 2nd instars but not adults, supporting the hypothesis that diffusion was more important for the former. Lateral diffusing capacities of the tracheal walls were 12‐fold greater in adults than 2nd instars. This was primarily due to differences in the smallest tracheal class (tracheoles), which had thinner epidermal and cuticular layers, greater surface to volume ratios, and greater mass‐specific surface areas in adults. Adults also had greater mitochondrial contents, larger cell sizes and more intracellular tracheae. Thus, larger insects do not necessarily face greater problems with oxygen delivery; adult grasshoppers have superior oxygen delivery systems and greater mass‐specific aerobic capacities in their legs than smaller/younger insects. J. Morphol. 262:800–812, 2004. © 2004 Wiley‐Liss, Inc.     

SEXUAL SIZE DIMORPHISM AND REPRODUCTIVE INVESTMENT BY FEMALE SPIDERS: A COMPARATIVE ANALYSIS

We investigate the association between female reproductive investment, absolute size, and sexual size dimorphism in spiders to test the predictions of the fecundity-advantage hypothesis. The relationships between absolute size and sexual size dimorphism and aspects of female reproductive output are examined in comparative analyses using phylogenetically independent contrasts. We provide support for the idea that allometry for sexual dimorphism is the result of variation in female size more so than male size. Regression analyses suggest selection for increased fecundity in females. We argue that fecundity selection provides the only general explanation for the evolution of sexual size dimorphism in spiders.     

THE EFFECTIVE SIZE OF A HIERARCHICALLY STRUCTURED POPULATION

A knowledge of the effective size of a population (N_e) is important in understanding its current and future evolutionary potential. Unfortunately, the effective size of a hierarchically structured population is not, in general, equal to the sum of its parts. In particular, the inbreeding structure has a major influence on N_e. Here I link N_e to Wright's hierarchical measures of inbreeding, F_IS and F_ST, for an island-structured population (or metapopulation) of size N_T. The influence of F_ST depends strongly on the degree to which island productivity is regulated. In the absence of local regulation (the interdemic model), interdemic genetic drift reduces N_e. When such drift is combined with local inbreeding under otherwise ideal conditions, the effects of F_IS and F_ST are identical: increasing inbreeding either within or between islands reduces N_e, with N_e = N_T/[(1 + F_IS)(1 + F_ST) ? 2F_ISF_ST]. However, if islands are all equally productive because of local density regulation (the traditional island model), then N_e = N_T/[(1 + F_IS)(1 –F_ST)] and the effect of F_ST is reversed. Under the interdemic model, random variation in the habitat quality (and hence productivity) of islands act to markedly decrease N_e. This variation has no effect under the island model because, by definition, all islands are equally productive. Even when no permanent island structure exists, spatial differences in habitat quality can significantly increase the overall variance in reproductive success of both males and females and hence lower N_e. Each of these basic results holds when other nonideal factors are added to the model. These factors, deviations from a 1:1 sex ratio, greater than Poisson variance in female reproductive success, and variation in male mating success due to polygynous mating systems, all act to lower N_e. The effects of male and female variance on N_e have important differences because only females affect island productivity. Finally, it is noted that to use these relationships, F_IS and F_ST must be estimated according to Wright's definition (and corrected to have a zero expectation under the null model). A commonly used partitioning (θ, θ_g) can be biased if either island size or the number of islands is small.     

Trade-offs limiting the evolution of coloniality: ecological displacement rates used to measure small costs

Multicellular organisms that benefit from division of labour are presumably descended from colonial species that initially derived benefits from larger colony size, before the evolution of specialization. Life in a colony can have costs as well as benefits, but these can be hard to measure. We measured physiological costs to life in a colony using a novel method based on population dynamics, comparing growth rates of unicells and kairomone-induced colonies of a green alga Desmodesmus subspicatus against a reference co-occurring species. Coloniality negatively affected growth during the initial log growth phase, while no adverse effect was detected under nutrient-limited competitive conditions. The results point to costs associated with traits involved in rapid growth rather than those associated with efficient growth under resource scarcity. Some benefits of coloniality (e.g. defence from herbivory) may be different from when this trait evolved, but our approach shows how costs would have depended on conditions.