Moral commitment without objectivity or illusion: Comments on Ruse and Woolcock

Peter Woolcock, in Ruse's Darwinian Meta-Ethics: A Critique, argues that the subjectivist (nonobjectivist) Darwinian metaethics proposed by Michael Ruse (in Taking Darwin Seriously) cannot work, because the illusion of objectivity that Ruse claims is essential to morality breaks down when it is recognized as illusion, and there then remain no good reasons for acknowledging or following moral obligations. Woolcock, however, is mistaken in supposing that moral behaviour requires rational motivation. Ruse's Darwinian metaethical analysis shows why such objective support for morality is neither plausible nor necessary; and when that is recognized, it can also be seen that Ruse's proposed illusion of moral objectivity is superfluous.     

蓝氏贾第虫核被膜缺口的电镜观寨

双滴虫类是迄今所知的现存最原始的真核生物类群。以蓝氏贾第虫作为双滴虫类的代表,对其细胞核进行了电镜观察。除了未见有核仁外,还发现其核被膜的横切面上存在有缺口。在缺口的边缘处,核内膜与校外膜是相互连接着的,表明并非切片时所造成的假象。核被膜缺口处常有一核纤层样的薄层分隔核质与细胞质。用高锰酸钾固定细胞以求只保存膜结构时,核被膜缺口仍然可见,上述的薄层即未见到。核被膜缺口的发现证实了李靖炎（１９７９）的核被膜起源假说所作出的推断。     

白额鹱卵壳的扫描电镜观察

本文报道白额鹱卵壳的壳膜、孔锥层、海绵层、表层等的超微结构,并对卵壳元素进行ＴＮ－５５００能谱分析。     

CAM variations in the leaf-succulent Delosperma tradescantioides (Mesembryanthemaceae), native to southern Africa

Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides , a succulent that grows in drought-prone microenvironments in summer rainfall and all-year rainfall regions of southern Africa. When well-watered, this species exhibited Crassulacean acid metabolism (CAM)-cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low-level CAM or to CAM-idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre-stressed values within two days. Whole-shoot carbon uptake rates suggested that leaf growth had continued unabated during a short-term (∼ one week) drought. This emphasises that CAM-idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM-idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C₃ gas exchanges when well-watered to water-conserving CAM-idling during drought.     

Physiological aspects of Taxus brevifolia seeds in relation to seed storage characteristics

Water relations, desiccation tolerance and longevity of Taxus brevifolia (Nutt.) seeds were studied to determine the optimal stage of development and storage conditions for seeds of this species. Seeds equilibrated to a range of relative humidities (RHs) had unusually low water contents which can be accounted for by the high lipid content of gametophyte tissues (71% of the dry mass). Water relations of embryonic tissue were more typical of those reported for other seed species. The water content below which freezing transitions were not observable in the embryo was ca 0.24 g H₂O (g dry weight)⁻¹ (g g⁻¹) for all maturity classes studied. Embryos did not achieve significant levels of desiccation tolerance (survival to water contents less than 0.5 g g⁻¹) until the latter stages of development when dry matter was maximal. Mature embryos could be dried to 0.025 g g⁻¹ (seed water content of 0.010 g g⁻¹) with no loss of viability. Thus, at the latter stages of development, embryo water content could be optimized to avoid both desiccation and freezing damage. Survival of mature seeds declined over a 2-year period when seeds were stored at temperatures between 5 and 35°C and RHs between 14 and 75%, corresponding to seed water contents between 0.015 and 0.07 g g⁻¹. The deterioration rate was slowest for seeds stored at the lowest RH and temperature. Our data indicate that seeds of Taxus brevifolia show orthodox rather than recalcitrant storage characteristics, but that the optimum water content for storage was extremely low. The results suggest that even if stored at optimal water contents and low temperatures, T. brevifolia seeds will be relatively short lived. The high quantity of lipids or reducing sugars may be contributing factors in the poor storage characteristics.     

Changes in leaf expansion and epidermal screening effectiveness in Liquidambar styraciflua and Pinus taeda in response to UV-B radiation

Absorption or screening of ultraviolet-B (UV-B) radiation by the epidermis may be an important protective method by which plants avoid damage upon exposure to potentially harmful UV-B radiation. In the present study we examined the relationships among epidermal screening effectiveness, concentration of UV-absorbing compounds, epidermal anatomy and growth responses in seedlings of loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.). Seedlings of each species were grown in a greenhouse at the University of Maryland under either no UV-B radiation or daily supplemental UV-B radiation levels of 4, 8 or 11 kJ m^?2 of biologically effective UV-B (UV-B_BE) radiation. Loblolly pine seedlings were subsequently grown in the field under either ambient or supplemental levels of UV-B radiation. At the conclusion of the growing season, measurements of epidermal UV-B screening effectiveness were made with a fiber-optic microprobe. In loblolly pine, less than 0.5% of incident UV-B radiation was transmitted through the epidermis of fascicle needles and about 1% was transmitted in primary needles. In contrast, epidermal transmittance in sweetgum ranged from about 20% in leaves not preconditioned to UV-B exposure, to about 10% in leaves grown under UV-B radiation. The concentration of UV-absorbing compounds was unaffected by UV-B exposure, but generally increased with leaf age. Increases in epidermal thickness were observed in response to UV-B treatment in loblolly pine, and this accounted for over half of the variability in UV-B screening effectiveness. In spite of the low levels of UV-B penetration into the mesophyll, delays in leaf development (both species) and final needle size (loblolly pine) were observed. Seedling biomass was reduced by supplemental UV-B radiation in loblolly pine. We hypothesize that the UV-induced growth reductions were manifested by changes in either epidermal anatomy or epidermal secondary chemistry that might negatively impact cell elongation.     

Relative growth rate, biomass allocation pattern and water use efficiency of three wheat cultivars during early ontogeny as dependent on water availability

We have investigated the water use efficiency of whole plants and selected leaves and allocation patterns of three wheat cultivars (Mexipak, Nesser and Katya) to explore how variation in these traits can contribute to the ability to grow in dry environments. The cultivars exhibited considerable differences in biomass allocation and water use efficiency. Cultivars with higher growth rates of roots and higher proportions of biomass in roots (Nesser and Katya) also had higher leaf growth rates, higher proportions of their biomass as leaves and higher leaf area ratios. These same cultivars had lower rates of transpiration per unit leaf area or unit root weight and higher biomass production per unit water use. They also had higher ratios of photosynthesis to transpiration, and lower ratios of intercellular to external CO₂ partial pressure. The latter resulted from large differences in stomatal conductance associated with relatively small differences in rates of photosynthesis. There was little variation between cultivars in response to drought, and differences in allocation pattern and plant water use efficiency between cultivars as found under well-watered conditions persisted under dry conditions. At the end of the non-watered treatment, relative growth rates and transpiration rates decreased to similar values for all cultivars. High ratios of photosynthesis to transpiration, and accordingly high biomass production per unit of transpiration, is regarded as a favourable trait for dry environments, since more efficient use of water postpones the decrease in plant water status.     

Induction of leaf senescence in Arabidopsis thaliana by long days through a light-dosage effect

Given the influence of photoperiod on reproductive development and whole-plant senescence in monocarpic plants, one would suspect that leaf senescence in these plants might be under photoperiodic control. In Arabidopsis thaliana , which is monocarpic and also a nonobligate long-day (LD) plant, LDs (16 h, 300 μmol m⁻² s⁻¹) caused leaves to die earlier than did short days (SDs, 10 h). Since leaf longevity was not paralleled by the reproductive development in the present study, the reproductive structures did not seem to be the primary controls of leaf senescence. The LD effect appeared to depend on the amount of light rather than on day length, for leaves given LDs at reduced light intensity (180 μmol m⁻² s⁻¹) lived longer than those in LDs with full light. In addition, the higher light intensity promoted chlorophyll loss and anthocyanin accumulation in LDs. Thus, senescence of these leaves seems to be governed by light dosage rather than photoperiod. Light may play a natural role in promoting the senescence of A. thaliana leaves.     

Fibre length and gibberellins A1 and A20 are decreased in Eucalyptus globules by acylcyclohexanedione injected into the stem

Trinexapacethyl (TriEt), an acylcyclohexanedionetype inhibitor of gibberellin (GA) biosynthesis, was applied to 3-year-old Eucalyptus globules saplings by localised injection near the base of each stem. The objective was to alter cambial region GA levels and to study the effects on secondary xylem fibre development. Seven weeks later wood samples, with bark and cambial region intact, were removed 10 and 30 cm above the point of injection. Fusiform cambial cell dimensions were compared with those of fibre-tracheids in the most recently formed 100 um of secondary xylem. Increasing TriEt applications from 5 to 5 000 mg active ingredient significantly reduced average fibre length, and to a lesser extent average fusiform cambial cell length. Also reduced was the number of cells in the cambial zone and the number of differentiating fibres with primary walls. However, no trends were evident for changes in fibre diameter, the proportion of vessel elements or the ratio of cambial ray cells to fusiform cambial cells. Two gibberellins (GA₁ and GA₂₀), indole-3-acetic acid (IAA) and abscisic acid (ABA) were quantified in cambial region tissues by gas chromatographymass spectrometry using stable isotope labelled internal standards. Increasing TriEt application reduced both GA₁ and GA₂₀ levels. Effects on IAA and ABA were not significant, although their levels tended to be lower at the highest TriEt application rate. The elongation of secondary xylem fibres was positively correlated with higher levels of endogenous GA₁ (r_s= 0.74, P < 0.01) and GA₂₀ (r_s= 0.72, P < 0.01). These results support a causal role for GA₁ in cambial cell division. They are also consistent with the hypothesis that the elongation of differentiating secondary xylem fibres in woody an–giosperms is dependent on GA₁ levels in the cambial region.     

Turnover of organic nitrogen in soils and its availability to crops

The root development of barley seedlings grown for one week in an aerated nutrient solution was studied in the presence of dissolved organic matter from an aqueous chestnut leaf litter extract. In particular, the different effects of low and high molecular weight fractions (small molecules: molecular weight <1000; large molecules: >10,000) of the leaf litter extract were examined. In the presence of large molecules root growth was inhibited, an irregular root tip morphology was observed, and Ca and Mg concentrations in the shoots were lower than in control plants. These phytotoxic effects were not caused by the formation of an impermeable layer of large molecules on the root surfaces that lower accessibility for nutrient cations as inferred from voltammetric experiments. A germination assay using spruce seeds, however, indicated allelochemical effects of large molecules, which exhibit a higher aromaticity than the small molecules as indicated by spectroscopic characterisation. In the growth experiments with small molecules, no influence on the root development of barley was evident, but an increase of Ca and Mg in the shoots was detected. During these growth experiments, a large amount of the small molecules, mainly simple phenols and amino acids, disappeared from the nutrient solution. The loss of small molecules was most likely the effect of mineralisation.Abbreviations DOC dissolved organic carbon - DOM dissolved organic matter - LLE leaf litter extract - MW molecular weight - HMDE hanging mercury drop electrode