Toxicity and Mutagenesis of Chrysotile Asbestos toAgrobacterium radiobacter

The mutation of Agrobacterium radiobacter cells exposed to chrysotile asbestos was examined by the random amplified polymorphic DNA (RAPD) method. Approximately 1.4 kbp of DNA in A. radiobacter, which was not amplified strongly in the cells that were not exposed to asbestos, was amplified in the cells that were exposed to asbestos. Mutation in genomic DNA of A. radiobacter was found to be induced by asbestos. Specific DNA that was amplified by asbestos present in PCR products and that which exists latently in genomic DNA were cloned, and these sequences were then determined and compared. It was shown that one of the mutations by the asbestos in the A. radiobacter occurred only in the primer annealed region and was a point mutation or deletion.     

Relationships between bird-dispersed plants and avian fruit consumers with different feeding strategies in Japan

We examined the interactions between bird-dispersed plants and fruit-consuming birds with various feeding strategies, by reviewing the plant species consumed by 14 bird species in Japan with four feeding types: gulpers (five species), grinders (four species), crushers (four species), and peckers (one species). Our literature review provided information on the plant species consumed by the birds in Japan and the morphological traits of the fruits: fruit volume, seed mass and number, pulp type (fleshy, dry, or arillate), and plant height (tall, medium, or small). Using these data, we examined the diversity of plant species consumed by each bird and the fruit morphological traits that affected fruit selection. The five gulpers consumed fruits from the largest number of plants, followed by the four grinders, the four crushers, and the one pecker. The gulpers and grinders consumed a wider variety of fruits than were consumed by the crushers and the pecker. Logistic regression analysis revealed that some crushers and the pecker preferred plants with dry or arillate pulp around the seeds. Our results suggest that a frugivorous bird’s feeding strategies, and particularly its fruit-handling behaviors and the fruit parts it ingests, influence the diversity of plants it consumes. The crushers and the pecker, which feed exclusively on seeds, require more effort and time to consume this type of food, and this might cause a strong preference for specific fruit traits and thus, consumption of a lower diversity of plant species.     

Does individual variation in fruit profitability override color differences in avian choice of red or white <Emphasis Type="Italic">Ilex serrata</Emphasis> fruits?

Although avian color preferences have been studied and documented in controlled experiments, they have not been demonstrated under natural conditions in most cases. We hypothesized that avian fruit choice reflects intraspecific variation in fruit characteristics other than color, rather than fruit color differences. By planting one Ilex serrata Thunb. (red form) and one I. serrata forma leucocarpa Beissner (white form), which produce red and white fruits, respectively, at each of five points, we examined the proportion of fruits removed per tree and fruit choice by three avian species based on fruit color and other fruit characteristics. The proportion of fruits removed increased with pulpy sugar concentration and fruit diameter, but it did not differ between fruit colors. The main foragers, resident brown-eared bulbuls Hypsypetes amaurotis, consumed fruits regardless of color, but correspondingly to fruit removal, and appeared to base their fruit choice on pulpy sugar concentration and fruit diameter rather than on color. In contrast, the minor foragers, migrant Daurian redstarts Phoenicurus auroreus (Pallas) and Siberian bluechats Tarsiger cyanurus (Pallas), tended to choose red fruits and were possibly attracted by them. In conclusion, fruit removal per tree reflected individual variation in fruit profitability more strongly than differences in fruit color, even though the individual variation was not remarkable. The importance of color in fruit choice differed based on species, residency status, and major/minor foragers.     

Distribution of clubroot disease of a cruciferous weed, Cardamine flexuosa, in major isolated islands, Hokkaido and Okinawa in Japan

To investigate the distribution of clubroot of a cruciferous weed, Cardamine flexuosa, caused by Plasmodiophora brassicae, field surveys were conducted in Hokkaido, Aomori, and Okinawa, and major isolated islands in Japan during 1993–2004. The disease was newly recorded in Aomori and nine islands in five different prefectures, including Sado (Niigata), Oki (Shimane), Mishima (Yamaguchi), Tsushima, Iki and Goto (Nagasaki), and Koshiki, Yakushima, and Tanegashima (Kagoshima). The diseased plants were not found in Hokkaido and Okinawa (islands of Okinawa, Kumejima, Ishigaki, Iriomote, and Kohama). However, inoculation tests showed that most C. flexuosa collected from Hokkaido and Okinawa included many susceptible plants. The result suggests that resistance of the plants is not the reason that the disease was not found in these areas. An erratum to this article is available at .     

Rapid determination of free D-serine with chicken D-serine dehydratase

We have developed a simple, rapid, and inexpensive method of measuring the concentration of intrinsic free D-serine in tissue samples. This method uses chicken D-serine dehydratase in an enzymatic reaction to produce pyruvate, which is detected spectrophotometrically. Pyridoxal 5'-phosphate (PLP), a cofactor of D-serine dehydratase, increased pyruvate formation by 28%. The presence of Zn(2+) or ethylenediaminetetraacetic acid (EDTA) did not have any effect on pyruvate formation under the present assay conditions. In addition, this method was not affected by the presence of a large excess of L-serine, nor by the presence of tissue extracts, and accurately determined concentrations of 2-30 μM (200 pmol-3 nmol) of D-serine. The entire assay requires only 60 min. With this method, we determined the concentration of D-serine in various silkworm tissues. The results were in agreement with high performance liquid chromatography measurements. We found high concentrations of D-serine in silkworm larvae at day 3 of the fifth instar; specifically, 509 nmol g(-1) wet tissue in the midgut, 434 nmol g(-1) in the ovary, and 353 nmol g(-1) in the testis.     

Dual modulation of airway smooth muscle contraction by Th2 cytokines via matrix metalloproteinase-1 production

Altered contractility of airway smooth muscle (SM) is one of the main causes of allergic asthma, in which the predominance of Th2 over Th1 cytokines plays a central role. In the present study, we examine the effects of Th2 cytokines on airway SM contraction. Treatment with a low concentration of IL-4 (0.2 ng/ml) for 6 h augmented, whereas higher concentrations (2-20 ng/ml) inhibited, agonist-induced contractions of collagen gels containing bovine tracheal SM cells. Another Th2 cytokine (IL-13) showed an augmentation of gel contraction in the concentration range of 20-200 ng/ml. IL-4 and IL-13 increased mRNA expression and protein secretion of matrix metalloproteinase (MMP)-1, but these cytokines did not affect Ca(2+)-mobilizing properties and phosphorylation levels of myosin L chain in bovine tracheal SM cells. These changes were sensitive to wortmannin, an inhibitor of PI3K, but not to leflunomide, an inhibitor of STAT6. Scanning electron microscope observation revealed that collagen fibers twining around SM cells were completely dissolved in 20 ng/ml IL-4-treated gels and reorganized into basket-like structure in 20 ng/ml IL-13-treated gels. Exogenous application of high and low concentrations of MMP-1 also induced the inhibition and augmentation of gel contraction, respectively. Furthermore, nonselective MMP inhibitor galardin suppressed the effects of IL-4 and IL-13 on gel contraction, and MMP-1-targeted small-interfering RNA reversed the inhibitory effects of IL-4 on gel contraction to the augmentation. This indicates that Th2 cytokines modulate airway contraction without affecting cellular contractility but by secreting MMP-1 from the SM cells via PI3K activation and changing cell-to-matrix interactions.     

Close relationship between leaf life span and seedling relative growth rate in temperate hardwood species

The life span of resource-acquiring organs (leaves, shoots, fine roots) is closely associated with species successional position and environmental resource availability. We examined to what extent leaf life span is related to inter- and intraspecific variation in seedling relative growth rate (RGR). We examined relationships between relative growth rate in mass (RGR_M) or height (RGR_H) and leaf life span, together with classical RGR_M components [net assimilation rate (NAR), specific leaf area (SLA), leaf weight ratio (LWR), and leaf area ratio (LAR)] for seedlings of five hardwood species of different successional position across a wide range of environmental resource availability, including the presence or absence of leaf litter in shaded forest understory, small canopy gaps, and large canopy gaps. Both SLA and LAR were negatively correlated with RGR_M along the environmental gradient for all species. However, positive correlations were observed among species within microsites, indicating that these two components cannot consistently explain the variation in RGR_M. Both NAR and LWR affect interspecific, but not intraspecific, variation in RGR_M. Leaf life span was negatively correlated with either RGR_M or RGR_H in both inter- and intraspecific comparisons. Species with short-lived, physiologically active leaves have high growth rates, particularly in resource-rich environments. Consequently, leaf life span is a good predictor of seedling RGR. Leaf life span affects plant performance and has a strong and consistent effect on tree seedling growth, even among contrasting environments.     

Winter photosynthesis by saplings of evergreen broad-leaved trees in a deciduous temperate forest

* Here we investigated photosynthetic traits of evergreen species under a deciduous canopy in a temperate forest and revealed the importance of CO2 assimilation during winter for annual CO2 assimilation. * Saplings were shaded by the canopy trees from spring through to autumn, but were less shaded during the winter months. Photosynthetic rates at light saturation (Aarea) were lower during winter than during the growing season. Aarea was higher in Camellia, Ilex and Photinia than in Castanopsis, Cleyera and Quercus during the winter, but differed little during summer and autumn. * Estimated daily CO2 assimilation (Aday) was higher during the winter than during the growing season in Camellia, Ilex and Photinia but was higher than that during the growing season only at the beginning and end of winter in Castanopsis, Cleyera and Quercus. Aday was higher in Camellia, Ilex and Photinia than in Castanopsis, Cleyera and Quercus but differed little among them during the growing season. * These results reveal the importance of winter CO2 assimilation for the growth of Camellia, Ilex and Photinia. Furthermore, differences in annual CO2 assimilation among species are strongly modified by species-specific photosynthetic traits during the winter under deciduous canopy trees.     

Significance of leaf longevity in plants

The cost–benefit model of leaf life span is extended by incorporating the cost of construction and maintenance of supporting structures, such as shoots and roots. Published data on leaf longevities were reviewed, and they support qualitative predictions of optimal leaf life span based on the present model. In relation to life form, leaf life span increases in the following sequence, due to increasing costs of support structures: floating leaves of aquatic plants < annual herbs < perennial herbs < deciduous trees. Within species, leaf life span increases with plant size as support costs per unit of leaf increase. This prediction is supported by comparisons of seedlings and adults of temperate trees. These results suggest that the construction and maintenance costs of supporting structures significantly influence life span of individual leaves. Leaf longevity, in turn, connects the ecophysiology of the individual leaf to growth of the individual plant and energy and matter cycling at the ecosystem level.