DNA-based analysis of planktonic methanotrophs in a stratified lake

1. The assemblage of planktonic methanotrophs in a stratified freshwater lake was investigated. Vertical patterns were analysed by denaturing gradient gel electrophoresis, using the primer pair specific for 16S rRNA genes of type I methanotrophs.
2. The resulting banding patterns could be divided into three distinct groups, and sequenced bands were all related to the Methylobacter species. No amplicon was obtained with the primer pair specific for type II methanotrophs.
3. Cloning analysis of the pmoA gene was performed using samples from three water depths (epilimnion, metalimnion and hypolimnion). The compositions of the clone libraries from the three depths were distinct from each other but all three libraries were dominated by clones related to Methylobacter species.     

Lacking chloroplasts in guard cells of crumpled leaf attenuates stomatal opening: both guard cell chloroplasts and mesophyll contribute to guard cell ATP levels

Controversies regarding the function of guard cell chloroplasts and the contribution of mesophyll in stomatal movements have persisted for several decades. Here, by comparing the stomatal opening of guard cells with (crl‐ch) or without chloroplasts (crl‐no ch) in one epidermis of crl (crumpled leaf) mutant in Arabidopsis, we showed that stomatal apertures of crl‐no ch were approximately 65–70% those of crl‐ch and approximately 50–60% those of wild type. The weakened stomatal opening in crl‐no ch could be partially restored by imposing lower extracellular pH. Correspondingly, the external pH changes and K⁺ accumulations following fusicoccin (FC) treatment were greatly reduced in the guard cells of crl‐no ch compared with crl‐ch and wild type. Determination of the relative ATP levels in individual cells showed that crl‐no ch guard cells contained considerably lower levels of ATP than did crl‐ch and wild type after 2 h of white light illumination. In addition, guard cell ATP levels were lower in the epidermis than in leaves, which is consistent with the observed weaker stomatal opening response to white light in the epidermis than in leaves. These results provide evidence that both guard cell chloroplasts and mesophyll contribute to the ATP source for H⁺ extrusion by guard cells.     

OBSERVATIONS OF PRIMORDIAL GERM CELLS IN THE TURTLE EMBRYO (CARETTA CARETTA): LIGHT AND ELECTRON MICROSCOPIC STUDIES

Primordial germ cells (PGCs) in the turtle embryo ( Caretta caretta ) were observed with light and transmission electron microscopes. Identification of the PGCs for light microscopy was made by the periodic acid-Schiff (PAS) technique. PGCs were first found in the yolk-sac endoderm through the 5th to 6th day of development. PGCs freed from the endoderm then migrated to the root area of the dorsal mesentery and the coelomic angle between the 7th and the 11th day of development, and finally settled down in the gonadal anlage by the 14th day. Turtle PGCs were characterized by a large size (16 μm in diameter) and large nuclei with distinct nucleoli, and by the presence of large numbers of lipid droplets, yolk platelets and glycogen particles in the cytoplasm. Cell organelles were well-developed in PGCs at later stages. Amoeboid features of the PGCs were observed in the mesenchyme, indicating active locomotion. PGCs were usually surrounded or encircled by neighboring somatic cells. No intravascular PGCs were detected at any stage of development examined.     

Strategies for the conservation and management of isolated salmonid populations: lessons from Japanese streams

1. Endangered native populations of stream salmonids in Japan face three major threats: (i) negative interactions with introduced hatchery‐reared fish, (ii) fragmentation of habitat by impassable dams and (iii) recreational angling. 2. To prevent imminent extinction of many local populations, we evaluated these threats and possible conservation actions for red‐spotted masu salmon (Oncorhynchus masou ishikawae) and white‐spotted charr (Salvelinus leucomaenis japonicus) in the Fuji River system in central Japan. 3. Red‐spotted masu salmon and white‐spotted charr occupied only 0.73 and 2.4% of suitable thermal habitats, respectively, with masu salmon typically occupying habitats closer to human population centres. 4. Population viability analysis resulted in a 100‐year probability of extinction of 78.1% for masu salmon and 48.1% for charr. However, extinction risk of both species was predicted to be <5% if the carrying capacity increased from 141 to 303 for masu salmon and from 94 to 125 for charr, by allowing fish passage at the lower end of the habitat, and if annual adult survival rate increased by 0.04. Adult survival rate was the principal factor associated with population persistence. 5. To conserve isolated populations of stream‐dwelling salmonids, we recommend (i) assessing the distribution of remnant native and non‐native fish populations, (ii) that fishing regulations are modified to improve adult survival and population persistence and (iii) that fragmented reaches be reconnected to adjacent habitat, for example by removing or modifying artificial barriers to increase the carrying capacity of the isolated populations. Reconnection of fragmented reaches should, however, be avoided if it results in non‐native fish invading isolated populations.     

A revised interpretation of the wing base structure in Odonata

Abstract Homology of the wing base structure in the Odonata is highly controversial, and many different interpretations of homology have been proposed. In extreme cases, two independent origins of insect wings have been suggested, based on comparative morphology between the odonate and other pterygote wing bases. Difficulties in establishing homology of the wing base structures between Odonata and other Pterygota result mainly from their extreme differences in morphology and function. In the present paper, we establish homology of the wing base structures between Neoptera, Ephemeroptera and Odonata using highly conservative and unambiguously identifiable characters (the basal wing hinge and subcostal veins) as principal landmarks. Homology of the odonate wing base structure with those of Ephemeroptera and Neoptera can be identified reliably. Based on this interpretation, the ancestral condition of the insect wing base structure is discussed.     

Spatiotemporal variations in an assemblage of closely related planktonic aerobic methanotrophs

1. The assemblage of aerobic methane‐oxidising bacteria (MOB) was investigated in different seasons in the water column of a stratified freshwater lake. Species composition was analysed by performing denaturing gradient gel electrophoresis (DGGE) of the 16S rRNA genes and cloning analysis of the pmoA gene, which encodes the α‐subunit of particulate methane monooxygenase. The relative abundance of MOB to total bacteria was deduced from the copy number of the pmoA gene and 16S rRNA gene using real‐time polymerase chain reaction. 2. The profiles of the DGGE banding patterns changed with water depth, and these changes correlated with oxygen concentration and water temperature. The sequences of the DGGE bands obtained were all associated with the genus Methylobacter. During the analysis of pmoA gene, all clones sequenced were that of the Methylobacter/Methylosarcina group. The relative abundances of pmoA gene peaked around the oxycline, and small peaks of pmoA gene were also observed near the surface when peaks of methane were observed at the corresponding depth. 3. Profiles of the DGGE banding patterns suggested that ecophysiological characteristics differ among members of the genus Methylobacter; this indicates the importance of investigating the MOB assemblage at the species level or lower. Planktonic MOB seemed to be abundant around oxycline.