Mesophyll conductance decreases in the wild type but not in an ABA‐deficient mutant (aba1) of Nicotiana plumbaginifolia under drought conditions

Under drought conditions, leaf photosynthesis is limited by the supply of CO₂. Drought induces production of abscisic acid (ABA), and ABA decreases stomatal conductance (g_s). Previous papers reported that the drought stress also causes the decrease in mesophyll conductance (g_m). However, the relationships between ABA content and g_m are unclear. We investigated the responses of g_m to the leaf ABA content [(ABA)_L] using an ABA‐deficient mutant, aba1, and the wild type (WT) of Nicotiana plumbaginifolia. We also measured leaf water potential (Ψ_L) because leaf hydraulics may be related to g_m. Under drought conditions, g_m decreased with the increase in (ABA)_L in WT, whereas both (ABA)_L and g_m were unchanged by the drought treatment in aba1. Exogenously applied ABA decreased g_m in both WT and aba1 in a dose‐dependent manner. Ψ_L in WT was decreased by the drought treatment to ?0.7 MPa, whereas Ψ_L in aba1 was around ?0.8 MPa even under the well‐watered conditions and unchanged by the drought treatment. From these results, we conclude that the increase in (ABA)_L is crucial for the decrease in g_m under drought conditions. We discuss possible relationships between the decrease in g_m and changes in the leaf hydraulics.     

Oenothorachona ectenolaemus n.g., n.sp. and Spirochona halophila n.sp., Two New Marine Chonotrichous Ciliates

SYNOPSIS. Two new species of chonotrichous ciliates, Oenophorachona ectenolaemus n.g., n.sp. and Spirochona halophila n.sp. were found on Anisogammarus sp. collected from the waters of Humboldt County, California and Argyle Bay, San Juan Island, Washington. This is the 1st reported occurrence of 2 genera of chonotrichous ciliates on a single host species as well as the 1st of the occurrence of Spirochona in marine and brackish water environments.     

The Site and Time of Expression of MIF in Frog Development

A ventrally localized melanization-inhibiting factor (MIF) has been suggested to play a role in the expression of dorsal-ventral pigment patterns in amphibia. Here we investigate the onset and localization of MIF appearance in frog development. The expression of MIF was analyzed in the wild-type and gray-eyed mutant (g/g) of Rana japonica by immunoblotting and immunohistochemistry using an anti-MIF neutralizing monoclonal antibody. Western blot analysis revealed that the anti-MIF antibody recognized ～51 kDa and ～58 kDa bands. The 51 kDa band first appeared at the external gill stage, while 58 kDa band was additionally detected at the hindlimb bud stage. With the use of immunohistochemistry, it was found that the anti-MIF antibody stained the whole epidermis of the embryos at the external gill stage; however, the staining was stronger in lateral and ventral epidermis than in dorsal. Staining with the anti-MIF antibody was observed only in the outer epidermis of the ventral skin, but not in the dorsal skin during and after metamorphosis. The spatial expression of MIF in the wild-type was the same as that in the gray-eyed mutant. The same immunohistochemical result was obtained in the adults of R. nigromaculata. These results suggest that MIF is involved in the formation of the dorsal-ventral pigment pattern.     

Detection of recombinant haplotypes in wild mice (Mus musculus) provides new insights into the origin of Japanese mice

Japanese house mice (Mus musculus molossinus) are thought to be a hybrid lineage derived from two prehistoric immigrants, the subspecies M. m. musculus of northern Eurasia and M. m. castaneus of South Asia. Mice of the western European subspecies M. m. domesticus have been detected in Japanese ports and airports only. We examined haplotype structuring of a 200 kb stretch on chromosome 8 for 59 mice from throughout Eurasia, determining short segments (≈ 370–600 bp) of eight nuclear genes (Fanca, Spire2, Tcf25, Mc1r, Tubb3, Def8, Afg3l1 and Dbndd1) which are intermittently arranged in this order. Where possible we identified the subspecies origin for individual gene alleles and then designated haplotypes for concatenated alleles. We recovered 11 haplotypes among 19 Japanese mice examined, identified either as ‘intact’ haplotypes derived from the subspecies musculus (57.9%), domesticus (7.9%), and castaneus (2.6%), or as ‘recombinant’ haplotypes (31.6%). We also detected recombinant haplotypes unique to Sakhalin. The complex nature of the recombinant haplotypes suggests ancient introduction of all three subspecies components into the peripheral part of Eurasia or complicated genomic admixture before the movement from source areas. ‘Intact’domesticus and castaneus haplotypes in other Japanese wild mice imply ongoing stowaway introductions. The method has general utility for assessing the history of genetic admixture and for disclosing ongoing genetic contamination.     

Molecular phylogeny of wood mice (Apodemus, Muridae) in East Asia

Sequences of the mitochondrial cytochrome b (1140 bp) and nuclear IRBP (1152 bp) genes were used to assess the evolutionary history of Apodemus , using the complete set of Asian species. Our results indicate that speciation in Asia involved three radiations, which supports an earlier study. The initial radiation yielded A. argenteus (Japanese endemic), A. gurkha (Nepalese endemic), and the ancestral lineage of the remaining Asian species. This lineage subsequently diverged into four groups: agrarius-chevrieri ( agrarius group), draco-latronum-semotus ( draco group), A. peninsulae , and A. speciosus (Japanese endemic). The final step consisted of divergence within two species groups as a consequence of the geography of the Yunnan-Guizhou plateau and Taiwan. The ecological ability of two Apodemus species to inhabit one locality via niche partitioning likely drove the second radiation and shaped the basic geographical pattern seen today: A. argenteus and A. speciosus in Japan, A. agrarius and A. peninsulae in northern China, and the A. agrarius and A. draco groups in southern China. The three radiations are estimated to have occurred 7.5, 6.6, and 1.8–0.8 Mya respectively, using the IRBP clock, based on rat–mouse divergence 12 Mya.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 469–481.     

Melanosome Formation in Cultured Amelanotic Melanophores of Rana brevipoda by a Frog Tyrosinase cDNA Transfection

A cDNA encoding tyrosinase of Rana nigromaculata was introduced into cultured, tyrosinase-negative amelanotic melanophores of R. brevipoda by a calcium phosphate precipitation method. Within a few days following transfection, dark pigmentation became visible in a small number of cells. Light microscopic observation revealed that the morphology of these transformed cells was comparable to that of normal melanophores in culture, and their proliferative activity was lower than that of amelanotic cells. Ultrastructural examination verified that amelanotic melanophores possessed a relatively small number of premelanosomes while the transformants contained numerous melanosomes at various stages of pigment deposition. The result indicated that tyrosinase cDNA of R. nigromaculata was expressed in amelanotic melanophores of R. brevipoda inducing the maturation of premelanosomes. It was also suggested that the expression of transfected tyrosinase cDNA had promoted differentiation of the amelanotic cells into fully developed melanophores.     

Comparative Anatomy and Morphology of Leaves between C3 and C4 Species in Panicum

Anatomical and morphological structures of leaf blades werecompared between C₃ and C₄ species in Panicum. Inter-specificvariation of stomatal density, longitudinal vein density andmesophyll thickness was highly correlative either plus or minuswithin respective groups. The two groups could not be distinguishedby a single character, since the variation ranges overlappedeach other. However, the quantitative relations between veindensity and the other two characters differentiated the twogroups well. In C₃, stomatal density seemed to be a primaryfactor for regulating water balance, while in C₄ vein systemwas considered to be important for the regulation. The specieswith intermediate photosynthesis behaved similar to the C₃ species.In the C₃ group, correlative variation was observed betweenleaf width, leaf angle and the three characters mentioned above.Variation of light-receiving area due to the changes of widthand angle of leaf blades was considered to be one of the adaptivestrategies of this group. Increase of light-receiving area wasin connection with the thinning of leaves. On the other hand,in the C₄ correlations between length, width and angle of leaveswere low. Such loose character correlation may be achieved byits efficiency of CO₂ utilization and its well developed veinsystems. Besides, NAD-me type species tended to have relativelylower stomatal and vein densities as compared with the otherdecarboxylation types in this group. Panicum, photosynthesis, C₃, C₄, decarboxylation types, leaf, stomata, vein     

On a New Collar Ciliate of a Gribble: Lobochona prorates n. sp. on Limnoria tripunctata

SYNOPSIS. Lobochona prorates n. sp., a collar cliate (CHONOTRICHIDA) ectocommensal on the pleopodal bristles of Limnoria tripunctata , is described. Lobochona prorates differs from the previously described chonotrichidan ectocommensal of the gribble, Lobochona limnoriae Dons on Limnoria lignorum (Rathke), in the outlines of the body and of the marginal lappets of the collar. The genus Lobochona Dons and the species Lobochona limnoriae Dons are redescribed.