Changes in the synthesis of rubisco in rice leaves in relation to senescence and N influx

BACKGROUND AND AIMS: The amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) synthesized in a leaf is closely correlated with N influx into the leaf throughout its lifetime. Rubisco synthesis and N influx are most active in the young leaf during expansion, but are very limited in the senescent leaf. However, it is not established whether Rubisco synthesis can be observed if N influx is increased, even in a very senescent leaf. This study first investigated changes in the relationships between rbcS and rbcL mRNA contents and Rubisco synthesis per unit of leaf mass with leaf senescence. Next, leaves were removed during late senescence, to examine whether Rubisco synthesis is re-stimulated in very senescent leaves by an increase in N influx. METHODS: Different N concentrations (1 and 4 mm) were supplied to Oryza sativa plants at the early (full expansion), middle and late stages (respectively 8 and 16 d after full expansion) of senescence of the eighth leaf. To enhance N influx into the eighth leaf 16 d after full expansion, all leaf blades on the main stem, except for the eighth leaf, and all tillers were removed and plants received 4 mm N (removal treatment). KEY RESULTS: Rubisco synthesis, rbcS and rbcL mRNAs and the translational efficiencies of rbcS and rbcL mRNAs decreased with leaf senescence irrespective of N treatments. However, in the removal treatment at the late stage, they increased more strongly with an increase in N influx than in intact plants. CONCLUSIONS: Although Rubisco synthesis and rbcS and rbcL mRNAs decrease with leaf senescence, leaves at the late stage of senescence have the potential actively to synthesize Rubisco with an increase in N influx.     

DNA barcoding of freshwater zooplankton in Lake Kasumigaura,Japan

Although DNA barcoding is a promising tool for the identification of organisms, it requires the development of a specific reference sequence library for sample application. In the present study we developed a Lake Kasumigaura, Japan, zooplankton DNA barcode library to increase the sensitivity of future zooplankton monitoring for detecting lake ecosystem condition changes. Specifically, the mitochondrial cytochrome c oxidase subunit I (mtCOI) haplotype, i.e., the primary DNA barcode, was examined for each zooplankton taxon. In crustaceans, 37 mtCOI haplotypes were obtained from 99 individuals, representing four and 15 morpho-species of Copepoda and Cladocera, respectively. Comparing these sequences with those in GenBank shows that the lake harbors putative non-indigenous species, such as Daphnia ambigua. In rotifers, 132 mtCOI haplotypes were obtained from 302 individuals, representing 11 genera and one unclassified taxon. The automatic barcode gap discovery (ABGD) algorithm separated these haplotypes into 43 species. Brachionus cf. calyciflorus was divided into five ABGD species, and different ABGD species tended to occur in different seasons. Seasonal ABGD-species succession was also observed within Polyarthra spp. and Synchaeta spp. These seasonal successions were not detected by inspections of external morphology alone. Accepting up to 7% sequence divergence within the same species, mtCOI reference sequences were available in GenBank for three, 13, and 17 species in Copepoda, Cladocera, and Rotifera, respectively. The present results, therefore, reveal the serious shortage of mtCOI reference sequences for rotifers, and underscore the urgency of developing rotifer mtCOI barcode libraries on a global scale.     

<Emphasis Type="Italic">Tropicibacter phthalicus</Emphasis> sp. nov., A Phthalate-Degrading Bacterium from Seawater

An aerobic, Gram-negative bacterial strain, designated KU27E1^T, which degrades phthalate and dimethylphthalate, was isolated from seawater obtained from the coastal region of Ishigaki Island, Japan. Cells are motile rods with polar flagella. Strain KU27E1^T grew at 15–30°C, pH 6.0–8.0, in the presence of 1.0–2.0% (w/v) NaCl. The 16S rRNA gene sequence analysis revealed that this strain was affiliated with the family Rhodobacteraceae in the class Alphaproteobacteria, and was most closely related to Tropicibacter naphthalenivorans (96.8%). The predominant respiratory lipoquinone was ubiquinone-10, and the major cellular fatty acid was C_18:1ω7c (88.5%). The G+C content of genomic DNA was 58.7 mol%. Based on the physiological, chemotaxonomic, and phylogenetic data, strain KU27E1^T is suggested to represent a novel species of the genus Tropicibacter, for which the name Tropicibacter phthalicus sp. nov. is proposed. The type strain of Tropicibacter phthalicus is designated as KU27E1^T (=JCM 17793^T = KCTC 23703^T).     

Induction of diabetes by PolyI:C and anti-RT6.1 antibody treatment in DR-BB rats.

To determine whether environmental factors could affect the incidence of diabetes in RT6.1+ lymphocytes-depleted diabetes resistant (DR) BB rats, we tested polyinosinic-polycytidylic acid (Poly I:C), as an immune activator, in conjunction with anti-RT6.1 antibody in DR-BB rats which were bred in a specific pathogen free (SPF) condition. Diabetes was induced by the combined administration of poly I:C and anti-RT6.1 antibody. The use of poly I:C or anti-RT6.1 antibody alone did not cause diabetes. These results suggest that RT6.1+ T lymphocytes regulate autoimmune diabetes and that non-specific immune activation caused by environmental factors plays a key role in inducing diabetes in DR-BB rats.     

Genetic analysis for insulitis in NOD mice

Non-obese diabetic (NOD) mice spontaneously develop diabetic signs akin to those of Type I diabetes in man. Insulitis, i.e., lymphocytic infiltration around and into the pancreatic islets is one of the characteristics of such mice. It is also the etiologic pathological lesion in the development of diabetes mellitus in NOD mice. Thus, we chose insulitis as a marker for genetic analysis of the development of diabetes mellitus in NOD mice and clarified the mode of its inheritance. In breeding studies between NOD and C57BL/6J mice, insulitis was not observed in the F1 and (F1 X C57BL/6J) backcross generations, but was found with incidences of 3.9% in females and 1.4% in males in the F2 generation and 23.7% in females and 12.1% in males in the (F1 X NOD) backcross generation. These incidences in the F2 and (F1 X NOD) backcross females corresponded approximately to 1/16 and 1/4 of the incidences of 89.7% in the NOD females, respectively. A similar relationship was observed between the F2 and (F1 X NOD) backcross males and the NOD males. When the gene expressivity of both sexes for a double recessive homozygote was assumed to be the incidences of insulitis in 9-week-old NOD females and males, respectively, the expected numbers of both sexes with and without insulitis in the F2 and backcross generations agreed well with the observed ones. These observations suggest that two recessive genes on independent autosomal chromosomes are necessary for the development of insulitis in NOD mice.