Hypoxic conditions induce centrum defects in red sea bream Pagrus major (Temminck and Schlegel)

A previous study elucidated that an extreme hypoxia during somitogenesis induced the most frequent skeletal malformation centrum defects in red sea bream (RSB), Pagrus major. In this study, details of the hypoxic conditions to induce them in RSB, dissolved oxygen (DO) concentration and exposure time to hypoxia, were investigated. Fertilized eggs were exposed to seawater of six DO concentrations (0%, 10%, 25%, 50%, 75% and 100% of saturation) for seven different periods (5, 10, 30, 60, 120, 240 and 360 min) during somitogenesis. Somitic disturbances in newly hatched larvae were induced by exposure to 0% and 10% DO concentration for 10 and 120 min and longer respectively. Rearing eggs exposed to hypoxic condition of 10% DO for 240 min for 40 days post‐hatch showed that the location and the frequency of somitic disturbances in larvae and centrum defects in juveniles were significantly correlated (P<0.01). Dissolved oxygen concentration of the interstitial water in the egg high density layer formed at the water surface in a stationary state abruptly decreased to 3.7% within 7 min. Centrum defect induction by exposure of eggs to extreme low DO concentrations for a short period, which is the probable situation in the practical juvenile production, suggests that careful maintenance of DO concentration is important in the incubating water of fertilized eggs during egg sorting and transportation, where eggs are made into a pile and undergo hypoxia, for the prevention of centrum defects.     

Topographical differences in soil N transformation using15N dilution method along a slope in a conifer plantation forest in Japan

Soil N transformation was investigated using¹⁵N dilution method along a slope on a conifer plantation forest. Although there was no significant difference in the net N mineralization rates by laboratory incubation, net nitrification rates increased downslope. Gross N transformation by¹⁵N dilution method showed a distinct difference not only on the rates, but also on the main process between the lower and the upper of the slope. Half of minelarized N was immobilized and the other half was left in NH ₄ ⁺ pool at the upper part of the slope, while all of mineralized N was used for immobilization or nitrification and NH ₄ ⁺ pool decreased at the lower of the slope. Soil N transformations were classified into two groups: one was shown below 773 m and the other was shown above 782 m. The incubation with nitrification inhibitor showed that nitrification was mainly conducted by autotrophs irrespective of the position of the slope. Microbial biomass and microbial C/N were similar among the sites. However, the gross mineralization rate was higher below 773 m than above 782 m under similar respiration rates. This suggests that the substrate quality may be one of the controlling factors for soil N transformation. Extractable organic C/N was similar to microbial C/N at the lower of the slope. It indicated that the substrate was more decomposable below 773 m. It is considered that soil N transformation is affected by topographical gradient of moisture and nutrient which makes plant growth and decomposition rate different.     

Characteristics water balance in paddy fields with pipelines or open channels in Hokkaido

Paddy and Water Environment - Hokkaido is an important agricultural area of Japan. The amount of arable land managed per farming household has been increasing because of the aging of farmers and...     

Soil nitrogen dynamics during stand development after clear-cutting of Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) plantations

We examined soil N dynamics, including inorganic N concentration, net N transformation rates, and estimated plant N uptake (EPNU) from soil N budgets, and litterfall inputs, in five Japanese cedar plantation stands of different ages (5, 16, 31, 42, and 89 years) in the Mt Gomadan Experimental Forest (GEF). Net soil N mineralization and nitrification rates did not differ significantly between the youngest and oldest stands; soil moisture and inorganic N concentration were higher in the youngest stand. The EPNU was highest in the 16-year-old stand and lowest in the 31-year-old stand, and had a significant negative correlation with litter C:N ratio. The oldest (89-year-old) stand had a higher soil C:N ratio, lower proportion of nitrification rate to mineralization rate (%NIT), and higher estimated plant NH₄ ⁺ uptake than did the other stands, indicating that changes of soil organic matter quality can alter soil N dynamics. These results suggest that as a Japanese cedar plantation develops, soil N dynamics can be altered by the quantity and quality of input litter and soil organic matter, and can generate the imbalance between N supply from soil and N demand by plant.     

A device in the determination of si in dithionite-citrate-bicarbonate extract

In the determination of Si in dithionite-citrate-bicarbonate (DCB) extract (2) by the molybdenum blue heteropply method, the color develppment, is interfered by the presence of dithionite and citrate. Weaver el al. (4) have eliminated the interference by introducing air-bubbling for oxidation of the former and by the use of a large excess of molybdate solution as a complexing agent of the latter. This method, while,giving satisfactory results, has a disadvantage that air-bubbling is time-consuming. Moreover it often occurs that the analysis is delayed also due to the limitation of bubbling facilities particularly when many samples are treated at a time.     

Adsorption of polyphosphates by allophane

Although many investigations have been carried out on the reaction of phosphates with allophane as well as with crystalline clays, they have been almost with the orthophosphates (2, 13, 19, 21). Recent investigations have revealed that certain condensed phosphates (polyphosphates) have a considerable promise as a long-term, slow-release source of phosphorus for plants (3, 7, 9, 10. 14, 17. 18, 20. 25). Relatively little information is available, however, on the reaction of those substances with soil clay minerals (8. 15).     

Upregulation of the genes for ferritin,RNase, and DnaJ in leaves of rice plants in response to sulfur deficiency

Microarray analysis was carried out with mRNAs isolated from aerial portions of rice plants subjected to sulfur deficiency. Among the candidate clones regulated by sulfur deficiency, three genes were identified by northern analysis that showed altered levels of mRNA accumulation. Genes similar to those for ferritin, S-like ribonuclease, and DnaJ-like protein were down-, down-, and upregulated by sulfate deficiency, respectively. These genes were found for the first time to be responsive to sulfur nutrition in the present study.     

A rice FRD3-like (OsFRDL1) gene is expressed in the cells involved in long-distance transport

We identified four putative AtFRD3-like genes (OsFRDL) in the rice genome that exhibited 39.1 to 56.7% amino acid sequence similarities to Arabidopsis FRD3. Of these, we cloned three OsFRDL genes from a cDNA library prepared from iron-deficient rice roots: OsFRDL1, OsFRDL2, and OsFRDL3. OsFRDL1 was expressed weakly in Fe-sufficient roots, and slight expression was induced in the roots of Fe-deficient plants. OsFRDL2 was expressed constitutively in both roots and leaves, and Fe deficiency reduced its expression in leaves. OsFRDL3 was expressed in leaves, but not in roots; Fe deficiency induced slight expression in leaves. An OsFRDL1-sGFP fusion protein was localized in the plasma membrane in onion epidermal cells. The promoter GUS analysis showed that OsFRDL1 was localized in the cells involved in long-distance transport, in both Fe-sufficient and Fe-deficient plants. Furthermore, OsFRDL1 expression was observed during the reproductive stage. These results suggest that OsFRDL1 is a transporter that resides in the plasma membrane of cells involved in long-distant transport.     

Thermal stress responses of a sterile mutant of Ulva pertusa (Chlorophyta)

SUMMARY: The thermal stress responses of a sterile mutant of the marine alga Ulva pertusa were investigated at 20°C and 30°C. The amounts of the photosynthetic pigments, β-carotene, chlorophylls a and b , lutein, neoxanthin, and violaxanthin, were 1.4–2.4 times higher in the 30°C-cultivated alga than in the 20°C-cultivated alga. The free amino acids, asparagine, aspartic acid, glutamine, glutamic acid, glycine, and serine, were abundant in the 20°C-cultivated alga, and increased 1.9–10.5-fold in response to thermal stress (30°C). Total carbon and nitrogen contents also increased in the 30°C-cultivated alga. Sodium dodecylsulfate-polyacrylamide gel electrophoretic patterns of total proteins extracted from both temperature-treated algae showed the increases of 20, 25, and 90 kDa proteins in the 30°C-cultivated alga. Isozyme assays for 20 enzymes showed a different banding pattern only in the case of glutamate dehydrogenase (GDH). Although it was observed that both temperature-treated algae possessed NAD⁺- and NADP⁺-specific GDH, the 30°C-cultivated alga had an additional NADP⁺-specific GDH (NADP-GDH). These results suggest that NADP-GDH compensates for the thermally induced decreases in nitrogen assimilation efficiency and thereby regulates nitrogen metabolism under conditions of temperature stress.