Possible Involvement of Abscisic Acid in Increases in Activities of Two Vacuolar H+-Pumps in Barley Roots under Aluminum Stress

Levels of abscisic acid (ABA) in barley roots increased upontreatment with AlCl₃. Treatment with AlCl₃ or ABA increasedboth ATP-dependent and PP_i-dependent H⁺-pumping activities intonoplast-enriched membrane vesicles. Increase in the H⁺-pumpingactivities caused by aluminum stress could result from increasedlevels of ABA. ¹Present address: Department of Botany, Faculty of Science,Hirosaki University, Hirosaki, Aomori, 036 Japan     

Mutations in Escherichia coli aceE and ribB Genes Allow Survival of Strains Defective in the First Step of the Isoprenoid Biosynthesis Pathway

A functional 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway is required for isoprenoid biosynthesis and hence survival in Escherichia coli and most other bacteria. In the first two steps of the pathway, MEP is produced from the central metabolic intermediates pyruvate and glyceraldehyde 3-phosphate via 1-deoxy-D-xylulose 5-phosphate (DXP) by the activity of the enzymes DXP synthase (DXS) and DXP reductoisomerase (DXR). Because the MEP pathway is absent from humans, it was proposed as a promising new target to develop new antibiotics. However, the lethal phenotype caused by the deletion of DXS or DXR was found to be suppressed with a relatively high efficiency by unidentified mutations. Here we report that several mutations in the unrelated genes aceE and ribB rescue growth of DXS-defective mutants because the encoded enzymes allowed the production of sufficient DXP in vivo. Together, this work unveils the diversity of mechanisms that can evolve in bacteria to circumvent a blockage of the first step of the MEP pathway.     

Involvement of the C-terminal Region in Phosphate Inhibition of Plasma Membrane Proton Pumping Activity

Received 28 August 2000/ Accepted in revised form 10 February 2001     

Identification of the cDNA of differentially expressed genes in the transition zone of cucumber seedlings by fluorescent differential display.

Cucumber seedlings have potential to develop two pegs on the transition zone between the hypocotyl and root. Seedlings grown in a horizontal position suppress the development of the peg on the upper side of the transition zone in response to gravity. To understand how the response to gravity suppresses peg formation, we screened cucumber mRNAs to identify the mRNA in the non-peg side that accumulates more than in the peg side. For screening, we determined conditions of fluorescent differential display (FDD). Then, we carried out FDD and found 4 cDNA bands that repeatedly showed stronger intensity in the non-peg side than the peg side. We isolated one of these RT-PCR products. Northern blotting showed the pattern of its mRNA accumulations corresponding to the results of FDD.     

Determination of sugar phosphates and nucleotides related to photosynthetic metabolism by high-performance anion-exchange liquid chromatography with fluorometric and ultraviolet detection

A high-performance anion-exchange liquid chromatography system was constructed to identify sugar phosphates and nucleotides involved in photosynthetic metabolism. First sugar phosphates and nucleotides were separated by a gradient elution with boric acid and sodium phosphate, then they were detected by a fluorescence detector (as fluorescent derivatives with arginine) and UV detector, respectively. Eight authentic sugar phosphates and 11 authentic nucleotides could be analyzed using the system. The applicability of the system to the determination of the corresponding sugar phosphates and nucleotides in extracts from only five soybean leaf discs (8.95 cm2) was shown.     

Study of community assembly patterns and interspecific interactions involved in insect succession on rat carcasses

Although many forensic entomological studies have described patterns of carrion insect succession and theoretical studies have explained interspecific interactions that drive succession, empirical studies on the quantitative and ecological aspects of carrion insect succession, such as the degree of historical contingency in community assembly and interspecific interactions during succession, are limited. In this study, I investigated variability in the successional pathways of carrion insect communities in rat carcasses and their decomposition processes, and examined the interspecific interactions involved in succession, such as the effects of carcass utilization by early‐arriving species on late‐arriving species. Members of the families Calliphoridae and Formicidae and the species Eusilpha japonica (Motschulsky) and Nicrophorus concolor Kraatz were chiefly observed. In almost all carcasses, formicid species arrived first, and calliphorid species and E. japonica arrived simultaneously or immediately after. Nicrophorus concolor arrived last, with its time of colonization occurring earlier in carcasses with greater E. japonica abundance. Meanwhile, the early‐arriving species decreased when N. concolor arrived. Nicrophorus concolor tended to reproduce on carcasses with lower cumulative abundance of early‐arriving species and tended to feed on carcasses with greater cumulative abundance of early‐arriving species. These results show that the successional pathways of the chief carrion insect species are highly consistent among carcasses. In contrast, early‐arriving species seem to influence the utilization patterns of carcasses by late‐arriving species, and therefore produce variability in the decomposition process. These results also show that succession could be driven by facilitation and interspecific competition between early‐arriving and late‐arriving species.     

<Emphasis Type="Italic">p</Emphasis>-Chlorophenoxyisobutyric acid impairs auxin response for gravity-regulated peg formation in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis>) seedlings

Cucumber (Cucumis sativus L.) seedlings form a specialized protuberance, the peg, on the transition zone between the hypocotyl and the root. When cucumber seeds germinate in a horizontal position, the seedlings develop a peg on the lower side of the transition zone. To verify the role of auxin action in peg formation, we examined the effect of the anti-auxin, p-chlorophenoxyisobutyric acid (PCIB), on peg formation and mRNA accumulation of auxin-regulated genes. Application of PCIB to cucumber seedlings inhibited peg formation. The application of indole-3-acetic acid (IAA) competed with PCIB and induced peg formation. Furthermore, application of PCIB decreased auxin-inducible CsIAA1 mRNA and increased auxin-repressible CsGRP1 mRNA in the lower side of the transition zone. The differential accumulation of CsIAA1 and CsGRP1 mRNAs in the transition zone of cucumber seedlings grown in a horizontal position was smaller in the PCIB-treated seedlings. These results demonstrate that endogenous auxin redistributes and induces the differential expression of auxin-regulated genes, and ultimately results in the suppression or induction of peg formation in the gravistimulated transition zone of cucumber seedlings.     

Regulation of leaf photosynthetic rate correlating with leaf carbohydrate status and activation state of Rubisco under a variety of photosynthetic source/sink balances

There is evidence suggesting that in plants changes in the photosynthetic source/sink balance are an important factor that regulates leaf photosynthetic rate through affects on the leaf carbohydrate status. However, to resolve the regulatory mechanism of leaf photosynthetic rate associated with photosynthetic source/sink balance, information, particularly on mutual relationships of experimental data that are linked with a variety of photosynthetic source/sink balances, seems to be still limited. Thus, a variety of manipulations altering the plant source/sink ratio were carried out with soybean plants, and the mutual relationships of various characteristics such as leaf photosynthetic rate, carbohydrate content and the source/sink ratio were analyzed in manipulated and non-manipulated control plants. The manipulations were removal of one-half or all pods, removal of one-third or two-third leaves, and shading of one-third or one-half leaves with soybean plants grown for 8 weeks under 10 h light (24 degrees C) and 14 h darkness (17 degrees C). It was shown that there were significant negative correlations between source/sink ratio (dry weight ratio of attached leaves to other all organs) and leaf photosynthetic rate; source/sink ratio and activation ratio (percentage of initial activity to total activity) of Rubisco in leaf extract; leaf carbohydrate (sucrose or starch) content and photosynthetic rate; carbohydrate (sucrose or starch) content and activation ratio of Rubisco; amount of protein-bound ribulose-1,5-bisphosphate (RuBP) in leaf extract and leaf photosynthetic rate; and the amount of protein-bound RuBP and activation ratio of Rubisco. In addition, there were significant positive correlations between source/sink ratio and leaf carbohydrate (sucrose or starch) content; source/sink ratio and the amount of protein-bound RuBP; carbohydrate (sucrose or starch) content and amount of protein-bound RuBP and the activation ratio of Rubisco and leaf photosynthetic rate. The plant water content, leaf chlorophyll and Rubisco contents were not affected significantly by the manipulations. There is a previous report in Arabidopsis thaliana that the amount of protein-bound RuBP in leaf extract correlates negatively with the activation ratio of Rubisco in the leaf extract. Therefore, the results obtained from the manipulation experiments indicate that there is a regulatory mechanism for the leaf photosynthetic rate that correlates negatively with leaf carbohydrate (sucrose and starch) status and positively with the activation state of Rubisco under a variety of photosynthetic source/sink balances.     

Characteristics of gas exchange and morphology of a spring ephemeral, Erythronium japonicum, in comparison with a sun plant, Glycine max

Morphological characteristics and responses of gas exchanges to light intensity were examined in a typical vernal species, Erythronium japonicum Decne (E. japonicum), grown (i) on the floor of a deciduous broad-leaved Quercus mongolica forest (one of its native habitats, the Q. mongolica stand); (ii) bare land left undisturbed for 9 years after forest clearing (the bare stand); and (iii) in a sun crop, soybean, grown for 110 days in an experimental field and for 17 days in pots, in order to evaluate the adaptability of the photosynthetic process of this vernal species to its shady native habitats. The daytime solar radiation, ai and leaf temperatures and leaf–air vapor pressure difference (VPD) were significantly higher at the bare stand than at the Q. mongolica stand. When environmental factors observed at the Q. mongolica and bare stands were reproduced in an assimilation chamber, leaf temperatures of E. japonicum plants increased markedly with increased radiation, whereas those of soybean plants differed little from the respective air temperatures. The photosynthetic and transpiration rates and stomatal conductance in the former plants placed under conditions at the Q. mongolica stand increased with radiation and reached respective steady state values at maximum radiation at the site; whereas, under the conditions at the bare stand, they also increased and reached respective steady state values, but then continuously decreased to be lower than the respective value at the Q. mongolica stand. However, both rates and the conductance in the soybean plants under both conditions increased significantly with radiation and reached much higher respective values at the respective maximum radiations. Water use efficiency for E. japonicum plants was much higher under conditions at the Q. mongolica stand than at the bare stand and was practically equal to those for soybean plants under both conditions. Water potential in the leaves of E. japonicum at maximum radiation at the bare stand was one-third that of those at the Q. mongolica stand. The potential in soybean leaves differed little between both conditions and was roughly equal to the low value in E. japonicum leaves at the bare stand conditions. The stomatal densities on upper and lower leaf surfaces and the ratio of root weight to leaf area (R : L) differed little between E. japonicum plants grown at both stands as well as between young and adult soybean plants. However, the densities on the upper and lower surfaces of E. japonicum were 25% and 60% of the respective values of both soybean plants. The ratios of R : L of the E. japonicum plants were only one-quarter that of the young and adult soybean plants. The cooperation between these morphological and gas exchange characteristics in E. japonicum plants is discussed in relation to adaptation to the environment in native habitats.     

The Effects of CO2 on the Photosynthetic Fixation of CO2 and the Activity of Ribulose-1,5-Bisphosphate Carboxylase in Single-Rooted Soybean Leaves under Sink-Limited Conditions

Ribulosebisphosphate carboxylase activity of single-rooted soybeanleaves was lowered under sink-limited conditions. The low photosyntheticand enzymatic activities of the sink-limited leaves returnedto the high levels, similar to those of the control leaves,within 30 min of the treatment with high CO₂. (Received March 2, 1996; Accepted September 18, 1996)