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.     

Changes in Lysozyme due to Interaction with Vaporized Hexanal

In order to elucidate the mechanism of the alteration of proteins induced by vaporized aldehydes, unmodified and chemically-modified lysozymes were exposed in the solid state to vaporized hexanal at 50°C and 5.8 or 75% relative humidity (RH). On exposure at 75%RH, the unmodified lysozyme exhibited polymerization, browning, loss of solubility, fluorescence production and impairment of lysine, tryptophan and methionine residues. Methionine residues seemed to be oxidized to methionine sulfoxide residues. The polymerization did not proceed at 5.8RH. All the above alterations were almost completely prevented by the removal of oxygen from the reaction cells. Acetylation of lysozyme retarded these alterations fairly well except that the impairment of tryptophan residues was unaffected.

On the basis of all the results it is suggested that at the first step the concerned reaction essentially requires hexanal derivatives such as peroxyhexanoic acid and/or related radicals induced through the reaction with oxygen. The second step seems to consist at least of two routes which are independent of each other and require water. One route is assumed to be an amino-carbonyl reaction involving lysine residues. The other route seems responsible for the attack on tryptophan and methionine residues through oxidation involving the radicals.     

Synthesis of novel benzbromarone derivatives designed to avoid metabolic activation

We synthesized six novel BBR derivatives that were designed to avoid metabolic activation via ipso-substitution and evaluated for their degree of toxicity and hURAT1 inhibition. It was found that all of the derivatives demonstrate lower cytotoxicity in mouse hepatocytes and lower levels of metabolic activation than BBR, while maintaining their inhibitory activity toward the uric acid transporter. We propose that these derivatives could serve as effective uricosuric agents that have much better safety profiles than BBR.     

Physiological nitrogen efficiency in rice: Nitrogen utilization,photosynthesis, and yield potential

Characteristics of rice (Oryza sativa) as a crop plant are briefly introduced, and the relationship between formation of yield potential and nitrogen (N) nutrition is described on the basis of studies using 15N as a tracer. In addition, the relationship between the leaf photosynthetic capacity and leaf N, and the factors limiting leaf photosynthesis under different growth conditions are reviewed. Finally, targets for improving rice yield potential are discussed with a focus on the role of increased photosynthesis efficiency in relation to leaf N status and the photosynthetic components in the leaves.     

Photosynthesis and Plant Growth at Elevated Levels of CO2

In this review, we discuss the effects of elevated CO₂ levelson photosynthesis in relation to the whole plant growth in terrestrialhigher C₃ plants. Short-term CO₂ enrichment stimulates the rateof photosynthesis. Plant mass is also enhanced by CO₂ enrichment.However, the effects of long-term CO₂ enrichment on photosynthesisare variable. Generally, the prolonged exposure to CO₂ enrichmentreduces the initial stimulation of photosynthesis in many species,and frequently suppresses photosynthesis. These responses areattributed to secondary responses related to either excess carbohydrateaccumulation or decreased N content rather than direct responsesto CO₂. Accumulation of carbohydrates in leaves may lead tothe repression of photosynthetic gene expression and excessstarch seems to hinder CO₂ diffusion. Therefore, the specieswhich have the sink organs for carbohydrate accumulation donot show the suppression of photosynthesis. The suppressionof photosynthesis by CO₂ enrichment is always associated withdecreases in leaf N and Rubisco contents. These decreases arenot due to dilution of N caused by a relative increase in theplant mass but are the result of a decrease in N allocationto leaves at the level of the whole plant, and the decreasein Rubisco content is not selective. Leaf senescence and plantdevelopment are also accelerated by CO₂ enrichment. However,they are independent of each other in some species. Thus, variousresponses to CO₂ observed at the level of a single leaf resultfrom manifold responses at the level of the whole plant grownunder conditions of CO₂ enrichment. (Received July 8, 1999; Accepted August 12, 1999)     

Therapeutic protective effects of IL-12 combined with soluble IL-4 receptor against established infections of herpes simplex virus type 1 in thermally injured mice.

The effect of combination therapy between IL-12 and soluble IL-4R (sIL-4R) on the established infection of HSV-1 in thermally injured mice (TI mice) was investigated. All of the TI mice infected with lethal amounts of HSV-1 died when IL-12 was given therapeutically at a dose of 500 U/mouse. However, 80% of these mice treated prophylactically with IL-12 survived compared with 0% survival of the same mice treated with saline. The therapeutic administration of IL-12 to TI mice currently infected with HSV-1 caused an 80% survival of these mice when the treatment was combined with sIL-4R. Although IL-12 did not stimulate IFN-gamma production in cultures of splenic T cells from TI mice, IFN-gamma was produced by stimulation with IL-12 when the producer cells were prepared from TI mice that had been treated previously with sIL-4R. After stimulation with anti-CD3 mAb, splenic T cells from TI mice with the established infection of HSV-1 produced IL-4 into their culture fluids. However, IL-4 was not produced by splenic T cells that were prepared from the same infected mice treated with IL-12 and sIL-4R in combination. The results obtained herein indicate that the efficacies of the combination therapy against the established infection of HSV-1 may result from the IFN-gamma production stimulated by IL-12 in TI mice that are treated with sIL-4R for reducing burn-associated type 2 T cell responses.     

Identification of small RNAs in late developmental stage of rice anthers

Small RNAs including microRNA (miRNA) and small interfering RNA (siRNA) are known as repressors of gene expression. There are many plant proteins involved in small RNA-mediated gene silencing, such as Dicer ribonucleases and RNA-dependent RNA polymerases. However, most of these proteins have been reported to be absent in the late developmental stage of the plant male gamete, pollen. In order to clarify the existence of the small RNAs during maturation of pollen, we cloned and sequenced small RNAs from rice anthers including tricellular pollen. From fifty six candidates of small RNAs, we identified two known miRNAs (miR166 and miR167), eight potential miRNAs, and ten putative heterochromatic siRNAs (hc-siRNAs). RNA gel blot analyses clearly showed that miR166 and miR167 were accumulated in the uninuclear pollen stage of anther development and remained until the tricellular pollen stage. Our cloning and RNA gel blot analyses of small RNAs led us to propose a possible function of small RNA-mediated gene regulation for the development of male gametes in rice.     

Cav2.1 Voltage-dependent Ca<Superscript>2+</Superscript> Channel Current is Inhibited by Serum from Select Patients with Guillain-Barré Syndrome

To investigate the pathophysiological mechanisms of immune-mediated peripheral neuropathies, we studied the effects of sera from patients with Guillain-Barré syndrome (GBS) on the Cav2.1 voltage-dependent calcium channel (VDCC) current in Purkinje cells. Using the whole-cell recording technique, Cav2.1 VDCC current was measured in cerebellar Purkinje cells in the presence of serum from GBS patients with acute motor axonal neuropathy (AMAN) or acute inflammatory demyelinating polyneuropathy (AIDP). The AMAN patient sera significantly inhibited the Cav2.1 VDCC current compared with healthy volunteer sera, and this inhibition was fully reversible by washing out the AMAN serum. Similarly, IgG purified from AMAN sera also inhibited the Cav2.1 VDCC current. However, the activation and inactivation kinetics of the Cav2.1 VDCC currents were not affected by serum from an AMAN patient. Moreover, the VDCC current of Purkinje cells was also inhibited by IgG anti-GM1 monoclonal antibody (anti-GM1 mAb). In an immunocytochemical study using double fluorescence staining, Purkinje cells were stained by monoclonal IgG anti-GM1 mAb. In contrast, AIDP patient and healthy volunteer sera did not affect the Cav2.1 VDCC current. These results suggest that in some case of GBS, particularly of AMAN patients with IgG anti-GM1 mAb, muscle weakness may be induced by dysfunction of Cav2.1 VDCC functioning at the motor nerve terminals. Special issue article in honor of Dr. George DeVries.     

Association between antibody response against cytomegalovirus strain-specific glycoprotein H epitopes and HLA-DR

The gH of CMV is a major target for strain-specific neutralizing antibodies. To verify whether there is a correlation between HLA-DR type and strain-specific antibodies, antibodies against CMV gH in potential donors and recipients for renal transplantation were investigated. Among 471 subjects, 404 (86%) showed reactivity to CMV gH, but no antibodies against gH were detected in 67 (14%) subjects. The positive rates were over 80% in most HLA subpopulations. Fewer subjects with HLA-DR10 and DR11 had antibodies to CMV gH than did those without HLA-DR10 and DR11. HLA-DR10 and DR11 may be associated with fewer/non-responders for strain-specific neutralizing antibodies.     

Differences in binding and effector functions between classes of TNF antagonists

There are currently two Food and Drug Administration-approved classes of biologic agents that target tumor necrosis factor-α (TNF-α): anti-TNF monoclonal antibodies (mAbs) (adalimumab and infliximab), and soluble TNF receptors (etanercept). This study examined the ability of the TNF antagonists to: (1) bind various polymorphic variants of cell surface-expressed Fc receptors (FcγRs) and the complement component C1q, and (2) mediate Ab-dependent cellular cytotoxicity (ADCC) and complement-mediated cytotoxicity (CDC) killing of cells expressing membrane-bound TNF (mTNF) in vitro. Both mAbs and the soluble TNF receptor demonstrated low-level binding to the activating receptors FcγRI, FcγRIIa, and FcγRIIIa, and the inhibitory receptor FcγRIIb, in the absence of exogenous TNF. However, upon addition of TNF, the mAbs, but not etanercept, showed significantly increased binding, in particular to the FcγRII and FcγRIII receptors. Infliximab and adalimumab induced ADCC much more potently than etanercept. In the presence of TNF, both mAbs bound C1q in in vitro assays, but etanercept did not bind C1q under any conditions. Infliximab and adalimumab also induced CDC in cells expressing mTNF more potently than etanercept. Differences in the ability to bind ligand and mediate cell death may account for the differences in efficacy and safety of TNF antagonists.