Two Long-Term Effects of Light that Control the Stability of Proteins Related to Photosynthesis during Senescence of Rice Leaves

Rate of light-saturated photosynthesis (P_max) decreased duringsenescence, with no or small changes in the initial slope ofthe light-response curve (     

Tollip and Tom1 form a complex and recruit ubiquitin-conjugated proteins onto early endosomes

Tom1 (target of Myb1) is a protein of unknown function. Tom1 and its relative Tom1L1 have an N-terminal VHS (Vps27p/Hrs/Stam) domain followed by a GAT (GGA and Tom1) domain, both of which are also found in the GGA (Golgi-localizing, gamma-adaptin ear domain homology, ADP-ribosylation factor-binding protein) family of proteins. Although the VHS and GAT domains of GGA proteins bind to transmembrane cargo proteins and the small GTPase ADP-ribosylation factor, respectively, the VHS and GAT domains of Tom1 are unable to interact with these proteins. In this study, we show that the GAT domains of Tom1 and Tom1L1 interact with ubiquitin and Tollip (Toll-interacting protein). Ubiquitin bound the GAT domains of Tom1, Tom1L1, and GGA proteins, whereas Tollip interacted specifically with Tom1 and Tom1L1. Ubiquitin and Tollip bound to an overlapping region of the Tom1-GAT domain in a mutually exclusive manner. Tom1 was predominantly cytosolic when expressed in cells. On the other hand, Tollip was localized on early endosomes and recruited Tom1 and ubiquitinated proteins. These observations suggest that Tollip and Tom1 form a complex and regulate endosomal trafficking of ubiquitinated proteins.     

Performance of affinity chromatography columns

Performance of affinity chromatography columns was studied by measuring the rates of adsorption and elution of trypsin in a Sepharose 4B-soybean trypsin inhibitor column and a Sepharose 4B-arginine peptides column. The volumetric coefficient for trypsin transfer was evaluated from the break-through curves of trypsin, and elution profiles bed height of Sepharose 4B-STI column was estimated based on these results.     

Quantification of mcrA by quantitative fluorescent PCR in sediments from methane seep of the Nankai Trough

A quantitative fluorogenic PCR method for group-specific methyl coenzyme M reductase subunit A genes (mcrA) from methanotrophic archaea was established and applied to the characterization of microbial communities in anoxic methane seep sediments at the accretionary prism of the Nankai Trough. All of the previously identified subgroups of anaerobic methanotroph (ANME) mcrA genes were detected in the cores up to 25 cm below the seafloor, but distributional patterns of mcrA genes were found to differ according to depth. These findings suggest a distinct distribution of phylogenetically and physiologically diverse methanotrophic archaea that mediate methane oxidation in the anoxic sediments. This quantification method will contribute to future investigations of methanotrophic microbial ecosystems in anoxic marine sediments.     

Early research on the role of plastocyanin in photosynthesis

A review is presented of the early history of investigations into the function of the blue copper-protein plastocyanin in photosynthesis. The controversy or confusion that arose as to the function of plastoycanin in conjunction with cytochrome f and cytochrome c ₆ is discussed and investigations contributing to the establishment of the role of plastocyanin as the mobile electron carrier between the Photosystem I reaction center complex and the cytochrome b ₆/f complex are described. This revised version was published online in August 2006 with corrections to the Cover Date.     

Permeabilities of composite membranes containing phospholipids

Two types of artificial membranes containing a phospholipid were prepared and their permeabilities were measured around the phase-transition temperature of the phospholipid. The permeability of the membranes to a hydrophobic solute was higher than to a hydrophilic solute, and showed an abrupt change at the phase-transition temperature of the phospholipid, similar to that in biomembranes and liposomes, caused by the fluidity change of the phospholipid at this temperature.     

DNA polymerase mu interacts with a meiosis-specific RecA homolog Lim15 during meiosis in Coprinus cinereus

Meiosis is a fundamental process in eukaryotes. Homologous chromosomes are paired and recombined during meiotic prophase I, which results in variation among the gametes. However, the mechanism of recombination between the maternal and paternal chromosome is unknown. In this study, we report on the identification of interaction between Coprinus cinereus DNA polymerase mu (CcPol mu) and CcLim15/Dmc1, a meiosis-specific RecA-like protein, during meiosis. Interaction between these two proteins was confirmed using a GST-pull down assay. A two-hybrid assay revealed that the N-terminus of CcPol mu, which includes the BRCT domain, is responsible for binding the C-terminus of CcLim15. Furthermore, co-immunoprecipitation experiments indicate that these two proteins also interact in the crude extract of the meiotic cell. A significant proportion of CcPol mu and CcLim15 is shown to co-localize in nuclei from the leptotene/zygotene stage to the early pachytene stage during meiotic prophase I. Moreover, CcLim15 enhances polymerase activity of CcPol mu early in the reaction. These results suggest that CcPol mu might be recruited by CcLim15 and elongate the D-loop structure during homologous recombination in meiosis.     

Proadrenomedullin N-Terminal 20 Peptide (PAMP), an Endogenous Anticholinergic Peptide: Its Exocytotic Secretion and Inhibition of Catecholamine Secretion in Adrenal Medulla

Abstract: In cultured bovine adrenal medullary cells, stimulation of nicotinic receptors by carbachol evoked the Ca²⁺-dependent exocytotic cosecretion of proadrenomedullin N-terminal 20 peptide (PAMP) (EC₅₀ = 50.1 µ M ) and catecholamines (EC₅₀ = 63.0 µ M ), with the molar ratio of PAMP/catecholamines secreted being equal to the ratio in the cells. Addition of PAMP[1–20]NH₂ inhibited carbachol-induced ²²Na⁺ influx via nicotinic receptors (IC₅₀ = 2.5 µ M ) in a noncompetitive manner and thereby reduced carbachol-induced ⁴⁵Ca²⁺ influx via voltage-dependent Ca²⁺ channels (IC₅₀ = 1.0 µ M ) and catecholamine secretion (IC₅₀ = 1.6 µ M ). It did not alter high K⁺-induced ⁴⁵Ca²⁺ influx via voltage-dependent Ca²⁺ channels or veratridine-induced ²²Na⁺ influx via voltage-dependent Na⁺ channels. PAMP seems to be a novel antinicotinic peptide cosecreted with catecholamines by a Ca²⁺-dependent exocytosis in response to nicotinic receptor stimulation.     

Changes in the Number and Size of Chloroplasts during Senescence of Primary Leaves of Wheat Grown under Different Conditions

Changes in the number and size of chloroplasts in mesophyllcells were investigated in primary leaves of wheat from fullexpansion to yellowing under different growth conditions. Thenumber of chloroplasts per cell decreased slowly, although thedecrease was steady and statistically significant, until thelast stage of leaf senescence, when rapid degradation of chloroplaststook place. Rates of leaf senescence, or the decline in thenumber of chloroplasts, varied greatly among plants grown atdifferent seasons of the year, but about 20% of chloroplastsalways disappeared during the phase when steady loss of chloroplastsoccurred. The area of chloroplast disks also decreased graduallybut significantly, with a rapid decrease late in senescence.Thus, the total quantity of chloroplasts per mesophyll celldecreased substantially during leaf senescence. Yellowed leavescontained numerous structures that resemble oil drops but nochloroplasts. Decreases in rates of photosynthesis that occurduring senescence may, therefore, be largely due to decreasesin the quantity of chloroplasts. However, a better correlationwas found between the decrease in the maximum capacity for photosynthesisand the degradation of RuBP carboxylase. When plants had beengrown with a sufficient supply of nutrients, the number of chloroplastsdecreased steadily but at a reduced rate and the reduction inthe area of chloroplast disks was strongly suppressed. Thus,the quantitative decrease in chloroplasts in senescing leavesappears to be regulated by the requirements for nutrients (nitrogen)of other part of the plant. ³Present address: Department of Biology, Faculty of Science,Toho University, Miyama, Funabashi, Chiba, 274 Japan