Effects of leaf age, nitrogen nutrition and photon flux density on the organization of the photosynthetic apparatus in leaves of a vine (Ipomoea tricolor Cav.) grown horizontally to avoid mutual shading of leaves

Effects of leaf age, nitrogen nutrition and photon flux density (PFD) on the organization of the photosynthetic apparatus in leaves were investigated in a vine, Ipomoea tricolor Cav., which was grown horizontally so as to avoid mutual shading of leaves. The plants were grown hydroponically at two nitrate levels under two growth light treatments. For one group of the plants, leaves were exposed to full sunlight. For another group, respective leaves were artificially shaded in a manner that simulated changes in the light gradient with the development of an erect herbaceous canopy: old leaves were placed under progressively shadier conditions with growth of the plants (canopy-type shading). In all the treatments, chlorophyll (Chl) content gradually decreased with leaf age. Photosystem I (PSI) per Chl was constant, independent of leaf age, nitrogen nutrition and/or PFD. Photosystem II (PSII) and cytochrome / per Chl, and Chl a/b ratio were independent of leaf age and/or nitrogen nutrition but decreased with the decrease in growth PFD. Ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39, RuBPCase) per Chl steeply decreased with decrease in PFD. When leaves grown at the same PFD were compared, RuBPCase/Chl was lower in the plants grown under lower nitrogen availability and also decreased with leaf age in the plants grown without shading. These decreases were attributed to the curvilinear relationship between RuBPCase and Chl in leaves grown at full sunlight, that was independent of nitrogen availability and leaf age. From these results, it is concluded that the composition of the photosynthetic apparatus is independent of leaf age but changes depending on the light environment and total amount of photosynthetic components of the leaf.Abbreviations Chl chlorophyll - cyt f cytochrome f - PFD photon flux density - RuBPCase ribulose-1,5-bisphosphate carboxylase The author thanks Drs. K. Sonoike, Y. Kashino, K. Okada, H. Hatanaka, Y. Suzuki and A. Aoyama for technical advise. The author also thanks Drs. I. Terashima, A. Makino (Tohoku University, Sendai, Japan), Dr. J.R. Evans (Research School of Biological Sciences, Australian National University, Canberra) and Prof. A. Watanabe for valuable suggestions.     

Cocoon predation on diprionid sawflies: the effect of forest fertility

Predation by small mammals is thought to be one of the main regulators of outbreaking sawfly species. It has been suggested that predation may be lower in poor and dryish forests, and this is the reason why outbreaks often begin from this type of environment. We studied experimentally how fertility of the forest site affects cocoon predation experienced by two sawfly species, the common pine sawfly Diprion pini (Linnaeus) and the European pine sawfly Neodiprion sertifer (Geoffroy). We applied a fertilization treatment to selected pine-dominated barren forest sites in Finland, and 2–4 years later monitored predation on the sawfly cocoons in fertilized and control areas. The results did not support the idea that forest fertility was related to cocoon predation. We also could not verify that small mammal abundance was related to fertility of the forest. The most obvious pattern we observed was that the two sawfly species differed dramatically in predation experienced. N. sertifer has its cocoon phase in mid-summer and experienced only moderate predation (37%) whereas D. pini, with its cocoon phase in autumn, suffered from very heavy predation (96%). Our observations suggest that if predation is important in controlling the population dynamics of the species, its impact depends more on the sawfly species and season than on the fertility of the forest site. Received: 1 March 1998 / Accepted: 25 May 1998     

Knee stiffness is a major determinant of leg stiffness during maximal hopping

Understanding stiffness of the lower extremities during human movement may provide important information for developing more effective training methods during sports activities. It has been reported that leg stiffness during submaximal hopping depends primarily on ankle stiffness, but the way stiffness is regulated in maximal hopping is unknown. The goal of this study was to examine the hypothesis that knee stiffness is a major determinant of leg stiffness during the maximal hopping. Ten well-trained male athletes performed two-legged hopping in place with a maximal effort. We determined leg and joint stiffness of the hip, knee, and ankle from kinetic and kinematic data. Knee stiffness was significantly higher than ankle and hip stiffness. Further, the regression model revealed that only knee stiffness was significantly correlated with leg stiffness. The results of the present study suggest that the knee stiffness, rather than those of the ankle or hip, is the major determinant of leg stiffness during maximal hopping.     

Sulfatide is required for efficient replication of influenza A virus

Sulfatide is abundantly expressed in various mammalian organs, including the intestines and trachea, in which influenza A viruses (IAVs) replicate. However, the function of sulfatide in IAV infection remains unknown. Sulfatide is synthesized by two transferases, ceramide galactosyltransferase (CGT) and cerebroside sulfotransferase (CST), and is degraded by arylsulfatase A (ASA). In this study, we demonstrated that sulfatide enhanced IAV replication through efficient translocation of the newly synthesized IAV nucleoprotein (NP) from the nucleus to the cytoplasm, by using genetically produced cells in which sulfatide expression was down-regulated by RNA interference against CST mRNA or overexpression of the ASA gene and in which sulfatide expression was up-regulated by overexpression of both the CST and CGT genes. Treatment of IAV-infected cells with an antisulfatide monoclonal antibody (MAb) or an anti-hemagglutinin (HA) MAb, which blocks the binding of IAV and sulfatide, resulted in a significant reduction in IAV replication and accumulation of the viral NP in the nucleus. Furthermore, antisulfatide MAb protected mice against lethal challenge with pathogenic influenza A/WSN/33 (H1N1) virus. These results indicate that association of sulfatide with HA delivered to the cell surface induces translocation of the newly synthesized IAV ribonucleoprotein complexes from the nucleus to the cytoplasm. Our findings provide new insights into IAV replication and suggest new therapeutic strategies.     

Dual inhibition of SNARE complex formation by tomosyn ensures controlled neurotransmitter release

Neurotransmitter release from presynaptic nerve terminals is regulated by soluble NSF attachment protein receptor (SNARE) complex–mediated synaptic vesicle fusion. Tomosyn inhibits SNARE complex formation and neurotransmitter release by sequestering syntaxin-1 through its C-terminal vesicle-associated membrane protein (VAMP)–like domain (VLD). However, in tomosyn-deficient mice, the SNARE complex formation is unexpectedly decreased. In this study, we demonstrate that the N-terminal WD-40 repeat domain of tomosyn catalyzes the oligomerization of the SNARE complex. Microinjection of the tomosyn N-terminal WD-40 repeat domain into neurons prevented stimulated acetylcholine release. Thus, tomosyn inhibits neurotransmitter release by catalyzing oligomerization of the SNARE complex through the N-terminal WD-40 repeat domain in addition to the inhibitory activity of the C-terminal VLD.     

Characterization of fibrillation process of alpha-synuclein at the initial stage

α-Synuclein is the major component of the filamentous Lewy bodies and Lewy-related neurites, neuropathological hallmarks of Parkinson’s disease. Although numerous studies on α-synuclein fibrillation have been reported, the molecular mechanisms of aggregation and fibrillation at the initial stage are still unclear. In the present study, structural properties and propensities to form fibrils of α-synuclein at the initial stage were investigated using 2D ¹H-¹⁵N NMR spectroscopy, electron microscope, and small angle X-ray scattering (SAXS). Observation of the 2D ¹H-¹⁵N HSQC spectra indicated significant attenuation of many cross peak intensities in the regions of KTKEGV-type repeats and the non-Aβ component of Alzheimer’s disease amyloid (NAC), suggesting that these regions contributed fibril formation. Oligomerization comprising heptamer was successfully monitored at the initial stage using the time-dependent SAXS measurements.     

Formation of aquaporin-4 arrays is inhibited by palmitoylation of N-terminal cysteine residues

Tetramers of the mammalian water channel aquaporin-4 (AQP4) assemble into square arrays and mediate bidirectional water transport across the blood-brain interface. The aqp4 gene expresses two splicing isoforms. Only the shorter AQP4M23 isoform assembles into square arrays, while the longer AQP4M1 isoform interferes with array formation, presumably due to the additional 22 N-terminal residues. To understand why the N-terminus of AQP4M1 interferes with array formation, we constructed a series of N-terminal deletion mutants and examined their ability to form square arrays in Chinese hamster ovary (CHO) cells using SDS-digested freeze fracture replica labeling. Mutants with deletions of less than seventeen N-terminal residues did not form square arrays and showed dispersed immunogold labels against AQP4 molecules, whereas more deletions led to the formation of square arrays labeled with immunogolds. Furthermore, mutagenic substitution of the two cysteine residues at the position 13 and 17 in the N-terminus of AQP4M1 also resulted in the square array formation. Biochemical analysis and metabolic labeling of transfected CHO cells revealed that the two N-terminal cysteines of AQP4M1 are palmitoylated. These results suggest that palmitoylation of the N-terminal cysteines is the reason for the inability of AQP4M1 to form square arrays.     

Expression in E. coli and tissue distribution of the human homologue of the mouse Ke 6 gene, 17β-hydroxysteroid dehydrogenase type 8

Expression of the human Ke 6 gene, 17β-hydroxysteroid dehydrogenase type 8, in E. coli and the substrate specificity of the expressed protein were examined. The tissue distribution of mRNA expression of the human Ke 6 gene was also studied using real-time PCR. Human Ke 6 gene was expressed as an enzymatically-active His-tag fusion protein, whose molecular weight was estimated to be 32.5 kDa by SDS-polyacrylamide gel electrophoresis. Expressed human Ke 6 gene effectively catalyzed the conversion of estradiol into estrone. Testosterone, 5α-dihydrotestosterone, and 5-androstene-3β,17β-diol were also catalyzed into the corresponding 17-ketosteroid at 2.4–5.9% that of estradiol oxidation. Furthermore, expressed enzyme catalyzed the reduction of estrone to estradiol, but the rate was a mere 2.3%. Human Ke 6 gene mRNA was expressed in the various tissues examined, such as brain, cerebellum, heart, lung, kidney, liver, small intestine, ovary, testis, adrenals, placenta, prostate, and stomach. Expression of human Ke 6 gene mRNA was especially abundant in prostate, placenta, and kidney. The levels in prostate and placenta were higher than that in kidney, where it is known to be expressed in large quantities.     

Changes in composition and content of mycolic acids in glutamate-overproducing Corynebacterium glutamicum

Overproduction of glutamate by Corynebacterium glutamicum is induced by biotin limitation or by the supplementation of specific detergents, sublethal amounts of penicillin, or cerulenin. But, it remains unclear why these different treatments, which have different sites of primary action, produce similar effects.In this study, it was found that the cellular content of mycolic acids--characteristic constituents of Corynebacterineae that are synthesized from fatty acids and form a cell surface layer--decreased under all conditions that induced glutamate overproduction. Furthermore, short mycolic acids increased under conditions of biotin limitation and cerulenin supplementation. These results suggest that different treatments produce the same effect that causes defects in the mycolic acid layer. This is perhaps one of the key factors in overproduction of glutamate by C. glutamicum.