Comparison of histological responses and tissue damage expansion between resistant and susceptible Pinus thunbergii infected with pine wood nematode Bursaphelenchus xylophilus

Pine wilt disease caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, has been epidemic and has had disastrous impacts on pine forests and forest ecosystems in eastern Asia. Many pine species in this area are susceptible to this disease. Pinus thunbergii is particularly susceptible. In Japan, tree breeders have selected surviving trees from severely damaged forests as resistant candidates, and have finally established several resistant varieties of P. thunbergii. However, this breeding procedure requires much time and effort due to the lack of physiological and phenotypical information about resistance. To investigate the resistance mechanisms of selected P. thunbergii, we compared histochemical responses, tissue damage expansion, and PWN distribution in resistant and susceptible clones of P. thunbergii after PWN inoculation. The results suggested that the mechanisms of resistance are as follows: damage expansion in the cortex, cambium, and xylem axial resin canals are retarded in resistant trees soon after inoculation, probably due to the induction of wall protein-based defenses. Suppression of PWN reproduction was particularly caused by inhibition of damage expansion in the cambium. The slow expansion of damage in each tissue provides time for the host to complete the biosynthesis of lignin in the walls of cells that surround the damaged regions. This lignification of cell walls is assumed to effectively inhibit the migration and reproduction of the PWNs. The mechanism of initial damage retardation is presumed to be a key for resistance.     

Plant cell walls as suppliers of potassium and sodium ions for induced resistance in pea (Pisum sativum L.) and cowpea (Vigna unguiculata L.)

When an elicitor is applied to plants to induce resistance, one of the first detectable events is the efflux of ions from the treated tissue. Here we are the first to demonstrate that an elicitor from Mycosphaerella pinodes evokes leakage of Na⁺ and K⁺ ions from isolated cell walls of pea and cowpea in vitro, as observed for epicotyl tissues. Pharmacological experiments showed that this elicitor-stimulated leakage was sensitive to vanadate and N-(3-methylphenyl)biphenyl-4-sulfonamide (NGXT-191), that inhibit a cell wall-associated ATPase (apyrase). Vanadate or NGXT-191 suppressed elicitor-induced superoxide generation and expression of defense genes in vivo. On the basis of these results, we assume that the leakage of these ions, probably associated with an ATP-dependent process(es) in the cell wall, is likely associated with induced defenses of pea and cowpea.     

Suppression of mRNAs for lipoxygenase (LOX), allene oxide synthase (AOS), allene oxide cyclase (AOC) and 12-oxo-phytodienoic acid reductase (OPR) in pea reduces sensitivity to the phytotoxin coronatine and disease development by Mycosphaerella pinodes

Using a recently developed model pathosystem involving Medicago truncatula and Mycosphaerella pinodes, causal agent of Mycosphaerella blight on pea to understand host molecular response to a fungal suppressor, we applied the suppressor to leaves of M. truncatula and identified 151 nonredundant cDNA fragments as newly expressed genes. These included genes encoding lipoxygenase (LOX) and enoyl-CoA hydratase, which are presumably involved in jasmonic acid (JA) synthesis. Potential genes encoding plastidic enzymes, including allene oxide synthase (AOS) and allene oxide cyclase (AOC), and other peroxisomal enzymes involved in β-oxidation were predicted from the Medicago Gene Index EST database and tested for altered expression by semiquantitative RT-PCR. The coordinated expression of genes encoding both plastidic and peroxisomal enzymes showed that the suppressor likely conditions certain cellular process(es) through the JA synthesis in M. truncatula. To explore the role of JA or JA-regulated cellular process(es) in conditioning susceptibility, we used an Apple latent spherical virus (ALSV)-based virus-induced gene silencing (VIGS) technology to silence pea genes including LOX, AOS, AOC and 12-oxo-phytodienoic acid reductase (OPR). In LOX-, AOS-, AOC- or OPR-silenced pea plants, disease development induced by M. pinodes was remarkably reduced. Similarly, silencing of mRNA for LOX, AOS, AOC or OPR reduced the sensitivity to a phytotoxin, coronatine, which is believed to act through a JA-dependent process. On the basis of these results, it is conceivable that M. pinodes has evolved a strategy to condition susceptibility by manipulating the physiology of host cells, in particular JA-regulated cellular process(es), to promote disease development in pea.     

Schema-dependent gene activation and memory encoding in neocortex

When new learning occurs against the background of established prior knowledge, relevant new information can be assimilated into a schema and thereby expand the knowledge base. An animal model of this important component of memory consolidation reveals that systems memory consolidation can be very fast. In experiments with rats, we found that the hippocampal-dependent learning of new paired associates is associated with a striking up-regulation of immediate early genes in the prelimbic region of the medial prefrontal cortex, and that pharmacological interventions targeted at that area can prevent both new learning and the recall of remotely and even recently consolidated information. These findings challenge the concept of distinct fast (hippocampal) and slow (cortical) learning systems, and shed new light on the neural mechanisms of memory assimilation into schemas.     

Time course of final oocyte maturation and ovulation in chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> induced by hCG and GnRHa

Abstract:   The question of whether the ovulation and spawning time in chub mackerel Scomber japonicus is entrained by a circadian rhythm was raised by our previous experiments. Further questions were also raised about whether the time course of human chorionic gonadotropin (hCG)-induced final oocyte maturation (FOM) and ovulation reflected the natural time course induced by endogeneous pituitary gonadotropin (GtH). To address these questions, hCG and gonadotropin-releasing hormone analog (GnRHa) were administered at two 'opposite' times, 14:00 and 02:00 hours, and the time courses of FOM and ovulation were compared. When hCG was injected, ovulation occurred 33 h post-injection in both groups, regardless of the timing of the hCG injection. The timing of ovulation in chub mackerel depends on the timing of hCG injection, but apparently not on circadian rhythms. When GnRHa was injected, ovulation began at 36 h post-injection of GnRHa, regardless of the timing of injection. These results indicate that the time course of FOM and ovulation in the chub mackerel followed a similar pattern whether stimulated by hCG injection or spontaneous luteinizing hormone (LH) surge because GnRHa induces the secretion of endogenous GtH (primarily LH) from the fish pituitary. Thus, it is concluded that the time course of hCG-induced FOM and ovulation in chub mackerel follows the natural time course induced by endogenous pituitary LH.     

Abiotic and biotic factors affecting recruitment variability of walleye pollock (Theragra chalcogramma) off the Pacific coast of Hokkaido,Japan

Abiotic and biotic factors affecting the recruitment variability of the Japanese Pacific stock (JPS) of walleye pollock (Theragra chalcogramma) were examined using a bivariate regression and multivariate combined model. Of the abiotic variables around Funka Bay (spawning ground), February sea surface temperature (SST) and wind direction index showed significant bivariate relationships with recruitment. February SST was positively related to recruitment, suggesting that warmer water temperature in February favors JPS recruitment. On the other hand, the relationship between February wind direction index and recruitment predicts high JPS recruitment under predominant northwest winds in February. For the biotic variables in the Doto area (nursery ground), significant and negative bivariate relationships with recruitment were observed for catch per unit effort of Kamchatka flounder (Atheresthes evermanni), Pacific cod (Gadus macrocephalus), and walleye pollock, implying an important impact of predation by these groundfishes on JPS recruitment. The overall model incorporating these abiotic and biotic factors successfully reproduced the variability in JPS recruitment. Temperature and wind conditions around the spawning ground along with predator condition in the nursery ground appear to play a dominant role in the recruitment dynamics of JPS. Based on these results and prior knowledge, we propose a new hypothesis to explain the processes controlling JPS recruitment.     

Spawning frequency of the Tsushima Current subpopulation of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> off Kyushu,Japan

Female Japanese chub mackerel Scomber japonicus of the Tsushima Current subpopulation were collected during the spawning season from March to May 2001. A total of 137 adult females were caught between midnight and daybreak. A considerable number of fish displayed new postovulatory follicles (POF), whereas there was no evidence of germinal vesicle breakdown or hydrated oocytes in any of the fish collected. This suggests a daily spawning synchronicity toward midnight. To estimate the spawning frequency (S), the female reproductive state was classified into four criteria based on the degenerative stage of the POFs and the developmental stage of the oocytes. To stage the POFs according to age and determine the stage duration, ovaries from S. japonicus were induced to spawn in the laboratory and were sampled 0–72 h after ovulation at appropriate intervals. The average S, which is evaluated from four different indices, was 16.9%, corresponding to the average female chub mackerel spawned every 5.9 days (8.5 times) during the 50 days.     

Molecular cloning of CD4 from ginbuna crucian carp <Emphasis Type="Italic">Carassius auratus langsdorfii</Emphasis>

ABSTRACT:   The clonal triploid ginbuna crucian carp Carassius auratus langsdorfii , a naturally occurring gynogenetic fish, is a useful model for studying T-cell-mediated immunity. CD4, a T-cell receptor (TCR) coreceptor, is a membrane-bound glycoprotein found on helper T-cells, and assists in the binding of major histocompatibility complexes. In the present study, full-length cDNAs encoding the CD4 molecule from the S3n strain of ginbuna crucian carp were cloned and characterized. 5'-rapid amplification of cDNA ends (RACE) and 3'-RACE yielded two distinct cDNA clones of CD4 homolog from the ginbuna, and these sequences share 95% identity at the amino acid level. These ginbuna CD4 molecules consisted of a signal peptide, immunoglobulin superfamily (IgSf) like domains, a transmembrane domain, and a cytoplasmic domain similar to other known CD4. A tyrosine protein kinase p56^lck binding motif is conserved in the cytoplasmic tail of ginbuna CD4. Phylogenetic tree analysis indicated that ginbuna CD4 sequences are closely related to CD4L-1 from other fish species. Expression of ginbuna CD4 mRNA was detected in the gill, thymus, head kidney, trunk kidney and peripheral blood leukocytes, indicating that its expression pattern is similar to that of ginbuna TCRβ mRNA. The results suggest that ginbuna CD4 sequences are useful as molecular probes for helper T-cells.