N-Acetylchitooligosaccharides,biotic elicitor for phytoalexin production,induce transient membrane depolarization in suspension-cultured rice cells

Summary N-acetylchitooligosaccharides (fragments of chitin) elicit the production of phytoalexin in suspension-cultured rice cells. This oligosaccharide elicitor induced rapid and transient membrane depolarization at sub-nanomolar concentrations. Only the oligomers with a certain degree of polymerization were active, while deacetylated chitooligosaccharides caused no effect. Such specificity coincided well with that for the elicitor activity, suggesting possible involvement of this transient change in membrane potential as one of the initial signals in the signal transduction sequence for the activation of defense responses.     

A model for feature linking via collective oscillations in the primary visual cortex

A neural network model for explaining experimentally observed neuronal responses in cat primary visual cortex is proposed. In our model, the basic functional unit is an orientation column which is represented by a large homogeneous population of neurons modeled as integrate-and-fire type excitable elements. The orientation column exhibits spontaneous collective oscillations in activity in response to suitable visual stimuli. Such oscillations are caused by mutual synchronization among the neurons within the column. Numerical simulation for various stimulus patterns shows that as a result of activity correlations between different columns, the amplitude and the phase of the oscillation in each column depend strongly on the global feature of the stimulus pattern. These results satisfactorily account for experimental observations.     

Cytotoxic cell function and phenotypic analysis of peripheral blood mononuclear cells in cancer patients treated with low-dose interleukin-2 and mitomycin C

We previously found that the ability of peripheral blood mononuclear cells (PBM) of cancer patients to generate lymphokine-activated killer (LAK) cells became remarkably augmented after mitomycin C administration. On the basis of the clinical finding, we designed a treatment regimen comprised of 12 mg/m² mitomycin C i. v. on day 1 and 700 U/m² recombinant interleukin-2 (IL-2) i.v. every 12 h from day 4 through day 8. Of 25 patients with advanced carcinoma, 9 had a partial response and 3 had a minor response. Cytotoxic cell function, including natural killer activity, lymphokine-activated killer (LAK) activity, and the ability to generate LAK cells, and lymphocyte subsets in PBM was measured 1 day before and after either the first or second course of this therapy. The relationship between these parameters and the clinical antitumor response to this treatment was examined. Although the cytotoxic activities were significantly augmented after either the first or second treatment course, no positive correlation was observed between the changes in these cytotoxic activities and the clinical response to this therapy, when patients who either showed a partial response or whose disease remission was partial or minor were defined as responders. Further, phenotypic analysis showed a significant increase in CD2⁺, CD3⁺ CD4⁺ and CD4⁺Leu8^– cells after the firs course, and CD25⁺ cells after either the first or second course of this treatment. The precentages of CD2⁺ and CD25⁺ cells were significantly elevated only in responders but not in nonresponders, suggesting the increase in these subsets was related to clinical response.     

Mos induces the in vitro activation of mitogen-activated protein kinases in lysates of frog oocytes and mammalian somatic cells.

Mitogen-activated protein kinases (MAPKs) are rapidly and transiently activated when both quiescent Go-arrested cells and G2-arrested oocytes are stimulated to reenter the cell cycle. We previously developed a cell-free system from lysates of quiescent Xenopus oocytes that responds to oncogenic H-ras protein by activating a MAPK, p42MAPK. Here, we show that the oncogenic protein kinase mos is also a potent activator of p42MAPK in these lysates. Mos also induces p42MAPK activation in lysates of activated eggs taken at a time when neither mos nor p42MAPK is normally active, showing that the mos-responsive MAPK activation pathway persists beyond the stage where mos normally functions. Similarly, lysates of somatic cells (rabbit reticulocytes) also retain a mos-inducible MAPK activation pathway. The mos-induced activation of MAPKs in all three lysates leads to phosphorylation of the pp90rsk proteins, downstream targets of the MAPK signaling pathway in vivo. The in vitro activation of MAPKs by mos in cell-free systems derived from oocytes and somatic cells suggests that mos contributes to oncogenic transformation by inappropriately inducing the activation of MAPKs.     

Comparison of dispersal ability between the green leafhoppers,Nephotettix virescens andN. cincticeps (hemiptera: Cicadellidae) by tethered flight

Dispersal propensity of green leafhoppers was compared between a tropical species, Nephotettix virescens, and a temperate species, N. cincticeps. The flight ability was measured with tethered flight technique under laboratory conditions (25°C, 16L-8D). The pre-flight period was shorter and the flight duration was longer in N. virescens than in N. cincticeps in both sexes. No significant correlations were found between the flight activity and morphometric characters for either of the two species. The results suggested that dispersal propensity of N. virescens is higher than that of N. cincticeps.     

Influence of a menhaden oil diet on cercarial penetration of Schistosoma mansoni.

The ability of a menhaden oil (MO) diet to influence cercarial penetration into mouse tail skin was evaluated. Male CD-1 mice 4-6 wk old (15.2 g average weight) were fed a 0, 10%, or 20% MO-supplemented diet for 2 wk. After this time mice were infected with either 65 +/- 3 or 145 +/- 3 [35S]methionine/cysteine-labeled cercariae for 1 hr by tail immersion. Twenty-four hours and 7 days later groups of mice were killed and their tail skin removed and autoradiographed. At 24 hr postinfection, mice fed a 20% MO diet had significantly higher cercarial penetration than controls and 10% MO diets (56% +/- 5.2 vs. 44% +/- 2.9, P = 0.02, 1-tailed t-test). After 7 days mice fed a 20% MO diet retained more radioactive foci than controls or 10% MO diets (21% +/- 2.0 vs. 15% +/- 1.3, P = 0.01, 1-tailed t-test).     

Tissue-Specific Isoforms of Catalase Subunits in Castor Bean Seedlings

Catalases purified from endosperm glyoxysomes and non-specializedmicrobodies from hypocotyls of castor bean seedlings differedin their specific activity [90–164 and 0.89–4.9kunits (mg protein)^–1, respectively] and in their constituentsubunits [two subunits of 54 and 56 kDa for the endosperm enzymeand only one of 56 kDa for the hypocotyl enzyme]. Immunoblotanalysis also showed that particulate fractions from the endospermsand from etiolated and green cotyledons contained two catalasesubunits of 54 and 56 kDa, whereas such fractions from the hypocotylsand roots contained only the 56-kDa subunit. Leaf peroxisomesfrom green leaves had two catalase subunits of around 55 kDaeach. Results of translation in vitro indicated that the 54-and 56-kDa subunits were translated from distinct mRNAs andlevels of both mRNAs increased in the endosperms during germination,prior to increases in levels of catalase proteins. In the hypocotyls,the 56-kDa subunit seemed to be synthesized constitutively. ¹Present addresses: YO, Toyota Central Institute, 31-9 Musashizuka,Nagabuchi, Nagakute, Aichi 480-11, Japan     

Suppression of Quantum Yield of Photosystem II by Hyperosmotic Stress in Chlamydomonas reinhardtii

Addition of ethylene glycol (EG) or NaCl to cells of Chlamydomonasreinhardtii induced transient non-photochemical quenching ofChl fluorescence correlated with the inhibition of photosyntheticoxygen evolution. The induction of the quenching and subsequentrecovery proceeded not only in the light but also in the dark.The quenching was almost unaffected by the protonophore nigericin,suggesting the involvement of a type of non-photochemical quenchingattributable to a state 2 transition. Higher concentrationsof EG or NaCl caused a delay of the recovery of the maximumfluorescence yield (Fm'). Dark reduction rate of P700⁺ afterthe application of a flash light in the presence of DCMU wasenhanced by the hyperosmotic shock, suggesting a stimulatedreduction of the intersystem electron carriers. It is proposedthat the osmotic stress stimulates electron donation from stromalcomponents via the NAD(P)H dehydrogenase, which results in thereduction of the intersystem chain and triggering of a state2 transition leading to stimulated cyclic PSI activity. (Received May 16, 1995; Accepted July 26, 1995)