Allelopathic impact of artificially applied coumarin on <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f.sp. <Emphasis Type="Italic">niveum</Emphasis>

Watermelon production is threatened by fusarium wilt caused by Fusarium oxysporum f.sp. niveum (FON) in continuous cultivation system. Some elements, mainly allelochemicals, released from living roots or decayed plants might be associated with the disease. The purpose of this work was to evaluate the possible impact of coumarin, one kind of watermelon allelochemical, on FON. Furthermore, possible new mechanisms might be investigated during the ecological interactions of plant-microbe. Results showed that coumarin strongly inhibited growth of FON leading to a decrease in its biomass, dry weight of mycelia of FON in a liquid culture. The dry weight was decreased by 62.9% compared with control. The hyphal growth of FON on plates was stopped at high (>400 mg l⁻¹) concentrations of coumarin. At 320 mg l⁻¹, sporulation and enzyme activities of FON were also severely suppressed by coumarin. The yield of conidia, and the activities of proteinase, cellulase, and amylase were reduced by 98.9%, 79.7%, 29.8% and 15.9% respectively. However, conidial germination and mycotoxin (MT) production of FON were greatly stimulated, being increased by 55.7% and 14.9 fold at 320 mg l⁻¹ respectively. We conclude that coumarin acted as an allelochemical substance to inhibit growth and pathogenic enzyme activities of FON but to stimulate mycotoxin production and conidial germination. It was suggested that coumarin acted as a signal transduction element bridging plant and pathogen in the process of plant-microbe interactions.     

Th17 cells undergo Fas-mediated activation-induced cell death independent of IFN-gamma

IL-17-secreting CD4+ T cells (Th17 cells) play a critical role in immune responses to certain infections and in the development of many autoimmune disorders. The mechanisms controlling homeostasis in this cell population are largely unknown. In this study, we show that murine Th17 cells undergo rapid apoptosis in vitro upon restimulation through the TCR. This activation-induced cell death (AICD), a common mechanism for elimination of activated T cells, required the Fas and FasL interaction: Fas was stably expressed, while FasL was up-regulated upon TCR reactivation of Th17 cells; Ab ligation of Fas induced Th17 cell death; and AICD was completely absent in Th17 cells differentiated from gld/gld CD4+ T cells. Thus, the Fas/FasL pathway is essential in regulating the AICD of Th17 cells. Interestingly, IFN-gamma, a cytokine previously found to be important for the AICD of T cells, did not affect Th17 cell apoptosis. Furthermore, Th17 cells derived from mice deficient in IFN-gamma receptor 1 (IFN-gammaR1-/-) underwent AICD similar to wild-type cells. Thus, AICD of Th17 cells occurs via the Fas pathway, but is independent of IFN-gamma.     

On-line optimization of glutamate production based on balanced metabolic control by RQ

In glutamate fermentations by Corynebacterium glutamicum, higher glutamate concentration could be achieved by constantly controlling dissolved oxygen concentration (DO) at a lower level; however, by-product lactate also severely accumulated. The results of analyzing activities changes of the two key enzymes, glutamate and lactate dehydrogenases involved with the fermentation, and the entire metabolic network flux analysis showed that the lactate overproduction was because the metabolic flux in TCA cycle was too low to balance the glucose glycolysis rate. As a result, the respiratory quotient (RQ) adaptive control based “balanced metabolic control” (BMC) strategy was proposed and used to regulate the TCA metabolic flux rate at an appropriate level to achieve the metabolic balance among glycolysis, glutamate synthesis, and TCA metabolic flux. Compared with the best results of various DO constant controls, the BMC strategy increased the maximal glutamate concentration by about 15% and almost completely repressed the lactate accumulation with competitively high glutamate productivity.     

Acoustic stiffness and change in plug cartilage over time after autologous osteochondral grafting: correlation between ultrasound signal intensity and histological score in a rabbit model

We investigated quantitative changes over time in ultrasound signal intensity (an index of stiffness), signal duration (an index of surface irregularity), and interval between signals (an index of thickness) of plug cartilage in an animal model of autologous osteochondral grafting. A full-thickness osteochondral plug was surgically removed and replaced in male Japanese white rabbits (n = 22). Specimens obtained at day 0 and weeks 2, 4, 8, 12 and 24 postoperatively were assessed using an ultrasound system and by macroscopic and histological evaluation (modified Mankin's score). Histology revealed that the plug sank until 2 weeks postoperatively, and that newly formed cartilage-like tissue covered the plug, but at 24 weeks the tissue detached. The plug itself survived well throughout the period of observation. Although the signal intensity at the plug site was same as that in the sham operated contralateral knee at day 0, from 2 to 24 weeks postoperatively it was less than that in the sham knee. At 8 weeks, this difference was significant (P < 0.05). Modified Mankin's score revealed early degenerative changes at the site, but macroscopic examination did not. Signal intensity correlated significantly with score (both at day 0 and at the five postoperative time points [P < 0.05, r = -0.91] and as a whole [P < 0.05, r = -0.36]). Signal intensity also significantly correlated with the individual subscores for 'cartilage structure' (P < 0.05, r = -0.32) and 'cartilage cells' (P < 0.05, r = -0.30) from the modified Mankin's score, but not significantly with subscores for 'staining' and 'tidemark'. Signal duration correlated significantly with total score (as a whole [P < 0.05, r = 0.34]), but not significantly with the score for cartilage structure (P = 0.0557, r = 0.29). The interval between signals reflected well the actual thickness of the plug site. The significant relationships between ultrasound signal intensity and scores suggest that early degenerative changes in plug cartilage and cartilage-like tissue, especially in the superficial layer, are detectable by high-frequency ultrasound assessment.