Pyrococcus furiosus is a hyperthermophilic archaeon. Its ribulose-1,5-bisphosphate carboxylase/oxygenase (PfRubisco) has only large subunit (L). PfRubisco has a novel (L2)5, decameric structure and it possesses higher carboxylase activity and thermotolerance. To assess the potential functionality of PfRubisco in higher plants under high-temperature stress, PfRubisco coding sequence was transiently expressed in Nicotiana benthamiana by Pea early browning virus mediated ectopic expression. The transgenic PfRubisco plants produced chlorotic yellow stripes in their leaves. Relative to the control leaves, those with yellow stripes exhibited decreased net photosynthetic rate and chlorophyll content, altered chloroplast ultrastructure, and more severe photoinhibition of both photosystem I and II. We concluded that the ectopic expression of PfRubisco might disrupt the chloroplast development and function in N. benthamiana. The potential cause of the disruption was discussed. and X. -G. Li ... [et al.].
A voltammetric technique was used (differential pulse voltammetry with a carbon fibre microelectrode) to investigate dynamics of the changes of catecholamine overflow in the corpus striatum following electroconvulsive stimulation (ECS) of chloral hydrate-anaesthetized rats. Application of "maximal" ECS (50 Hz, AC, sine wave, approximately 150 mA, 0.2 s) caused large enhancement of catechol-oxidative current (CA.OC): In the first minute after its arrest, the CA.OC peak raised to 1032±405% (n=5, mean±S.D.) of the controls (P<0.001, Student's t-test). This large elevation of the extracellular catecholamine content ceased rapidly - the baseline level was attained in the second minute. CA.OC changes evoked by a "minimal" ECS (50 Hz, AC, sine wave, approximately 30 mA, 0.2 s) were equivocal in the first minute (increase, decrease: 145 ±56 %, P>0.05, n=6). Possible mechanisms of the ECS therapeutic effect are discussed.
The interactive effect of elevated CO2 (EC) and moisture stress (MS) on Brassica juncea cv. Pusa Bold was studied using open-top chambers. The EC markedly increased net photosynthetic rate and internal CO2 concentration and reduced variable and maximal chlorophyll fluorescence. Under MS, EC increased water potential and relative water content, and reduced transpiration rate. The greater allocation of biomass to the roots, which serve as a strong sink for assimilated carbon under EC, helped in better root growth. and B. K. Rabha, D. C. Uprety.
We compared the effect of elevated temperature on morphological development, biomass accumulation and allocation, and gas exchange of three dominant plants (Caragana intermedia Kuanget H.C. Fu, Hedysarum mongolicum Turcz., and Artemisia ordosica Krasch.) growing in Chinese Maowusu sandland. Plants were grown in two temperature chambers (25/20, 28/23 °C, day/night) during 60 d. Tree height, number of leaves, and leaf area were increased in C. intermedia and H. mongolicum seedlings, while in A. ordosica temperature only affected tree height. Elevated temperature increased biomass and reduced the root : shoot ratio in C. intermedia and H. mongolicum seedlings, but not in A. ordosica seedlings. The net photosynthetic rate (PN) and transpiration rate (E) were increased at days 40 and 60 in C. intermedia and H. mongolicum seedlings, while in A. ordosica seedlings no significant effects on E were observed, and PN was increased only at day 60. Water use efficiency (WUE) was reduced at days 40 and 60 in H. mongolicum seedlings, and at day 60 in C. intermedia seedlings. No temperature effect on WUE was observed in A. ordosica seedlings. These different responses indicate that climate change could alter plant communities in Maowusu sandland. and Chun-Wang Xiao, Guang-Sheng Zhou, R. Ceulemans.
Most plants growing in temperate desert zone exhibit brief temperature-induced inhibition of photosynthesis at midday in the summer. Heat stress has been suggested to restrain the photosynthesis of desert plants like Alhagi sparsifolia S. It is therefore possible that high midday temperatures damage photosynthetic tissues, leading to the observed inhibition of photosynthesis. In this study, we investigated the mechanisms underlying heat-induced inhibition of photosynthesis in A. sparsifolia, a dominant species found at the transition zone between oasis and sandy desert on the southern fringe of the Taklamakan desert. The chlorophyll (Chl) a fluorescence induction kinetics and CO2 response curves were used to analyze the thermodynamic characters of both photosystem II (PSII) and Rubisco after leaves were exposed to heat stress. When the leaves were heated to temperatures below 43°C, the initial fluorescence of the dark-adapted state (Fo), and the maximum photochemical efficiency of PSII (Fv/Fm), the number of active reaction centers per cross section (RCs) and the leaf vitality index (PI) increased or declined moderately. These responses were reversed, however, upon cooling. Moreover, the energy allocation in PSII remained stable. The gradual appearance of a K point in the fluorescence curve at 48°C indicated that higher temperatures strongly impaired PSII and caused irreversible damage. As the leaf temperature increased, the activity of Rubisco first increased to a maximum at 34°C and then decreased as the temperature rose higher. Under high-temperature stress, cell began to accumulate oxidative species, including ammoniacal nitrogen, hydrogen peroxide (H2O2), and superoxide (O2 .-), suggesting that disruption of photosynthesis may result from oxidative damage to photosynthetic proteins and thylakoid membranes. Under heat stress, the biosynthesis of nonenzyme radical scavenging carotenoids (Cars) increased. We suggest that although elevated temperature affects the heat-sensitive components comprising of PSII and Rubisco, under moderately high temperature the decrease in photosynthesis is mostly due to inactivation of dark reactions. and W. Xue ... [et al.].
Ascorbic acid (Asc) is a major plant antioxidant. L-galactono-1,4-lactone dehydrogenase (GLDH) is an enzyme that catalyzes the last step of Asc biosynthesis in higher plants. Effects of endogenous Asc on resistance to high-temperature stress were studied by using GLDH-overexpressed (GO-2) and GLDH-suppressed transgenic rice (GI-2) as experimental materials. After high-temperature treatment, the maximal quantum yield of PSII was significantly lower in GI-2, and higher in GO-2 compared to wild type rice. The content of reactive oxygen species (ROS) was the highest in GI-2. The higher Asc content resulted in lower lipid peroxidation in GO-2. The contents of chlorophyll, soluble proteins, and Rubisco large and small subunit were positively correlated to the Asc content. These results show that the higher Asc content reduced the accumulation of ROS and maintained the function of rice leaves. We suggest that the higher Asc content could improve the rice resistance to high-temperature stress., Q. L. Zhang, Y. X. Wei, C. L. Peng., and Obsahuje bibliografii
We previously found that Endothelin-11-31 (ET-11-31) exhibited a pro-arrhythmogenic effect in isolated rat hearts. In this study, we further investigated the effects of ET-11-31 on a cell viability and observed [Ca2+]i in cultured cardiomyocytes. Cultured neonatal rat cardiomyocytes were treated with 0.1, 1, and 10 nM ET-11-31 for 24h in the presence or absence of ETA receptor antagonist (BQ123) or phosphoramidon, a NEP/ECE inhibitor. Cell injury was evaluated by supernatant lactate dehydrogenase (LDH) assay, superoxide dismutase (SOD activity, and malondialdehyde (MDA) content. Cell viability was assessed by MTT assay. [Ca2+]i was measured with Fluo-3/AM under a laser confocal microscope. 1) ET-11-31 dose-dependently increased LDH release and decreased cell viability. 2) LDH and MDA levels were significantly elevated and SOD activity decreased after administration of 1 nM ET-11-31 for 24h, and these changes were markedly attenuated by 1 uM BQ123. 3) Exposure to 10 nM ET-11-31 caused a continuous increase in [Ca2+]i to cultured beating cardiomyocytes and termination of [Ca2+]i transient within 6 min, and this change was reversed by 1 uM BQ123 and attenuated by 0.5 mM phosphoramidon. These results suggest that ET-11-31 could cause cell injury, and that the effect of ET-11-31 on [Ca2+]i transients is mainly mediated by ETA receptor and partially attributed to the conversion of ET-11-31 to ET-11-21., A.-J. Ren, X. Yuan, L. Lin, Y.-X. Pan, Y.-W. Qing, W.-J. Yuan., and Obsahuje bibliografii a bibliografické odkazy
Abnormal cholesterol metabolism, including low intestinal cholesterol absorption and elevated synthesis, is prevalent in diabetes, obesity, hyperlipidemia, and the metabolic syndrome. Diet-induced weight loss improves cholesterol absorption in these populations, but it is not known if endurance exercise training also improves cholesterol homeostasis. To examine this, we measured circulating levels of campesterol, sitosterol, and lathosterol in 65 sedentary subjects (average age 59 years; with at least one metabolic syndrome risk factor) before and after 6 months of endurance exercise training. Campesterol and sitosterol are plant sterols that correlate with intestinal cholesterol absorption, while lathosterol is a marker of whole body cholesterol synthesis. Following the intervention, plant sterol levels were increased by 10 % (p<0.05), but there was no change in plasma lathosterol. In addition, total and LDL-cholesterol were reduced by 0.16 mmol and 0.10 mmol, respectively (p<0.05), while HDL-C levels increased by 0.09 mmol (p<0.05). Furthermore, the change in plant sterols was positively correlated with the change in VO2 max (r = 0.310, p=0.004), independent of other metabolic syndrome risk factors. These data indicate that exercise training reduces plasma cholesterol despite increasing cholesterol absorption in subjects with metabolic syndrome risk factors., K. R. Wilund ... [et al.]., and Obsahuje seznam literatury
We investigated the effect of enhanced atmospheric ammonia (NH3) in combination with low and high nitrogen (LN and HN, respectively) growth medium on photosynthetic characteristics of two maize (Zea mays L.) cultivars (NE5 with high- and SD19 with low N-use efficiency) across long-term growth period and their diurnal change patterns exposed to 10 nl l-1 and 1,000 nl l-1 NH3 fumigation in open-top chambers (OTCs). Regardless of the level of N in medium, increased NH3 concentration promoted maximum net photosynthetic rate (Pmax) and apparent quantum yield (AQY) of both cultivars at earlier growth stages, but inhibited Pmax of NE5 from silking to maturity stage and that of SD19 at maturity stage only above the ambient concentration. Greater positive/less negative responses were predominant in the LN than in the HN treatment, especially for SD19. Dark respiration rate (RD) remained more enhanced in the LN than in the HN treatment for SD19 as well as increased in the LN while decreased in the HN treatment for NE5 at their silking stage, following exposure to elevated NH3 concentration. Additionally, enhanced atmospheric NH3 increased net photosynthetic rate (PN) and stomatal conductance (gs) but reduced intercellular CO2 concentration (Ci) of both cultivars with either the LN or HN treatment during the diurnal period at tasseling stage. The diurnal change patterns of PN and gs showed bimodal curve type and those of Ci presented single W-curve type for NE5, when NH3 concentration was enhanced. As for SD19, single-peak curve type was showed for both PN and gs while single V-curve type for Ci. All results supported the hypothesis that appropriately enhanced atmospheric NH3 can increase assimilation of CO2 by improving photosynthesis of maize plant, especially at earlier growth stages and after photosynthetic "noon-break" point. These impacts of elevated NH3 concentration were more beneficial for SD19 as compared to those for NE5, especially in the LN supply environment. and L. X. Zhang ... [et al.].
The effects of enhanced UV-B radiation on growth and photosynthetic activities were investigated in fronds of the aquatic fern Azolla microphylla Kaulf. The fronds were exposed to UV-B radiation intermittently once in 3 d during 12 d. Biomass and relative growth rate of UV-B treated Azolla plants and the heterocyst frequency of the UV-B treated symbiont decreased resulting in an increase in doubling time over the control. The doubling time was 3.08 d for control and 3.35 d for UV-B irradiated plants. Chl and carotenoid contents per unit fresh mass and photosystem 2 (PS2) activity also decreased under UV-B treatment. Measurements of photosynthetic activity in terms of fluorescence kinetics and PS2 mediated O2 evolution showed that the aquatic fern Azolla is sensitive to UV-B damage. and M. Jayakumar ... [et al.].