Behavior of plant plasma membranes under hydrostatic pressure as monitored by fluorescent environment-sensitive probes

We monitored the behavior of plasma membrane (PM) isolated from tobacco cells (BY-2) under hydrostatic pressures up to 3.5 kbar at 30 °C, by steady-state fluorescence spectroscopy using the newly introduced environment-sensitive probe F2N12S and also Laurdan and di-4-ANEPPDHQ. The consequences of sterol depletion by methyl-β-cyclodextrin were also studied. We found that application of hydrostatic pressure led to a marked decrease of hydration as probed by F2N12S and to an increase of the generalized polarization excitation (GPex) of Laurdan. We observed that the hydration effect of sterol depletion was maximal between 1 and 1.5 kbar but was much less important at higher pressures (above 2 kbar) where both parameters reached a plateau value. The presence of a highly dehydrated gel state, insensitive to the sterol content, was thus proposed above 2.5 kbar. However, the F2N12S polarity parameter and the di-4-ANEPPDHQ intensity ratio showed strong effect on sterol depletion, even at very high pressures (2.5-3.5 kbar), and supported the ability of sterols to modify the electrostatic properties of membrane, notably its dipole potential, in a highly dehydrated gel phase. We thus suggested that BY-2 PM undergoes a complex phase behavior in response to the hydrostatic pressure and we also emphasized the role of phytosterols to regulate the effects of high hydrostatic pressure on plant PM.     

Impact of tannic acid on blood pressure,oxidative stress and urinary parameters in L-NNA-induced hypertensive rats

Hypertension is a major health problem with increasing prevalence around the world. Tannic acid is water-soluble polyphenol that is present in tea, green tea, coffee, red wine, nuts, fruits and many plant foods. It has been reported to serve as an antioxidant or a pro-oxidant depending on the type of cells and its concentration. The purpose of our study was to evaluate the effect of tannic acid on systolic blood pressure, oxidative stress and some urinary parameters in the rat model of essential hypertension. Blood pressures of all rats were measured using the tail-cuff method. The nitric oxide synthase inhibitor N (omega)-nitro-L-arginine was administered orally at a dose of 0.5 g/l/day for 15 days to rats in order to create an animal model of hypertension. Tannic acid was intraperitoneally injected at a dose of 50 mg/kg for 15 days. Superoxide dismutase, catalase activity and the concentration of malondialdehyde (MDA) were determined in blood plasma and homogenates of heart, liver and kidney. In order to evaluate renal functions, urine pH, urine volume, urine creatine, uric acid, and urea nitrogen values were measured. Compared with the hypertension group, a decrease in MDA concentrations of heart tissue (p < 0.01), urea nitrogen values (p < 0.01) and urine volumes (p < 0.001) were established in hypertension + tannic acid group. There was also a decrease in blood pressure values (20th and 30th days) of this group, but there was no a statistical difference according to hypertension group. The findings of our research show the effect of tannic acid in lowering blood pressure in hypertensive rats.     

Amelioration of Bacterial Genomes: Rates of Change and Exchange

Although bacterial species display wide variation in their overall GC contents, the genes within a particular species' genome are relatively similar in base composition. As a result, sequences that are novel to a bacterial genome—i.e., DNA introduced through recent horizontal transfer—often bear unusual sequence characteristics and can be distinguished from ancestral DNA. At the time of introgression, horizontally transferred genes reflect the base composition of the donor genome; but, over time, these sequences will ameliorate to reflect the DNA composition of the new genome because the introgressed genes are subject to the same mutational processes affecting all genes in the recipient genome. This process of amelioration is evident in a large group of genes involved in host-cell invasion by enteric bacteria and can be modeled to predict the amount of time required after transfer for foreign DNA to resemble native DNA. Furthermore, models of amelioration can be used to estimate the time of introgression of foreign genes in a chromosome. Applying this approach to a 1.43-megabase continuous sequence, we have calculated that the entire Escherichia coli chromosome contains more than 600 kb of horizontally transferred, protein-coding DNA. Estimates of amelioration times indicate that this DNA has accumulated at a rate of 31 kb per million years, which is on the order of the amount of variant DNA introduced by point mutations. This rate predicts that the E. coli and Salmonella enterica lineages have each gained and lost more than 3 megabases of novel DNA since their divergence. Received: 7 July 1996 / Accepted: 27 September 1996     

Photosynthesis is limited at high leaf to air vapor pressure deficit in a mutant of Arabidopsis thaliana that lacks trienoic fatty acids

We have investigated the role of polyunsaturated fatty acids in photosynthesis using a triple mutant of Arabidopsis thaliana that lacks trienoic fatty acids (fad 3-2 fad 7-2 fad 8). Though this mutant is male sterile, vegetative growth and development under normal conditions are largely unaffected (McConn and Browse, 1996 Plant Cell 8: 403–416). At 0.2–1.0 kPa vapor pressure deficit (low VPD), maximum photosynthetic rates of wild-type and mutant plants were similar while stomatal conductance rates were up to 2 times higher in mutant plants. However, light-saturated rates of carbon assimilation and stomatal conductance in the mutant were lower than in wild-type plants when measured at ambient (35 Pa) CO₂ and 2.0–2.8 kPa vapor pressure deficit (high VPD). The limitation to photosynthesis in the mutant plants at high VPD was overcome by saturating partial pressures of CO₂ suggesting a stomatal limitation. Chlorophyll fluorescence measurements indicate that differences observed in maximum assimilation rates were not due to limitations within the photochemical reactions of photosynthesis. Stomatal response to VPD and intrinsic water use efficiency was drastically different in mutant versus wild-type plants. The results of this investigation indicate that for Arabidopsis, polyunsaturated fatty acids may be an important determinant of responses of photosynthesis and stomatal conductance to environmental stresses such as high VPD. This revised version was published online in June 2006 with corrections to the Cover Date.     

Activity,sleep and ambient light have a different impact on circadian blood pressure,heart rate and body temperature rhythms

The aim of the present study was to investigate the impact of endogenous and exogenous factors for the expression of the daily rhythms of body temperature (BT), blood pressure (BP) and heart rate (HR). One hundred and seventy-three young adults (YA), 17–24 years old (y.o.), of both genders were studied under a modified constant-routine (CR) protocol for 26 h. Participants were assigned randomly to groups with different lighting regimens: CR-LD, n = 77, lights (>400 l×) on from 09:00 to 17:00 h and off (<10 l×) from 17:00 to 09:00 next morning; CR-LL, n = 81, lights on (>400 l×) during the whole experimental session; CR-DD, n = 15, constant dim light (<10 l×) during the whole experiment. Systolic (SBP) and diastolic (DBP) BP, HR and BT were measured every 2 h. For comparison, the results of the former studies performed under conditions of regular life with an activity period from 07:00 to 23:00 h and sleep from 23:00 till 07:00 h (Control) were reanalyzed. Seven-day Ambulatory Blood Pressure Monitoring (ABPM) records from 27 YA (16–38 y.o.) and BT self-measurement data from 70 YA (17–30 y.o.) taken on ≥ 3 successive days at 08:00, 11:00, 14:00, 17:00, 20:00, 23:00 and 03:00 were available.

The obtained daily patterns were different between Control and CR-DD groups, due to effects of activity, sleep and light. The comparison of Control and CR-LD groups allowed the effects of sleep and activity to be estimated since the lighting conditions were similar. The activity level substantially elevated SBP, but not DBP. Sleep, on the other hand, lowered the nighttime DBP, but has no effect on SBP. HR was affected both by activity and sleep. In accordance with previous studies, these results confirm that the steep BP increase in the morning is not driven by the circadian clock, but rather by sympathoadrenal factors related to awakening and corresponding anticipatory mechanisms. The effect on BT was not significant.

To investigate the impact of light during the former dark time and darkness during the former light time, the CR-LL and CR-DD groups were each compared with the CR-LD group. Light delayed the evening decrease of BT, most likely via a suppression of the melatonin rise. Besides, it had a prominent arousal effect on SBP both in the former light and dark phases, a moderate effect on DBP and no effect on HR. Darkness induced decline in BT. BP values were decreased during the former light time. No effects on HR were found. Altogether, the results of the present paper show that BT, BP and HR are affected by exogenous factors differently. Moreover, the effect was gender-specific. Especially, the response of BT and BP to ambient light was evident only in females.

We suppose that the distinct, gender-specific responses of SBP, DBP and HR to activity, sleep and ambient light do reflect fundamental differences in the circadian control of various cardiovascular functions. Furthermore, the presented data are important for the elaboration of updated reference standards, the interpretation of rhythm disorders and for personalized chronotherapeutic approaches to prevent adverse cardiovascular events more effectively.     

The effects of ovariectomy and strech on the regulatory profile and activity of the uterus

Following ovariectomy of five New Zealand white rabbits at day 25 of pregnancy, the intrauterine pressure (IUP) and uterine progesterone (P) and prostaglandin (PG) levels were measured sequentially at days 25, 26 and 27. At day 25, when the uterine P and PGE and PGF were high, massive intrauterine treatment with 500 μg PGF2α provoked only a sustained contracture on which only low level oscillation in IUP was superimposed. At day 26, when the P levels had decreased significantly (P<0.001) and the PG levels had not changed significantly, 50 μg PGF2α significantly increased cyclic IUP as compared with the day 25 value (P<0.001). At day 27, when the P levels decreased further, as little as 5 μg PGF2α provoked still higher cyclic IUP, in spite of a significant reduction in PG levels (P<0.05).Stretching the uterus of six post partum and six 26 days pregnant rabbits (after removing the uterine contents) significantly increased the uterine PGF levels (P<0.001). However, stretch increased only cyclic IUP of the post partum uterus and was without effect on the pregnant uterus, which still had high P levels. These results indicate that the myometrium activated by exogenous PG or stretch, regardless of whether the uterine PG levels increase, remain unchanged or even moderately decrease, provided that the uterine P levels are reduced to a critical value.     

Consumption of benthic invertebrates by waterbirds in the Oosterschelde estuary,SW Netherlands

The number of waders in the Oosterschelde, S.W. Netherlands, declined after a reduction in intertidal area due to the construction of a storm surge barrier and secondary dams, suggesting that the carrying capacity had been reached (Schekkerman et al., 1993). In this paper we present data on consumption and predation pressure by birds to explore whether the reduction in their numbers is due to prey depletion or to other factors.The total annual consumption of benthic invertebrates by birds in the Oosterschelde amounted to 1573 × 10³ g ADW y^–1 in the period before the coastal engineering works (pre-barrier) and 1500 × 10³ kg ADW y^–1 in the post-barrier period. More than half of the total amount of biomass is eaten by the Oystercatcher, and only seven (pre-barrier) or even six (post-barrier) bird species together take 90% of the total.Although the consumption by individual species may vary considerably among years, the total consumption was remarkably stable, with a CV of only 3–4% of the mean, especially compared to the variability of the prey populations. In the pre-barrier period, consumption was lowest in mid summer, increased sharply from August onwards until a peak was reached in January. A sharp decrease took place in March. In the post-barrier period, consumption peaked in October.The total consumption per unit area per year does not differ much between different sectors of the Oosterschelde, apart from a distinctly lower value in the eastern part. Of the total amount of food taken by birds, only 0.1–0.4% is taken in the subtidal compartment. In several study plots on an individual tidal flat, there was a clear relation between consumption and benthic biomass.The predation pressure was 13 and 23% of the standing stock, in the post- and pre-barrier period respectively. When cockles, mussels and their main predator, the Oystercatcher, are excluded from the calculations, the predation pressure of the other species was 30 and 37% of the biomass, respectively.Predation pressure of Oystercatchers in individual study plots varied from less than 10% to more than 70% of the standing stock. On cockle beds the predation pressure was positively related to the average length of the cockles present.Based on these results and a comparison with the literature we conclude that, at least for several species that feed intertidally, carrying capacity could be limited by the stocks of food. This does not mean that birds face food shortage each season. As the variability of the benthos populations is much higher than that of the bird densities it is likely that at some times food is not limiting, at other times it is. On the other hand, consumption is very low in the subtidal compartment and species feeding here could potentially increase substantially in numbers in the Oosterschelde.     

Root Pressure of Tropical Lianas and Their Relationships with Phylogeny and Environments

Lianas usually possess large vessels, which are vulnerable to cavitation. Root pressure may play an important role in embolism repair of vessels. However, little is known about the generality of root pressure in tropical lianas. To characterize root pressure of lianas in tropical rainforests, we used pressure transducers to measure root pressure in the rainy and dry seasons for a total of 32 lianas from 14 families common in Xishuangbanna. We further analyzed the associations of maximum root pressure with phylogeny and of transient root pressure with environmental factors. We found that all lianas we selected had root pressure, with maximum root pressure ranging from 2-138kPa. In the dry season, about 72% (23 species) of the lianas had relatively low root pressure (<15kPa) and maintained positive throughout the day. This may be important for water balance for roots and basal stems of lianas. There were three types of diurnal changes in liana root pressure. In Type I, root pressure had obvious diurnal variation in the dry and rainy seasons. In Type II, root pressure did not show obvious diurnal variation in the dry and rainy seasons. In Type III, either in the dry or in the rainy season, root pressure showed obvious diurnal variation. Root pressure varied substantially among lianas, with lianas from two families, Fabaceae and Vitaceae, usually having relatively higher root pressure, suggesting that phylogeny may influence root pressure. Transient root pressure closely responded to photosynthetically active radiation. In most cases, however, it was not related to rainfall and vapour pressure deficit. These results suggest that the associations of liana root pressure with environments need further investigation.