Sap flow of the southern conifer, <Emphasis Type="Italic">Agathis australis</Emphasis> during wet and dry summers

Key message

Analysis of sap flux density during drought suggests that the large sapwood and rooting volumes of larger trees provide a buffer against drying soil.

Abstract

The southern conifer Agathis australis is amongst the largest and longest-lived trees in the world. We measured sap flux densities (F _d) in kauri trees with a DBH range of 20–176 cm to explore differences in responses of trees of different sizes to seasonal conditions and summer drought. F _d was consistently higher in larger trees than smaller trees. Peak F _d was 20 and 8 g m^?2 s^?1 for trees of diameters of 176 and 20 cm, respectively, during the wet summer. Multiple regression analysis revealed photosynthetically active radiation (PAR) and vapour pressure deficit (D) were the main drivers of F _d. During drought, larger trees were more responsive to D whilst smaller trees were more responsive to soil drying. Our largest tree had a sapwood area of 3,600 cm². Preliminary analysis suggests stem water storage provides a buffer against drying soil in larger trees. Furthermore, F _d of smaller trees had higher R ² values for soil moisture at 30 and 60 cm depth than soil moisture at 10 cm depth (R ² = 0.68–0.97 and 0.55–0.67, respectively) suggesting that deeper soil moisture is more important for these trees. Larger trees did not show a relationship between F _d and soil moisture, suggesting they were accessing soil water deeper than 60 cm. These results suggest that larger trees may be better prepared for increasing frequency and intensity of summer droughts due to deeper roots and/or larger stem water storage capacity.

     

Comparative study of daytime and nighttime sap flow of <Emphasis Type="Italic">Populus euphratica</Emphasis>

In order to quantify and characterize the variance in desert riparian forest tree sap flow, we measured the sap flow from Populus euphratica and compared the daytime and nighttime patterns and responses to environmental variables. Results showed that daytime sap flow velocity was significantly higher (P?<?0.05). Daytime and nighttime mean sap flow velocities were 7.65 and 4.01 cm h^?1 in spring, 21.38 and 9.60 cm h^?1 in summer, and 11.04 and 5.21 cm h^?1 in autumn, respectively. Moreover, results indicated that the stoma remained partially open (15% minimum) throughout the night, providing sufficient evidence for the existance of nighttime transpiration. The vapor pressure deficit (VPD), stomatal conductance (Cs), photosynthetically active radiation (PAR), air temperature (Ta), wind speed (WS), and soil moisture (θ) all had significant positive effects on P. euphratica sap flow velocity (P?<?0.05). Furthermore, the relationship between daytime sap flow velocity and VPD showed clockwise hysteresis, while the relationship between nighttime sap flow velocity and VPD showed counter-clockwise hysteresis. It was evident that PAR and VPD were the key factors impacting daytime sap flow velocity, while Cs and θ were the key factors impacting nighttime sap flow velocity. Furthermore, linear regression results showed that daytime sap flow had a significant positive effect on nighttime sap flow throughout the growing season (P?<?0.05).     

Water relations of ponderosa pines in Patagonia Argentina: implications for local water resources and individual growth

Replacement of grasslands by forests may result in increased water consumption, and the magnitude of this will depend on stand density. To test this hypotheses and evaluate the impact of pine plantations on hydric resources in Patagonia Argentina, we measured over two seasons (1999–2000 and 2000–2001) and at two densities of ponderosa pine plantations (350 and 500 trees ha^?1) the following variables: soil water content, leaf water potential (ψ), individual tree growth, individual sap flow, and response of sap flow density (u) to vapor pressure deficit (VPD). Stand transpiration (T) and whole-plant liquid-phase hydraulic conductance (L) were also estimated. Pre-dawn ψ varied from about –0.5 to –1.0 MPa. No differences were found in midday maximum u (1100–1800 hours) on clear days between the 2 measurement years, throughout each season, or between different densities of plantation. Sapflow density was also not correlated with soil water storage up to 1.4 m soil depth. Sapflow increased until VPD of about 2.3 kPa, and decreased at VPD >4 kPa, describing a hysteresis in the afternoon. Values of L in Patagonian trees were similar to those recalculated from published data for pines of the same height in the USA. Average stand transpiration increased with increased density (2.07 and 3.08 mm day^-1 for 350 and 500 pines ha^-1, respectively) and size of the trees. We conclude that ponderosa pines in Patagonia Argentina use more water, in a magnitude depending on the density of the trees, than native grasslands. Accordingly, ponderosa pines use deep water to maintain high water potential and transpiration rates even during the dry season.     

Gas exchanges of an endangered species <Emphasis Type="Italic">Syringa pinnatifolia</Emphasis> and a widespread congener <Emphasis Type="Italic">S. oblata</Emphasis>

Net photosynthetic rate (P_N), transpiration rate (E), water use efficiency (WUE), stomatal conductance (g_s), and stomatal limitation (L_s) were investigated in two Syringa species. The saturation irradiance (SI) was 400 µmol m^-2s^-1 for S. pinnatifolia and 1 700 µmol m^-2s^-1 for S. oblata. Compared with S. oblata, S. pinnatifolia had extremely low g _s . Unlike S. oblata, the maximal photosynthetic rate (P_max) in S. pinnatifoliaoccurred around 08:00 and then fell down, indicating this species was sensitive to higher temperature and high photosynthetic photon flux density. However, such phenomenon was interrupted by the leaf development rhythms before summer. A relatively lower P_N together with a lower leaf area and shoot growth showed the capacity for carbon assimilation was poorer in S. pinnatifolia.     

Temperature Responses of Photosynthesis and Respiration of Maize (<Emphasis Type="Italic">Zea mays</Emphasis>) Plants to Experimental Warming

Understanding the key processes and mechanisms of photosynthetic and respiratory acclimation of maize (Zea mays L.) plants in response to experimental warming may further shed lights on the changes in the carbon exchange and Net Primary Production (NPP) of agricultural ecosystem in a warmer climate regime. In the current study, we examined the temperature responses and sensitivity of foliar photosynthesis and respiration for exploring the mechanisms of thermal acclimation associated with physiological and biochemical processes in the North China Plain (NCP) with a field manipulative warming experiment. We found that thermal acclimation of A_n as evidenced by the upward shift of A_n-T was determined by the maximum velocity of Rubisco carboxylation (V_cmax), the maximum rate of electron transport (J_max), and the stomatal- regulated CO₂ diffusion process (g_s), while the balance between respiration and photosynthesis (R_d/A_g), and/or regeneration of RuBP and the Rubisco carboxylation (J_max/V_cmax) barely affected the thermal acclimation of A_n. We also found that the temperature response and sensitivity of R_d was closely associated with the changes in foliar N concentration induced by warming. These results suggest that the leaf-level thermal acclimation of photosynthesis and respiration may mitigate or even offset the negative impacts on maize from future climate warming, which should be considered to improve the accuracy of process-based ecosystem models under future climate warming.     

Urban Tree Species Show the Same Hydraulic Response to Vapor Pressure Deficit across Varying Tree Size and Environmental Conditions

Background

The functional convergence of tree transpiration has rarely been tested for tree species growing under urban conditions even though it is of significance to elucidate the relationship between functional convergence and species differences of urban trees for establishing sustainable urban forests in the context of forest water relations.

Methodology/Principal Findings

We measured sap flux of four urban tree species including Cedrus deodara, Zelkova schneideriana, Euonymus bungeanus and Metasequoia glyptostroboides in an urban park by using thermal dissipation probes (TDP). The concurrent microclimate conditions and soil moisture content were also measured. Our objectives were to examine 1) the influence of tree species and size on transpiration, and 2) the hydraulic control of urban trees under different environmental conditions over the transpiration in response to VPD as represented by canopy conductance. The results showed that the functional convergence between tree diameter at breast height (DBH) and tree canopy transpiration amount (E _c) was not reliable to predict stand transpiration and there were species differences within same DBH class. Species differed in transpiration patterns to seasonal weather progression and soil water stress as a result of varied sensitivity to water availability. Species differences were also found in their potential maximum transpiration rate and reaction to light. However, a same theoretical hydraulic relationship between G _c at VPD = 1 kPa (G _cref) and the G _c sensitivity to VPD (−dG _c/dlnVPD) across studied species as well as under contrasting soil water and R _s conditions in the urban area.

Conclusions/Significance

We concluded that urban trees show the same hydraulic regulation over response to VPD across varying tree size and environmental conditions and thus tree transpiration could be predicted with appropriate assessment of G _cref.     

Photosynthetic behavior of Spanish Arbequina and Italian Maurino olive (<Emphasis Type="Italic">Olea europaea</Emphasis> L.) cultivars under super-intensive grove conditions

The study was carried out in a four-year-old super-high density olive grove in Central Italy to compare leaf gas exchanges of Spanish Arbequina and Italian Maurino olive cultivars. Overall, from mid July to mid November, Maurino had a slightly higher maximum light-saturated net photosynthetic rate (P _Nmax) than Arbequina. The lowest and the highest P _Nmax values were recorded at the end of July and in mid November, respectively. Current-season leaves showed similar or slightly higher P _Nmax values than one-year-old leaves. During the day Maurino always had slightly higher values or values similar to Arbequina, with the highest P _Nmax being in the morning. Maurino had similar or higher dark respiration rate (R _D) values compared to Arbequina. During the day, in both cultivars the R _D was lower at 9:00 than in the afternoon. The pattern of the photosynthetic irradiance-response curve was similar in the two genotypes, but the apparent quantum yield (Y _Q) was higher in Maurino. In both cultivars intercellular CO₂ concentration (C _i) tended to increase when P _Nmax decreased. The increase in C _i corresponded to a decrease in stomatal conductance (g _s). The transpiration rate (E) increased from mid July to the beginning of August, then decreased in September and increased again in November. Particularly in the morning, the current-season leaves showed similar or slightly higher E values than the one-year-old leaves. During the day, in both cultivars and at both leaf ages, E was higher in the afternoon. No effects on leaf gas exchanges due to the presence or absence of fruit on the shoot were found. Overall, there was satisfactory physiological adaptation for Arbequina to the conditions of Central Italy and for Maurino to the superintensive grove conditions.     

Effects of the interaction between vapor-pressure deficit and salinity on growth and photosynthesis of <Emphasis Type="Italic">Cucumis sativus</Emphasis> seedlings under different CO<Subscript>2</Subscript> concentrations

We studied growth and photosynthesis of cucumber (Cucumis sativus) seedlings under two vapor-pressure deficit levels (VPD; 0.4 and 3.0 kPa), two salinity levels (0 mM and 34 mM NaCl), and two CO₂ concentrations ([CO₂]; 400 and 1,000 μmol mol^–1). Relative growth rate (RGR) decreased with increasing VPD, but the causal factor differed between salinity levels and CO₂ concentrations. Under ambient [CO₂], RGR decreased with increasing VPD at low salinity mainly due to decreased leaf area ratio (LAR), and decreased net assimilation rate (NAR) at high salinity. The decrease in intercellular [CO₂] (C_i) with decreasing stomatal conductance caused by high VPD did not significantly limit net photosynthetic rate (P_N) at low salinity, but P_N was potentially limited by C_i at high salinity. At high [CO₂], high VPD reduced LAR, but did not affect NAR. This is because the decrease in C_i occurred where slope of P_N–C_i curve was almost flat.     

Assessment of photosynthetic potential of indoor plants under cold stress

Photosynthetic parameters including net photosynthetic rate (P_N), transpiration rate (E), water-use efficiency (WUE), and stomatal conductance (g_s) were studied in indoor C₃ plants Philodendron domesticum (Pd), Dracaena fragans (Df), Peperomia obtussifolia (Po), Chlorophytum comosum (Cc), and in a CAM plant, Sansevieria trifasciata (St), exposed to various low temperatures (0, 5, 10, 15, 20, and 25°C). All studied plants survived up to 0°C, but only St and Cc endured, while other plants wilted, when the temperature increased back to room temperature (25°C). The P_N declined rapidly with the decrease of temperature in all studied plants. St showed the maximum P_N of 11.9 μmol m^?2 s^?1 at 25°C followed by Cc, Po, Pd, and Df. E also followed a trend almost similar to that of P_N. St showed minimum E (0.1 mmol m^?2 s^?1) as compared to other studied C₃ plants at 25°C. The E decreased up to ≈4-fold at 5 and 0°C. Furthermore, a considerable decline in WUE was observed under cold stress in all C₃ plants, while St showed maximum WUE. Similarly, the g_s also declined gradually with the decrease in the temperature in all plants. Among C₃ plants, Pd and Po showed the maximum g_s of 0.07 mol m^?2 s^?1 at 25°C followed by Df and Cc. However, St showed the minimum g_s that further decreased up to ～4-fold at 0°C. In addition, the content of photosynthetic pigments [chlorophyll a, b, (a+b), and carotenoids] was varying in all studied plants at 0°C. Our findings clearly indicated the best photosynthetic potential of St compared to other studied plants. This species might be recommended for improving air quality in high-altitude closed environments.     

Transpiration of trees in a cool temperate forest on Mt. Aso,Japan: comparison of model simulation and measurements

In the large caldera of Mt. Aso, Japan, artificial grasslands were converted into forests of different species due to the decline of the livestock industry in this region. These changes in species composition are thought to have changed not only the transpiration rates (E), but also the responses in E to variations in environmental conditions. For three introduced forest types, we monitored E using sap flux sensors and computed E with a multilayer model parameterized by independently obtained leaf-scale ecophysiological traits. Modeled E replicated the time series of measured E reasonably well, but did not reproduce a decrease in E lasting 20 days after a short rainless period in conifer plantation. Mean leaf-scale stomatal conductance of two deciduous broadleaved tree species was as low as that of trees under dry conditions in other studies, possibly an adaptation for the avoidance of excessive E during rainless periods. These results suggest that land use change influenced E and its response to the rainfall patterns of the region and that drought plays an important role in influencing species-specific E characteristics in this rainy region. The multilayer model in combination with sap flux measurements was found to be a useful tool not only for the extrapolation of E, but also for the detection of the unexpected events, as long as the measured parameter values capture the species-specific seasonality in leaf ecophysiological traits.     

Catalytic properties of aminoacylase of strain <Emphasis Type="Italic">Rhodococcus armeniensis</Emphasis> AM6.1

Studies of substrate specificity revealed that the D-aminoacylase of Rhodococcus armeniensis AM6.1 strain exhibits absolute stereospecificity to the D-stereoisomers of N-acetyl-amino acids. The enzyme is the most active reacted with N-acetyl-D-methionine, as well as with aromatic and hydrophobic N-acetylamino acids and interacts weakly with the basic substrates. It is practically not reacted with acidic and hydrophilic N-acetyl-amino acids. Michaelis constants (K_m) and maximum reaction velocities (V_max) were calculated, using linear regression analysis, for the following substrates: N-acetyl-D-methionine, N-acetyl-D-alanine, N-acetyl-D-phenylalanine, N-acetyl-D-tyrosine, N-acetyl-D-valine, N-acetyl-D-oxyvaline, N-acetyl- D-leucine. Substrate inhibition of D-aminoacylase was displayed with N-acetyl-D-leucine (K_s = 35.5 ± 28.3 mM) and N-acetyl-DL-tyrosine (K_s = 15.8 ± 4.5 mM). Competitive inhibition of the enzyme with product–acetic acid (K_i = 104.7 ± 21.7 mM, K_m = 2.5 ± 0.5 mM, V_max = 25.1 ± 1.5 U/mg) was observed.     

Biocidal effect of (<Emphasis Type="Italic">E</Emphasis>)-anethole on the cyanobacterium <Emphasis Type="Italic">Aphanizomenon gracile</Emphasis> Lemmermann

Biocidal natural substances of botanical origin offer a promising ecofriendly option for controlling toxic cyanobacteria. Herein, we study 11 essential oils and some of their major components for their activity on Aphanizomenon gracile. On the basis of our results we support that Origanum vulgare and O. dictamnus, Ocimum basilicum, Eucalyptus meliodora, Melissa officinalis, and Pimpinella anisum exhibited the strongest activities, and the IC_50/1d values of the extracts were calculated to be between 168.43 and 241.97 μg mL^?1. When the major components of the biocidal essential oils were tested individually, (E)-anethole was found active, exhibiting an IC_50/1d value of 71.35 μg mL^?1. On the other hand, the half-life (t _1/2 ) of (E)-anethole was calculated at 1 h. A preliminary attempt of (E)-anethole microencapsulation was conducted, in order to slowly release this biocidal agent, increasing the residual life under open air conditions and thus the biological activity. Results were promising since the microencapsulated product exhibited better activity than did the non-formulated (E)-anethole. This is a first report on the biocidal activity of EOs and (E)-anethole on A. gracile and a preliminary indication of the microencapsulated (E)-anethole potential use as a natural biocidal in fresh waters.

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Graphical abstract Filaments of Aphanizomenon gracile capable of bloom forming (strain SAG 31.79, in a batch culture) and (E)-anethole

     

Gas exchange,carbon balance and stomatal traits in wild and cultivated rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) genotypes

Carbon balancing within the plant species is an important feature for climatic adaptability. Photosynthesis and respiration traits are directly linked with carbon balance. These features were studied in 20 wild rice accessions Oryza spp., and cultivars. Wide variation was observed within the wild rice accessions for photosynthetic oxygen evolution or photosynthetic rate (A), dark (R _d), and light induced respiration (LIR) rates, as well as stomatal density and number. The mean rate of A varied from 10.49 μmol O₂ m^?2 s^?1 in cultivated species and 13.09 μmol O₂ m^?2 s^?1 in wild spp., The mean R _d is 2.09 μmol O₂ m^?2 s^?1 and 2.31 μmol O₂ m^?2 s^?1 in cultivated and wild spp., respectively. Light induced Respiration (LIR) was found to be almost twice in wild rice spp., (16.75 μmol O₂ m^?2 s^?1) compared to cultivated Oryza spp., Among the various parameters, this study reveals LIR and A as the key factors for positive carbon balance. Stomatal contribution towards carbon balance appears to be more dependent on abaxial surface where several number of stomata are situated. Correlation analysis indicates that R _d and LIR increase with the increase in A. In this study, O. nivara (CR 100100, CR 100097), O. rufipogon (IR 103404) and O. glumaepatula (IR104387) were identified as potential donors which could be used in rice breeding program. Co-ordination between gas exchange and patchiness in stomatal behaviour appears to be important for carbon balance and environmental adaptation of wild rice accessions, therefore, survival under harsh environment.     

Genetic engineering of polyamine metabolism changes <Emphasis Type="Italic">Medicago truncatula</Emphasis> responses to water deficit

In the current scenario of climate change and increasing water scarcity there is an increased need to combine research efforts for the development of abiotic stress resistant crops, specifically plants able to support water deficit (WD). Polyamines (PAs) have been described as being involved in the regulation of many physiological processes and a variety of stress responses in plants. Arginine decarboxylase (ADC) is considered a key enzyme of the polyamine (PA) biosynthetic pathway. In this study, a T₂ transgenic homozygous line of Medicago truncatula expressing the oat Adc under the control of CaMV 35S was obtained and was shown to have higher leaf accumulation of putrescine, spermidine and norspermidine compared to wild type plants. The photosynthetic parameters, leaf internal CO₂ concentration (Ci), net CO₂ assimilation rate (A), transpiration (E) and stomatal conductance (gs) of transformed and untransformed lines during WD and water deficit recovery experiments were measured by IRGA (infrared gas analyzer) and compared over time. Two light intensities were used, growth light intensity (391 μmol m^?2 s^?1) and saturating light intensity (1044 μmol m^?2 s^?1). Independently of the light intensity, and under WD, the transgenic line stood out with increased Ci, A, E and gs; suggesting a possible benefit of the augmented PAs under such disturbing environmental conditions. We showed that the constitutive expression of the oat Adc gene improve the physiological responses to WD and that WD recovered transgenic plants had higher seed yield, suggesting a possible benefit of PA metabolism manipulation in legumes.     

Stomatal regulation in Douglas fir following a fungal-mediated chronic reduction in leaf area

Pathogens can cause chronic premature needle abscission in coniferous species. To assess the potential impacts on tree productivity, stomatal regulation was investigated in Douglas fir with chronic stomatal occlusion and defoliation from varying levels of the Swiss needle cast (SNC) fungus, Phaeocryptopus gaeumannii. Levels of SNC disease and subsequent defoliation were manipulated by choosing six sites with varying levels of disease and by foliar applications of fungicides on six trees per site. Diurnal measurements of leaf water potential (Ψ_leaf), stomatal conductance (g _s) and vapor pressure deficit (D) were made on six fungicide treated and six control trees per site. In addition, leaf specific hydraulic conductance was calculated on a single branch (K _{L_B}) from three trees per treatment per site. Stomatal conductance at D=1 kPa (g _sref) was negatively correlated with fungal colonization (number of fruiting bodies present in needle stomata) and positively correlated with K _{L_B}. Despite reduced needle retention in diseased trees, K _L declined due to a reduction in sapwood area and permeability (i.e., increasing presence of latewood in functional sapwood). In general, stomatal sensitivity to D for all foliage was consistent with stomatal regulation based on a simple hydraulic model [g _s=K _L(Ψ_soil?Ψ_leaf)/ D], which assumes strict stomatal regulation of Ψ_leaf. However, when fungal presence reduced maximum g _s below the potential maximum supported by hydraulic architecture, stomatal sensitivity was lower than expected based on the theoretical relationship: dg _s/dlnD=0.6·g _sref. The results indicate that losses in productivity associated with physical blockage of stomata and defoliation are compounded by additional losses in K _L and a reduction in g _s in remaining functional stomata.     

Stomatal conductance in mature deciduous forest trees exposed to elevated CO<Subscript>2</Subscript>

Stomatal conductance (g _s) of mature trees exposed to elevated CO₂ concentrations was examined in a diverse deciduous forest stand in NW Switzerland. Measurements of g _s were carried out on upper canopy foliage before noon, over four growing seasons, including an exceptionally dry summer (2003). Across all species reductions in stomatal conductance were smaller than 25% most likely around 10%, with much variation among species and trees. Given the large heterogeneity in light conditions within a tree crown, this signal was not statistically significant, but the responses within species were surprisingly consistent throughout the study period. Except during a severe drought, stomatal conductance was always lower in trees of Carpinus betulus exposed to elevated CO₂ compared to Carpinus trees in ambient air, but the difference was only statistically significant on 2 out of 15 days. In contrast, stomatal responses in Fagus sylvatica and Quercus petraea varied around zero with no consistent trend in relation to CO₂ treatment. During the 2003 drought in the third treatment year, the CO₂ effect became reversed in Carpinus, resulting in higher g _s in trees exposed to elevated CO₂ compared to control trees, most likely due to better water supply because of the previous soil water savings. This was supported by less negative predawn leaf water potential in CO₂ enriched Carpinus trees, indicating an improved water status. These findings illustrate (1) smaller than expected CO₂-effects on stomata of mature deciduous forest trees, and (2) the possibility of soil moisture feedback on canopy water relations under elevated CO₂.     

A morphophysiological analysis of the effects of drought and shade on <Emphasis Type="Italic">Catalpa bungei</Emphasis> plantlets

The interactive effects of shade and drought on the morphological and physiological traits of Catalpa bungei plantlets were assessed. Seedling growth, biomass, biomass allocation, leaf morphology, chlorophyll (Chl) content and gas-exchange parameters were measured in plants raised for 3 months under three light levels [80% (HI), 50% (MI), 30% (LI)] and two water levels [moisture (M) and drought (D)]. The results showed that shade greatly decreased growth, biomass, leaf area (LA) and Chl a/b; increased specific leaf area (SLA) and Chl content; and reduced photosynthetic rate (P _n). Drought reduced the growth, biomass, LA, SLA, Chl a/b, P _n, stomatal conductance (G _s), transpiration rate (T _r) and intercellular carbon dioxide concentration (C _i) and increased the Chl content. Stomatal closure was an early physiological response to water stress. Light, water and their interaction significantly affected plant traits and their bivariate relationships. The phenotypic plasticity index of light (0.47) was much higher than that of water (0.21), indicating that light was the main driver of the variations observed. Under drought stress, growth, biomass, leaf and stem biomass allocation significantly decreased in the HI and MI environments, whereas no significant difference was observed in growth or biomass parameters under the LI condition. Furthermore, no significant difference was observed in P _n, G _s, or T _r under the LI condition under water stress. Our results showed that shade did not alter the negative effects caused by drought stress in MI but did alleviate the negative effects of the LI condition. In summary, the effect of drought on C. bungei plantlets depends on the irradiance conditions.     

First study on characterization of virulence and antibiotic resistance genes in verotoxigenic and enterotoxigenic <Emphasis Type="Italic">E</Emphasis>. <Emphasis Type="Italic">coli</Emphasis> isolated from raw milk and unpasteurized traditional cheeses in Romania

The study focused on the incidence of enterotoxigenic Escherichia coli (ETEC) and verotoxigenic E. coli (VTEC) in raw milk and traditional dairy cheeses marketed in Romania, characterizing the virulence and antibiotic resistance genes of these isolates. One hundred and twenty samples of raw milk and 80 samples of unpasteurized telemy cheese were collected and cultured according to the international standard protocol. All the characteristic E. coli cultures were analyzed for the presence of STa, STb, LT, stx1, and stx2 toxicity genes. The ETEC/VTEC strains were tested for the presence of antibiotic resistance genes, such as aadA1, tetA, tetB, tetC, tetG, dfrA1, qnrA, aaC, sul1, bla _SHV , bla _CMY , bla _TEM , and ere(A), using PCR. The results showed that 27 samples (18.62%) were positive for one of the virulence genes investigated. 48.1% (n = 13) tested positive at the genes encoding for tetracycline resistance, tetA being the most prevalent one (61.5%; n = 8). A high percent (33.3%; n = 9) revealed the beta-lactamase (bla _TEM ) resistance gene, and none of the samples tested positive for bla _CMY and bla _SHV genes. The genes responsible for resistance to sulfonamides (sul1) and trimethoprim (dfrA1) were detected in rates of 14.8% (n = 4) and 7.4% (n = 2), respectively. E. coli is highly prevalent in raw milk and unpasteurized cheeses marketed in Romania. These strains might represent an important reservoir of resistance genes which can easily spread into other European countries, given the unique market.     

Better tolerance to water deficit in doubled diploid ‘Carrizo citrange’ compared to diploid seedlings is associated with more limited water consumption

Tolerance to water deficit in diploid (2x) and doubled diploid (4x) ‘Carrizo citrange’ (Citrus sinensis [L.] Osbeck × Poncirus trifoliata [L.] Raf) was investigated. Water deficit was applied for 4 weeks. Physiological parameters, including stomatal conductance (g _s), photosynthesis (A), transpiration (E), leaf and soil water potentials (Ψ _leaf; Ψ _soil), and pot water loss, were monitored throughout the stress. Moreover, ABA, H₂O₂ contents, and the expression of genes involved in ABA biosynthesis (NCED3), regulation of abscisic acid signaling (ABI1), and coding for a catalase enzyme (CAT2) known to favor H₂O₂ scavenging were monitored. During the experiment g _s, A, and E values were most of the time higher in 2x compared to 4x. During the water deficit period, pot water loss decreased faster in 2x compared to 4x, leading to a faster decrease in all physiological parameters in 2x. The higher sensitivity of 2x compared to 4x was correlated with more numerous thinner roots, higher leaf ABA and H₂O₂ contents, and with the lower leaf water potential. ABI1 and NCED3 expression was not strictly correlated with the ABA content. However, the higher CAT2 expression in 4x was correlated with the lower leaf H₂O₂ contents. Therefore, the better tolerance observed in 4x ‘Carrizo citrange’ compared to 2x was associated with more limited water consumption and better and H₂O₂ scavenging.