Differential response of leaf gas exchange to enhanced ultraviolet-B (UV-B) radiation in three species of herbaceous climbingplants

We measured diurnal changes in photosynthetic rate, transpiration rate, stomatal conductance and water use efficiency in three species of herbaceous climbing plants (Luffa cylindrica, Trichosanthes kirilowii and Dioscorea opposita) exposed to two intensities of UV-B radiation: 3.0 μw cm^?2 (R1) and 8.0 μw cm^?2 UV-B (R2) radiation under ambient growth conditions. Responses differed per species and per treatment. In Luffa all values increased compared to the Control in both treatments, except for stomatal conductance in R2. In Trichosanthes photosynthetic rates and water use efficiency increased, while the transpiration rates decreased under both treatments, and stomatal conductance was lower in R1. In Dioscorea photosynthetic rates and water use efficiency decreased under both treatments, while the transpiration rates and stomatal conductance increased. The results suggested that to some extent increased UV-B radiation was beneficial to the growth of L. cylindrica and T. kirilowii, but detrimental to D. opposita.     

Partial protection of photosynthetic apparatus from UV-B-induced damage by UV-A radiation

Alteration in the photosynthetic apparatus of clusterbean (Cyamopsis tetraganoloba) cotyledons owing to UV-B irradiation in the absence or presence of UV-A radiation (UV-A + UV-B) during steady phase of its growth has been studied. UV-B radiation induces a decline in the photosynthetic pigments content and O₂ evolution along with a modification in the absorption spectra of chloroplasts. UV-A + UV-B irradiation moderately reverses these changes. The partial restoration of F_V/F_M value and other fluorescence transient parameters in UV-A + UV-B treated sample compared to that of UV-B treated one suggest that UV-A helps in developing a protective pathway against UV-B-induced impairment. UV-B-mediated alteration in S state transition of Mn cluster associated with oxygen evolving complex, as appeared from TL glow curves, is retrieved by UV-A radiation and Car is considered to negotiate against UV-B-induced damage of photosynthetic apparatus.     

Interactive effects of α-NAA and UV-B radiation on the endogenous hormone contents and growth of Trichosanthes kirilowii Maxim seedlings

The impact of UV-B radiation on endogenous hormones in plants has recently drawn attention from researchers. The mechanism for reduced stem elongation by UV-B might be due to changes in the phytohormone levels, especially IAA, which plays a role in stem elongation. In this study, effects of UV-B radiation on Trichosanthes kirilowii Maxim (T. kirilowii) seedlings in greenhouse-grown plants were investigated. The results indicated that: (1) In comparison to controls, exposure to 0.029 Jm^?2 s^?1. UV-B radiation led to accumulation of endogenous abscisic acid (ABA) and zeatinriboside (ZR) in the plant contents, and decreased contents of endogenous indole-3-acetic acid (IAA) and gibberellic acid (GA_1/3). Exposure to UV-B radiation reduced the height and leaf area of plants. As a result, total biomass (plant dry weight) was lower. (2) In comparison to controls, addition of 2 mg l^?1 α-naphthaleneacetic acid (α-NAA) slightly increased the contents of IAA, GA_1/3 and ZR, and decreased the content of ABA in leaves. This addition of α-NAA significantly increased plant height and leaf area, but only slightly increased total biomass. (3) Addition of α-NAA to UV-B-exposed plants: increased the content of endogenous IAA, GA_1/3 and ZR; decreased accumulation of endogenous ABA; and increased plant height and leaf area in comparison to plants that only were exposed to UV-B. Moreover, total biomass increased slightly. This suggests that addition of α-NAA may compensate to a certain extent for the lack of IAA resulting from UV-B radiation; it also increases the content of GA_1/3 and ZR, decreases the accumulation of ABA, and promotes the growth of plants.     

Interaction of Elevated Ultraviolet-B Radiation and CO(2) on Productivity and Photosynthetic Characteristics in Wheat, Rice, and Soybean

Wheat (Triticum aestivum L. cv Bannock), rice (Oryza sativa L. cv IR-36), and soybean (Glycine max [L.] Merr cv Essex) were grown in a factorial greenhouse experiment to determine if CO₂-induced increases in photosynthesis, biomass, and yield are modified by increases in ultraviolet (UV)-B radiation corresponding to stratospheric ozone depletion. The experimental conditions simulated were: (a) an increase in CO₂ concentration from 350 to 650 microliters per liter; (b) an increase in UV-B radiation corresponding to a 10% ozone depletion at the equator; and (c) a and b in combination. Seed yield and total biomass increased significantly with elevated CO₂ in all three species when compared to the control. However, with concurrent increases in UV-B and CO₂, no increase in either seed yield (wheat and rice) or total biomass (rice) was observed with respect to the control. In contrast, CO₂-induced increases in seed yield and total plant biomass were maintained or increased in soybean within the elevated CO₂, UV-B environment. Whole leaf gas exchange indicated a significant increase in photosynthesis, apparent quantum efficiency (AQE) and water-use-efficiency (WUE) with elevated CO₂ in all 3 species. Including elevated UV-B radiation with high CO₂ eliminated the effect of high CO₂ on photosynthesis and WUE in rice and the increase in AQE associated with high CO₂ in all species. Elevated CO₂ did not change the apparent carboxylation efficiency (ACE) in the three species although the combination of elevated CO₂ and UV-B reduced ACE in wheat and rice. The results of this experiment illustrate that increased UV-B radiation may modify CO₂-induced increases in biomass, seed yield and photosynthetic parameters and suggest that available data may not adequately characterize the potential effect of future, simultaneous changes in CO₂ concentration and UV-B radiation.     

Exposures to elevated CO2, elevated temperature and enhanced UV-B radiation modify activities of polyphenol oxidase and guaiacol peroxidase and concentrations of chlorophylls,polyamines and soluble proteins in the leaves of Betula pendula seedlings

The activity of polyphenol oxidase (PPO) and guaiacol peroxidase (POD) and the concentrations of chlorophylls, free polyamines and soluble proteins were determined from the leaves of six genotypes of silver birch (Betula pendula Roth) seedlings exposed to short-term elevated carbon dioxide (CO₂), temperature (T), ultraviolet-B irradiation (UV-B, 280-315 nm) and their combinations. Results showed that the activity of PPO in the leaves was low but increased by elevated CO₂ and elevated T. The POD activity varied between the genotypes due to an interactive effect of CO₂ × UV-B. The soluble proteins were clearly decreased by elevated CO₂, but the level of response varied among the genotypes. The concentrations of chl a and total chlorophylls were lower in the leaves treated with elevated CO₂ than in leaves grown at ambient CO₂. An interactive effect of CO₂ × UV-B on the chl a/b ratio was found. Elevated T increased chl b concentration and decreased chl a/b ratio. Temperature treatments also caused variation in the concentrations of chl a, chl b and total chlorophylls among the genotypes. Polyamine analyses showed that the concentrations of putrescine were increased and spermine decreased in leaves treated with elevated T. However, the change in putrescine by elevated T was clearer at ambient CO₂ than in eCO₂ environment (significant effect of T × CO₂). In conclusion, the defensive enzymes, photosynthetic pigments, soluble proteins and growth-regulating polyamines in silver birch leaves were not susceptible to enhanced UV-B radiation. In contrast, all the variables responded to elevated T and/or elevated CO₂, reflecting the enhancive effects of climate change conditions not only on leaf productivity, but also on leaf turn-over rate. Most of these climate-driven changes were not regulated by UV-B radiation.     

Photooxidation and antioxidant responses in the earthworm Amynthas gracilis exposed to environmental levels of ultraviolet B radiation

Ultraviolet (UV) radiation leads to photooxidation in various organisms. Our previous study demonstrated that ultraviolet B (UV-B) radiation is lethal for particular species of earthworms, but the mechanisms responsible for the lethality are unclear. In our current study, we investigated that ultraviolet light causes photooxidative damage and reduces antioxidant responses in the earthworm Amynthas gracilis. Intact earthworms and skin/muscle tissue extracts were exposed to UV-B radiation for in vivo and in vitro studies. Both in vitro and in vivo results showed that the products of photooxidative damage, MDA and H₂O₂, increased after UV-B exposure. Glutathione peroxidase (GPx) and catalase were inhibited immediately after exposure to high doses (3000 J/m²) of UV-B radiation in vivo. Catalase activity was increased following a low UV-B dose (500 J/m²) in vivo, but decreased in response to all dosage levels in vitro. These data indicate that a relationship exists between UV-B induced damage and photooxidation and also that catalase and GPx act as important antioxidants to prevent photooxidation. According to these data, A. gracilis exhibits high sensitivity to environmental levels of UV-B. Therefore, A. gracilis represents a sensitive and cost-effective model organism for investigations of UV-radiation damage and environmental UV stress.     

Does UV-B influence biomass growth in lichens deficient in sun-screening pigments?

This study aimed to assess biomass growth as a response variable in lichens during short-term laboratory experiments. To do this, we studied the influence of UV-B and temperature on lichen performance including the synthesis of solar radiation screening cortical compounds. The pioneer lichen Xanthoria aureola from exposed sea cliffs and the old forest lichen Lobaria pulmonaria were cultivated for 15 days in the laboratory in a factorial experiments with temperature (12 and 21 °C) and UV-B (0, 0.1, 0.3 and 1.0 W m^?2) as treatments. Prior to the experiment, the cortical pigment parietin was non-destructively extracted from X. aureola, whereas the sampled shade-adapted thalli of L. pulmonaria lacked cortical melanic compounds. Therefore both lichens were deficient in cortical sun-screening compounds when the UV-B exposure started. At 12 °C, the relative growth rate was 7.2 ± 0.6 and 3.0 ± 0.8 mg g^?1 day^?1 in L. pulmonaria and X. aureola, respectively, reduced to 1.8 ± 0.5 and ?2.6 ± 0.9 mg g^?1 day^?1, at 21 °C. These figures showed that lichen growth is a useful response variable in short-term laboratory experiments. Growth was not influenced by UV-B alone in these pigment-deficient transplants, suggesting that UV-B had little adverse effects on either of the lichen bionts. The cortical sun screens (parietin and melanic compounds) were synthesized in the presence of UV-B, and increased statistically significantly with increasing UV-B at both cultivation temperatures. However, in X. aureola the synthesis was highest at the lowest temperature (12 °C). At 12 °C, changes in chlorophylls, F_v/F_m and NPQ during cultivation were consistent with a substantial level of acclimation to the growth chamber conditions for both species, whereas strong reductions in photosynthetic pigments, F_v/F_m and Ф_II at 21 °C indicated serious damage and chlorophyll degradation at high temperature. In conclusion, lichen growth and the synthesis of protective compounds are highly responsive lichen processes in short-term experiments.     

Stomatal,biochemical and morphological factors limiting photosynthetic gas exchange in the mangrove associate Hibiscus tiliaceus under saline and arid environment

The effect of salinity on leaf area and the relative accumulation of Na⁺ and K⁺ in leaves of the mangrove associate Hibiscus tiliaceus were investigated. Photosynthetic gas exchange characteristics were also examined under arid and non-arid leaf conditions at 0, 10, 20 and 30‰ substrate salinity. At salinities ≥ 40‰, plants showed complete defoliation followed by 100% mortality within 1 week. Salinities ≤ 30‰ were negatively correlated with the total leaf area per plant (r² = 0.94). The reduction in the total plant leaf area is attributed to the reduction in the area of individual leaves (r² = 0.94). Selective uptake of K⁺ over Na⁺ declined sharply with increasing salinity, where K⁺/Na⁺ ratio was reduced from 6.37 to 0.69 in plants treated with 0 and 30‰, respectively. Under non-arid leaf condition, increasing salinity from 0 to 30‰ has significantly reduced the values of the intrinsic components of photosynthesis V_c,max (from 50.4 to 18.4 μmol m⁻² s^-1), J_max (from 118.0 to 33.8 μmol photons m⁻² s⁻¹), and V_TPU (from 6.90 to 2.30 μmol m⁻² s⁻¹), while stomatal limitation to gas phase conductance (S_L) increased from 14.6 to 38.4%. Water use efficiency (WUE) has subsequently doubled from 3.20 for the control plants to 8.93 for 30‰ treatment. Under arid leaf conditions, the stomatal factor (S_L) was more limiting to photosynthesis than its biochemical components (73.4 to 26.6%, respectively, at 30‰). It is concluded that salinity causes a drastic decline in photosynthetic gas exchange in H. tiliaceus leaves through its intrinsic and stomatal components, and that the apparent phenotypic plasticity represented by the leaf area modulation is unlikely to be the mechanism by which H. tiliaceus avoids salt stress.     

Effects of UV-B radiation on soybean yield and seed quality: a 6-year field study

Two soybean [ Glycine max (L.) Merr.] cultivars, Essex and Williams, were grown in the field for 6 consecutive seasons under ambient and supplemental levels of ultravio-Set-B radiation to determine the potential for alterations in yield or seed quality with a reduction in the stratospheric ozone column. The supplemental UV-B fluences simulated a 16 or 25% ozone depletion. The data presented here represent the first field experiment conducted over multiple seasons which assesses the effects of increased UV-B radiation on seed yield. Overall, the cultivar Essex was found to be sensitive to UV-B radiation (yield reductions of 20%) while the cultivar Williams was tolerant. However, the effectiveness of UV-B radiation in altering yield was strongly influenced by the seasonal microclimate, and the 2 cultivars responded differently to these changing factors. Yield was reduced most in Essex during seasons in which water availability was high and was reduced in Williams only when water was severely limiting. The results of these experiments demonstrate the necessity for multiple-year experiments and the need to increase our understanding of the interaction between UV-B radiation and other environmental stresses in order to assess the potential consequences of stratospheric ozone depletion.     

Effects of ozone fumigation on cotton (Gossypium hirsutum L.) morphology,anatomy, physiology,yield and qualitative characteristics of fibers

This experiment was conducted to study the effect of high ozone concentrations on two cotton (Gossypium hirsutum L.) cultivars. Two cotton cultivars (Romanos and Allegria) were exposed to control (CF < 4 ppb O₃) and 100 ppb O₃. Plant exposure to ozone began eight days after emergence and was interrupted one day before removing the leaves, to calculate the leaf area. Plants were exposed to ozone 7 h/day, in closed and controlled-environment chambers, during their illumination with artificial visible light.In comparison to control plants, plants exposed to O₃ showed chlorotic and necrotic patches on their leaves, increased stomatal or epidermal cell density and yellowness of cotton fibers. Elevated ozone concentration did not have a significant effect on stomatal width, total leaf thickness and thickness of histological components of leaves. Exposure to ozone concentration reduced non-glandular hair density of main leaf veins, plant height, mainstem internode length, chlorophyll content, net photosynthetic rate, stomatal conductance and length and area of bracts and petals. Elevated ozone treatment reduced the maximum length of staminal tube, anther number, pollen grain germination, leaf area, leaf dry weight, boll number, raw cotton weight, total branch length, dry weight of the mainstem–branches–bracts–carpophylls and of root dry weight. Furthermore, exposure to O₃ reduced the seed weight, the lint weight, the yield, the ratio of lint weight to seed weight, the fiber strength, the micronaire, the maturity index and the fiber uniformity index values. This study shows that the exposure to high ozone concentrations mainly affected the rate of photosynthesis, raw cotton weight and strength of cotton fibers.     

Stomatal,biochemical and morphological factors limiting photosynthetic gas exchange in the mangrove associate Hibiscus tiliaceus under saline and arid environment

The effect of salinity on leaf area and the relative accumulation of Na⁺ and K⁺ in leaves of the mangrove associate Hibiscus tiliaceus were investigated. Photosynthetic gas exchange characteristics were also examined under arid and non-arid leaf conditions at 0, 10, 20 and 30‰ substrate salinity. At salinities ≥ 40‰, plants showed complete defoliation followed by 100% mortality within 1 week. Salinities ≤ 30‰ were negatively correlated with the total leaf area per plant (r² = 0.94). The reduction in the total plant leaf area is attributed to the reduction in the area of individual leaves (r² = 0.94). Selective uptake of K⁺ over Na⁺ declined sharply with increasing salinity, where K⁺/Na⁺ ratio was reduced from 6.37 to 0.69 in plants treated with 0 and 30‰, respectively. Under non-arid leaf condition, increasing salinity from 0 to 30‰ has significantly reduced the values of the intrinsic components of photosynthesis V_c,max (from 50.4 to 18.4 μmol m⁻² s^-1), J_max (from 118.0 to 33.8 μmol photons m⁻² s⁻¹), and V_TPU (from 6.90 to 2.30 μmol m⁻² s⁻¹), while stomatal limitation to gas phase conductance (S_L) increased from 14.6 to 38.4%. Water use efficiency (WUE) has subsequently doubled from 3.20 for the control plants to 8.93 for 30‰ treatment. Under arid leaf conditions, the stomatal factor (S_L) was more limiting to photosynthesis than its biochemical components (73.4 to 26.6%, respectively, at 30‰). It is concluded that salinity causes a drastic decline in photosynthetic gas exchange in H. tiliaceus leaves through its intrinsic and stomatal components, and that the apparent phenotypic plasticity represented by the leaf area modulation is unlikely to be the mechanism by which H. tiliaceus avoids salt stress.     

Morphological and physiological responses of nine southern U.S. rice cultivars differing in their tolerance to enhanced ultraviolet-B radiation

The impact of climatic change on crop production is a major global concern. One of the climatic factors, ultraviolet-B radiation (UV-B; 280–320 nm), which is increasing as a result of depletion of the global stratospheric ozone layer, can alter crop productivity. As the initial step in development of UV-B tolerant rice cultivars for the southern U.S., in this study we screened popular southern U.S. rice cultivars for variation in tolerance to elevated UV-B radiation with respect to morphological, phenological and physiological parameters. Plants grown in the greenhouse at the Texas AgriLife Research and Extension Center in Beaumont, Texas, U.S. were exposed to 0, 8 or 16 kJ m⁻² day⁻¹ UV-B radiation for 90 days. Our results showed differences among southern US rice cultivars in response to UV-B treatments with respect to leaf photosynthetic rate (P_n), leaf phenolic concentration, pollen germination (PG), spikelet fertility (SF), leaf number, leaf area, and yield. For most of the cultivars, plants exposed to enhanced UV-B radiation showed decreased P_n, PG, SF and yield and increased spikelet abortion and leaf phenolic concentration compared to the plants grown in a UV-B-free environment. In this study, cultivar ‘Clearfield XL729’ performed better than the other cultivars under enhanced UV-B radiation.     

An LED-based UV-B irradiation system for tiny organisms: System description and demonstration experiment to determine the hatchability of eggs from four Tetranychus spider mite species from Okinawa

We developed a computer-based system for controlling the photoperiod and irradiance of UV-B and white light from a 5 × 5 light-emitting diode (LED) matrix (100 × 100 mm). In this system, the LED matrix was installed in each of four irradiation boxes and controlled by pulse-width modulators so that each box can independently emit UV-B and white light at irradiances of up to 1.5 and 4.0 W m⁻², respectively, or a combination of both light types. We used this system to examine the hatchabilities of the eggs of four Tetranychus spider mite species (T. urticae, T. kanzawai, T. piercei and T. okinawanus) collected from Okinawa Island under UV-B irradiation alone or simultaneous irradiation with white light for 12 h d⁻¹ at 25 °C. Although no eggs of any species hatched under the UV-B irradiation, even when the irradiance was as low as 0.02 W m⁻², the hatchabilities increased to >90% under simultaneous irradiation with 4.0 W m⁻² white light. At 0.06 W m⁻² UV-B, T. okinawanus eggs hatched (15% hatchability) under simultaneous irradiation with white light, whereas other species showed hatchabilities <1%. These results suggest that photolyases activated by white light may reduce UV-B–induced DNA damage in spider mite eggs and that the greater UV-B tolerance of T. okinawanus may explain its dominance on plants in seashore environments, which have a higher risk of exposure to reflected UV-B even on the undersurface of leaves. Our system will be useful for further examination of photophysiological responses of tiny organisms because of its ability to precisely control radiation conditions.     

Effects of intraspecific competition on growth and photosynthesis of Atriplex prostrata

We investigated the effect of intraspecific competition on growth parameters and photosynthesis of the salt marsh species Atriplex prostrata Boucher in order to distinguish the effects of density-dependent growth inhibition from salt stress. High plant density caused a reduction of 30% in height, 82% in stem dry mass, 80% in leaf dry mass, and 95% in root dry mass. High density also induced a pronounced 72% reduction in leaf area, 29% decrease in length of mature internodes and 50% decline in net photosynthetic rate. The alteration of net photosynthesis paralleled growth inhibition, decreasing from 7.6 ± 0.9 μmol CO₂ m⁻² s⁻¹ at low density to 3.5 ± 0.4 μmol CO₂ m⁻² s⁻¹ at high density, indicating growth inhibition caused by intraspecific competition is mainly due to a decline in net photosynthesis rate. Plants grown at high density also exhibited a reduction in stomatal conductance from 0.7 ± 0.1 mol H₂O m⁻² s⁻¹ at low density to 0.3 ± 0.1 mol H₂O m⁻² s⁻¹ at high density and a reduction in transpiration rate from 6.0 ± 0.3 mmol H₂O m⁻² s⁻¹ at low density to 4.3 ± 0.3 mmol H₂O m⁻² s⁻¹ at high density. Biomass production was inhibited by an increase in plant density, which reduced the rate of photosynthesis, stomatal conductance and leaf area of plants.     

Measures of leaf-level water-use efficiency in drought stressed endophyte infected and non-infected tall fescue grasses

Neotyphodium coenophialum [Morgan-Jones and Gams], grows in the above-ground parts of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]. It is an asexual fungus that is transmitted through seed of its host plant. This grass/endophyte association is enhanced by the protection of the host from herbivory and improved drought stress. We investigated how a decline in leaf-level stomatal conductance impacts the instantaneous water-use efficiency (WUE), in endophyte-infected (E+) versus non-infected (E?) Kentucky-31 tall fescue grasses grown in a controlled environmental chamber over a 10-week period. Grasses were cut at 6 weeks after germination and allowed to regrow under high and low soil moisture availability. One week after cutting, soil moisture was allowed to decline in the low water treatment for 2 weeks until severe stress was demonstrated through a decline in stomatal conductance to less than 100 mmol m^?2 s^?1. We found no differences in WUE between E+ and E? plants when water was not limiting while higher WUE was exhibited in E+ plants relative to E? plants under severe drought stress. The E? plants showed an 18-fold reduction in mean WUE and a 70-fold reduction in photosynthesis under drought stress, while there was no change in WUE and only a fourfold decline in photosynthesis between well-watered and drought stressed E+ plants at 21 days. While there were no differences in the rates of transpiration between E+ and E? plants under severe drought stress, differences in WUE can be attributed mainly to higher photosynthetic rates of E+ than E? plants. The difference in photosynthetic rates between E+ and E? plants under drought conditions could not be explained by differences in stomatal conductance and Rubisco (EC 4.1.1.39) activities.     

Effect of seed pretreatment by magnetic field on the sensitivity of cucumber (Cucumis sativus) seedlings to ultraviolet-B radiation

The effects of seed pretreatment by magnetic field (MF) on the impacts of ultraviolet-B (UV-B) radiation were tested using cucumber (Cucumis sativus) seedlings in phytotron. Soaked cucumber seeds were placed in MF of various strengths (0, 0.2 and 0.45 T). After germination the seeds were sowed in homogeneous garden soil and grown, then cucumber seedlings were exposed to 0 (as control) and 3.5 kJ m⁻² UV-B irradiation, respectively. Some effects of UV-B radiation and MF-pretreatment as well as their combination were investigated. MF-pretreatment increased seed germination rate, seedling growth and development, although also increased lipid oxidation and ascorbic acid contents. On the other hand, our results provided evidence that seed MF-pretreatment increased the sensitivity of cucumber seedlings to UV-B radiation. The seedling growth and development were significantly decreased by the combination of UV-B irradiation and MF-pretreatment. This combination also increased oxidative pressure and decreased actual quantum yield of PS II. Leaf UV-B absorbing compound was increased by MF-pretreatment or UV-B irradiation, whereas their combination significantly decreased it. These results suggested that the harmful effects of combination were partially due to the inhibition of secondary metabolism.     

Expression of orexin receptors 1 (OX1R) and 2 (OX2R) in the porcine pituitary during the oestrous cycle

Orexin A and B, also termed hypocretin 1 and 2, are associated with the stimulation of food intake and arousal. The biological actions of the hormones are mediated via two distinct G protein-coupled receptors, termed orexin receptor 1 (OX1R) and orexin receptor 2 (OX2R). OX1R is selective for orexin A and OX2R binds orexin A and orexin B with similar affinity. The present study analyzed mRNA and protein expressions of OX1R and OX2R in adenohypophysis (AP) and neurohypophysis (NP) of cycling pigs. The tissue samples were harvested on days 2–3, 10–12, 14–16, and 17–19 of the oestrous cycle. Using quantitative real-time PCR higher OX1R gene expression was detected in AP on days 2–3 relative to days 10–12, 14–16 and 17–19 (p < 0.05). In NP the OX1R mRNA level was elevated on days 10–12 compared to the remaining stages (p < 0.05). OX2R gene expression in AP was the lowest on days 10–12 (p < 0.05 compared to days 2–3 and 17–19) and the expression peak occurred on days 17–19 (p < 0.05 vs. the all studied stages). In NP the highest (p < 0.05) expression of OX2R mRNA was noted on days 17–19 in relation to the remaining periods. OX1R protein content in AP was greatest on days 10–12 (p < 0.05), whereas in NP it was greatest on days 2–3 and 14–16 (p < 0.05 vs. days 10–12 and 17–19). In both cases the lowest OX1R protein expression was observed during follicular phase (p < 0.05 in relation to three remaining studied stages). OX2R protein in AP was lower (p < 0.05) on days 2–3 and 14–16 compared to days 10–12 and 17–19. In NP the lowest (p < 0.05) expression of this protein was on days 17–19 and the highest on days 10–12 (p < 0.05 compared to days 2–3 and 17–19). In summary, the present findings provide the first evidence that OX1R and OX2R mRNAs and proteins occur in the pituitary of the pig and indicate the dependence of orexin receptor expression on the endocrine reproductive state.     

Low stomatal density and reduced transpiration facilitate strawberry adaptation to salinity

Water and soil salinization are major constraints to agricultural productions because plant adaptation to hyperosmotic environments is generally associated to reduced growth and ultimately yield loss. Understanding the physiological/molecular mechanisms that link adaptation and growth is one of the greatest challenges in plant stress research since it would allow us to better define strategies to improve crop salt tolerance. In this study we attempted to establish a functional link between morphological and physiological traits in strawberry in order to identify margins to “uncouple” plant growth and stress adaptation. Two strawberry cultivars, Elsanta and Elsinore, were grown under 0, 10, 20 and 40 mM NaCl. Upon salinization Elsanta plants maintained a larger and more functional leaf area compared to Elsinore plants, which were irreversibly damaged at 40 mM NaCl. The tolerance of Elsanta was correlated with a constitutive reduced transpirational flux due to low stomatal density (173 vs. 234 stomata mm⁻² in Elsanta and Elsinore, respectively), which turned out to be critical to pre-adapt plants to the oncoming stress. The reduced transpiration rate of Elsanta (14.7 g H₂O plant⁻¹ h⁻¹) respect to Elsinore (17.7 g H₂O plant⁻¹ h⁻¹) most likely delayed the accumulation of toxic ions into the leaves, preserved tissues dehydration and consented to adjust more effectively to the hyperosmotic environment. Although we cannot rule out the contribution of other physiological and molecular mechanisms to the relatively higher tolerance of Elsanta, here we demonstrate that low stomatal density may be beneficial for cultivars prescribed to be used in marginal environments in terms of salinity and/or drought.     

Principal component analysis of intraspecific responses of tartary buckwheat to UV-B radiation under field conditions

Fifteen populations of tartary buckwheat (Fagopyrum tataricum Gaertn.) occurring in habitats with different natural UV-B levels were sampled, and the plants were exposed to enhanced UV-B radiation under field conditions simulating 25% depletion of the stratospheric ozone layer. The experimental design was a 2 × 15 factorial, with two levels of UV-B radiation (ambient and enhanced UV-B radiation) and plants from 15 populations. The responses of plants in growth, morphology, productivity and in the composition of photosynthetic pigments were measured. The results demonstrated that there were significant differences among populations in responses to UV-B radiation: some populations exhibited a positive effect while others were negatively affected. The UV-B effects on plant traits were correlated with the constitutive values. A principal component analysis (PCA) was used to evaluate the overall sensitivity of responses to UV-B radiation. Our results suggest that the sensitivity of plants to UV-B radiation is not only associated with the ambient UV-B level in natural habitats but also with the relative growth rate and other factors.