Changes in forearm muscle temperature alter renal vascular responses to isometric handgrip

The purpose of the present study was to examine the effect of heating and cooling the forearm muscles on renal vascular responses to ischemic isometric handgrip (IHG). It was hypothesized that heating and cooling the forearm would augment and attenuate, respectively, renal vascular responses to IHG. Renal vascular responses to IHG were studied during forearm heating at 39 degrees C (n = 15, 26 +/- 1 yr) and cooling at 26 degrees C (n = 12, 26 +/- 1 yr). For a control trial, subjects performed the experimental protocol while the forearm was normothermic (approximately 34 degrees C). Muscle temperature (measured by intramuscular probe) was controlled by changing the temperature of water cycling through a water-perfused sleeve. The experimental protocol was as follows: 3 min at baseline, 1 min of ischemia, ischemic IHG to fatigue, and 2 min of postexercise muscle ischemia. At rest, renal artery blood velocity (RBV; Doppler ultrasound) and renal vascular conductance (RVC = RBV/mean arterial blood pressure) were not different between normothermia and the two thermal conditions. During ischemic IHG, there were greater decreases in RBV and RVC in the heating trial. However, RBV and RVC were similar during postexercise muscle ischemia during heating and normothermia. RVC decreased less during cooling than in normothermia while the subjects performed the ischemic IHG protocol. During postexercise muscle ischemia, RVC was greater during cooling than in normothermia. These results indicate that heating augments mechanoreceptor-mediated renal vasoconstriction whereas cooling blunts metaboreceptor-mediated renal vasoconstriction.     

Seasonal occurrence of Aphis glycines and physiological responses of soybean plants to its feeding

The soybean aphid Aphis glycines Matsumura （Hemiptera： Aphididae） is an important pest of soybean in China. To monitor and manage this pest effectively it is neces-sary to understand its population dynamics and demographics, as well as the physiological responses of soybean plants to its feeding. In this study, using field surveying and suction-trap monitoring, we investigated the population dynamics of the soybean aphid in Xiuyan County, Liaoning Province in northeastern China during 2009-2012. The results indicatedthat the population dynamics of the soybean aphid followed a unimodal curve distribution, with the insect generally colonizing soybean fields from the middle of June to early Julyand the population reaching a peak between early July and early August. On the whole, soybean aphids occurred in suction-traps at least 2 weeks earlier than they were foundin field surveys. A total of 72 alates were collected by suction-trapping over the 4 years, with the earliest alate captures occurring on 28 May in 2009, 2011, 2012 and 4 June in 2010. The life table parameters clearly showed that this aphid had a short doubling time （4.73 ± 0.21 days）, and 7.36± 0.98 nymphs were produced by a soybean aphid adult during its lifetime （13.57 ± 0.30 days）. Finally, biochemical assays indicated that the amount of malondialdehyde and the activities of four defense-related enzymes in soybean leavessignificantly changed between 0 day and 7 days of aphid infestation. Polyphenol oxidase （PPO） and catalase （CAT） activities increased more dramatically after 1 day of aphid feed-ing. In addition, significantly higher levels of superoxide dismutase and CAT were found after aphid feeding for 7 days, whereas there was no significant change in the activitiesof peroxidase and PPO. Consequently, this study will be beneficial in determining the seasonal occurrence of the soybean aphid and selecting insect-resistant soybean varieties,and thus in developing a theoretical framework for appropriate management strategies.     

Photosynthetic metabolism of an antarctic diatom and its physiological responses to fluctuations in light

Summary The short-term incorporation of NaH¹⁴CO₃ (10 to 60 s) into photosynthetic products has been studied in the antarctic diatom Nitzschia turgiduloides. It appears that there are two pathways of inorganic carbon assimilation: the C₃ pathway (Calvin cycle) principally, on which are superimposed -carboxylation reactions. Photorespiration, which contributes to decrease the net photosynthesis rate, has also been reported. With regard to these results the antarctic diatom was not different from the temperate one. However, the antarctic diatom presents some distinctive features. -carboxylation reactions which are probably favoured in Antarctic waters because of the high nitrate or ammonium concentrations, and also because they are more economical in terms of energy, are enhanced at the expense of the Calvin cycle reactions. On the other hand, the photorespiration rate is lower than that observed in temperate species, leading to an enhancement of net photosynthesis rate; this seems to occur principally by the more advantageous tartronic semialdehyde pathway. These two features are more pronounced for cells grown under light: dark cycles, particularly a 2:2 hour regime, as compared to continuous light. By contrast to the temperate species Skeletonema costatum, changes in the light regime modifies not only the relative amount of inorganic carbon assimilated by the C₃ or the -carboxylation pathways, but also the total amount of CO₂ incorporated per g Chl a. The productivity is highest in 2:2 regime, which simulates conditions of vertical mixing encountered in Antarctic Ocean more than does a 12:12 regime. This finding corroborates the view that the antarctic diatom is well adapted to its environment, although its production is not optimal compared to that of the temperate species grown under the same conditions of irradiance and temperature. Whether this is a genetic adaptation needs to be examined.     

Deep-water aquatic plant communities in an oligotrophic lake: physiological responses to variable light

1. Oligotrophic Lake Waikaremoana, New Zealand, is used for hydroelectric power generation and the lake levels are manipulated within an operating range of 3 m. There was concern that rapidly changing water levels adversely affected the littoral zone by decreasing light availability in two ways: local turbidity caused by shoreline erosion at low water levels; and decreased light penetration to the deep littoral zone caused by high water levels in summer. 2. The littoral zone was dominated by native aquatic plants with vascular species to 6 m and a characean meadow below this to 16 m. The biomass and heights of the communities in the depth zone 0–6 m were reduced at a site exposed to wave action relative to those at a sheltered site. However, the community structure below 6 m was similar at exposed and sheltered sites. The lower boundary of the littoral zone was sharply delimited at 16 m and this bottom boundary remained constant throughout the year despite large seasonal changes in solar radiation and the 3 m variation in lake level. 3. There was evidence that the deep-water community consisting of Chara corallina had adapted physiologically to low-light conditions. Net light saturated photosynthesis (CO₂ exchange) per unit chlorophyll a (Chl a) was reduced to 1.7 μg C (μg Chl a)^?1 h^?1 at the lower boundary, half of that recorded at 5 m. The concentration of Chi a per gram of biomass (dry weight), was considerably greater at the lower boundary than higher in the profile [c. 7 mg Chl a (g dry wt)^?1 at 16 m vs. 4 mg Chl a (g dry wt)^?1 at 5 m]. Chl b also increased with depth and there was no change in the ratio of Chl a and Chl b with increasing depth. The saturation light intensity (I_k) of the community at the lower boundary was only 78 μmol photons m^?2 s^?1. Photosynthetic parameters (I_k and α) as well as the Chl a content remained relatively constant throughout the seasonal and short-term changes in radiation. 4. The photosynthetic characteristics of the littoral community were therefore not greatly affected by the lake level change caused by the present hydroelectric operations. However, the sharpness of the lower boundary and its extreme shade characteristics imply that the deep-water community would be sensitive to any further changes in underwater light availability.     

Elevated light and nutrients alter the nutritional quality of stream periphyton

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Mutations in the gene for the red/far-red light receptor phytochrome B alter cell elongation and physiological responses throughout Arabidopsis development.

Phytochromes are a family of plant photoreceptors that mediate physiological and developmental responses to changes in red and far-red light conditions. In Arabidopsis, there are genes for at least five phytochrome proteins. These photoreceptors control such responses as germination, stem elongation, flowering, gene expression, and chloroplast and leaf development. However, it is not known which red light responses are controlled by which phytochrome species, or whether the different phytochromes have overlapping functions. We report here that previously described hy3 mutants have mutations in the gene coding for phytochrome B (PhyB). These are the first mutations shown to lie in a plant photoreceptor gene. A number of tissues are abnormally elongated in the hy3(phyB) mutants, including hypocotyls, stems, petioles, and root hairs. In addition, the mutants flower earlier than the wild type, and they accumulate less chlorophyll. PhyB thus controls Arabidopsis development at numerous stages and in multiple tissues.     

Early developmental responses to seedling environment modulate later plasticity to light spectral quality

Correlations between developmentally plastic traits may constrain the joint evolution of traits. In plants, both seedling de-etiolation and shade avoidance elongation responses to crowding and foliage shade are mediated by partially overlapping developmental pathways, suggesting the possibility of pleiotropic constraints. To test for such constraints, we exposed inbred lines of Impatiens capensis to factorial combinations of leaf litter (which affects de-etiolation) and simulated foliage shade (which affects phytochrome-mediated shade avoidance). Increased elongation of hypocotyls caused by leaf litter phenotypically enhanced subsequent elongation of the first internode in response to low red:far red (R:FR). Trait expression was correlated across litter and shade conditions, suggesting that phenotypic effects of early plasticity on later plasticity may affect variation in elongation traits available to selection in different light environments.     

Leaf heteroblasty is not an adaptation to shade: seedling anatomical and physiological responses to light

Heteroblastic plants produce markedly different leaf morphologies between juvenile and adult stages, while homoblastic plants exhibit little or gradual changes. We tested the hypothesis that the leaf morphology of the seedling stage of New Zealand heteroblastic species is advantageous in dealing with low light levels found in forest understorey. We used four independent contrasts of heteroblastic and homoblastic seedlings from the genera Aristotelia, Hoheria, Pseudopanax, and Melicope grown in full-sun (100% sunlight) and shade (5% sunlight) light environments in a glasshouse. The four heteroblastic species had consistently smaller leaves and lower specific leaf area than their paired homoblastic species both in sun and shade. In the shade, there were no consistent differences in leaf anatomy (thickness of leaf blade, cuticle, epidermis, and palisade mesophyll, and stomatal density × stomatal aperture length) or physiology (maximum photosynthetic rate, dark respiration, and light compensation point) between homoblastic and heteroblastic species. However, in the sun, heteroblastic A. fruticosa, P. crassifolius, and M. simplex had appreciably thicker leaf blades as well as higher maximum photosynthetic rates than their homoblastic congeners. These traits suggest heteroblastic seedlings possess leaf traits associated with an advantage in high-light environments. We conclude that the heteroblastic seedling leaf morphology is unlikely to be an adaptation to very low light. Alternative explanations for the functional significance of changing leaf morphology in association with life-stage should be sought.     

Comparing symbiotic performance and physiological responses of two soybean cultivars to arbuscular mycorrhizal fungi under salt stress

The presented experiments evaluated the symbiotic performance of soybean genotypes with contrasting salt stress tolerance to arbuscular mycorrhizal fungi (AMF) inoculation. In addition, the physiological stress tolerance mechanisms in plants derived from mutualistic interactions between AMF and the host plants were evaluated. Plant growth, nodulation, nitrogenase activity and levels of endogenous growth hormones, such as indole acetic acid and indole butyric acid, of salt-tolerant and salt-sensitive soybean genotypes significantly decreased at 200 mM NaCl. The inoculation of soybean with AMF improved the symbiotic performance of both soybean genotypes by improving nodule formation, leghemoglobin content, nitrogenase activity and auxin synthesis. AMF colonization also protected soybean genotypes from salt-induced membrane damage and reduced the production of hydrogen peroxide, subsequently reducing the production of TBARS and reducing lipid peroxidation. In conclusion, the results of the present investigation indicate that AMF improve the symbiotic performance of soybean genotypes regardless of their salt stress tolerance ability by mitigating the negative effect of salt stress and stimulating endogenous level of auxins that contribute to an improved root system and nutrient acquisition under salt stress.     

光质对水稻幼苗生长及生理特性的影响

以荧光灯为对照,采用发光二极管（light emitting diode,LED）精确调制不同光谱能量分布,研究了光质对‘武运粳7号’和‘抗优63’两种水稻幼苗生长及生理特性的影响.结果表明：光质对两个品种水稻幼苗生长有显著影响且存在差异.蓝光显著抑制幼苗株高,提高‘武运粳7号’叶片的可溶性蛋白含量及两个品种水稻五叶期幼苗的壮苗指数;红光显著提高三叶期幼苗的茎基直径、壮苗指数以及五叶期叶片的可溶性糖和淀粉含量;红蓝组合光显著提高三叶期幼苗的根数、茎基直径、壮苗指数、根系活力和可溶性糖含量,以及五叶期幼苗的鲜、干质量、壮苗指数、叶片可溶性糖和蔗糖含量;黄光可在幼苗生长初期明显增加株高,提高叶片色素含量.总体上,红蓝组合光有利于培育水稻壮苗.     

Stomatal responses to light and leaf-air water vapor pressure difference show similar kinetics in sugarcane and soybean

Stomatal responses to light and humidity (vapor pressure difference, VPD) are important determinants of stomatal conductance. Stomatal movements induced by light are the result of a transduction of the light stimulus into modulated ion fluxes in guard cells and concomitant osmotic adjustments and turgor changes. It is generally assumed that this transduction process is a general stomatal property, with different environmental stimuli integrated into guard cell metabolism through their modulation of ion fluxes. In contrast with this notion, the VPD response, which is unique because both its triggering signal and the turgor changes required for aperture modulations involve water molecules, has been considered to be hydropassive and thus independent of guard cell metabolism. We used a kinetic approach to compare the light and VPD responses in order to test the hypothesis that hydropassive changes in guard cell turgor could be faster than the metabolism-dependent light responses. Changes in stomatal conductance in intact leaves of sugarcane and soybean were measured after application of step changes in VPD and in light. In spite of a 5-fold difference in overall rates between the two species, the response rates following light or VPD steps were similar. Although a coincidental kinetic similarity between two mechanistically different responses cannot be ruled out, the data suggest a common mechanism controlling stomatal movements, with the VPD stimulus inducing metabolic modulations of ion fluxes analogous to other stomatal responses.     

朱砂根幼苗在不同光照强度下的形态和生理响应

通过人工遮荫模拟不同生境光强(100%、52%、33%、15%和6%的相对光照)的方法,对朱砂根(Ardisia crenata Sims)幼苗形态、生物量和生理指标的变化特征进行了分析。研究结果显示,朱砂根单株生物量在52%相对光照处理下显著高于其他光照处理,在15%～52%相对光照处理下分配给叶片的生物量比例高于全光照(100%)和极弱(6%)光照处理,但根冠比不受光强影响,其结构可塑性相对较低。硝酸盐含量随遮荫强度的增加而增大,且在6%相对光照处理下显著增加,硝酸盐还原酶的活性同硝酸盐含量变化规律一致,表明朱砂根主要通过改变叶面积和比叶面积等形态指标,以及调整生物量的分配和光合色素含量来适应不同的光环境。叶绿体超微结构分析结果显示,在15%～52%相对光照处理下,叶绿体数量较多且细胞结构较完整,而100%和6%光照处理下的叶绿体数量明显减少,且细胞结构严重受损发生质壁分离现象。因此,朱砂根适宜生长的光照条件为15%～52%,尤其是33%～52%的相对光照条件更佳。     

Development of methods to evaluate susceptibility of soybean aphid to imidacloprid and thiamethoxam at lethal and sublethal concentrations

The soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), is a recent introduction (2000) from Asia and has become a serious soybean [Glycine max (L.) Merr. (Fabaceae)] pest in North America. Seed treatments using the neonicotinoid insecticides, imidacloprid and thiamethoxam, have been suggested as a method of control, and the use of these insecticides is becoming widespread. As a consequence, there is increased potential to select for resistance to these compounds. In the case of soybean aphids, baseline susceptibility to neonicotinoid insecticides and standardized methods for bioassay are lacking. A bioassay technique that uses excised soybean leaves immersed in an insecticide solution was developed to determine systemic insecticidal activity at lethal and sublethal concentrations. Mortality and population growth inhibition were evaluated after 7 days. Life table parameters were calculated by exposing 1‐day‐old aphids to three concentrations of thiamethoxam. Aphid mortality and nymph production were recorded daily until the entire cohort collapsed. Soybean aphid age‐specific survivorship, fecundity, net reproductive rate, longevity, intrinsic rate of increase, discrete daily growth rate, and life expectancy were all significantly reduced at higher thiamethoxam concentrations. Soybean aphid response to both insecticides was similar, and both compounds were very toxic with LC₅₀s of 31.3 and 16.9 ng ml^?1 and EC₅₀s of 6.3 and 5.4 ng ml^?1 for imidacloprid and thiamethoxam, respectively. These results indicate that the methods developed in this study had negligible impact on the life table estimates measured and can be used to develop a baseline of susceptibility as a benchmark for subsequent resistance monitoring. Given the rapid and widespread adoption of this new insecticide class, vigilant monitoring for changes in susceptibility will be essential to its long‐term sustainability.     

Changes in temperature and light alter the flight speed of hornets (Vespa crabro L.)

Although the principal mechanisms of insect flight are well understood, knowledge about the influence of environmental factors on flight performance is scarce. We show that ambient temperature (TA) and illuminance have an influence on the flight performance of hornets. Moreover, the regulation of flight speed at different environmental conditions is sex specific. In roundabout experiments with tethered hornets, the flight speed of workers was independent of TA, while that of drones was negatively correlated with TA. We hypothesize that the reasons for these differences may lie in sex-specific cooling mechanisms; workers might regulate their body temperature through forced heat loss, whereas drones might reduce their heat production rates. At low illuminance, workers reduced their flight speed, whereas drones did not. Reduced flight speed at low illuminances is probably a behavioral mechanism of compensation for disadvantages caused by changing neuronal processes in the sensory neurons in darkness.     

Morphological and physiological responses to sediment type and light availability in roots of the submerged plant Myriophyllum spicatum

BACKGROUND AND AIMS: Both sediment and light are essential factors regulating the growth of submerged macrophytes, but the role of these two factors in regulating root morphology and physiology is far from clear. The responses of root morphology and physiology to sediment type and light availability in the submerged plant Myriophyllum spicatum were studied and the hypothesis was tested that a trade-off exists in root growth strategy between internal aeration and nutrient acquisition. METHODS: Plants were grown on two types of sediment (fertile mud and an infertile mixture of mud and sandy loam) and under three levels of light availability (600, 80 and 20 micro mol m(-2) s(-1)) in a greenhouse. KEY RESULTS: The significantly higher alcohol dehydrogenase (ADH) activity in root tissues indicated that oxygen deficiency existed in the plants growing in fertile mud and low (or high) light environments. Significantly, low plant N and P concentrations indicated that nutrient deficiency existed in the mixed sediment and high light environment. As a response to anoxia, plants did not change the porosity of the main roots. The effect of sediment type on root morphology was insignificant under higher light environments, whereas root diameter generally decreased but specific root length (SRL) increased with decreasing light availability. Both low light and fertile mud jointly led to lack of second-order laterals. More biomass was allocated to lateral roots in infertile environments, whereas mass fractions of laterals were lower in low light and mud environments. CONCLUSIONS: These data indicate that this plant can achieve the trade-off between internal aeration and nutrient acquisition by adjusting the structure of the root system and the pattern of biomass allocation to different root orders rather than root morphology and root porosity.     

Changes in morphological, photosynthetic and physiological responses of Mono Maple seedlings to enhanced UV-B and to nitrogen addition

In the southeast of the Qinghai-Tibetan Plateau of China, Mono Maple is a common species in reforestation processes. The paper mainly investigated the changes in morphological, photosynthetic and physiological responses of Mono Maple seedlings to UV-B radiation, nitrogen supply and their combination. The experimental design included two levels of UV-B treatments (ambient UV-B, 11.02 KJ m⁻² day⁻¹; enhanced UV-B, 14.33 KJ m⁻² day⁻¹) and two nitrogen levels (0; 20 g N m⁻² a⁻¹)—to determine whether the adverse effects of UV-B on plants are eased by nitrogen supply. Enhanced UV-B caused a marked decline in growth parameters, net photosynthetic rate, and photosynthetic pigments, whereas it induced an increase in reaction oxygen species (hydrogen peroxide accumulation and the rate of superoxide radical production) and malondialdehyde content. Enhance UV-B also induced an increase in antioxidant compounds of Mono Maple, such as UV-B absorbing compounds, proline content, and activities of antioxidant enzymes (peroxidase, superoxide dimutase and catalase). On the other hand, nitrogen supply caused an increase in some growth parameters, net photosynthetic rate, photosynthetic pigments and antioxidant compounds (peroxidase, proline content and UV-B absorbing compounds), and reduced the content of reaction oxygen species (H₂O₂ accumulation, the rate of O₂⁻ production) and malondialdehyde content under ambient UV-B. However, under enhanced UV-B, nitrogen supply inhibited some growth parameters, and increased H₂O₂ accumulation, the rate of O₂⁻ production and MDA content, though proline content, UV-B absorbing compounds and activities of POD and SOD increased. These results implied that enhanced UV-B brought harmful effects on Mono Maple seedlings and nitrogen supply made plants more sensitive to enhanced UV-B, though increased some antioxidant activity.