Does nitrogen fertilization have an impact on the trade-off between willow growth and defensive secondary metabolism?

The effect of nitrogen fertilization on the phytomass production, shoot length and leaf secondary phenolics in nine Salix myrsinifolia clones was investigated. Cuttings taken from 1-year-old and 2-year-old shoot parts of field cultivated clones were grown at three concentrations of nitrogen (7, 150 and 300 ppm) in a greenhouse for one growing season. The willow clones differed significantly in phytomass yield and secondary phenolics content. Nitrogen fertilization affected significantly the growth and secondary metabolism of willow clones. In most clones, the addition of nitrogen from a sub-optimum concentration (7 ppm) to an optimum concentration (150 ppm) appeared to reduce the amounts of salicortin, chlorogenic acid and unknown salicylate and increased shoot phytomass, but a supraoptimum nitrogen concentration (300 ppm) resulted in highly variable growth and secondary phenolic responses. A significantly negative correlation between leaf phytomass and amount of total phenolics at sub-optimum and optimum N-treatments indicates trade-off between growth and secondary metabolism in willow clones at these treatments. However, the leaf phytomass:total amount of phenolics ratio varied significantly among clones, and in all clones it was not significantly lower at sub-optimum N-treatment than at optimum N-treatment.     

Studies of the effect of environmental factors on the rotifer predator–prey system in freshwater

The aim of this work is to evaluate the effect of environmental factors: temperature and photoperiod on the zooplankton predator–prey system. Rotifers, an important and cosmopolitan group of zooplankton in freshwater, were used in our study. We investigated the effect of temperature (20, 23, and 30°C) and of photoperiod (L:D = 12:0 and 0:12) on the predatory rotifer Asplanchna brightwelli consuming rotifer Brachionus calyciflorus as prey. Under A. brightwelli predation, populations of B. calyciflorus prey were consumed more slowly at 20 ± 1 and 30 ± 1°C as compared to 23 ± 1°C. Prey consumption by A. brightwelli increased from 0.63 ± 0.09 ind. predator⁻¹ at 20°C to a peak of 1.22 ± 0.12 ind. predator⁻¹ at 23°C, then decreased significantly to 0.93 ± 0.14 ind. predator⁻¹ at 30 ± 1°C. In addition, predation responded to temperature changing sensitively and rapidly. Statistical analysis showed that the prey consumption were significant different under altered temperature periods during 12 h. Photoperiod also significantly influenced the rate of A. brighwelli predation. B. calyciflorus suffered less predation in darkness than in light. The rate of prey consumption in light (1.06 ind. predator⁻¹) was twice the average of that in darkness (0.51 ind. predator⁻¹). Furthermore, predation rate varied under changing photoperiod but predators moved back into the light did not resume their original consumption rate. Our results demonstrate that whether the predation in rotifer successfully or not is strongly influenced by temperature and photoperiod.     

Pasture trees in tropical México: the effect of soil nutrients on seedling growth

Environment and seedling community under isolated trees in pastures are different from those in the open pasture. The effect of the pasture trees on the soil nutrients and on the seedling growth were investigated. Seven isolated trees and eight plots were selected in two pastures of 12-yr and 32-yr old derived from a lowland rain forest with nutrient-rich soil at Los Tuxtlas, Mexico. The soil concentrations of total N, P Bray, K+, Na+, Ca2+ and Mg2+, plus others physical and chemical characteristics, were compared between the pasture trees and the open-pasture. An experiment was done to test the hypothesis that soil from under the pasture trees was better for seedling growth than soil from the open pasture. Seedlings of two native tree species and two domesticated species were grown in soil from the two different sites in a shade-house. The dry weight of the shoot and root/shoot ratio were compared. Only total N, P and Na+ differed slightly in concentrations between the sites, but did not promote more seedling biomass. It seems that the soil at this location is sufficiently nutrient-rich even in the open pastures and over-ride any effect of the pasture trees on nutrient availability.     

Analysis of the ��shelter tree-effect�� of natural and exotic forest canopies on the growth of young Podocarpus falcatus trees in southern Ethiopia

Plantations of exotic trees on areas where tropical forest has been clear-felled have been reported to facilitate regrowth of indigenous tree species. This so-called nurse- or shelter tree effect was investigated in a montane semihumid site in southern Ethiopia where plantations of Pinus patula and Eucalyptus saligna grow in close vicinity to the natural Podocarpus falcatus mixed forest. Physiological performance of P. falcatus saplings growing in the exotic and the natural forests was investigated over the year. Compared with the natural forest, photosynthetic carbon gain and growth of the saplings were significantly enhanced under Pinus patula while likewise retarded under Eucalyptus saligna. Diverging effects of the differently dense shelter canopies on the saplings could be traced to differences in the sub-canopy microclimates and particularly to the intensities and temporal distribution of photosynthetic active radiation (PAR). Moisture also played an important role for photosynthetic carbon gain: while the morning patterns of CO₂ uptake were significantly correlated with the patterns of sunflecks, stomatal conductance was the determinant factor in the afternoon. Analysis of the photosynthetic efficiency of sunflecks revealed a lower quantum yield than the basic diffuse PAR intensity. Compared with a theoretically even distribution of the daily PAR, CO₂ uptake under the real light climate was 70% under Pinus and in the natural forest, and 59% under Eucalyptus. Relating growth rates of Podocarpus saplings to photosynthesis the microclimate under Pinus was 2.5 times as effective as that in the natural forest and five times more effective than under Eucalyptus.     

Does testosterone mediate the trade-off between nestling begging and growth in the canary (Serinus canaria)?

Nestling birds solicit food from their parents with vigorous begging displays, involving posturing, jostling and calling. In some species, such as canaries, begging is especially costly because it causes a trade off against nestling growth. Fitness costs of begging like this are predicted by evolutionary theory because they function to resolve conflicts of interest within the family over the provision of parental investment. However, the mechanism that links these costs with nestling behaviour remains unclear. In the present study, we determine if the relationships between nestling androgen levels, nestling begging intensities and nestling growth rates are consistent with the hypothesis that testosterone is responsible for the trade-off between begging and growth. We test this idea with a correlational study, using fecal androgens as a non-invasive method for assaying nestling androgen levels. Our results show that fecal androgen levels are positively correlated with nestling begging intensity, and reveal marked family differences in each trait. Furthermore, changes in fecal androgen levels between 5 and 8 days after hatching are positively associated with changes in nestling begging intensity, and negatively associated with nestling growth during this time. Although these correlational results support our predictions, we suggest that that experimental manipulations are now required to test the direct or indirect role of testosterone in mediating the trade-off between begging and growth.     

The effect of enhancing environmental factors on the quality of patients’ sleep in a cardiac surgical intensive care unit

The aim of this study was to investigate the effect of enhancing environmental factors on the duration and quality of sleep among patients in a cardiovascular surgery intensive care unit (CSICU). This quasi-experimental study was conducted upon 100 patients. The experimental group received nursing interventions to control the environmental factors that negatively affect nocturnal sleep. Data also were collected using a form to assess the environmental factors and the Richards–Campbell Sleep Questionnaire in the morning of the second day after the operation. The difference between the groups was statistically significant in favor of the experimental group for eight of the environmental factors. Compared with that in the control group, the duration of sleep was longer (experimental, 6.30 h; control, 3.98 h) and the quality of sleep was higher (experimental, 66.57 units; control, 44.43 units) in the experimental group. We conclude that nursing interventions should be used to control the environmental factors that negatively affect nocturnal sleep in CSICUs.     

Influence of ε-caprolactam on growth and physiology of environmental bacteria

ε-Caprolactam was found to have an effect on ecologically important soil bacteria. It inhibited the growth of several Bacillus sp. and Rhizobium sp. but cells of Arthrobacter sp. were able to grow in the presence of caprolactam. Sphingomonas sp. lost its inherent capacity to produce extracellular polymer (EPS) if grown in medium containing caprolactam. In the case of raw domestic sewage, the diversity of native bacteria was diminished in presence of caprolactam. Polluted sea water yielded predominantly one type of caprolactam-degrading bacteria of the genus Achromobacter. These cells efficiently utilized up to 10 g caprolactam/L as the sole source of carbon and nitrogen in synthetic medium even in the presence of 20 g NaCl/L. Compared to cells of Arthrobacter sp., cells of Achromobacter sp. accumulated high amount of 6-aminocaproic acid due to degradation of caprolactam. When using caprolactam as sole source of carbon and nitrogen, Achromobacter cells showed unique physiological ability to produce EPS upon prolonged incubation in solid medium and in broth with low phosphate (C:N:P ratio 100:20:0.05). Hydrolyzed cell-free EPS had glucose as its major component though the only substrate provided in the medium for growth was caprolactam.     

The effect of transforming growth factor β1 on the crosstalk between autophagy and apoptosis in the annulus fibrosus cells under serum deprivation

Autophagy and apoptosis are important in maintaining the metabolic homeostasis of intervertebral disc cells, and transforming growth factor-β1 (TGF-β1) is able to delay intervertebral disc degeneration. This study determined the effect of TGF-β1 on the crosstalk between autophagy and apoptosis in the disc cells, with the aim to provide molecular mechanism support for the prevention and treatment of disc degeneration. Annulus fibrosus (AF) cells were isolated and cultured under serum starvation. 10 ng/mL TGF-β1 reduced the apoptosis incidence in the cells under serum starvation for 48 h, down-regulated the autophagy incidence in the cells pretreated with 3-methyladenine (3-MA) or Bafilomycin A (Baf A), partly rescued the increased apoptosis incidence in the cells pretreated with 3-MA, while further reduced the decreased apoptosis incidence in the cells pretreated with Baf A. Meanwhile, TGF-β1 down-regulated the expressions of autophagic and apoptotic markers in the cells under starvation, partly down-regulated the expressions of Beclin-1, LC3 II/I and cleaved caspase-3 in the cells pretreated with 3-MA or Baf A, while significantly decreased the expression of Bax/Bcl-2 in the cells pretreated with Baf A. 3-MA blocked the phosphorylation of both AKT and mTOR and partly reduced the inhibitory effect of TGF-β1 on the expression of LC3 II/I and cleaved caspase-3. TGF-β1 enhanced the expression of p-ERK1/2 and down-regulated the expressions of LC3 II/I and cleaved caspase-3. U0126 partly reversed this inhibitory effect of TGF-β1. In conclusion, TGF-β1 protected against apoptosis of AF cells under starvation through down-regulating excessive autophagy. PI3K–AKT–mTOR and MAPK–ERK1/2 were the possible signaling pathways involved in this process.     

Is the increased vigour of invasive weeds explained by a trade-off between growth and herbivore resistance?

Blossey and Nötzold (1995) recently hypothesised that the increased vigour of certain invasive plant species has been at the expense of defences against natural enemies. A prediction of their evolution of increased competitive ability (EICA) hypothesis is that invasive genotypes are relatively poorly defended. We tested this prediction with herbivore bioassays and with direct quantification of plant secondary metabolites comparing non-indigenous genotypes of Lythrum salicaria L. (purple loosestrife) with indigenous forms. The herbivore bioassays revealed no significant intra-specific variation in herbivore resistance between indigenous and non-indigenous hosts. The phenolic content of L. salicaria leaves was significantly higher in indigenous genotypes, as predicted by the EICA hypothesis. The average phenolic content of leaves (regardless of their origin) was, however, low, implying that the role of plant phenolics in purple loosestrife anti-herbivore defence is probably limited. It is suggested that the EICA hypothesis, as tested in the current study, does not explain the increased vigour of L. salicaria in non-indigenous habitats.     

Study of the inhibitory effect of fatty acids on the interaction between DNA and polymerase β

The binding of human DNA polymerase β (pol β) to DNA template-primer duplex and single-stranded DNA in the absence or presence of pol β inhibitors has been studied using a surface plasmon resonance biosensor. Two fatty acids, linoleic acid and nervonic acid, were used as potent pol β inhibitors. In the interaction between pol β and DNA, pol β could bind to ssDNA in a single binding mode, but bound to DNA template-primer duplexes in a parallel mode. Both pol β inhibitors prevented the binding of pol β to the single strand overhang and changed the binding from parallel to single mode. The affinities of pol β to the template-primer duplex region in the presence of nervonic acid or linoleic acid were decreased by 20 and 5 times, respectively. The significant inhibitory effect of nervonic acid on the pol β-duplex interaction was due to both a 2-fold decrease in the association rate and a 9-fold increase in the dissociation rate. In the presence of linoleic acid, no significant change of association rate was observed, and the decrease in binding affinity of pol β to DNA was mainly due to 7-fold increase in the dissociation rate. Published in Russian in Biokhimiya, 2009, Vol. 74, No. 7, pp. 1000–1006. These authors contributed equally.     

Effects of environmental factors on MSP21–25 aggregation indicate the roles of hydrophobic and electrostatic interactions in the aggregation process

Merozoite surface protein 2 (MSP2), one of the most abundant proteins on the merozoite surface of Plasmodium falciparum, is recognized to be important for the parasite’s invasion into the host cell and is thus a promising malaria vaccine candidate. However, mediated mainly by its conserved N-terminal 25 residues (MSP2_1–25), MSP2 readily forms amyloid fibril-like aggregates under physiological conditions in vitro, which impairs its potential as a vaccine component. In addition, there is evidence that MSP2 exists in aggregated forms on the merozoite surface in vivo. To elucidate the aggregation mechanism of MSP2_1–25 and thereby understand the behavior of MSP2 in vivo and find ways to avoid the aggregation of relevant vaccine in vitro, we investigated the effects of agitation, pH, salts, 1-anilinonaphthalene-8-sulfonic acid (ANS), trimethylamine N-oxide dihydrate (TMAO), urea, and sub-micellar sodium dodecyl sulfate (SDS) on the aggregation kinetics of MSP2_1–25 using thioflavin T (ThT) fluorescence. The results showed that MSP2_1–25 aggregation was accelerated by agitation, while repressed by acidic pHs. The salts promoted the aggregation in an anion nature-dependent pattern. Hydrophobic surface-binding agent ANS and detergent urea repressed MSP2_1–25 aggregation, in contrast to hydrophobic interaction strengthener TMAO, which enhanced the aggregation. Notably, sub-micellar SDS, contrary to its micellar form, promoted MSP2_1–25 aggregation significantly. Our data indicated that hydrophobic interactions are the predominant driving force of the nucleation of MSP2_1–25 aggregation, while the elongation is controlled mainly by electrostatic interactions. A kinetic model of MSP2_1–25 aggregation and its implication were also discussed.     

Development of weighting factors for G20 countries—explore the difference in environmental awareness between developed and emerging countries

Purpose

Weighting is one of the steps involved in LCIA. This enables us to integrate various environmental impacts and facilitates the interpretation of environmental information. Many different weighting methodologies have already been proposed, and the results of many case studies with a single index have been published. LIME2 (Itsubo et al. Int J Life Cycle Assess 17(4):488-498, 2012) developed weighting factors for four different areas of protection that reflect environmental awareness among the Japanese public. This method has already been widely used in Japan, but difficulties exist universally using the Japanese weighting factors around the world. It is presumed that the weighting varies depending on economic, cultural, and social conditions, and there are still few cases in which weighting factors have been specifically invented or studied in consideration of variance in these elements. This study attempted to develop weighting factors applicable to the Group of Twenty (G20) countries with a view toward developing those that could be used in different countries. In the study, a survey was conducted with a uniform questionnaire in G20 countries to compare the weighting factors calculated for different countries, along with an investigation on development and utilization of global weighting factors.

Methods

A conjoint analysis was conducted to give a weighting between the four areas of protection defined by LIME: human health, social assets, biodiversity, and primary production. The analysis is suitable for measuring the value of each of the multiple attributes of the environment. This study conducted a questionnaire in all the G20 member states. The survey puts priority on making the questions understood by the respondents and minimizing bias, adopting interviews, visiting surveys, and surveys in venues in the 11 emerging countries. In the developed countries, Internet surveys were conducted after confirming that their results are statistically significant from the pretest results in these states. In both surveys, random sampling was performed to take 200–250 samples (households) in each of the emerging countries and 500–600 samples in each of the developed countries. The surveys collected a total of 6400 responses. Statistical values based on this model can be considered to reflect the variability between each individual’s environmental thoughts. The calculated results can then be used to compare the variety of environmental thoughts in developed and emerging countries.

Results and discussion

The study was able to obtain two different kinds of results: dimensionless weighting factors and economic indicators using the amount of willingness to pay. This paper solely presents the former. The weighting factors in the entire G20 community, in the group of developed countries (G8) and in the group of emerging countries (G20 states excluding the G8) and those in the individual G20 countries, were estimated. The calculated values were significant statistically at the 1 % level (all p values for the safeguard subject coefficients were less than 0.0001), with the exception of monetary attributes for several emerging countries. Converted into dimensionless values, so that the total sum for the four subjects equals 1, the weighting factor was the highest for human health in the entire G20 circles, at 0.34, followed by biodiversity at 0.29, and primary production at 0.23. The weighting for social assets was relatively poor, at 0.13. In the G8 developed states, the figures of biodiversity and primary production were relatively higher than those of the same two subjects in the full G20. Biodiversity had the highest value, at 0.34, and was followed by human health at 0.30. On the other hand, in emerging countries, the weighting of health impacts was particularly significant, at 0.44, whereas the three other subjects had almost equivalent weightings—biodiversity at 0.19, social assets at 0.18, and primary product at 0.18. The weighting factors by country and the variance of preference intensities by country showed minor differences among developed countries while they reflected considerable differences among emerging countries.

Conclusions

Accurate weighting factors representing the environmental attitudes of the world and national public are needed in order to conduct general purpose LCA. This study is the world’s first to conduct surveys with the use of the same questionnaire not only in developed countries but also in emerging countries, and to compare the findings. A total of 6400 responses were obtained via interviews and Internet surveys. The survey thus gained a statistically significant result on all the environmental attributes including the weighting factors for the G20 circles, G8 states, emerging countries exclusive of the G8 states, and individual countries in which surveys took place. The results have revealed a relatively minor difference in weighting factors and variation coefficients between the areas of protection in the developed countries whereas a considerable difference was observed between those subjects in emerging countries.

     

Effects of environmental conditions on cell growth and poly-β-hydroxybutyrate accumulation in Alcaligenes eutrophus

Influences of the control of glucose and oxygen concentrations on cell growth and poly--hydroxybutyrate (PHB) accumulation in Alcaligenes eutrophus were studied. Glucose affects both biosynthesis and glycolysis directly and the other pathways indirectly. PHB accumulation could also be stimulated under oxygen limitation conditions, but the final PHB content within the cells was less than in the case of nitrogen limitation. When the culture was shifted from the PHB accumulation state to balanced growth conditions, PHB degradation occurred in the cells. The cell growth was inhibited by high PHB content within the cells.     

Do the capacity and kinetics for modification of xanthophyll cycle pool size depend on growth irradiance in temperate trees?

The present study investigated the interaction of growth irradiance (Q_int) with leaf capacity for and kinetics of adjustment of the pool size of xanthophyll cycle carotenoids (sum of violaxanthin, antheraxanthin and zeaxanthin; VAZ) and photosynthetic electron transport rate (J_max) after changes in leaf light environment. Individual leaves of lower‐canopy/lower photosynthetic capacity species Tilia cordata Mill. and upper canopy/higher photosynthetic capacity species Populus tremula L. were either illuminated by additional light of 500–800 µmol m^?2 s^?1 for 12 h photoperiod or enclosed in shade bags. The extra irradiance increased the total amount of light intercepted by two‐fold for the upper and 10–15‐fold for the lower canopy leaves, whereas the shade bags transmitted 45% of incident irradiance. In control leaves, VAZ/area, VAZ/Chl and J_max were positively associated with leaf growth irradiance (Q_int). After 11 d extra illumination, VAZ/Chl increased in all cases due to a strong reduction in foliar chlorophyll, but VAZ/area increased in the upper canopy leaves of both species, and remained constant or decreased in the lower canopy leaves of T. cordata. The slope for VAZ/area changes with cumulative extra irradiance was positively associated with Q_int only in T. cordata, but not in P. tremula. Nevertheless, all leaves of P. tremula increased VAZ/area more than the most responsive leaves of T. cordata. Shading reduced VAZ content only in P. tremula, but not in T. cordata, again demonstrating that P. tremula is a more responsive species. Compatible with the hypothesis of the role of VAZ in photoprotection, the rates of photosynthetic electron transport declined less in P. tremula than in T. cordata after the extra irradiance treatment. However, foliar chlorophyll contents of the exposed leaves declined significantly more in the upper canopy of P. tremula, which is not consistent with the suggestion that the leaves with the highest VAZ content are more resistant to photoinhibition. This study demonstrates that previous leaf light environment may significantly affect the adaptation capacity of foliage to altered light environment, and also that species differences in photosynthetic capacity and acclimation potentials importantly alter this interaction.     

Gender dependent effects of testosterone and 17β-estradiol on bone growth and modelling in young mice

This study examined the effects of estrogen (17β-estradiol) and testosterone on the growth of long bones in male and female mice, with and without gonadectomy. Weight and nose-to-tail length were determined at 3 weeks of age at time of gonadectomy, 7 days later at the onset of hormone therapy, and throughout the treatment period. Gonadectomized mice exhibited an initial weight gain during the pretreatment period but length was unaffected. Hormone treatment altered weight gain in surgical and intact animals in a gender- and hormone-dependent manner. Estradiol enhanced weight gain in intact mice, but inhibited weight gain in ovariectomized mice. Lower doses of estradiol increased weight gain in orchiectomized mice at early time points. Testosterone increased weight in intact females and males, but not in gonadectomized mice. Estradiol increased nose-to-tail length in intact females at early time points, but inhibited length in ovariectomized females at later times, and it decreased length in intact males. Testosterone increased length in normal females and normal males. Serum Ca was unaffected by ovariectomy, but orchiectomy resulted in decreased levels. Estradiol reduced serum Ca in gonadectomized animals; serum Ca was increased by estradiol treatment in intact females. Changes in tibial bone weight, ash weight and mineral composition, and relative sizes of epiphyseal and metaphyseal bone were gender-, gonadectomy- and hormone-specific. Bone weight was greater in ovariectomized mice. Ash weight per bone was comparable, but there was an increase in Ca and P content with ovariectomy. Estradiol increased bone weight, ash content, and bone Ca and P in ovariectomized and intact females. Orchiectomy alone did not alter bone weight, ash content, or Ca and P, but orchiectomized mice were sensitive to estradiol; all parameters were increased in the orchiectomized animals treated with estradiol. Analysis of the ash content and Ca and P per mg bone, rather than per bone, demonstrated estradiol and testosterone alter net bone formation, but not the amount of mineral per unit bone. Ovariectomy increased hypertrophic cartilage. While estradiol did not alter tibial area in ovariectomized mice, it caused an increase in intact females. The total amount of growth plate cartilage in ovariectomized animals was decreased by estradiol to levels typical of intact animals due to a greater decrease in the hypertrophic cartilage in the ovariectomized mice, as well as a greater increase in metaphyseal bone area. Testosterone had no effect on these parameters in the females. Orchiectomy decreased the amount of growth plate cartilage, but increased the hypertrophic zone. Estradiol increased growth plate cartilage in intact male mice, but decreased it in orchiectomized mice. This difference was also seen in the hypertrophic zone. Total growth plate cartilage and hypertrophic cartilage were increased by testosterone in intact males, whereas metaphyseal and epiphyseal bone area were decreased. The results show for the first time that there is a gender-specific response in both male and female mice to both estradiol and testosterone, whether or not the animals have been gonadectomized. For many parameters, orchiectomized mice behave like females in response to both sex steroids, indicating that the male gonad is needed for mouse bone to exhibit the male phenotypic response to estradiol and testosterone.     

Extension growth and cold hardening of young ‘Valencia’ orange trees sprayed with AMO-1618

Rate of extension growth, as measured by height, of 2-month-old Valencia orange trees (Citrus sinensis (L.) Osbeck) on rough lemon rootstock (C. limon Burm. f.) was reduced to 0.5 mm from 5.0 mm day^–1 with 0.1% (w/v) sprays of the growth retardant AMO-1618 (4 hydroxy-5-isopropyl-2-methyl phenyl trimethyl-ammonium chloride, 1 piperdine carboxylate) every 2 weeks during 11 weeks under natural daylight in a glasshouse. Trees sprayed with AMO-1618 were 10-fold shorter, more compact in appearance, and leaves were greener and more oval shaped than those on untreated trees. There was no chemical burn. AMO-1618-sprayed trees were more cold hardy than untreated trees during controlled-temperature, cold-hardening regimes. Alone, AMO-1618 had no effect on freeze tolerance at -5.5° C. AMO-1618 also was associated with greater tree tolerance to freeze injury determined by O₂ uptake in Valencia leaves to as low as -6.7° C.This paper reports the results of research only. Mention of a trademark of a proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture, and does not imply its approval to the exclusion of other products that may also be suitable.