Domestic cat damage to plant leaves containing iridoids enhances chemical repellency to pests

Molecular background of the diverse metabolic profiles in leaves and inflorescences of naked catmint (Nepeta nuda L.)

Nepeta nuda L. shares a typical secondary chemistry with other Nepeta species (fam. Lamiaceae), characterized by the tendency to intensively produce monoterpenoid iridoids, whereas the phenylpropanoid chemistry is steered towards the production of a caffeic acid ester, rosmarinic acid. Combining complementary state-of-the-art analytical techniques, N. nuda metabolome was here comprehensively characterized in the quest for the organ-specific composition of phenolics and terpenoids that possess well-defined functions in plant-biotic interactions as well as therapeutic potential. N. nuda inflorescences showed generally higher constitutive levels of specialized metabolites, as compared to leaves, and the composition of major iridoids and phenolics in reproductive organs was found to be more conserved than in leaves across 13 populations from the Central Balkans. The results suggest that N. nuda plants most likely invest more in constitutive than inducible biosynthesis of functional metabolites in flowers, since they are of essential importance for both pollination and defense against herbivores and pathogens. Conversely, specialized metabolism of leaves is found to be more susceptible to reprograming in response to differential growth conditions. The defense strategy of leaves, primarily functioning in CO2 fixation during photosynthesis, more likely relies on the induction of metabolite levels following plant-environment interplay. Organ-specific biosynthesis of iridoids in N. nuda is found to be tightly regulated at the transcriptional level, and high constitutive levels of these compounds in inflorescences most likely result from the up-regulated expression of several key genes (NnG8H, NnNEPS1, NnNEPS2, and NnNEPS3) determining the metabolic flux through the pathway. The organ-specific content of rosmarinic acid and co-expression patterns of the corresponding biosynthetic genes were much less correlated, which suggests independent organ-specific transcriptional regulation of the iridoid and phenolic pathways. Knowledge gathered within the present study can assist growers to select productive genotypes and manipulate phenology of N. nuda towards maximizing yields and facilitating its integration into pest management systems and other applications related to human health.

A long-lasting gel-based diffuser of feline pheromone can help reduce undesirable behaviors in cats at home: comparison with an electric diffuser

Using pheromone diffusers is part of the strategy to control stress-related behaviors in cats (Felis catus). The goal of the study was to compare the efficacy of a novel long-acting, unpowered gel-based diffuser containing a facial pheromone analog (Zenifel® gel diffuser, Virbac) with a similar electrically powered feline pheromone diffuser that already has proven efficacy, on situational stress in cats, at home. The study involved 90 owners of cats presenting undesirable behaviors receiving one diffuser or the other: 46 received one gel diffuser and 44 received one plug-in device and a refill, for the 2-month study duration. The presence of the various undesirable behaviors was checked regularly and a general score was given to rate their presence. The most reported behaviors were related to hypervigilance, seeking the owner's attention, hiding, excessive vocalization, inactivity, and excessive scratching. All six behaviors significantly improved over time with Zenifel® while only four improved with the reference product (no improvement for excessive meowing and inactivity). The general score significantly improved as of day 7 in both groups, with no difference between groups. More owners said they would use the product throughout the year with Zenifel® than with the reference product (80% vs. 42%, p < 0.05). Therefore, both diffusers can be used to help control undesirable behaviors of cats at home but Zenifel® is more convenient to use throughout the year.

Implications of the Propagation Method for the Phytochemistry of Nepeta cataria L. throughout a Growing Season

Catnip (Nepeta cataria L.) plants produce a wide array of specialized metabolites with multiple applications for human health. The productivity of such metabolites, including nepetalactones, and natural insect repellents is influenced by the conditions under which the plants are cultivated. In this study, we assessed how field-grown catnip plants, transplanted after being propagated via either single-node stem cuttings or seeds, varied regarding their phytochemical composition throughout a growing season in two distinct environmental conditions (Pittstown and Upper Deerfield) in the state of New Jersey, United States. Iridoid terpenes were quantified in plant tissues via ultra-high-performance liquid chromatography with triple quadrupole mass spectrometry (UHPLC-QqQ-MS), and phenolic compounds (phenolic acids and flavonoids) were analyzed via UHPLC with diode-array detection (UHPLC-DAD). The highest contents of total nepetalactones in Pittstown were found at 6 weeks after transplanting (WAT) for both seedlings and cuttings (1305.4 and 1223.3 mg/100 g, respectively), while in Upper Deerfield, the highest contents for both propagules were at 11 WAT (1247.7 and 997.1 mg/100 g, respectively) for seed-propagated and stem cuttings). The highest concentration of nepetalactones was associated with floral-bud to partial-flowering stages. Because plants in Pittstown accumulated considerably more biomass than plants grown in Upper Deerfield, the difference in nepetalactone production per plant was striking, with peak productivity reaching only 598.9 mg per plant in Upper Deerfield and 1833.1 mg per plant in Pittstown. Phenolic acids accumulated in higher contents towards the end of the season in both locations, after a period of low precipitation, and flavone glycosides had similar accumulation patterns to nepetalactones. In both locations, rooted stem cuttings reached their maximum nepetalactone productivity, on average, four weeks later than seed-propagated plants, suggesting that seedlings have, overall, better agronomic performance.

Development of the gas chromatography/mass spectrometry-based aroma designer capable of modifying volatile chemical compositions in complex odors

Many volatile organic compounds (VOCs) are used to produce various commercial products with aromas mimicking natural products. The VOCs responsible for aromas have been identified from many natural products. The current major strategy is to analyze chemical compositions and aroma qualities of individual VOCs using gas chromatography/mass spectrometry (GC/MS) and GC-olfactometry. However, such analyses cannot determine whether candidate VOCs contribute to the characteristic aroma in mixtures of many VOCs. In this study, we developed a GC/MS-based VOC collection/omission system that can modify the VOC compositions of samples easily and rapidly. The system is composed of GC/MS with a switching unit that can change gas flow routes between MS and a VOC collection device. We first applied this system to prepare gas samples for omission tests, and the aroma qualities of VOC mixtures with and without some VOCs were evaluated by panelists. If aroma qualities were different between the 2 samples, the omitted VOCs were likely key odorants. By collecting VOCs in a gas bag attached to the collection device and transferring some VOCs to MS, specific VOCs could be omitted easily from the VOC mixture. The system could prepare omission samples without chemical identification, preparation of each VOC, and laborious techniques for mixing VOCs, thus overcoming the limitations of previous methods of sample preparation. Finally, the system was used to prepare artificial aromas by replacing VOC compositions between different samples for screening of key odorants. In conclusion, the system developed here can improve aroma research by identifying key odorants from natural products.

Assessing the safety and suitability of using silver vine as an olfactory enrichment for cats

Olfactory enrichment is a strategy that can improve welfare among animals managed in captivity, such as household domestic cats. Catnip (Nepeta cataria) and silver vine (Actinidia polygama) that produce iridoids are used as olfactory enrichments for cats, but little is known about the safety or the best plant resources to use that maximize positive cat responses. We report physiological effects and suitable harvest and drying methods for using silver vine as olfactory enrichment. Continuous exposure of cats to silver vine showed no hallmarks of addictive behavior, while blood indicators of stress and hepatic or renal injury showed no increase in cats stimulated with it. Drying the leaves changed the iridoid profile, enhancing the feline response. In conclusion, dried silver vine leaves are the most suitable resource for developing olfactory enrichment that maximizes feline typical response, which would not result in dependence, stress, or toxicity to the liver or kidneys in cats.

In vivo characterization of key iridoid biosynthesis pathway genes in catnip (Nepeta cataria)

Using virus-induced gene silencing, we demonstrated that the enzymes GES, ISY, and MLPL are responsible for nepetalactone biosynthesis in Nepeta cataria. Nepetalactone is the main iridoid that is found in the Nepeta genus and is well-known for its psychoactive effect on house cats. Moreover, there is a burgeoning interest into the effect of nepetalactone on insects. Although the enzymes for nepetalactone biosynthesis have been biochemically assayed in vitro, validation of the role that these enzymes have in planta has not been demonstrated. Virus-induced gene silencing (VIGS) is a silencing method that relies on transient transformation and is an approach that has been particularly successful when applied to a variety of non-model plants. Here, we use a recently designed visual-marker dependent VIGS system to demonstrate that the nepetalactone biosynthetic enzymes GES, ISY, and MLPL impact nepetalactone biosynthesis in Nepeta cataria.