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Dong Sik Yang, Ki-Cheol Son and Stanley J. Kays

A broad cross-section of volatiles emanating from four species of popular indoor ornamental plants (Spathiphyllum wallisii Regel, Sansevieria trifasciata Prain, Ficus benjamina L., and Chrysalidocarpus lutescens Wendl.) was identified and categorized based on source. Volatile organic compounds from individual plants were obtained using a dynamic headspace system and trapped on Tenax TA during the day and again at night. Using short-path thermal desorption and cryofocusing, the volatiles were transferred onto a capillary column and analyzed using gas chromatography–mass spectroscopy. The volatiles originated from the plants, media/micro-organisms, pot, and pesticides. A total of 23, 12, 13, and 16 compounds were identified from S. wallisii, S. trifasciata, F. benjamina, and C. lutescens, respectively. The night emanation rate was substantially reduced (i.e., by 30.1%, 69.5%, 73.7%, and 63.1%, respectively) reflecting in part the regulation of biosynthesis and the greater diffusion resistance when the stomata were closed. S. wallisii had the highest emanation rate, releasing 15 terpenoid compounds [e.g., linaloloxide, linalool, (Z)-β-farnesene, farnesal, (+)-δ-cadinene, (+)-β-costol] into the surrounding air. Alpha-farnesene (90.3%) was quantitatively the dominant volatile present followed by (Z)-β-farnesene (1.4%), (+)-β-costol (1.4%), and farnesal (1.1%). Substantially fewer terpenoids (i.e., two, nine, and eight) emanated from S. trifasciata, F. benjamina, and C. lutescens, which quantitatively emitted fewer volatiles than S. wallisii. Most terpenoids from the four species were sesquiterpenes rather than monoterpenes. Methyl salicylate, a plant-signaling compound, was emitted by all four species. Certain volatiles (e.g., 2-chlorobenzonitrile, 1-ethyl-3,5-dimethylbenzene) were released from growth media and/or micro-organisms therein; other sources included the plastic pot (e.g., 2-ethyl-1-hexanol, octamethyl cyclotetrasiloxane) and pesticide ingredients [e.g., 2-(2-methoxy- ethoxy)ethanol, 2-ethylhexyl salicylate, homosalate].

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Mung Hwa Yoo, Youn Jung Kwon, Ki-Cheol Son and Stanley J. Kays

Foliage plants of Hedera helix L. (english ivy), Spathiphyllum wallisii Regal (peace lily), Syngonium podophyllum Schott. (nephthytis), and Cissus rhombifolia Vahl. (grape ivy) were evaluated for their ability to remove two indoor volatile organic air pollutants, benzene and toluene. Removal was monitored when the aerial portion of plants was exposed singly to 1 μL·L-1 or to 0.5 μL·L-1 of each gas in a closed environment over 6-hour periods during the day and the night. Selected physiological processes were assessed before and immediately after treatment to determine the effect of the gases on the plants. The effectiveness of plants in the removal of air pollutant(s) varied with species, time of day, and whether the gases were present singly or as a mixture. When exposed to a single gas, S. wallisii, S. podophyllum, and H. helix displayed higher removal efficiencies (ng·m-3·h-1·cm-2 leaf area) of either gas than C. rhombifolia during the day. The efficiency of removal changed when both gases were present; H. helix was substantially more effective in the removal of either benzene or toluene than the other species, with the removal of toluene more than double that of benzene. When exposed singly, the removal of both compounds was generally higher during the day than during the night for all species; however, when present simultaneously, H. helix removal efficiency during the night was similar to the day indicating that stomatal diffusion for english ivy was not a major factor. The results indicated an interaction between gases in uptake by the plant, the presence of different avenues for uptake, and the response of a single gas was not necessarily indicative of the response when other gases are present. Changes in the rates of photosynthesis, stomatal conductance, and transpiration before and after exposure indicated that the volatiles adversely affected the plants and the effects were not consistent across species and gases. Deleterious effects of volatile pollutants on indoor plants may be critical in their efficacy in improving indoor air quality and warrant further study.

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Ki-Cheol Son, Ray F. Severson, Maurice E. Snook and Stanley J. Kays

Methanol extracts of external (outer 3 mm) and interior root tissue of four sweetpotato [Ipomoea batatas (L.) Lam.] cultivars (`Centennial', `Jewel', `Regal', and `Resisto') having different levels of susceptibility to the sweetpotato weevil [Cylas formicarius elegantulus Summer] were analyzed for simple carbohydrates (fructose, glucose, sucrose, inositol) and organic acids (malic, citric, quinic) by gas chromatography and for phenolics (caffeic acid, caffeoylquinic acids, rutin) by high-performance liquid chromatography. There were significant differences among cultivars in the concentrations of total sugars and phenolics in the external tissue (P < 0.05). In addition, the distribution of carbohydrates, organic acids, and chlorogenic acid [3-O-caffeoylquinic acid] differed between external and interior tissues. Sucrose was the major water-soluble carbohydrate in all cultivars. With the exception of malic acid, the concentration of carbohydrates, organic acids, and phenolics did not correlate with cultivar susceptibility to the sweetpotato weevil.

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Sang Deok Lee, Soon Jae Kim, Seung Il Jung, Ki-Cheol Son and Stanley J. Kays

CO2 assimilation rate of Crassula hybrid `Himaturi', a succulent ornamental species with the crassulacean acid metabolism (CAM) photosynthetic pathway, was affected by light intensity (50, 100, 300 μmol·m–2·s–1), photoperiod (16/8, 8/16 h day/night), and temperature (30/25, 25/20 °C day/night). Maximum assimilation of CO2 occurred at 300 μmol·m–2·s–1 of diurnal irradiance, 16/8 h day/night photoperiod, and a day/night temperature of 30/25 °C. Diurnal CO2 assimilation patterns of nine succulent ornamental CAM species were evaluated (300 μmol·m–2 s–1, 35/25 °C day/night and a 16/8-h day/night photoperiod) for CO2 fixation. Of the nine ornamentals, Crassula `Himaturi' had the highest and Echeveria derembergii the lowest maximum CO2 absorption rate (13.0 vs 2.4 μmol kg–1·s–1), total nighttime (179.3 vs 13.4 mmol·kg–1), and 24 h total (200.6 vs 19.0 mmol·kg–1) absorption. Based on the CO2 assimilation patterns, the nine ornamentals were separated into two groups: 1) full CAM (Faucaria tigrina, Gasteria gracilis var. minima, Haworthia cymbiformis, and Haworthia fasciata); and 2) weakly CAM (Adromischus clarifolius, Crassula hybrids `Moonglow' and `Himaturi', E. derembergii, and Haworthia retusa).

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Dong Sik Yang, Svoboda V. Pennisi, Ki-Cheol Son and Stanley J. Kays

Twenty-eight ornamental species commonly used for interior plantscapes were screened for their ability to remove five volatile indoor pollutants: aromatic hydrocarbons (benzene and toluene), aliphatic hydrocarbon (octane), halogenated hydrocarbon [trichloroethylene (TCE)], and terpene (α-pinene). Individual plants were placed in 10.5-L gas-tight glass jars and exposed to ≈10 ppm (31.9, 53.7, 37.7, 46.7, and 55.7 mg·m−3) of benzene, TCE, toluene, octane, and α-pinene, respectively. Air samples (1.0 mL) within the glass containers were analyzed by gas chromatography–mass spectroscopy 3 and 6 h after exposure to the test pollutants to determine removal efficiency by monitoring the decline in concentration over 6 h within sealed glass containers. To determine removal by the plant, removal by other means (glass, plant pot, media) was subtracted. The removal efficiency, expressed on a leaf area basis for each volatile organic compound (VOC), varied with plant species. Of the 28 species tested, Hemigraphis alternata, Hedera helix, Hoya carnosa, and Asparagus densiflorus had the highest removal efficiencies for all pollutants; Tradescantia pallida displayed superior removal efficiency for four of the five VOCs (i.e., benzene, toluene, TCE, and α-pinene). The five species ranged in their removal efficiency from 26.08 to 44.04 μg·m−3·m−2·h−1 of the total VOCs. Fittonia argyroneura effectively removed benzene, toluene, and TCE. Ficus benjamina effectively removed octane and α-pinene, whereas Polyscias fruticosa effectively removed octane. The variation in removal efficiency among species indicates that for maximum improvement of indoor air quality, multiple species are needed. The number and type of plants should be tailored to the type of VOCs present and their rates of emanation at each specific indoor location.

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Kwang Jin Kim, Hyun Hwan Jung, Hyo Won Seo, Jung A. Lee and Stanley J. Kays

Phytoremediation of volatile organic compounds in indoor air involves both the plant and microbes in the media; however, removal rate is typically expressed on a leaf area basis. We determined the effect of root media volume on phytoremediation rate of volatile toluene and xylene to determine if there is a change in phytoremediation efficiency. Phytoremediation rate was calculated based on the aboveground space occupied by the plant and on the leaf area. Foliage plants of Fatsia japonica and Draceana fragrans ‘Massangeana’ were grown in different-sized pots (1, 2, 4, 6, and 12 L) that gave aerial plant to root zone volume ratios of 21:1, 21:2, 21:3, and 21:6. Total root volume and root fresh weight increased in D. fragrans with increasing media volume, whereas root density per unit of media volume decreased in both species. The efficiency of volatile toluene and xylene removal by the plants was increased as the root zone volume increased, whereas removal efficiency per unit media volume increased and then decreased. The highest volatile toluene and xylene removal efficiency was at a ratio of 21:3 (aerial plant:root zone volume) in F. japonica and 21:2 in D. fragrans. When phytoremediation efficiency was expressed on a leaf area basis, the phytoremediation rate for toluene and xylene increased progressively for both species with increasing media volume and as root volume increased. Calculating the amount of plant material needed within a home or office to obtain sufficient volatile organic compound (VOC) removal cannot be accurately predicted base solely on a leaf area (LA) or aboveground volume basis.

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Jyh-Bin Sun, Ray F. Severson, William S. Schlotzhauer and Stanley J. Kays

Thermal degradation of fractions from sweetpotato roots (`Jewel') was conducted with gas chromatographymass spectrometry to identify precursors of critical flavor volatiles. Upon heating (200 C), sweetpotato root material that was insoluble in methanol and methylene chloride produced similar volatile profiles to those from sweetpotatoes baked conventionally. Volatiles derived via thermal degradation of the nonpolar methylene chloride fraction and the polar methanol fraction did not display chromatographic profiles similar to those from conventionally baked sweetpotatoes. Initial reactions in the formation of critical volatiles appear to occur in the methanol and methylene chloride insoluble components. Maltol (3-hydroxy-2-methyl-4-pyrone) was found to be one of the critical components making up the characteristic aroma of baked sweetpotatoes. Integration of an analytical technique for the measurement of flavor into sweetpotato breeding programs could potentially facilitate the selection of improved and/or unique flavor types.

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Myeong Whoon Seo, Dong Sik Yang, Stanley J. Kays, Gung Pyo Lee and Kuen Woo Park

The principal bitter sesquiterpene lactones (BSLs; latucin, 8-deoxylactucin, and lactucopicrin) in six red and four green-pigmented leaf lettuce (Lactuca sativa L. var. crispa L.) cultivars were identified and quantified using high-performance liquid chromatography, proton nuclear magnetic resonance, and liquid chromatography–mass spectrometry and the contribution of each to the overall bitterness was determined. The concentration of each BSL and the total varied significantly among cultivars and there were significant differences resulting from leaf color (green versus red) and morphology (cut versus curled leaves) with red and curled leaf cultivars having higher BSL concentrations. The concentrations of lactucin, 8-deoxylactucin, and lactucopicrin ranged from 2.9 to 17.2, 2.8 to 17.1, and 8.8 to 36.1 μg·g−1 dry weight, respectively, with the total concentration ranging from 14.6 to 67.7 μg·g−1. Bitterness of the cultivars was assessed using a bitter activity value calculated using the concentration and bitterness threshold value for each BSL. Lactucopicrin was the primary contributor to bitterness as a result of its concentration and lower bitterness threshold; its relative proportion of the total bitterness activity value across all cultivars was over 72%. The concentration of individual BSLs differed with leaf location on the plant (i.e., basal, midstalk, and flower stalk). The concentrations in lactucin, 8-deoxylactucin, and lactucopicrin in flower stalk leaves were significantly higher (i.e., 2.9, 12.4, and 5.4 times, respectively) than in basal leaves, with the concentrations increasing acropetally. Genetic differences among cultivars and with leaf location on the plant contribute to the wide range in bitterness in lettuce.

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Ki-Cheol Son, Ray F. Severson, Richard F. Arrendale and Stanley J. Kays

Methodology was developed for the extraction of surface components of sweetpotato [Ipomoea batatas (L.) Lam.] storage roots. Surface components of storage roots were quantitatively extracted with methylene chloride using 8-minute ultrasonication. After removal of the solvent, the extract was treated with 3 Tri Sil-Z:1 trimethylsilylimidazol (v/v) to convert components with hydroxyl moieties to silyl ethers and then separated on a SE-54 fused silica capillary column. Distinctly different gas chromatography profiles were found between lines displaying moderate levels of resistance (`Resisto', `Regal', `Jewel') to the sweetpotato weevil [Cylas formicarius elgantulus (summers)] and weevil-susceptible lines (`Centennial', SC 1149-19, W-115), indicating a possible role of surface components in insect response. Chromatographic fractionation techniques were developed for separation of major components or groups of components. The results will allow subsequent bioassaying for the presence of an ovipositional stimulant(s) and other weevil behavior-modulating compounds and their chemical characterization.

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Kwang Jin Kim, Mi Jung Kil, Jeong Seob Song, Eun Ha Yoo, Ki-Cheol Son and Stanley J. Kays

The contribution of aerial plant parts versus the root zone to the removal of volatile formaldehyde by potted Fatsia japonica Decne. & Planch. and Ficus benjamina L. plants was assessed during the day and night. The removal capacity of the entire plant, aerial plant parts, and root zone was determined by exposing the relevant parts to gaseous formaldehyde (2 μL·L−1) in airtight chambers (1.0 m3) constructed of inert materials. The rate of formaldehyde removal was initially rapid but decreased as the internal concentration diminished in the chamber. To compare the removal efficiency between species and plant parts, the time interval required to reach 50% of the initial concentration was determined (96 and 123 min for entire plants of F. japonica and F. benjamina, respectively). In both species, the aerial plant parts reduced the formaldehyde concentration during the day but removed little during the night. However, the root zone eliminated a substantial amount of formaldehyde during the day and night. The ratio of formaldehyde removal by aerial plant parts versus the root zone was similar for both species, at ≈1:1 during the day and 1:11 at night. The effectiveness of the root zone in formaldehyde removal was due primarily to microorganisms and roots (≈90%); only about 10% was due to adsorption by the growing medium. The results indicate that the root zone is a major contributor to the removal of formaldehyde. A better understanding of formaldehyde metabolism by root zone microflora should facilitate maximizing the phytoremediation efficiency of indoor plants.