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Volume 44 (2009): Issue 5 (Aug 2009) x
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Hiroshi Hamamoto and Keisuke Yamazaki

We investigated the reproductive responses of three cultivars of short-day plants to day-extension and night-break treatment with red, blue, and green light-emitting diodes (LEDs). The plants examined were all Malvaceae species: two cultivars of okra [Abelmoschus esculentus (L.) Moench.] and a cultivar of native rosella [Abelmoschus moschatus ssp. tuberosus (Span.) Borss.]. To create day extension or night break, we provided supplemental light from LED panels with peak photon emissions of 470 (blue), 520 (green), or 650 (red) nm. Day-extension treatment using red or blue LEDs inhibited flower and bud appearances; the response was especially pronounced with red LEDs. Night-break treatment with red LEDs also delayed flower bud appearance, but night break with blue LEDs did not produce a clear effect. Night break with green light delayed flowering more strongly than blue light but a little less than red light. We concluded that the dark period-regulated reproductive processes of these plants are most sensitive to disruption by red light, closely followed by green light, but that they are insensitive to blue light, especially when the exposure period is short.

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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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Grace Q. Chen, Louisa Vang and Jiann-Tsyh Lin

The morphological, physiological, and biochemical changes during seed development of Lesquerella fendleri were investigated from 7 days after pollination (DAP) to desiccation. The entire course of seed development lasted ≈49 days and it can be divided into seven sequential stages (I to VII). During the early stages (I to III, 7 to 21 DAP), seed grew rapidly, showing a dramatic increase in size and fresh weight. They contained ≈75% water. During midmaturation stages (IV to V, 28 to 35 DAP), storage lipids, proteins, and other components of dry weights accumulated at maximum rates. The accumulation curves followed a sigmoidal pattern during seed development. As a result of water loss, fresh weight dropped significantly when seed progressed to late-maturation/desiccation stages (VI to VII, 42 to 49 DAP). The size of the seed decreased slightly and the color changed from green to orange–brown. Seed proteins were also analyzed using SDS-PAGE. Proteins with high molecular weights were prominent in developing seed at early stages (I to III). At Stage IV (28 DAP), proteins with low molecular weight appeared, whereas the high-molecular-weight proteins decreased in proportion. These low-molecular-weight proteins became predominant throughout the remaining stages of seed development. Forty-seven percent of freshly harvested seed at 35 DAP were able to germinate after 7 days incubation. The germination percentage increased to a maximum of 95% at 42 DAP after 7 days incubation. The relationships among seed morphology, reserve synthesis, and germination are discussed.

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Mason T. MacDonald, Rajasekaran R. Lada, A. Robin Robinson and Jeff Hoyle

There is strong evidence that Ambiol® (a derivative of 5-hydroxybenzimazole) promotes drought tolerance in many plants; it is often suggested that this is the result of its antioxidant properties. Recent evidence has also shown that several natural antioxidants promote carrot germination under drought stress. Thus, it was hypothesized that seed preconditioning using natural antioxidants might confer drought tolerance. Ambiol®, ascorbic acid, β-carotene, lutein, and lycopene were chosen as antioxidants at concentrations of 0.1 mg·L−1, 1.0 mg·L−1, and 10 mg·L−1. A preconditioning treatment was applied by soaking tomato (Solanum lycopersicum L.) seeds in an antioxidant solution for 24 h. Of the antioxidants tested, 10 mg·L−1 Ambiol®, 1.0 mg·L−1 β-carotene, 1.0 mg·L−1 ascorbic acid, and 0.1 mg·L−1 lycopene were shown to increase shoot dry mass by 114%, 94%, 56%, and 83%, respectively, in droughted seedlings when compared with a droughted control. Similar benefits were observed in root dry mass, leaf area, photosynthesis, and water use efficiency. Proteins were extracted from the seeds of certain treatments, before and after germination, and separated using isoelectric focusing. Specific proteins were found to be induced through all preconditioning treatments, whereas Ambiol® and β-carotene were found to induce specific proteins, independent of those induced through imbibition, both before and after germination. This result suggests that Ambiol® and β-carotene evoke specific proteins that may confer drought tolerance to the key physiological processes studied. In addition, protein profiles of ascorbic acid, β-carotene, and Ambiol® after germination had fewer visible bands than the controls, suggesting an accelerated mobilization or conversion of proteins within the seed.

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Hamidou F. Sakhanokho, Kanniah Rajasekaran and Rowena Y. Kelley

An efficient primary somatic embryo (SE) and secondary somatic embryo (SSE) production system was developed for the ornamental ginger Hedychium bousigonianum Pierre ex Gagnepain. Addition of two ethylene inhibitors, salicylic acid (SA) and silver nitrate (AgNO3), to the culture media improved the system. Callus was initiated and proliferated on a medium containing Murashige and Skoog (MS) basal salts supplemented with 9.05 μM 2,4-dichlorophenoxyacetic acid and 4.6 μM kinetin. Friable callus was transferred to a liquid medium containing MS basal salts, B5 vitamins, 0.6 μM thidiazuron, and 8.9 μM 6-benzylaminopurine to induce somatic embryogenesis. The effects of various concentrations of SA (0, 25, 50, 75, 100, 125, 150 μM) and AgNO3 (0, 10, 20, 30, 40, 50, 60 μM) on callus growth, SE, and SSE development was further evaluated. The rate of callus growth decreased as the concentrations of SA or AgNO3 increased. AgNO3 and SA at all concentrations stimulated SE and SSE development better than the control although a decrease in embryo production was observed at higher concentrations of both SA and AgNO3. The best concentrations for SA were 75 and 100 μM, whereas for AgNO3, they were 30 to 50 μM for both SE and SSE production.

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Dennis J. Gray, Zhijian T. Li, Sadanand A. Dhekney, Donald L. Hopkins and Charles A. Sims

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Francisco García-Sánchez and James P. Syvertsen

To gain insight into salinity tolerance of citrus, we studied growth, leaf, and root Cl concentrations and physiological responses of 5-month-old seedlings of the citrus rootstock Carrizo citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliate L.] grown in a greenhouse in three different substrates: Candler sand soil, Floridana sandy clay soil, or a commercial soilless peat/perlite/vermiculite potting media. Plants were kept well-watered with a complete nutrient solution plus either no salt (control) or 50 mM NaCl for 9 weeks. Without salinity, substrate type did not affect total plant growth although there were differences in shoot/root dry weight ratio and mineral nutrient relationships attributable to substrate. Predawn leaf water potential, midday CO2 assimilation, and leaf water use efficiency were highest in seedlings grown in the soilless peat. The salt treatment decreased leaf and root growth, reduced leaf Ca2+, and increased leaf K+ concentration in all the three substrates. Overall, plant growth was negatively related to leaf Cl. Leaf growth reductions were least in Candler-grown seedlings and greatest in Floridana soil as Cl concentrations were lowest in Candler sand and highest in Floridana soil. Leaf Na+ was also highest in Floridana seedlings. In contrast to salt ions in leaves, roots of salinized seedlings in Candler sand had the highest Na+ and Cl concentration. Salinity reduced net gas exchange of leaves similarly in all three substrates. Salinity reduced both leaf water potential and osmotic potential such that leaf turgor was increased. Thus, salinity-induced reductions in growth and net gas exchange were not the result of loss of turgor but more likely resulting from toxic ion accumulation in leaves. Based on the relative rankings of leaf growth and leaf Cl concentrations, Carrizo seedlings from Candler sand had the highest salt tolerance and those grown in Floridana soil had the lowest salt tolerance. Substrate type should be considered when characterizing plant growth and physiological responses to salinity.

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David J. Norman, Qi Huang, Jeanne M.F. Yuen, Arianna Mangravita-Novo and Drew Byrne

Sixty-one cultivars of geraniums, including zonal, regal, ivy, and scented, were tested for susceptibility to three strains of Ralstonia solanacearum: a race 1, biovar 1 (R1B1) strain P597 isolated from tomato in Florida, a R1B1 strain P673 obtained from pothos originated from Costa Rica, and a race 3, biovar 2 (R3B2) strain UW551 isolated from geranium imported from Kenya. These three strains represent populations of R. solanacearum found in the United States or imported with infected plant propagative material. A genomic comparison of the geranium cultivars was also done using amplified fragment length polymorphisms. Both R1B1 strains were more virulent than the R3B2 strain, producing wilt symptoms on most cultivars of zonal, regal, and ivy types. Variation in susceptibility of geranium cultivars to the two R1B1 strains was observed. The R3B2 strain UW551 had a much more restricted host range and was not able to infect most regal geranium cultivars when applied as a soil drench. Many of the scented cultivars were found to be resistant to all three strains of R. solanacearum when tested using the drench inoculation method. However, most scented cultivars were found to be susceptible when plants were wound-inoculated. The greatest variation in type of resistance was observed between the scented geranium cultivars and specific strains of R. solanacearum.

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Jeong-Ho Lee

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Chad E. Finn, Patrick P. Moore, Chaim Kempler, Brian M. Yorgey, Bernadine C. Strik and Robert R. Martin