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Brent Tisserat, Danny Jones and Paul D. Galletta

Nutrient medium can be sterilized using a household-type microwave oven. The required microwave treatment time was influenced by the oven's microwave power intensity (70 to 700 W), vessel type, volume of medium employed, and the presence of energy sink water reservoirs (ESWR). Growth rates of strawberry (Fragaria vesca L.) shootlets, lemon [Citrus limon (L.) Burm. f.] fruit halves, or carrot (Daucus carota L.) callus cultured on either microwaved or autoclaved media were similar. Microwaving and autoclaving appeared to reduce GA3 activity compared with medium containing filter sterilized GA3. Chemical name used: gibberellic acid (GA3).

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Brent Tisserat, Robert Silman and Karen Ray

Ultra-high levels of CO2, i.e., >10,000 ppm, enhance tissue culture growth and offers a relatively simple and inexpensive method to improve plant productivity in vitro. Growth responses employing ultra-high CO2 levels differ considerably in the literature. Unfortunately, various culture vessels and systems have been employed, making comparisons difficult. In this study, the influence of the vessel container size, medium volume, and various CO2 concentrations (0 to 50,000 ppm) was studied on the growth obtained from lettuce and spearmint cultures. All three of these factors influence growth responses from plants cultured in vitro. Vessel types tested included: culture tubes, Magenta containers, 1-quart jars, 0.5-gallon jars, and 1-gallon jars having culture volumes of 55, 365, 925, 1850, and 3700 ml, respectively. Increasing the size of the culture vessel resulted in an increase growth regardless of the CO2 level tested. For example, fresh weight of spearmint increases of >250% can be obtained in by employing a 1-quart jar compared to using a culture tube. Increasing medium volume using various vessel types, especially using high concentrations of CO2, resulted in dramatic growth increases. For example, a >100% increase in fresh weight could be obtained by increasing the medium volume from 50 ml to 100 ml within a 1-quart jar. These studies suggest that plant growth promoted by supplemental CO2 is limited by the culture vessel size and medium volume. Differences in growth responses obtained in past CO2 studies could be related to vessel type and medium volume as well as the CO2 levels employed. Future in vitro studies should consider these factors in the evaluation of the influence of Ultra-high CO2 levels on plant growth. Peculiar growth responses, especially pertaining to rooting and shooting exhibited by cultures grown in ultra-high CO2 levels will also be discussed.

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Brent Tisserat, Daniel Jones and Paul D. Galletta

An inexpensive user-constructed ultrasonic misting system to grow plant tissues in vitro is presented. This system is constructed by coupling two commercially available products, a culture chamber and an ultrasonic humidifier. Plant cultures are grown within a culture chamber on a platform and bathed periodically by an ultrasonic nutrient mist. Carrot cultures were found to grow as much as four to 10 times as great as those grown on agar medium.

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Steven F. Vaughn, Mark A. Berhow and Brent Tisserat

Meadowfoam (Limnanthes alba Hartweg ex. Benth.) seedmeal, a coproduct of oil extraction from meadowfoam seeds, has been found to increase the growth of greenhouse plants when added to the growing medium. (3-Methoxyphenyl)acetonitrile (3-MPAN) is a biologically active glucosinolate degradation compound previously identified at high levels in meadowfoam seedmeal. 3-MPAN was tested as a foliar spray at several concentrations (0 μm, 0.18 mm, 0.37 mm, 0.73 mm, 2.2 mm, and 7.3 mm) on lime basil (Ocimum basilicum L.), spearmint (Mentha spicata L.), cuphea (Cuphea lanceolata L.), and French marigold (Tagetes patula L.) seedlings grown in the greenhouse. 3-MPAN increased the fresh and dry weights of all four species tested. However, this effect was dose-dependent among species with spearmint growth higher at all 3-MPAN application rates, whereas basil growth was promoted at only the 2.2-mm rate. 3-MPAN increased the tissue concentrations of the secondary compound (−)-carvone at the 7.3-mm application rate. In addition, 3-MPAN added to sterile nutrient media stimulated the growth of spearmint plants in vitro. These results indicate that 3-MPAN may have applicability as a postemergent growth stimulant for a wide variety of plants.

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Brent Tisserat, Christopher Herman, Robert Silman and Rodney J. Bothast

A continuous CO2 flow system was used to study the growth of carrot (Daucus carota L.), citrus (Citrus macrophylla L.), kale (Brassica oleracea L.), lettuce (Lactuca sativa L.), radish (Raphanus sativus L.), and tomato (Lycopersicum esculentum L.) cultures in vitro under photoautotrophic, photomixotrophic, and heterotrophic conditions. Lettuce plantlets were grown on Murashige and Skoog medium with 0%, 0.3%, 1%, and 3% sucrose within flow chambers containing 350, 750, 1500, 3000, 10,000, 30,000, and 50,000 μL·L−1 CO2. Increasing the levels of CO2, especially at the ultra-high levels (i.e., ≥3,000 μL·L−1 CO2), increased fresh weight, shoot length, leaf number, leaf length, leaf width, root number, and root length for plantlets grown regardless of sucrose levels tested compared to plantlets grown at normal atmospheric CO2 levels, i.e., 350 μL·L-1. For example, fresh weights of lettuce plantlets grown on medium containing 0% or 3% sucrose increased 11- and 13-fold, respectively, when supplemented with 30,000 μL·L-1 CO2 compared to growth of lettuce plantlets grown on the same media without CO2 enrichment. Similar fold increases in growth responses were obtained with carrot, citrus, kale, radish, and tomato plantlets grown in atmospheres enriched with high CO2 levels, elevated from 3000 to 30,000 μL·L-1. Optimum CO2 concentration varied among species, suggesting a species-related response. Varying the rate of CO2 application between 250, 500, 1500, or 2000 mL·min-1 did not effect the rate of growth of lettuce plantlets. The passive diffusion continuous flow-through system presented in this paper is inexpensive, easily constructed, and allows for testing ultra-high CO2 levels on plant culture growth in vitro.