The genus Betula contains many important forest and ornamental species and a method of rapid clonal propagation of superior genotypes is needed. Thidiazuron (TDZ) is a potent synthetic plant growth regulator with cytokinin-like activity. TDZ was used to differentiate shoots after long term exposure to dichlorophenoxyacetic acid (2.4-D) as part of a larger study on clonal fidelity. Birch calli were cultured on Woody Plant Medium supplemented with 10-5 M 2,4-D for up to 30 weeks. The calli were transferred to media containing TDZ at concentrations of 10-6 to 10-9M. Most of the tissue which had not been exposed to 2.4-D differentiated shoots five weeks after being exposed to 10-6M TDZ. Increasing the of time exposure to 2.4-D or decreasing the concentration of TDZ delayed differentiation. Calli exposed to 2.4-D for more than 18 weeks rarely differentiated shoots regardless of the concentration of TDZ used.
The Univ. of Minnesota hosts the PLANT-TC Listserv as a service to the international tissue culture community (http://www.agro.agri.umn.edu/plant-tc/listserv/). One of the most frequently sought types of information is a recommendation for a “beginning point” for culturing a wide variety of plant species. Many of these inquiries come from individuals without ready access to extensive library holdings, including those in industry, public schools, and international sites. A Web site prototype that includes a searchable database of tissue culture recipes is being constructed and offered for user input. The database currently is located at http://webtutor.tamu.edu/students/herring/project/, but will be redirected to its own URL if user feedback is positive. The database also includes information about equipment and materials, media suppliers and domestic and foreign sources for tissue cultures and micropropagated plants. Other educational resources, including a virtual tour of a commercial tissue culture lab, are available on the site. The Web site and database will be reviewed by a panel of experts and modified according to their input prior to being posted for public access.
Research was undertaken to optimize seed storage and vegetative propagation of Camptotheca acuminata. Camptotheca is a member of the Nyssaceae native to southern China and is important because it contains the medicinal alkaloid camptothecin. Seeds stored in polyethylene bags in a refrigerator (4 °C) or freezer (- 20 °C) maintained good germination (79% and 83%, respectively), while seeds stored at room temperature in open containers or polyethylene bags lost germination ability quickly (45% and 51%, respectively). Softwood cuttings of Camptotheca rooted readily in intermittent mist (4 s on every 6 min.) in coarse vermiculite when treated with K-IBA (indolebutyric acid, potassium salt) quick dips ranging from 1000 to 9000 ppm, with a 7000 ppm quick dip (5 s) promoting 82% rooting with little foliar damage. Actively growing shoot tip explants were tissue cultured on media containing Murashige and Skoog, Gamborg, and Woody Plant Medium (WPM) salts in factorial combinations with BA (benzyladenine). WPM containing 1.0 mg/lBA promoted excellent shoot proliferation; microcuttings were rooted, acclimated, and grown on in the greenhouse. Camptotheca is readily adaptable to modern nursery techniques for either seed or vegetative propagation.
The pinwheel flowering African violet `Silver Summit', a periclinal chimera, has bicolor flowers with violet-blue 93B corolla segment margins and white 155B central stripes. Several off-types were produced during in vitro culture of `Silver Summit', the two of greatest potential value having reversed color patterns with violet-blue stripes and white margins. The off-types varied in color, one with deep violet-blue stripes (DR, dark reverse) and the other with lighter stripes of the same color (LR, light reverse). Unexpanded inflorescences of both off types were cultured on Murashige and Skoog medium containing 0.1 mg/L benzyladenine and 0.1 mg/L naphthaleneacetic acid. Plantlets resulting from expansion and multiplication of the dormant buds in the inflorescences were removed, acclimated, and grown on to flowering. Thirteen LR inflorescences produced 55 plants; 51 were true to type and four had solid violet-blue flowers (non-chimeral). Thirteen DR inflorescences produced 64 plants; only eight were true to type, 17 produced solid violet-blue flowers, 38 produced flowers with mixtures of the DR chimeral pattern and solid violet-blue flowers, and one was solid white flowering. To visualize the chimeral arrangement of the meristems of the off-types, flower patterns of all plants were recorded and “fl oral maps” were constructed. Floral maps of LR were constant from plant to plant and varied little as the plants aged, indicating LR to be a stable periclinal chimera. Floral maps of DR were highly variable from plant to plant, and changed considerably over time indicating that the DR meristems were less stable.
The pinwheel-flowering African violet `Silver Summit', apericlinal chimera, has bicolor flowers with violet-blue corolla segment margins and white central stripes. Several off types were produced during in vitro culture of `Silver Summit'—solid violet-blue flowering from leaf or petiole explants, solid white flowering from petiole core explants, and two reverse pinwheel flowering types. The reverse pinwheel types varied in color; one had deep violet-blue stripes (DR, dark reverse) and the other had lighter stripes of the same color (LR, light reverse). Plantlets derived from inflorescence culture (Murashige and Skoog medium containing 0.1 mg/1 NAA, 0.1 mg/1 BA) were grown on to flowering. Of 55 plants from LR inflorescences, 51 were true-to-type. The remainder were solid violet-blue flowering. Of 64 plants from DR inflorescences, only 8 were true-to-type, 17 were solid violet-blue flowering, one was white flowering, and 38 were mixed flowering. In vitro inflorescence culture can be used to clone pinwheel flowering African violets; however, chimeral stability of the plant produced varies between clones.
Cotyledon explants and zygotic embryos of Lycopersicon esculentum H132, OH8442, and OH2253 were cultured on Murashige and Skoog medium containing varying concentrations of 2,4-D and NAA with and without 10-7 M zeatin. NAA above 10-5 M and 2,4-D above 10-6 M inhibited root formation from cotyledons. Zygotic embryos were removed from developing ovules at the globular, heart, and torpedo stages and later germinated on hormone-free medium. Globular structures that resembled immature zygotic embryos were produced at NAA concentrations between 10-4 and 10-3 M and 2,4-D concentrations between 10-5 and 10-4 M. Treatments reported to enhance maturation and germination of somatic embryos of other species, including subculture to a hormone-free medium with and without activated charcoal, the addition of an ABA treatment subsequent to the auxin treatment, isolation of individual structures from the explant, and a liquid medium rinse containing activated charcoal, have not been successful in stimulating further development of the globular structures.
Cultured leaf sections of 12 cultivars of tomato, Lycopersicon esculentum Mill., were evaluated concerning their morphogenic responses to 24 combinations of indoleacetic acid (IAA, 0–2.0 mg/liter) and 6-benzylamino purine (BA, 0–10 mg/liter). Morphogenic responses were cultivar-dependent and exhibited broad maxima over a range of growth regulator concentrations. Media containing 0.2 mg/liter IAA and 1.0 or 5.0 mg/liter BA were optimal callus induction media for most cultivars. Leaf explants of all cultivars rooted on a medium supplemented only with 0.2–2.0 mg/liter IAA. Genotypic differences were observed in ability to regenerate shoots and average number of shoots regenerated. Optimal shoot regeneration medium varied with cultivar, but most often contained 0.2 or 1.0 mg/liter IAA + 2.5 or 5.0 mg/liter BA. ‘Better Boy’, ‘Starfire’, and ‘UC 134-1-2’ regenerated shoots most readily, averaging more than 10 shoots per culture. ‘Starfire’ was most amenable to in vitro shoot regeneration with as many as 19 shoots per culture.
Microscopic examination of longitudinal tangential sections of stems of rose (Rosa hybrida L. cv. Red American Beauty) revealed vascular occlusions due to microbial growth and gum deposition. Microbial occlusions reacted positively with the protein stain mercuric bromphenol blue and were restricted to the basal 2.5 cm of the stem. Gum deposition was identified by a positive reaction with periodic acid-Schiff's reagent and gas liquid chromatographic analysis of monomer content of acid-hydrolyzed occluding material. Location of gum deposition was dependent on the depth of the holding solution on the stem, always occurring above the solution level. Quantitative and qualitative comparison of sugar and uronide monomer content between areas of no gum deposition and areas of high gum deposition showed no differences, suggesting that gum formation was due to redeposition rather than net synthesis of gum constituents.
Shoot tip explants taken from proliferating cultures of apple (Malus domestica ‘Jonathan’) survived freezing to −196°C in the presence of cryoprotectants. Regrowth following freezing to −196° was in the form of callus growth, indicating that the meristems were injured to such an extent that organized growth of the shoot meristem was precluded. A cold acclimation period of up to 6 weeks at 4° in the dark was required to obtain acceptable survival levels. Glycerol generally was more effective than DMSO in providing cryoprotection to cold acclimated shoot tips.
The performance and satisfaction of students enrolled in a traditionally structured lecture/lab floral design course and a Web-based version of the same course were compared. Students were assigned randomly to course sections by available seating. Data collected included a demographic survey, design and course evaluations, and test grades. Significant differences were noted in class grades, with students in the traditionally taught course outperforming the Web-based students in both lecture and lab grades. Results from a survey instrument designed to determine whether students were suited to the distance learning environment (given only to the Web-based students) indicated a direct correlation between distance preparedness and course grades. A higher level of distance course preparedness correlated with a higher grade in the course. There was also a direct correlation between grades and whether the student was in the course with the delivery method they preferred. Students who were assigned to the course they preferred had significantly higher grades than students who did not. These results indicate that overall, a course such as floral design may be more effectively taught through traditional teaching techniques. However, certain students with adequate computer skills and a preference for Web-based courses may be successful in courses such as floral design.