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Michael E. Kane, Nancy L. Philman, and Matthew A. Jenks

Only a few plants are suitable for reliably demonstrating rapid direct and indirect shoot organogenesis in vitro. A laboratory exercise has been developed using internodes of Myriophyllum aquaticum, an amphibious water garden plant. Stock shoot cultures are established and maintained in vitro from nodal explants cultured on agar-solidified medium consisting of half-strength Murashige & Skoog salts (MS) and 30 g·liter-1 sucrose. Students use these cultures as the source of internode explants. Explants are cultured on agar-solidified full-strength MS with 30 g·liter-1 sucrose, 100 mg·liter-1 myo-inositol, and 0.4 mg·liter-1 thiamine·HCL and factorial combinations of 0 to 10 μM 2iP and 0 to 1.0 μM NAA. Adventitious shoot development occurs directly from the explant epidermis within 4 days and is promoted in media supplemented with 2iP alone. Cytokinin-supplemented media amended with NAA induce organogenetic callus formation, but reduce 2iP promotion of direct shoot organogenesis. After 4 weeks, shoot organogenesis on the various media is quantified and can be analyzed statistically. Chemical names used: N-(3-methyl-2-butenyl)-1H-purin-6-amine (2iP); α-naphthaleneacetic acid (NAA).

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Fabiola Domínguez, Xavier Lozoya, and James Simon

An efficient whole plant regeneration method from callus cultures of Piper auritum was achieved through organogenesis derived from leaf tissue. Proliferating callus and shoot cultures derived from leaf tissue explants placed on Murashige and Skoog (MS) medium supplemented with 2.0 mg·L–1 2, 4-dichlorophenoxyacetic acid (2,4-D) plus 1.5 mg·L–1 kinetin. Optimum combination of hormones (mg·L–1) for shoot induction was 0.5 2,4-D: 1.5 mg·L–1 kinetin (by volume), that resulted in a high rooting rate (49.6 shoots per explant). All of the plants elongated when using a medium consisting of 0.1 mg·L–1 2,4-D plus 1 mg·L–1 kinetin. Elongated shoots were successfully rooted (100%) on half-strength MS medium supplemented with 2.0 mg·L–1 indole-3-acetic acid. All plantlets survived to the growing conditions of a greenhouse. This study demonstrates that leaf tissue of P. auritum is competent for adventitious shoot regeneration and establishes an efficient and useful protocol for the multiplication and conservation of P. autirum for further investigation of its medicinally active constituents.

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Kathleen Heuss-LaRosa, Rosemarie Hammond, James M. Crosslin, Christine Hazel', and Freddi A. Hammerschlag

In vitro micrografting was tested as a technique for inoculating peach [Prunus persica (L.) Batsch] shoot cultures with Prunus necrotic ringspot virus (PNRSV). Cultured `Suncrest' shoots derived from a naturally infected tree (as indicated by ELISA testing) maintained virus in vitro, with virus concentrations in growing tips and folded leaves being several times those of fully expanded leaves. Infected shoots served as graft bases and source of the virus. Grafted tips were derived from `Suncrest' trees that had tested negative for the virus. Leaf samples were collected from the tips following grafting and analyzed for the presence of virus by slot-blot hybridization with a (DIG)-labeled cRNA probe derived from PNRSV RNA 3. Rates of successful grafting ranged from 55% to 73% in three trials and PNRSV was found in all tips analyzed. Virus concentrations approximated those found in source shoots, suggesting that in vitro micrografting should be useful for screening transformed peach shoots for coat protein-mediated resistance to PNRSV. Chemical name used: digoxigenin (DIG).

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F.A. Hammerschlag and A.C. Smigocki

Peach [Prunus persica (L.) Batsch] plants #94-1, #99-1, and #40-1, carrying a cytokinin biosynthesis (ipt) gene following transformation with the shooty mutant strain of Agrobacterium tumefaciens, were evaluated for altered growth habit and axillary shoot formation, both in vitro and in the greenhouse. After 9 weeks of in vitro propagation on four different levels of 6-benzyladenine (BA), only transformant #99-1 exhibited significantly greater axillary shoot formation (on 10 μm BA), and significantly greater fresh mass (on 3,10, and 30 μm BA) than the control #RG-3. Tolerance to a supra-optimal (30 μm) concentration of BA was indicated by fresh mass increases for #99-1 shoot cultures. Delayed senescence on 0 μm BA was exhibited by 87% of the transformants, but by only 12% of the control plants. Greenhouse-grown #99-1 and #40-1 were significantly shorter than #RG-3 plants at 6 weeks and at 1 year, but only #40-1 exhibited significantly greater branching than the controls. Chemical names used: 6-benzyladenine (BA); isopentenyl transferase (ipt).

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Chang-Hoo Lee, N. I. Hyung, and S. E. Kim

Experiments were conducted to investigate the factors influencing mesophyll protoplast isolation in `Fuji' apple. Half an hour pretreatment in 0.6M mannitol gave the highest protoplast yield.The enzyme solution containing 2% Cellulase Onozuka R-10 and 0.5% macrozyme R-10 with CPW 0.6M mannitol at pH 5.5 was most effective for protoplast isolation from leaf. Effective incubation time for the enzyme treatment was found to be 15-20 hrs at 25°C in the dark. Use of 1.0-2.0% PVP and 0.5mM MES was essential for higher yield and viability of protoplast. Supplementation of BA and IBA to the shoot culture media gave the higher yield of viable protoplast. From these protoplast, new cell walls were regenerated and 4 cell structures developed from one protoplast by cell division in K8P medium supplemented with 3A and NAA. Planting density higher than 10 protoplasts/ml was required for cell division from protoplast in liquid or 0.5% agarose culture.

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Barbara M. Reed

In vitro cold storage of Rubus germplasm was investigated using several environmental conditons and types of storage containers. Shoot cultures of Rubus species and cultivars were grown in either tissue culture bags or 20 × 150 mm glass tubes and compared for plant condition and survival under various storage conditions. Cultures stored at 10 C in the dark were in poor condition after 6 months. Cultures kept at 4 C were in much better condition and had higher survival rates after 18 months when stored with a 12 h daylength rather than total darkness. Overall there were no differences in survival or condition between cultures in tubes and bags. Contamination rates were 15% in tubes and 0% in bags. Plants in tissue culture bags could be stored for 9 months at 25 C with 16 h light when the nitrogen level of the MS medium was reduced to 25% and the medium volume was increased from 10 to 20 ml per bag. Genotype differences were apparent under all conditions tested. The best storage condition for Rubus germplasm was 4 C with 12 h light. Plastic tissue culture bags were preferred over tubes due to lower contamination rates.

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D. Sankhla, T.D. Davis, N. Sankhla, and A. Upadhyaya

This report describes an efficient in vitro regeneration protocol for H. patens (firebush), a heat-tolerant ornamental shrub native to tropical and subtropical America. Shoot cultures were initially established using shoot tips placed on MS-revised medium containing 2.3 μM 2,4-D, 2.3 μM kinetin, and 0.25% polyvinylpyrrolidone. Other types of explants (nodal and internodal segments, leaf pieces, floral buds) did not regenerate shoots when placed on this medium. Two-month-old plantlets derived from the shoot tips were subcultured on MS medium supplemented with 0.5 μM thidiazuron (TDZ), and within 3 to 4 weeks, some callus was produced at the root–shoot junction. When this callus, with a small portion of the root and shoots, was placed on MS medium with 0.05 μM TDZ and 0.01 μM ABA, prolific shoot formation occurred within 3 to 4 weeks followed by root formation. By regular subculturing every 5 to 6 weeks, hundreds of plantlets have been obtained over the past 3 years with no apparent decline in regeneration potential. Addition of activated charcoal (0.5%) to the culture medium has greatly improved growth of the plantlets.

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Wenhao Dai, Cielo Castillo, and Victoria Magnusson

In vitro shoot cultures for two birch species, Asian white birch (Betula platyphylla) and paper birch (Betula papyrifera), were initiated from shoot tips of mature trees and maintained in MS (Murashige and Skoog) medium containing 3% sucrose and 5–10 μM (micromolar) benzyladenine (BA). The effect of such factors as genotype, basal medium, and plant growth regulator (PGR) on proliferation was investigated. Shoots were proliferated in both MS and woody plant medium (WPM) supplemented with different concentrations of thidiazuron (TDZ), BA, and kinetin (Kin). Two birch species responded differently to these factors. In general, more shoots were proliferated in WPM than in MS medium. The maximum proliferation rate of Asian white birch was achieved by being cultured in WPM containing 4–8 μM TDZ, while paper birch gave rise to the maximum proliferation rate in WPM supplemented with 20 μM BA. Interactions between genotype and medium or cytokinin were found. Shoots produced on media with TDZ had thick stems and small, dark green leaves. Microshoots can be rooted both in vitro and ex vitro with or without IBA treatment. Plants were regenerated from leaf tissues of Asian white birch. Adventitious shoots regenerated when in vitro leaves were cultured on WPM supplemented with 10–20 μM BA with 2-week dark treatment. The effect of genotype, PGR, and culture condition on in vitro regeneration of birch species is being tested.

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Jorge F.S. Ferreira, James E. Simon, and Jules Janick

Artemisinin (qinghaosu), an endoperoxide sesquiterpene lactone with antimalarial activity and little human toxicity, is produced in A. annua L., a short-day plant with the critical photoperiod of 13.5 h. Artemisinin peaks at full flowering when it is 11 times higher in inflorescences than in leaves. Supplementation of MS medium with BA, kinetin, CCC, or daminozide decreased content in shoot cultures as compared to the control, with the exception of CCC at 6.3 μM. Artemisinin content (percent dry weight) in this experiment did not correlate with shoot number (r = –0.198) but was highly correlated (r = 0.775**) with root number, indicating that although roots do not produce artemisinin, they may be involved in its synthesis. Maximum artemisinin was produced in hormone-free medium. Friable calli were obtained with a combination of BA (4.4 μM) and 2,4-D (4.5 μM), but artemisinin was absent from calli, cells, and cell culture media. Biseriate glandular trichomes are present in leaves and flowers from the earliest developmental stages. Artemisinin was extracted by a 1-min dip in organic solvents from flowers and leaves, indicating that the biseriate glandular trichomes of A. annua are the probable site of accumulation or sequestration of artemisinin.

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Chunsheng Lu, Yiqin Ruan, and Mark Bridgen

Micropropagation has been used to rescue Leontochir ovallei, an endangered Chilean species in the Alstroemericeae. Cultures were initiated by aseptically germinating seeds of Leontochir on a medium containing 1/10 MS salts and vitamins and 0.3% sucrose. Three types of cytokinins (BAP, 2-iP and kinetin) at four concentrations (0, 2, 4, and 8 uM) were studied for shoot proliferation. In the 4 uM BAP treatment, new shoots were produced at an average of six per culture after four weeks of culture. Overall, there was an average of four shoots/culture/4 weeks for all BAP treatments. This was significantly higher than the 2-iP and kinetin treatments. Moreover, the increase of culture fresh weight over time was significantly greater in BAP treatments than those in other treatments. A rooting study compared the effect of NAA and IBA on root initiation. Over 85% of the cultures in 10 and 20 uM NAA treatments produced healthy and large roots. This was significantly higher than the 10 and 20 uM IBA treatments. In summary, a concentration of 4 uM BAP combined with 1 uM IBA in MS salts and vitamins supplemented with 146 mg glutamine/l is the best for shoot proliferation of leontochir; an MS basal medium containing 10 uM NAA is the best for root initiation. Micropropagated plantlets have been successfully transplanted into the greenhouse for further genetic and breeding studies.