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The development of bud dormancy in poplar plants is initiated by short-day photoperiods (SD). During the development of bud dormancy, there was a gradual increase in the force required to peel off the bark from the stems. We measured the force required for bark peeling and investigated the cellular changes associated with this phenomenon. Stem samples were collected from plants which had been grown under SD for different period of time up to 10 weeks. At each sampling date, the forces required to peel off the bark were measured by a tensiometer. At the same time, samples were fixed to examine ultrastructural changes by transmission electron microscopy. We have observed that there was a significant increase in the force (in Newtons) required to peel off bark from poplar stems when the development of dormancy was initiated by SD treatment. Many ultrastructural changes were observed, including the accumulation of bark storage proteins, the break down of the central vacuole to form many small vacuoles, thickened cell walls, etc. Efforts have been made to relate ultrastructural alterations to changes in the force required for bark peeling.
In poplar (Populus deltoides Bartr.ex Marsh), the development of bud dormancy is initiated by short-day (SD) photoperiods. The degree of bud dormancy, expressed as days to budbreak, increased from ≈10 days for plants grown under long-days to >200 days after 10 weeks of SD exposure. We investigated quantitative and qualitative changes in protein fractions extracted from terminal buds, lateral buds, bark, and leaves of poplar plants during the induction of bud dormancy by 2-D PAGE. While total protein contents(as milligrams per gram fresh weight) in leaves, terminal, and lateral buds did not change significantly during SD treatment, bark protein content increased about five-fold in 10 weeks. The results of 2-D PAGE analysis indicated that there was a significant change in protein profiles in terminal and lateral buds, leaves, and bark. The results suggested that SD treatment in poplar plants causes substantial changes in protein profiles during the induction of bud dormancy.
A protocol was developed for efficient plant regeneration of Iris germanica L. `Skating Party' from suspension cultures. Suspension cultures were maintained in Murashige and Skoog (MS) basal medium (pH 5.9) supplemented with 290 mg·L–1 proline, 50 g·L–1 sucrose, 5.0 μm 2,4-D, and 0.5 μm Kin. Suspension-cultured cells were transferred to a shoot induction medium (MS basal medium supplemented with 10 mg·L–1 pantothenic acid, 4.5 mg·L–1 nicotinic acid, 1.9 mg·L–1 thiamine, 250 mg·L–1 casein hydrolysate, 250 mg·L–1 proline, 50 g·L–1 sucrose, 2.0 g·L–1 Phytagel, 0.5 μm NAA, and 12.5 μm Kin). Cell clusters that proliferated on this medium differentiated and developed shoots and plantlets in about 5 weeks. Regeneration apparently occurred via both somatic embryogenesis and shoot organogenesis. A series of experiments was conducted to optimize conditions during suspension culture to maximize subsequent plant regeneration. Parameters included 2,4-D and Kin concentrations, the subculture interval, and the size of cell clusters. The highest regeneration rate was achieved with cell clusters ≤280 μm in diameter, derived from suspension cultures grown for 6 weeks without subculturing in liquid medium containing 5 μm 2,4-D and 0.5 μm Kin. Up to 4000 plantlets with normal vegetative growth and morphology could be generated from 1 g of suspension-cultured cells in about 3–4 months. Chemical names used: 2,4-dichlorophenoxyacetic acid (2,4-D); kinetin (Kin); 1-naphthaleneacetic acid (NAA).
To improve the efficiency of iris plant regeneration, we tested the influence of several combinations of Kin and NAA in culture media on the induction of morphogenesis and the subsequent development of plantlets. The highest rates of regeneration (67%) were consistently observed in induction media containing 0.5 μm NAA and either 2.5 or 12.5 μm Kin. Developing medium containing 1.25 μm BA was optimal for high regeneration rates and a high percentage of plantlets simultaneously developing shoots and roots. Rooted plantlets were easily acclimatized and transplanted to various soil mixtures, then grown in the greenhouse. Under optimal conditions as many as 8000 plantlets could be regenerated from 1 g of cells in ≈4 months. Chemical names used: kinetin (Kin); 1-naphthaleneacetic acid (NAA); N6-benzyladenine (BA).
A protocol was developed for production of transgenic iris plants (Iris germanica L. `Skating Party') from regenerable suspension cultures via Agrobacterium-mediated transformation. We tested a series of selection agents, and identified hygromycin and geneticin as the most suitable for selecting transformed iris cells. Suspension cultures of iris were cocultured for 3 days with A. tumefaciens LBA 4404(pTOK233) carrying an intron-interrupted uidA (GUS) gene encoding β-glucuronidase, and hpt (hygromycin) and nptII (geneticin) selectable marker genes. Hygromycin- or geneticin-resistant calli having GUS enzyme activity were identified and used to induce plant regeneration. More than 300 morphologically normal transgenic iris plants were obtained in ≈6 months. About 80% of the transformants were GUS-positive and NPTII-positive (paromomycin-resistant). Integration of transgenes into the nuclear genome of iris plants was confirmed by Southern blot analysis. We have, therefore, developed an efficient A. tumefaciens-mediated transformation system for Iris germanica, which will allow future improvement of this horticulturally important ornamental monocot via genetic engineering.