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Yucca elephantipes is an important commercial ornamental pot plant, excellent for growing in flats, patios or winter gardens. Traditional vegetative propagation of the most decorative yuccas is complicated due to a very low rate of propagation, so in vitro culture is an alternative method for commercial propagation of these plants. The influence of BA (0.4, 2.2, 4.4, 11.1, 22.2 µM) and TDZ (0.5, 2.3, 4.5, 11.4, 22.7 µM) on shoot multiplication of Yucca elephantipes Regel on Murashige and Skoog (MS) medium was studied. Explants cultured on medium without growth substances were used as a control. The two types of explants used in the experiment: shoot tips and nodal segments of shoots, were obtained from aseptically grown shoot clusters. When comparing regeneration capability of 2 types of Yucca elephantipes explants, it was found that more newly formed shoots and roots were obtained from nodes. The highest formation of shoots was obtained from nodes on MS medium supplemented with 4.5 µM TDZ or 11.1 and 22.2 µM BA (6.5, 6.0, 5.8, respectively). The shoots regenerated from nodes showed best elongation. On the control medium and on the media with the lowest level of BA or TDZ, their average length was 31.0–37.8 mm. The growth regulator-free medium and the media with a low level of BA were the most effective in inducing roots.
Microcuttings of easy-to-root dwarf rose cv. Starina, showing early symptoms of leaf senescence and shoot-tip necrosis in rooting stage, were chosen for the study. The effects of inhibitors of ethylene biosynthesis (AOA, AIB) and action (AgNO₃), and Ca²⁺ and Mg²⁺ were studied in relation to rooting, leaf senescence and shoot-tip necrosis. The effects of these substances were examined with respect to IAA presence in a medium, which stimulated leaf yellowing and shoot-tip necrosis. AOA strongly inhibited rooting of microcuttings, but did not affect ethylene biosynthesis. AIB at 250 mg·l⁻¹ and AgNO₃ 2.5 mg·l⁻¹ in the presence of IAA did not affect rooting but effectively prevented leaf senescence. Ca²⁺ alone or combined with Mg²⁺ at raised concentration, or an ethylene action inhibitor Ag⁺, reduced shoot-tip necrosis in microcuttings treated with IAA. Addition of Ag⁺ to IAA medium drastically increased ethylene production by the shoots. Interaction between endogenous levels of auxin, ethylene and calcium in relation to rooting, shoot-tip necrosis and leaf senescence was discussed. Ethylene could enhance tissue sensitivity to auxin. Moreover, the tissue of rose shoots is very sensitive in the in vitro condition on standard medium because of the calcium deficiency. Thus, the raised Ca/Mg level counteracted shoot-tip necrosis through enhancing cell membrane and wall resistance to ethylene and IAA.
Shoot regeneration in five pea (Pisum sativum L.) cultivars (Atlas, Avola, Karina, Mali provansalac and Tristar) was achieved by direct culture of mature seeds on MSB5 medium supplemented with either N6-benzylaminopurine (BAP), N-phenyl-N’(-l,2,3-thiadiazol-5-yl)urea (thidiazuron, TDZ) or N-(2-chloro-4-pyridyl)-N’-phenylurea (forchlorfenuron, CPPU). Multiple shoots formed de novo without an intermediary callus phase at the cotyledonary notch, in the axillary meristem regions of the seedlings, and in the hypocotyl subepidermal tissues within two to three weeks of culture initiation. Bud formation began after 5 to 7 days of treatment and the number of buds increased with the duration of culture and increasing concentration of growth regulators. Transient exposure to plant growth regulators (24-28 h) was sufficient to induce bud formation. CPPU was the most effective and BAP the least effective for the induction of regeneration. Separated shoots (1-2 cm) were rooted (60%) on MSB5 medium supplemented with 1.1 µM indole-3- acetic acid (IAA) and 2.0 µM α-naphthaleneacetic acid (NAA) and developed into flowering plants.
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