No abstract

Bulb size is an important factor determining phase change in Lilium: phase change only occurs in bulblets over a certain threshold weight. After phase change has occurred, bulblets sprout with a stem with many leaves. Juvenile bulblets sprout with only a few leaves. The factors contributing to bulb size were studied during in vitro regeneration of bulblets on scale segments. The larger the explants, the larger the regenerated bulblets. Explant size influenced bulb growth during the complete culture period. Bulb growth was stimulated by a high sucrose concentration. The contribution of the medium and the explant reserves to bulb growth were studied in large and small explants using labelled sucrose. Sucrose was mainly taken up through the cut surfaces. In freshly cut explants, the rate of uptake was correlated with the size of the contact area, but at later stages, when regenerating organs were present, the difference in uptake rate of small and large explants almost disappeared. Small explants had a larger sink activity than large ones. Explants with regenerating organs took up more sucrose than freshly cut explants. Sucrose uptake and bulb growth were rather constant in the later phases and doubled when the sucrose concentration was doubled. Partitioning of label from the sucrose over the various organs, was also rather constant in time: approximately 25% was accumulated in the bulblets, 35–45% in the explant and 30–35% was converted to CO2. About half of the label in the explant was recovered at the proximal side where regeneration takes place. Sucrose, once incorporated in the storage pools in the explant, either remained in the explant or was converted to CO2. Redistribution to the growing bulblets hardly occurred. The percentage of bulb growth that could be attributed to uptake of medium components was constant over the regeneration period: 45–50% for large and 65–75% for small explants.

No abstract

Cucumber (Cucumis sativus L.) leaf explants were cultured either continuously on standard medium containing 4.5 #M 2,4-dichlorophenoxyacetic acid (2,4-D) and 4.4 #M benzylaminopurine, or first cultured for various periods at different levels of 2,4-D, picloram or naphthaleneacetic acid (NAA), and then transferred to standard medium. When cultured continuously on standard medium, less than 10% of the explants formed embryogenic callus. Initial culture on picloram or NAA, or on 2,4-D at a low concentration (1.4 #M) did not result in any embryogenic callus formation. Embryogenic callus formation increased to 40% if during the initial phase of the culture (10 days), the 2,4-D concentration was raised to 14 #M. Prolonged culture on 14 #M 2,4-D resulted in less embryogenic callus formation.Abbreviations: BA -benzylaminopurine; 2,4-D-2,4-dichlorophenoxyacetic acid; NAA -naphthaleneacetic acid Embryogenic callus formation from leaf explants of cucumber has been reported by various authors (Malepszy and Nadolska-Orczyk 1983;Chee and Tricoli, 1988;Bergervoet et al. 1989;Debeaujon and Branchard, 1993;Lou and Kako, 1994). In our hands, the published procedures resulted in low frequencies of embryogenic callus formation. Here we report a method to improve the formation of embryogenic callus. Our research is based on the assumption that embryogenesis, just as other regeneration processes, consists of several phases each with its specific growth regulator requirements (Christianson, 1987).Seeds of Cucumis sativus L., cvs. Profito and Cordito, were kindly supplied by De Ruiter Seeds, Bleiswijk, The Netherlands. They were surface-sterilized for 45 min in 2% (w/v) sodium hypochlorite followed by three rinses in sterile distilled water, and cultured in glass jars at 25 °C and a 16-h photoperiod (35 #mol m -2 s -1). The medium contained full-strength MS macro-and micronutrients (Murashige and Skoog, 1962), McCown's woody plant vitamin mixture without glycine (Lloyd and McCown, 1981), 2% (w/v) sucrose and 0.6% (w/v) agar (Becton and Dickinson, granulated). The pH of the medium was adjusted to 5.8 before adding agar. Germination occurred after 3 days. Seedlings were raised in vitro until the appearance of the third normal leaf.We used the first and second normal leaves. From each leaf, five to seven explants were cut (5 x 5 mm, each explant contained a vein). The position of an explant in the leaf did not influence callus formation. The explants were placed with their abaxial side on the medium. They were cultured in the dark at 25 °C in 9-cm Petri dishes (10 explants per dish) on the same medium (25 ml) as above but with 3% (w/v) sucrose, 250 mg 1-1 bacteriological pepton (Oxoid), and various types and concentrations of auxin and cytokinin. The explants were subcultured at 3-week intervals. Each value in the graph is based on at least 25 explants. The significance of differences was determined with a X2-test.Explants of both cultivars, cultured continuously on standard medium with 4.5 #M 2,4-D and 4.4 #M BA (Bergervoet et al. 1989) f...

No abstract