• KOREAN JOURNAL OF CROP SCIENCE
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• v.44 no.3
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• pp.263-266
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• 1999

Tobacco (Nicotiana tabacum L. ‘KF109’) seeds were primed in polyethylene glycol 6000 (PEG 6000) solutions to determine a) what osmotic potential of the solution would be optimal for priming, i.e., critical potential level for preventing germination, and b) what temperature and duration would be the most effective in priming. The germination was completely prevented below -0.8 MPa of PEG 6000, that indicates a optimum water potential for seed priming. Seeds were primed for 0, 1, 2, 3, 5, 10 and 15 days at 15, 20 and $25^{\circ}C$, respectively, under the-0.8 MPa PEG 6000 solution to find out the most effective temperature and duration for priming. The effectiveness of priming, particularly in germination speed, was observed more distinctly when the primed seeds were germinated at 15$^{\circ}C$ than 2 5$^{\circ}C$. The greatest reduction of the time to 50% germination (T/sob 50/) was when the seeds were primed at $25^{\circ}C$. The reduction rate of the $T_{50}$ was rapid when primed from 1 day to 8 days and then slowed down in the seeds primed for longer than 8 days. The time from 10 to 90% germination ( $T_{10-90}$ increased in the primed seeds for longer than 8 days which showed the reversed effect of synchronous germination. However, $T_{50}$ was reduced continuously in the seeds even primed over 8 days. Thus, the optimum condition for tobacco seeds priming with PEG 6000 solution was -0.8 MPa in osmotic potential of the solution at $25^{\circ}C$ for 8 days.ays.

• Korean Journal of Plant Tissue Culture
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• v.27 no.4
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• pp.299-307
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• 2000

A large amount of information is currently available for somatic embryogenesis of plants. However, one common problem related to somatic embryos is that the conversion rate can be low for some species. Apical meristems are responsible for post-embryonic growth of the embryo. The low percentage observed is most likely a result of poor apical meristem development or defects in the meristem organization during somatic embryogenesis. In flowering plants, apical meristems are well developed by the late heart stage of zygotic embryo development. In conifers, such as white spruce, apical meristems are formed at the pre-cotyledon stage. Thus, apical meristem development occurs very early, prior to the maturation stage of embryo development. Once formed, meristems are stably determined. In the somatic embryo, as exemplified by white spruce, since embryo development is not synchronous, tissue differentiation including apical meristem formation occurs throughout the“maturation”stage. Different apical meristem organizations can be found among different individuals within a population. In contrast to their zygotic counterparts, the apical meristems appear not to be stably determined as their organization, as the shoot apical meristem especially, can be easily modified or disrupted. Precocious germination seldom results in functional plantlets. All these observations suggest that the conditions for somatic embryo maturation have not been optimized or are not suitable for meristem formation and development. The following strategies could improve meristem development and hence conversion: 1. Simulate in ouuio conditions to promote meristem development prior to the“maturation”treatment.2. Prevent deterioration of apical meristem organization during somatic embryo maturation.3. Promote further meristem development during embryo germination.

• The Korean Journal of Mycology
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• v.15 no.3
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• pp.149-157
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• 1987

This study was undertaken to investigate the differentiation, from spore germination to hyphae growth and phialide formation, of Aspergillus niger through the method of synchronous and submerged culture. Through continuous experiments by shake culture with potassium acetate medium, we observed the formation of spores at appropriate concentration and pH. Potassium acetate medium was set pH 5.5, 6.0, 6.5 and 7.0 on each scale, and control, 20 mM, and 40 mM, 80 mM and 160 mM concentrations on the other scale. Aspergillus niger was cultured in the defined media at $28^{\circ}C$, and mycelial dry weight, changes of pH and the onset of sporulation were checked. The mycelial dry weight, increased in potassium acetate medium, and pH increased during mycelial growth and gradually decreased after the spore formation. When pH increased excessively in Potassium acetate medium with pH 7.0, the mycelia could not adapt and mycelial dry weight decreased gradually. At pH 5.5, the onset of sporulation was done within one day at 20 mM it took, at 80 mM three days and at 160 mM concentration. in two days, at 40 mM one to four days were taken, 80 mM concentration respectively. At pH 6.5, the onset of sporulation was done in three days and four days at 80 mM concentrations respectively. Spore formation was not shown at pH 7.0. In controlled medium with all levels of pH, spore formation was not shown.