J Integr Plant Biol. ›› 1998, Vol. 40 ›› Issue (2): -.

• Research Articles •    

Somatic Embryogenic Potential Determined by the Morphological Polarity of the Explant in Tissue Cultures of Freesia refracta

WANG Li, BAO Xiao-Ming, HUANG Bai-Qu and HAO Shui   

Abstract: Inflorescence explants of Freesia refracta Klatt placed on modified N6 medium supplemented with 2 mg/L indole-3-acetic acid (IAA) and 3 mg/L 6-benzyl aminopurine (BAP) might undergo direct somatic embryogenesis leading to plant regeneration. A noticeable phenomenon observed in this morphogenetic process was that all the somatic embryos appeared exclusively at the original morphological lower end of the segments cut from the inflorescence axes (termed the embryogenic end, EE), while no embryos were formed at the morphological upper end (termed the non-em- bryogenic end, NEE), irrespective of the gravity of earth and the position of the explants placed on the medium. Divisions of embryogenic initial cells were observed solely at the EEs of the segments in the early stages of culture. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed that two polypeptides appeared specifically at the EEs of the explanted segments after one day in culture, but they were undetectable at the NEEs. Four polypeptides detectable at both ends of the explants at day 1 of culture disappeared from the NEEs at late stages of culture. There was no significant difference in the distribution of the endogenous IAA before culture between the two ends of the segments as measured by high-performance liquid chromatography. However, the level of IAA was remarkably higher at the EE than at the NEE after a certain period of culture. This result showed that the endogenous hormone might play a key role in the process of somatic embryogenesis. The differences in molecular composition and physiological status between the two morphological ends of the explant in relation to the induction of the somatic embryogenesis in F. refracta may be considered as a useful marker in studying the mechanisms of this in vitro morphogenesis.

Key words: Freesia refiacta, Somatic embryogenesis, Polarity of explant

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