In Vitro Embryogenesis in Plants
In vitro Embryogenesis in Plants is the first book devoted exclusively to this topic. As the ultimate demonstration of totipotency in plants, somatic and haploid embryogenesis is of vital importance to all those working on or interested in basic and appli
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Contents
I. Introduction II. Early Reports of PlantIet Regeneration in Carrot Cultures III. Early Reports of Embryogenesis in Carrot Cell Cultures IV. Controversies and Unresolved Problems A. Are There Special Chemical Factors which Promote Embryogenesis?
B. Is Cell Isolation Required to
Induce Embryogenesis?
10
C. Single vs. Multiple Cell Origin of
3 5
Embryos and its Bearing on the Concept of Isolation D. Do Buds Form in Carrot Cultures? V. Embryos from Pollen Grains References
11 13 14 15
7
I. Introduction
Readers interested in a general discussion of the history of plant tissue culture cannot do better than to read the first two chapters of Philip White's book, The Cultivation of Animal and Plant cells [1). White was a pioneer in the 1930s and 1940s, along with R.J. Gautheret and P. Nobecourt, in developing tissue culture techniques. The following discussion will concentrate on carrot cultures since most of the early work was on Daucus carata and it is still the most studied system. Additional early work of significance which merits some discussion is the discovery that haploid embryos can be derived from cultured anthers.
II. Early reports of plantlet regeneration in carrot cultures The story of embryogenesis in vitro begins with observations by early workers then plantlets were often regenerated in carrot callus cultures. The circumstances under which plantlets appeared in these early studies were diverse and offer only a few hints as to the controlling factors in organ regeneration. In
T.A. Thorpe (ed.). In Vitro Embryogenesis in Plants, pp. 1-16.
© 1995 Kluwer Academic Publishers, Dordrecht.
2 1950, Levine [2] reported that carrot callus grown in a medium containing indoleacetic acid (IAA) would regenerate roots and shoots, in that order, when IAA was removed from the medium. Since no histological details were given, we do not know whether preexisting primordia were merely released from auxin inhibition by the removal of IAA or were initiated by the treatment. Levine reported that the shoots bore "primitive" leaves of a cotyledonous type and that these were followed by pinnatifid leaves resembling the mature leaves of carrot. He did not know how entire plantlets were ultimately produced from these isolated organ systems. In 1954, Wiggans [3] also observed carrot plantlet formation, but under different circumstances. His medium contained adenine sulfate. When the tissue was transferred to a medium lacking adenine, "buds" appeared and these gave rise to plantlets. Wiggans did not describe leaf morphology, but did state that tissue grown in the adenine-free medium "exhibited much less auxin activity than the original tissue did, thereby making bud formation possible". Thus, Levine concluded that the removal of auxin led to root formation, followed by whole plantlets; whereas Wiggans concluded that lowering of the auxin content of the tissue led to bud formation, followed by plantlets. Without exactly repeating their work, we cannot explain why in the one case roots appeared first and in the oth
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