Selection of a super-growing legume root culture that permits controlled switching between root cloning and direct embryogenesis |
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Authors: | R Akashi S-S Hoffmann-Tsay F Hoffmann |
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Institution: | (1) Department of Developmental and Cell Biology, University of California Irvine, CA 92697-2300, USA, US |
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Abstract: | Root cultures, displaying vigorous growth and high embryogenic capacity, were established in the legume forage species Lotus corniculatus (bird’s-foot trefoil). Root cloning as well as plant regeneration was achieved on hormone-free medium, in agitated culture
in the dark or under stationary conditions in the light, respectively. These qualities of vigorous growth and regeneration
faded with time in hormone-free culture, with slow-growing roots turning brown in color. Addition of the synthetic cytokinin-like
hormone benzylaminopurine to the culture medium, however, re-established the aging tissue’s capacity for somatic embryogenesis
and plant formation. During continuous initiation of new cultures, it was possible to obtain one root culture (selected from
11 960 seeds at a 65% germination rate) which did not show the typical decline of qualities after prolonged proliferation
but distinguished itself by displaying even faster growth and more vigorous embryogenic plant production on hormone-free medium.
There was no decline since its initiation 9 months earlier. This super-growing root culture produces plants that show no morphological
differences as compared to wild-type regenerants or seedlings. Roots, dissected from plantlets derived from super-root embryogenesis,
expressed all the super-root qualities again when cultured in vitro. This is the first report on somatic embryogenesis from
sustained root cultures without exogenous hormone application. Such a hormone-free, continuous root culture should provide
a superior experimental system for genetic or developmental studies that might be sensitive to exogenous hormones, such as
somaclonal variation in transgenesis or, since introduced in a legume species, nodulation in vitro.
Received: 22 September 1997 / Accepted: 21 October 1997 |
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Keywords: | Bird’ s-foot treefoil Lotus corniculatus Root culture Somatic embryogenesis Super-growth |
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