EFFECTS OF MEDIUM COMPONENTS AND LIGHT ON CALLUS INDUCTION, GROWTH, AND FROND REGENERATION IN LEMNA-GIBBA (DUCKWEED)

Basal media, plant growth regulator type and concentration, sucrose, a nd light were examined for their effects on duck-weed (Lemna gibba) fr ond proliferation, callus induction and growth, and frond regeneration . Murashige and Skoog medium proved best for callus induction and grow th, while Schenk and Hildebrandt medium proved best for frond prolifer ation. The ability of auxin to induce callus was associated with the r elative strength of the four auxins tested, with 20 or 50 mu M 2,4-dic hlorophenoxyacetic acid giving the highest frequency (10%) of fronds p roducing callus. Auxin combinations did not improve callus induction f requency. Auxin in combination with other plant grow-th regulators was needed for long-term callus growth; the two superior plant growth reg ulator combinations were 10 mu M naphthaleneacetic acid, 10 mu M gibbe rellic acid, and 2 mu M benzyladenine with either 1 or 20 mu M 2,4-dic hlorophenoxyacetic acid. Three percent sucrose was best for callus ind uction and growth. Callus induction and growth required light. Callus that proliferated from each frond's meristematic zone contained a mixt ure of dedifferentiated and somewhat organized cell masses, Continual callus selection was required to produce mostly dedifferentiated, slow -growing callus cell lines. Frond regeneration occurred on Schenk and Hildebrandt medium without plant growth regulators hut res promoted by 1 mu M benzyladenine. Callus maintained its ability to regenerate fro nds for at least 10 mo. Regenerated fronds showed a slower growth rate than normal fronds and a low percentage of abnormal morphologies that reverted to normal after one or two subcultures.