2,4-D is the traditionally used hormone in maize tissue culture; however, with many lines the callus obtained on 2,4-D media is less than ideal. A recent paper (Hangarter, R. P., Peterson, M. D., and Good, N. E., Plant Phys., in press) demonstrates that certain IAA-conjugates can be used as hormone sources for tobacco and tomato tissue cultures. IAA-L-alanine and IAA-L-glycine suppress organogenesis and promote rapid callus growth, whereas other conjugates (e.g., IAA-L-phenylalanine) allow shoot formation but suppress root formation.
Using the more active of the IAA-conjugates it has been possible to establish friable callus cultures from various anthocyanin genetic stocks in either W23 background or F2 progeny of a W23 x K55 cross. Mesocotyl sections of 14-day-old seedlings were plated on Green's media with 50 µM IAA-conjugate substituted for the 2,4-D. The resulting calli were maintained on the same media and sub-cultured at 3-week intervals. IAA-L-alanine, IAA-L-glycine and IAA-myoinositol all gave similar results in early tests; IAA-L-alanine is routinely used. Some of these lines are now more than one year old and are still friable and growing rapidly, although they are somewhat rooty in appearance.
Suspension cultures are easily obtained from these calli in liquid media of the same composition. The suspensions are very finely divided (1-20 cell clusters) and have a doubling time of about 7 days. These suspensions are not long-lived, however, the maximum thus far being 3 months. Experiments in progress are aimed at plating out cells from these suspensions and regenerating roots.
Some of the callus lines initially produced anthocyanin pigment; this expression was greatly reduced or lost upon further subculture. Transfer of callus to 50 PM IAA-L-phenylalanine media greatly enhances anthocyanin pigmentation. IAA-L-phenylalanine also allows the formation of normal roots from the callus.
In summary, IAA-conjugates may be useful in initiating callus from recalcitrant maize stocks, and combinations of different conjugates may be useful in controlling morphogenesis in maize tissue cultures. Procedures for the synthesis of the conjugates are outlined in Hangarter et al. (This study supported by NSF grant SP178-15616.)
*Present address: Carnegie Inst. Wash., 115 W. University Parkway, Baltimore, MD 21210
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