Cell lines (dedifferentiated, rapidly dividing, friable and thus clonable cultures) arise rarely from cereal explants. In corn only three examples are documented (from Black Mexican Sweet, BMS, by W. Sheridan, see Green, 1977, Hortsci. 12:131; from B73, Potrykus et al., 1977, MGG 156:347; and from Orla 266, Funk Seeds Int., King et al., 1978, Physiol. Vegetale 16:381). We are examining several aspects of the biochemistry and physiology of cell line initiation. As in most areas of tissue culture, the genotype of the explant also governs the response. For example, BMS and other flint corns (as originally reported by W. Sheridan, North Dakota) are consistently responsive in our hands. We have studied characters of BMS which might relate to cell line initiation, e.g.: 1) In view of the correlation which clearly exists between cell line status and ploidy abnormalities (not necessarily causal), is the presence of B chromosomes in BMS important for the response? 2) In view of the importance of 2,4-D for culture initiation in dicots, is BMS more sensitive to 2,4-D than typical dent corns? Cultures were initiated from root or shoot explants at either 2 or 5 mg/l 2,4-D; A and B are two lines backcrossed to a common inbred. Cell lines were isolated from trials marked X below:
Whilst BMS cultures are atypical of our stock corn cultures in rapidly accumulating dividing polyploid cells, the results suggest that the presence of B chromosomes in the explanted tissues in fact reduces the incidence of cell line initiation.
The data given in Fig. 1 also reverse the hypothesis being tested. Newly initiated cultures of BMS (plus or minus B chromosomes) appear less sensitive to 2,4-D than cultures obtained from a commercial hybrid. Higher levels of 2,4-D were required both for growth stimulation and inhibition of BMS compared to the dent corn. The idea that BMS is more responsive to 2,4-D perhaps through a lower rate of degradation is thus destroyed. It would be interesting to hear of data on BMS 2,4-D sensitivity in the field. A further characteristic of BMS is its high prolificacy; we are currently testing several possible biochemical relationships between high tillering and in vitro responses. (We gratefully acknowledge David Weber, Illinois State University for seeds and discussion).
P. J. King, H. Dhaliwal and A. Strauss
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