Tissue cultures competent to regenerate plants have previously been initiated from undeveloped ears of mature 18-20 week-old plants of A188 (Molnar, Gordon and Rice, MNL 54:52-53, 1980). Ears from young plants tend to be well suited for this type of study since they can be obtained earlier, as a more physiologically uniform population and with less contamination than ears from mature plants.
Plants of A188 were grown in a controlled environment chamber under a 16-hour photoperiod at 20 C in light and 15 C in darkness. Axillary and dominant ears were harvested from plants at various stages of growth and treated as reported for ears of mature plants. The ears were removed aseptically, sliced transversely and placed onto culture media. The media contained the macronutrient and micronutrient salts of Murashige and Skoog (Physiol. Plant. 15:473, 1962) + 0.25 mg thiamine-HCl/l + 20 or 40 g sucrose/l + 8 g agar/l + 1.0 or 2.0 mg 2,4-D/l and plates were incubated at 25 C in darkness. Plates were monitored regularly and the production of scutellar-like tissue scored as a positive response.
Thirty-nine slices from a total of 20 ears responded positively by producing scutellar-like tissue in a sample of 98 ears tested. The data in Table 1 demonstrate that both the fraction of ears that responded and the average number of positive slices per responding ear are a function of ear length. Both are maximal for ears 10.5-20 mm in length. This dependence on length was expected as a result of the earlier study and closely parallels the results reported for immature tassels of A188 (Rhodes, Green and Phillips, MNL 56:148-149). It has been suggested that the optimal size correlates with a responsive developmental stage. Conversely, the data do not indicate a major effect either of 2,4-D concentration or of the node at which the ear developed (data not shown). The role of these and other parameters are under continued study in this system.
Table 1. Effect of Ear Length on Tissue Culture Response
Larry A. Holbrook and Stephen J. Molnar
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