Recently published work in China has demonstrated that it is possible to obtain haploid green maize plants from pollen by culturing anthers on agar medium containing high concentrations of sucrose (10-15%) (Anon., Acta Botanica Sinica 19:89-94, 1977). Yet, even under optimal conditions, the production of pollen callus or embryos is rarely observed in more than 1% of the cultured anthers. Although haploid maize plants are already available through the use of Coe Stock 6 and the ig mutation, the development of techniques permitting the growth of large numbers of microspores may be more useful for mutagenesis and the subsequent selection of desirable mutants in vitro.
During the summer months of 1978, over 100,000 anthers of maize and maize x teosinte were cultured in our laboratory from both greenhouse and field-grown material. Calluses that were distinct from the anther wall or filament were observed on a number of anthers after 6-8 weeks in culture, but these did not undergo morphogenesis. However, a single embryo was also produced on one anther of cultivar G-4507 (Funk Seeds International) cultured for 7 weeks on an N6-medium containing 12% sucrose and 0.35 mg/l TIBA as recommended by the Chinese workers (G. Melchers, personal comm.). This embryo initially grew rapidly to produce a well-defined coleoptile, but after reaching a length of 5 mm could not be induced to develop further. No chromosome counts were obtained.
Cytological examination of the anthers showed that the normal processes of pollen development were generally inhibited in culture. Associated with this was a rapid deterioration of the microspores. Under certain conditions, however, a proportion of the microspores were able to continue developing towards maturity in the cultured anthers. Thus, normal development resulting in starch accumulation appeared to occur in microspores cultured just prior to the first microspore mitosis. Multinucleate structures were observed rarely, but it was not possible to speculate as to whether they might represent the first steps of an androgenetic pathway.
The lack of significant success in our experiments might in part be attributed to a failure to optimize the many variables (such as genotype of the donor plant and its growth environment) which condition a favorable anther response. Further experiments are in progress to fractionate populations of isolated maize and sorghum microspores on percoll gradients (c.f. W. Wernicke et al., 1978, Naturwiss 65:540). We hope that these experiments in conjunction with the anther culture work will help us to define conditions required for the induction of maize androgenesis in vitro.
E. Thomas, R. Brettel and W. Wernicke
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