A mutant (hcf-26) blocked in light reaction photosynthesis was shown to be controlled by a locus distal to the midpoint of the heterochromatic portion of the nucleolus organizer region (NOR) in chromosome 6 (Leto and Miles, MGCNL 51:57-59). The mutant hcf-26 possesses a yellow-green phenotype and was uncovered by TB-6a. In order to more precisely cytogenetically locate hcf-26, we crossed several heterozygous NOR--and satelite--interchanges as the female parent with heterozygous hcf-26 plants as male parents. Under our greenhouse sandbench conditions, seed from self-pollinations of the heterozygous hcf-26 plants resulted in green and nearly luteus seedlings. Several crosses between the heterozygous interchanges as female and heterozygous hcf-26 as male also yielded some near-luteus seedlings. The results suggest that hcf-26 is located in the distal chromomere of the satellite (Table 1).
The lack of chlorophyll deficient plants in crosses with certain interchanges that should have uncovered hcf-26 may have been the result of incorrectly identifying a plant as an interchange heterozygote. These crosses will be repeated. Tests with interchanges that appear to have breaks in the most distal satellite chromomere (Phillips and Wang, MGCNL 51:52) all gave negative results but should be repeated.
Previous tests (Phillips et al. MGCNL 51:49-52) localized polymitotic (Po) most likely to the first chromomere of the satellite by the same Dp-Df technique used above. Those results and those reported above for hcf-26 indicate that deficiencies for up to 90% of the NOR can occasionally be transmitted through the ovules. The hcf-26 marker located in the satellite and the rgd marker located most likely proximal to the NOR (Phillips et al. MGCNL 51:49-52) serve as seedling markers flanking the NOR.
The valuable assistance of Joe Ruegemer is gratefully acknowledged.
R. L. Phillips and S. A. Thompson
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