Last year we reported (MGCNL 53) that a mutant (hcf*-26) blocked in light reaction photosynthesis was beyond the middle chromomere of the satellite and could be located in the distal chromomere. The mutant hcf*-26 possesses a yellow-green phenotype and had been reported to be uncovered by TB-6Sa (Leto and Miles, MGCNL 51:57-59). In order to more precisely cytogenetically locate hcf*-26, we crossed heterozygous satellite-interchanges as the female parent with heterozygous hcf*-26 plants as male parent. Under our greenhouse sandbench conditions, seed from self-pollinations of the heterozygous hcf*-26 plants resulted in green and near-luteus seedlings. None of the crosses between the heterozygous interchanges as female and heterozygous hcf*-26 as male yielded near-luteus seedlings when the satellite breakpoint was distal to the breakpoint of interchange T4-6(5227), which is located between the middle and distal chromomeres. Our results indicate that hcf*-26 is located between the breakpoint of T4-6(5227) and the proximal end of the distal chromomere marked by T3-6b. Thus, hcf*-26 is either between the middle and distal chromomeres or in the proximal portion of the distal chromomere. The breakpoint of T5-6(8219) has not been localized cytologically within the satellite; the lack of near-luteus seedlings in testcrosses of heterozygous T5-6(8219) and heterozygous hcf*-26 plants suggests that the breakpoint is in the distal chromomere.
Table 1. Tests to cytogenetically locate hcf-26. Smaller seed and a
portion of remaining seed from crosses of heterozygous interchanges as
female parent with heterozygous hcf-26 plants were planted. Data were collected
from seed produced during the summers of 1978 and 1979.
|Smaller seed2||Remnant seed|
|Interchange||Satellite1 break pt.||Number of crosses||Green||Chlorophyll deficient||Green||Chlorophyll deficient|
|3-6b||proximal end of distal chromomere||4||144||0||259||0|
|2-6(001-15)||distal end of distal chromomere||3||162||0||273||0|
|6-7(7036)||distal end of distal chromomere||6||115||0||325||0|
1The satellite is comprised of 3 chromomeres in these strains.
2Smaller seeds are expected to include Dp-Df heterozygotes.
R. L. Phillips and S. A. Thompson
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