A number of recessive nuclear mutations have been isolated from the M2 generation following crosses between an active Mutator line (DR8091 x 7092) supplied by Don Robertson and standard inbred lines W23 and Mo17. The chromosome arm locations of two high chlorophyll fluorescent (hcf) mutations, hcf3-Mu and hcf102 (reported as 1113-3) have been reported previously (MNL 61:44). The chromosome arm locations of two additional hcf mutations have been determined. hcf104 was uncovered by TB-7Lb and hcf113 by TB-9Sb.
Plants homozygous for hcf104 possess a normal green color, but produce a high level of chlorophyll fluorescence when illuminated by long wave UV light. Chloroplasts isolated from mutant plants support a normal rate of electron transport through Photosystem II (PSII) but only 40% of the normal rate of electron transport through Photosystem I (PSI) and through both photosystems. The concentration of chemically oxidized minus reduced P700, the reaction center pigment of PSI, is approximately 40% of the normal concentration on a chlorophyll basis. Polyacrylamide gel electrophoresis (PAGE) of thylakoid polypeptides reveals a loss of 60% of the 110 kilodalton (kDa) chlorophyll protein complex (CP1) and its 66kDa apoprotein, both of which are associated with PSI. Twelve of 100 F1 progeny of a cross between a plant heterozygous for hcf104 and TB-7Lb stock expressed the hcf104 phenotype.
hcf113 mutant plants are yellow-green and also exhibit an hcf phenotype. Mutant chloroplasts support 58% and 76% of normal electron transport rates through PSII and PSI respectively, but only 38% of the normal rate through both photosystems. PAGE of thylakoid polypeptides isolated from hcf113 reveals severe reductions in CP1 and its 66kDa apoprotein as well as other polypeptides associated with PSI and the b6/f complex. These data suggest that hcf113 has multiple effects including disruption of electron transport in at least two locations and interference with the proper assembly of the chlorophyll protein complexes. Between 9 and 20 mutant plants were identified among 100 F1 progeny of each of 3 crosses between hcf113 heterozygotes and TB-9Sb stock.
Two other mutations recovered from these Mutator stocks were also mapped to chromosome arms. 1258-7 and 1253-6 are independent isolates arising from different male and female parents in the mutagenic crosses. Both exhibit typical glossy phenotypes. Several crosses between plants homozygous for the two mutations yielded uniformly glossy progeny. The mutation present in 1258-7 was uncovered by TB-7Lb. Allelism between the two glossy isolates and gl1 has not been tested.
Bill Cook and Don Miles
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