ALBERT

Description / Table of Contents: Summary The present publication is in conjunction with my paper of 1958, in which the occurrence of somatic conversion insulf + sulf heterozygotes of the tomato has been reported. Now further data are presented which corroborate the conclusions drawn at that time. The findings of the studies so far carried through are summarized: 1. Thesulf series ofLycopersicon esculentum consists of the dominant normal allelesulf + and two groups of mutant alleles:sulfurea pura (sulf pura ) andsulfurea variegata (sulf vag ); the general symbol for the two groups issulf (fig. 1). The dominance relations are:sulf + 〉sulf vag 〉sulf pura . 2. Thesulf + sulf plants have green cotyledons. But during further development, beginning with the formation of foliage leaves, part of the heterozygotes become green-yellow variegated: on the shoot areas withsulf-mutant phenotype occur (fig. 2 and 3). Variegated plants can form different types of branches: pure green, variegated, uniformly yellow-green speckled (sulf vag -phenotype) and pure yellow (sulf pura -phenotype). 3. The progenies of green heterozygotes and of green branches (of variegated plants) segregate in a normal Mendelian ratio 3sulf +.: 1sulf sulf (table 1, columm „AN“ of tables 2, 3, 7, 8 and column „calyx green“ of table 9). 4. In progenies of variegated branches deviations appear from the monohybrid ratio, resulting in an increase ofsulf sulf seedlings. The more intense the variegation of a branch i. e. the greater the extent of mutant tissue, the greater is the portion of homozygoussulf sulf seedlings in its progeny (column „AT-AB“ of tables 2, 3, 7, 8 and column „calyx not green“ of table 9). 5. The progenies of branches with mutant phenotype (sulf pura orsulf vag ) consist of mutant seedlings, either pure yellow or yellow-green speckled ones. Pure green plants are lacking (tables 4 and 5). 6. Thus hereditary differences exist between the different types of branches, and ontogenetic change of dominance or variable manifestation of a dominant mutant allele can be no explanation. 7. After reciprocal crosses betweensulf-homozygotes and homozygous normal plants there are no significant differences in the percentage and extent of variegation, found among the heterozygotes (table 6). Mutated extrachromosomal factors are not involved in this variegation. 8. Extensive tests have shown that the variegation of thesulf + sulf plants is not the result of mitotic crossing-over in the four-strand-stage, becausesulf + sulf + cells, which would occur simultaneously withsulf sulf cells by the process of mitotic crossing-over, are entirely lacking in variegated plants (tables 7, 8 and 9). 9. In the meiosis ofsulf + sulf plants no cytologial irregularities have been found. 10. These results lead to the conclusion, that the variegation of thesulf + sulf plants is caused by somatic conversion: Thesulf +-allele is stable in homozygous condition. In vegetative cells ofsulf + sulf heterozygotes, however, thesulf +-allele becomes unstable under the influence of thesulf allele, present in the same nucleus, and mutates with a definite frequency to asulf allele (either asulf pura or asulf vag allele).