Spontaneous somatic mutation frequencies for flower color in several Tradescantia species and hybrids

Abstract

Normal wild-type flowers of Tradescantia species and of certain interspecific hybrids vary in color from blue to violet to purple, but in many species occasional pink-flowered plants occur. Spontaneous pink mutant cells can be observed in petals and stamen hairs of plants heterozygous for flower color and mutation frequencies can be calculated per 10 3 hairs on per 10 5 stamen hair cells. These two frequencies are highly correlated but not completely proportional because of clonal differences in number of cells per hair. The lowest spontaneous frequencies were found in hybrid or putative hybrid clones and the highest (except for one mutable clone) found in heterozygous clones of pure species. The spontaneous frequency per hair varied from 0·48±0·15 to 5·21±0·20 × 10 −3 for hybrid (4430) or putative hybrid (02) clones, and from 2·15±0·16 to 16·98±1·25 × 10 −3 per hair for clones of T. bracteata, T. gigantea, T. ohiensis, T. paludosa and T. subacaulis. The pink mutation frequencies per 10 5 cells were calculated for three clones of T. subaccalis and varied from 11·8 to 58·9. Frequencies per 10 5 stamen hair cells varied from 3·65 for one scoring of the putative hybrid clone 02 to 23·0 for young plants of clone 4430 (a hybrid of T. hirsutiflora × subacaulis). Spontaneous frequencies for one set of scorings on petals of clone 02 gave an average of 27·5 × 10 −5 per cell—higher than the corresponding stamen hair frequencies, but scorings were at different times. For the mutable clone 0106, derived from clone 02, spontaneous pink mutation frequencies per 10 3 hairs varied from about 8·8±2·15 to 46·0±9·8 and per 10 5 cells from 35·7 to 227·8, depending upon length of time after cuttings were made. The variation in frequencies among clones is assumed to have a genetic basis but within a clone is thought to be influenced by such factors as age of plant or inflorescence, environmental conditions under which the plants are grown, the year or time of year scoring was done, and possibly by variation in scoring efficiency among different observers. The variation observed with date of scoring suggests the possibility of unidentified environmental mutagen(s) as the casual agent(s), but this has not been confirmed. The mutation frequencies observed in Tradescantia are compared with frequencies or rates in gametic and somatic cells of various plant and animal species.