GENETIC HISTORY AND GENERAL COMPARISONS OF TWO ALBINO MUTATIONS OF HELIANTHUS ANNUUS

WALLACE, RAYMOND H. (U. Connecticut, Storrs.), AND HELEN M. HABERMANN. Genetic history and general comparisons of two albino mutations of Helianthus annuus. Amer. Jour. Bot. 46(3): 157-162. Illus. 1959.-The genetic history of the progeny of a single ultrasonically-treated seedling of Helianthus annuus L. has been summarized for the 6 generations for which quantitative data are available. A yellow mutation was found in the F2 generation and later in the F5 a second, white mutation occurred. Both mutants have been grown to maturity by grafting them onto normal green host plants and they have set viable seeds. Both pigment-deficient conditions are inherited as single recessive factors. These albino strains form chlorophyll during their seedling stages if they are grown at low light intensities. Chlorophyll is destroyed, however, under bright illumination and, once bleached, the capacity for chlorophyll formation appears to be lost. The yellow mutant contains xanthophyll but no traces of carotene have been found. In the white mutant, neither carotene nor xanthophyll have been detected. Flower color in the yellow mutant is normal while the flowers of the white mutant have no apparent pigmentation. The growth pattern of grafted yellow mutants is normal, save for a stiffer and woodier condition and a greater resistance to wilting. These characteristics have also been observed in grafted white mutants. In addition, there is a pronounced reduction in leaf size in the white mutant. THE PIGMENT-DEFICIENT mutations of Helianthus annuus L. have been used as the experimental material for such varied studies as the effects of inorganic nutrient levels on enzyme activities (Weinstein and Robbins, 1955), chlorophyll development (Wallace and Schwarting, 1954), transfer of flowering stimulus (Habermann and Wallace, 1958) and seed dormancy (Wallace and Habermann, 1958). In this paper we will summarize the genetic data which have been kept through 4 generations of the yellow mutant and through 2 generations of the white mutant. To provide a general comparison of these albino mutants with their normal green sibs, we will survey briefly the variety of morphological and physiological observations which have been made. Studies of albino mutations are certainly not new in the literature of botany. Extensive comparisons of albino (or variegated) with normal green leaves were made by Church (1879, 1880, 1886), Grandsire (1926) and Schumacher (1928). An appreciation of the usefulness of albino forms has been reflected in the studies of respiration of normal and albino tissues by Smirnow (1926), Schumacher (1928), Groner (1936) and Spoehr (1942). During recent years there has been renewed interest in the use of pigment mutants of both higher and unicellular plants. Koski et al. (1951) used an albino mutant of corn to study the con'Received for publication July 10, 1958. 2 Some parts of the experimental work reported in this paper were completed by one of the authors (H.M.H.) at the Dept. of Botany, Univ. of Minn. and at the Research Institutes (Fels Fund), Univ. of Chicago. The author wishes to thank Professors Allan H. Brown and Hans Gaffron for the use of laboratory facilities. version of protochlorophyll to chlorophyll in the light. Sistrom et al. (1956) recently reported studies on a blue-green mutant of the photosynthetic bacterium, Rhodopseudomonas spheroides, which is completely devoid of colored carotenoids. It was suggested by these workers and supported by the observations of Claes (1954) on Chlorella mutants that the carotenoid pigments function as chemical buffers against light damage. Only the yellow mutant had been discovered when the first comparative studies of the albino and normal forms of the sunflower were undertaken. Superficially, this mutant appeared to differ from its normal green sibs only in the ability to form chlorophyll. Since that time a second, white mutant has been found and it has become clear that the genetic aberrations causing albinism in these mutant forms directly affect the synthesis of carotenoids as well as the ability to stabilize chlorophyll under normal growing conditions. GENETIC HISTORY OF YELLOW AND WHITE MUTANT FORMS. A paper by Wallace et al. (1948) reported evidence that cytogenetic variations had been produced in seedlings of Helianthus annuus L., var. 'Russian Giant,' by exposure of their growing points to ultrasonic vibrations. The most interesting phenotypic modification observed was a variation in the pigmentation of the progeny of a single treated plant which had been exposed as a 2-day-old seedling to 50 W. of ultrasonic energy for 25 sec. This plant grew to maturity in the greenhouse with no apparent abnormalities. The F1 generation was also entirely normal. No albinos were found in a total of over 20,000 P1 and F1 plants grown as controls. With the large numbers of plants grown in these tests of the P1 and F1 generation, it was concluded that the Darent stock was free of albinism.