Auxin-induced heritable variants in yeast with special reference to physiological and genetic characters

A high concentration (400 mg/l) of an auxin, -naphthaleneaceticacid produced heritable variants differing in cell form andsize and in sporulation ability in a diploid strain of Saccharomycescerevisiae. These variants showed altered absorption spectrain the region of cytochromes a + a₃, b and/or c, but could growin a glycerol medium. Cultures of dissected spores from thesevariants involved many non-maters. These variants showed irregularsegregation of nutritional markers and/or a high DNA contentper cell. Since most of the variants grow more slowly on anauxin medium than does the original strain, they seem to beproduced by the induction by auxin rather than by selectiveenrichment. Genetic control of the ability to respond to auxinand the biological significance of auxin-induced variation inyeast is discussed. (Received January 12, 1968; )     

PRODUCTION OF YEAST VARIANTS BY AUXIN AND EFFECTS OF PLANT GROWTH REGULATORS ON THESE VARIANTS

Using diploid strains of Saccharomyces cerevisiae and S. ellipsoideus,the following facts were found:

1. Indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid and -naphthaleneaceticacid produced stable variants differing in the cell form andin the response to the actions of auxin to elongate cells, toinduce respiration- deficient mutation and to promote sporulation.
2. The auxins also produced stable variants differing in theabilityto form spores.
3. Acetic acid had no above-menthionedactions of auxin.
4. Spore-formation and cell elongation of someof auxin-inducedvariants were controlled by auxin.

Biological significance of the auxin-induced variation is discussedand the usefulness of some of these variants as experimentalmaterial for auxin physiology in general is pointed out. (Received November 1, 1966; )     

RESPONSIVENESS OF YEAST CELLS TO AUXIN, ANIMAL SEX HORMONES AND YEAST SEXUAL HORMONES IN RELATION TO SEX CONTROLLING GENES

Genetic control of the ability of yeast cells to respond to cell-expanding action of animal, plant and yeast hormones was studied. Mating type specificity in the ability to respond to yeast sexual hormones was changed by introduction of homothallism-controlling genes, D and HM. Auxin, a plant hormone can expand cells of most homothallic strains, but not those of heterothallic strains as far as tested. Animal sex hormones showed the action similar to that of yeast sexual hormones.     

Separation of hormone-sensitive yeast cells by density gradient centrifugation

Cells in cultures of haploid strains of Saccharomyces cerevisiaein stationary phase were separated into interface fraction andpellet fraction by density gradient centrifugation. Cells inpellet fraction expanded in response to yeast sexual hormoneand animal sex hormones, whereas cells in interface fractiondid not. ¹Present address: Department of Biology, Faculty of Science,Osaka City University, Sumiyoshi-ku, Osaka, Japan (Received July 16, 1970; )     

EFFECT OF YEAST SEXUAL HORMONES ON ELONGATION OF AVENA COLEOPTILE

Effect of yeast (Saccharomyces cerevisiae) sexual hormones on the elongation of etiolated Avena coleoptile segments was studied. The elongation was promoted by a hormone excreted by cells of mating type a, but not by α hormone excreted by cells of α type. The effect of the former was as great as that of 5 mg/1 indole-3-acetic acid in the first hour of application. The optimal concentration of a hormone was 10 units/ml. Its growth promoting effect was greatly inhibited by an antiauxin, 2,4,6-trichlorophenoxyacetic acid. a Hormone increased cell wall extensibility just as auxin does. Testosterone, β-estradiol, progesterone and ergosterol showed very little effect on the elongation of coleoptile segments.     

YEAST SPORULATION AND RNA AS AFFECTED BY GIBBERELLIC ACID

Comparison with respect to the promoting effect on the yeastsporulation was made between RNA fractions prepared by a phenolmethod from two strains of yeast (Saccharomyces ellipsoideus),the one (KV2) which needs GA-treatment to be responsive to thecell-elongating action of auxin and the other (P 602) whichdoes not need it. For obtainting RNA preparation active in promotingthe sporulation, cells of the former strain had to be pretreatedwith GA, but the GA-treatment was unnecessary in the latterstrain. An RNA fraction that remarkably promoted sporulation in yeastwas obtained from the GA-treated tuber tissue of Jerusalem artichoke.The tuber tissue is known to become highly responsive to thecell expansion-promoting action of auxin through GA-treatment. In any case, the sporulation-promoting effect was found onlyin "phenol RNA" but not in "water RNA", and the former "RNA"was inactivated by the treatment with RNase. (Received November 1, 1966; )     

FURTHER STUDIES ON THE RNA FUNCTIONAL IN AUXIN ACTION

Avena coleoptile and a respiration-deficient mutant of yeastwhose cells are elongated by the action of auxin in the absenceof GA added were subjected to the phenol method of RNA fractionation."RNA" from the phenol layer promoted the auxin-induced expansionof Jerusalem artichoke tuber slices just as GA did, whereas"RNA" from the water layer was ineffective. The GA-like activityof the former "RNA" was reduced by treatment with RNase or alkali. No active "RNA" was extractable from a respiration-sufficientyeast strain which does not respond to auxin without GA supplemented. (Received August 19, 1964; )     

CHEMICAL NATURE OF YEAST SEXUAL HORMONES

From culture media of yeast cells of the two mating types, a and α, hormones, which made cells of the opposite mating type expand, were extracted with methylene chloride. They were then isolated by either thin layer chromatography or vacuum distillation. The isolated hormones showed color reactions of steroidal compounds. According to Rf values and UV absorption spectra, the two yeast hormones apparently are different from testosterone and estradiol, which have activity similar to that of the yeast sexual hormones excreted by a and α type cells, respectively.     

Mating Reaction in Saccharomyces cerevisiae. IV. Retardation of Deoxyribonucleic Acid Synthesis

When a and a type haploid cells of Saccharomyces cere-visiae were mixed and cultured, deoxyribonucleic acid synthesis was retarded but ribonucleic acid and protein syntheses were not. It was found that culture filtrate of a type cells inhibited deoxyribonucleic acid synthesis of a type cells and that of a type cells inhibited that of a type cells. Thus, sex-specific diffusible substances secreted by opposite mating type cells are thought, at least partly, to be responsible for the retardation of deoxyribonucleic acid synthesis.     

Relation of special RNA to sensitivity of yeast strains to auxin

RNA functional in auxin action was studied in the followingfour strains of yeasts differing in their sensitivity to auxin:KV2, diploid strain of Saccharomyces ellipsoideus irresponsiveto auxin but made responsive by gibberellic acid treatment;N55, auxinresponsive mutant derived from KV2; A2-0, diploidstrain of 5. cerevisiae irresponsive even when gibberellic acidis given; and A2–N102, responsive mutant derived fromA2–0. The RNA fraction extracted from N55 and partitionedin a phenol layer sensitized KV2 to auxin. This kind of RNAwas not detected in KV2 cells. The functional RNA from N55 wasof low molecular weight, as was functional RNA isolated fromgibberellic acid-treated Jerusalem artichoke tuber. Gibberellicacid-treated KV2 cells have been known to contain RNA whichfunctions similarly to the RNA mentioned above. Both A2–0and A2–N102 contained RNA which made KV2 cells responsiveto auxin. Some factors other than functional RNA may determinethe difference in the sensitivity to auxin between A2–0and A2–N102. (Received August 20, 1968; )