Mutagenic effects of streptomycin in Chlamydomonas

Evidence for persistence of chloroplast markers in the heteroplasmic state in Chlamydomonas reinhardtii

In the green alga Chlamydomonas reinhardtii, reciprocal crosses between strains carrying non-allelic chloroplast mutations to streptomycin dependence (sd-u) produce streptomycin sensitive (sd-u (+)) recombinant progeny. Transfer of these sd-u (+)progeny to streptomycin-containing medium results in a much higher frequency of recovery of streptomycin dependent isolates than expected by mutation. Failure to recover the more commonly encountered class of streptomycin resistant mutants also suggests that mutation is not responsible for appearance of the new dependent isolates. Backcrosses of these new sd-u isolates to strains carrying the original sd-u mutations demonstrate their allelism with the sd-u mutation contributed by the mt (+)parent. Earlier work by Schimmer and Arnold (1969, 1970a-d) indicated that newly isolated sensitive revertants of the streptomycin dependent mutant sd-u-3-18 also yielded high frequencies of sd-u cells but these were never analyzed genetically. We have now obtained new sd-u. isolates from streptomycin sensitive revertants of sd-u-318 and shown them all to be allelic with the original sd-u3-18 mutation. Thus "hidden" sd-u alleles can coexist with sd-u (+)alleles in heteroplasmic cells. These heteroplasmic cells are streptomycin sensitive in phenotype and may arise in crosses or from new mutation.

Three new yellow loci in Chlamydomonas reinhardtii

Three phenotypically 'yellow', mendelian mutants of Chlamydomonas reinhardtii have been isolated and tested for allelism with the yellow mutant y-1 a1 and with each other. The three mutants represent three new yellow loci, two of which are located on linkage group I. Like y-1a, the mutants accumulate protochlorophyllide when grown under dim light, but have a wildtype phenotype when grown in the light. We conclude that the control of light-independent protochlorophyllide reduction is more complex than has been thought previously.

Linkage of six genes in Chlamydomonas reinhardtii and the construction of linkage test strains

Linkage relationships were determined for six genes in Chlamydomonas reinhardtii: pyr, act, can-la, ey, y-1, and nic-7. Four of these were combined with five other genes to form linkage test strains.

Genetic control of chlorophyll biosynthesis in Chlamydomonas. Analysis of mutants at two loci mediating the conversion of protoporphyrin-IX to magnesium protoporphyrin

In this report we describe two nonallelic Mendelian protoporphyrin accumulating mutants br(s)-1 and br(c)-1. Results of experiments with these mutants lead us to postulate that porphyrin biosynthesis branches into light and dark steps between protoporphyrin-IX and magnesium protoporphyrin. We hypothesize that the br(c) locus controls a dark step while the br(s) locus either controls a step in the main pathway before the branch or mediates the preparation of the magnesium ion for its insertion into protoporphyrin-IX. The br(s)-1 mutant is thought to be light sensitive because a block prior to the branch point in the porphyrin pathway prevents chlorophyll formation in either the light or the dark. The br(c)-1 mutant, which also accumulates protoporphyrin in the dark, forms chlorophyll and chloroplast lamellae when transferred to the light, showing that function of the porphyrin pathway is normal in the light.

The induction of gene mutation and chromosome aberration in Chlamydomonas eugametos by a phenylalanine analog

Evidence is presented which indicates that the phenylalanine analog 2-amino-3-phenylbutanoic acid (APBA) induces mutation to APBA, streptomycin, and neamine resistance in the green algaChlamydomonas eugametos. Apparent chromosome abnormalities (reciprocal translocations and inversions) were also found among some clones recovered after APBA treatment. The two, mutation and chromosome aberration, are separable.

Biogenesis of chloroplast membranes. I. Plastid dedifferentiation in a dark-grown algal mutant (Chlamydomonas reinhardi)

This paper describes the morphology and photosynthetic activity of a mutant of Chlamydomonas reinhardi (y-1) which is unable to synthesize chlorophyll in the dark. When grown heterotrophically in the light, the mutant is indistinguishable from the wild type Chlamydomonas. When grown in the dark, chlorophyll is diluted through cell division and the photosynthetic activity (oxygen evolution, Hill reaction, and photoreduction of NADP) decays at a rate equal to or faster than that of chlorophyll dilution. However, soluble enzymes associated with the photosynthetic process (alkaline FDPase, NADP-linked G-3-P dehydrogenase, RuDP carboxylase), as well as cytochrome f and ferredoxin, continue to be present in relatively high concentrations. The enzymes involved in the synthesis of the characteristic lipids of the chloroplast (including mono- and digalactoside glycerides, phosphatidyl glycerol, and sulfolipid) are still detectable in dark-grown cells. Such cells accumulate large amounts of starch granules in their plastids. On onset of illumination, dark-grown cells synthesize chlorophyll rapidly, utilizing their starch reserve in the process. At the morphological level, it was observed that during growth in the dark the chloroplast lamellar system is gradually disorganized and drastically decreased in extent, while other subchloroplast components are either unaffected (pyrenoid and its tubular system, matrix) or much less affected (eyespot, ribosomes). It is concluded that the dark-grown mutant possesses a partially differentiated plastid and the enzymic apparatus necessary for the synthesis of the chloroplast membranes (discs). The advantage provided by such a system for the study of the biogenesis of the chloroplast photosynthetic membranes is discussed.