Ultra-violet induced mutants of Chlorella pyrenoidosa

Development of the photosynthetic apparatus during light-dependent greening of a mutant of Chlorella fusca

The formation of chlorophyll, cytochrome f, P-700, ribulose bisphosphate carboxylase as well as photosynthesis and Hill reaction activities were tested during the light-dependent greening process of the Chlorella fusca mutant G 10. Neither chlorophyll nor protochlorophyllide was detected in the darkgrown cells. When transferred to light the mutant cells developed chlorophyll and established its photosynthetic capacity after a short lag phase. In the in vivo absorption spectra a spectral shift of the red absorption peak position from 674 to 680 nm was indicated during the first 3 h of greening. Cytochrome f was already present in the dark-grown cells, but during the greening phase a threefold increase in the cytochrome f content could be seen. At the early stages of greening a characteristic primary oscillation in the content of cytochrome f was observed. P-700 was lacking in the dark and during the first 30 min of illumination. From the first to the second h of light a forced synthesis of P-700 took place and the time-course curve for the ratios of P-700/chlorophyll rose to a sharp maximum. The synthesis of P-700 started together with photosystem I activity and showed similar kinetics. We found the simultaneous appearance of photosystem II, photosystem I, and photosynthetic activities 30 min after the beginning of the illumination. Based on chlorophyll content they attained maximum activity after 2 h of light, but at this time photosystem I capacity proved to be remarkably higher than photosynthetic and photosystem II activities. Highest carboxylase activity existed in darkgrown cells. During the greening process the activity of the enzyme decreased continuously. After 2 h of illumination chlorophyll synthesis partially served to increase the size of the photosynthetic unit, which consequently led to a decrease in the light energy needed to saturate photosynthesis and also to a decrease of photosynthetic rate based on chlorophyll content.

[On the essential oil of green algae. III. The oils of some Chlorella mutants (author's transl)]

The stability against mutation of essential oil formation in the genus Chlorella is similar to that of hydrogenase. Both characters are therefore of special value in Chlorella taxonomy. All the 21 mutants of C. fusca C-1.1.10 produce essential oils, but only a few of them produce proazulenes. Two mutants of C. kessleri C-1.1.12 produce essential oils and proazulenes like the wild type.

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.

Sporopollenin in the cell wall of Chlorella and other algae: Ultrastructure, chemistry, and incorporation of (14)C-acetate, studied in synchronous cultures

Cells of Chlorella fusca var. vacuolata (Cambridge 211/8p) resisted efforts aimed at producing naked protoplasts by enzymatic degradation of the cell wall, and a study of the development and composition of the wall was therefore undertaken. 1. After cytokinesis has produced naked autospores within the mother cell wall, cell wall formation commences outside the autospore plasma membrane with the appearance of small trilaminar plaques. These enlarge while inter-autospore granular material diminishes in quantity, and they eventually fuse to produce a complete trilaminar sheath around each autospore. 2. A microfibrillar, cellulase digestible, layer is deposited between the trilaminar component and the plasma membrane. Meanwhile the corresponding microfibrillar component of the mother cell wall is digested leaving only its resistant trilaminar component. 3. The trilaminar component includes a substance considered to be the polymerized carotenoid, sporopollenin, on the basis of its resistance to extreme extraction procedures including acetolysis, and its infra red absorption spectrum. 4. Two phases of sporopollenin biosynthesis were detected by means of pulse and pulse-chase treatments with (14)C-acetate at intervals during the cell cycle in synchronous cultures. One coincides with the formation of the sporopollenin-containing trilaminar wall component, and the other is 6-8 hours earlier while the cells are in karyokinesis. The former yields labelled sporopollenin directly and the latter probably represents formation of a precursor. 5. Of five other strains of Chlorella tested, only one possesses sporopollenin, and so does one Scenedesmus and two out of three strains of Prototheca. 6. Examination of the wall structure of the above algae suggest a relationship between the presence of sporopollenin and the development of an outer, trilaminar wall component. 7. A survey of the literature gives support to this hypothesis and further suggests that the ability to synthesise sporopollenin is related to the ability to produce secondary carotenoids. 8. The significance of the findings is discussed.