GLYCOLATE DEHYDROGENASE IN PRIMITIVE GREEN ALGAE

Glycolate dehydrogenase occurs in nine species of the Prasinophyceae. The occurrence of glycolate dehydrogenase in these unicellular flagellated organisms does not correspond to the lines of evolution suggested for the green algae based on glycolate enzymology and the nature of the spindle at telophase of mitosis. It is proposed that the evolutionary divergence of the glycolate enzyme came after the evolutionary divergence of the spindle features in the green algae.     

THE FINE STRUCTURE OF GREEN BACTERIA

The fine structure of several strains of green bacteria belonging to the genus Chlorobium has been studied in thin sections with the electron microscope. In addition to having general cytological features typical of Gram-negative bacteria, the cells of these organisms always contain membranous mesosomal elements, connected with the cytoplasmic membrane, and an elaborate system of isolated cortical vesicles, some 300 to 400 A wide and 1000 to 1500 A long. The latter structures, chlorobium vesicles, have been isolated in a partly purified state by differential centrifugation of cell-free extracts. They are associated with a centrifugal fraction that has a very high specific chlorophyll content. In all probability, therefore, the chlorobium vesicles are the site of the photosynthetic apparatus of green bacteria.     

SEPTAL PLUGS IN A GREEN ALGA

Septal plugs, resembling those found in red algae, occur in the transverse wall between all cells in a newly discovered marine green alga, Pilinia earleae Gallagher & Humm.³ No plasmodesmata traverse the cross-wall, and the septal plug blocks cytoplasmic continuity between cells. The septal plug consists of an electron-translucent core bordered at each end by two electron-opaque caps. Cytochemical procedures demonstrate that the plug consists of protein and polysaccharide, but lacks peroxidase. The outer cap is highly proteinaceous while the inner cap is composed primarily of polysaccharide. The plug core is not routinely stained by Coomassie Blue but it is pronase sensitive and probably proteinaceous. Historically, septal plugs have been considered unique to the red algae and the fungi, but ultrastructural and biochemical data provide no support for derivation of the septal plug in this green alga from a symbiotic relationship. The discovery of septal plugs in a green alga makes the hypothesis of an independent origin of this structure in a number of plant groups more likely.     

NUTRITION OF THE GREEN ALGA GOLENKINIA

Defined media were established for four strains of Golenkinia. Strains 929 and 930 require thiamine and vitamin B₁₂, strain 931 requires the latter and is stimulated by thiamine; only strain 320 and a mutant of strain 931 are capable of completely autotrophic growth. The optimal nitrogen concentration is 0.025 m except for strain 931 where it is 0.015 m and the requirement may be met by nitrate, ammonium, or urea. Optimal levels of the other components are: 0.0025 m KH₂PO₄, 0.0005 to 0.001 m MgSO₄, and 50 ml of a stock trace-element solution per liter. Only strain 931 required calcium; however, its addition stimulates the growth of strains 929 and 930. The optimal pH before autoclaving is 6.8. Maximal growth rates of two to three cell doublings per day and yields of 26 to 30 (log₂) cells per ml were obtained. These growth data compare favorably with those for other unicellular green algae.     

DIFFERENTIATION OF THE GREEN ALGA CODIUM FRAGILE

Clonal cultures of Codium fragile were established from both swimming cells and vegetative filaments. In the laboratory axis primordia differentiate from heterotrichous juveniles only when cultures are agitated on a reciprocating shaker. The shear forces created by mechanical agitation are essential both for initiation and maintenance of primordia. Contact guidance of growing coenocytic filaments indicates mutual adhesion of filaments as the basis for the differentiation process.     

SUMMARY OF GREEN PLANT PHYLOGENY AND CLASSIFICATION

Abstract— A cladogram of green plants involving all major extant groups of green algae, bryophytes, pteridophytes, and seed plants is presented. It is partly based on contributions by B. Mishler and S. Churchill, H. Wagner, and P. Crane. The relationships of green plants to other green organisms ( Prochloron , euglenophytes) are discussed. The characters and subclades of the cladogram are briefly discussed, with an attempt to indicate weak points. The possibility of including some major extinct groups is considered. A cladistic classification consistent with the cladogram is presented. Grades are abandoned as taxa and major clades like the division Chlorophyta (green algae excluding micro-monadophytes and charophytes sensu Mattox and Stewart), the division Streptophyta (charophytes + embryophytes), the subdivision Embryophytina (land plants or embryophytes), the superclass Tracheidatae (tracheophytes), and the class Spermatopsida (seed plants) are recognized.     

EFFECTS OF GREEN LIGHT ON BIOLOGICAL SYSTEMS

Green light (510-565 nm) constitutes a significant portion of the visible spectrum impinging on biological systems. It plays many different roles in the biochemistry, physiology and structure of plants and animals. In only a relatively small number of responses to green light is the photoreceptor known with certainty or even provisionally and in even fewer systems has the chain of events leading from perception to response been examined experimentally. This review provides a detailed view of those biological systems shown to respond to green light, an evaluation of possible photoreceptors and a review of the known and postulated mechanisms leading to the responses.     

THE CHLOROPHYLL-PROTEIN COMPOUND OF THE GREEN LEAF

1. Aqueous extracts of spinach and Aspidistra leaves yield highly opalescent preparations which are not in true solution. Such extracts differ markedly from colloidal chlorophyll in their spectrum and fluorescence. The differences between the green leaf pigment and chlorophyll in organic solvents are shown to be due to combination of chlorophyll with protein in the leaf. 2. The effect of some agents on extracts of the chlorophyll-protein compound has been investigated. Both strong acid and alkali modify the absorption spectrum, acid converting the compound to the phaeophytin derivative and alkali saponifying the esterified groups of chlorophyll. Even weakly acid solutions (pH 4.5) denature the protein. Heating denatures the protein and modifies the absorption spectrum and fluorescence as earlier described for the intact leaf. The protein is denatured by drying. Low concentrations of alcohol or acetone precipitate and denature the protein; higher concentrations cause dissociation liberating the pigments. 3. Detergents such as digitonin, bile salts, and sodium desoxycholate clarify the leaf extracts but denature the protein changing the spectrum and other properties. 4. Inhibiting agents of photosynthesis are without effect on the absorption spectrum of the chlorophyll-protein compound. 5. The red absorption band of chlorophyll possesses the same extinction value in organic solvents such as ether or petroleum ether, and in aqueous leaf extracts clarified by digitonin although the band positions are different. Using previously determined values of the extinction coefficients of purified chlorophylls a and b, the chlorophyll content of the leaf extracts may be estimated spectrophotometrically. 6. It was found that the average chlorophyll content of the purified chloroplasts was 7.86 per cent. The protein content was 46.5 per cent yielding an average value of 16.1 parts per 100 parts of protein. This corresponds to a chlorophyll content of three molecules of chlorophyll a and one of chlorophyll bfor the Svedberg unit of 17,500. It is suggested that this may represent a definite combining ratio of a and b in the protein molecule.     

REDUCTION OF DEHYDRO-L-ASCORBIC ACID IN GREEN LEAVES

1. The capacity of green leaves for absorbing and converting substancesrelated to L-ascorbic acid was investigated, using detachedleaves of various plants, including soybean, pea, barley andspinach.
2. The greater portion of the absorbed dehydroascorbicacid wasrecovered in the leaves as ascorbic acid, minor portionsbeingdiscovered as dehydroascorbic acid and 2,3-diketogulonicacid. The recovery was about 60% of the absorbed dehydro ascorbicacid, in the cases of detached soybean and barley leaves, forinstance, thus suggesting the instability of the substance invivo.
3. The absorption and conversion of ascorbic acid and 2,3-di-ketogulonic acid in detached green leaves were also investigated.Most of the absorbed ascorbic acid reappeared in the leaves.On the other hand, no evidence for the conversion of 2,3-diketogulonicacid into ascorbic and dehydroascorbic acids was observed. Thegreater portion of the absorbed 2, 3-diketogulonic acid seemsto be decomposed in the leaves, under the condition of the presentstudy.

(Received April 17, 1961; )