An Analysis of the Formation of Ciliary Primordia in the Hypotrich Ciliate Urostyla weissei*

SYNOPSIS. The protargol technic was used in a study of the development of oral, cirral, and dorsal primordia of Urostyla weissei fixed during division, reorganization, and regeneration following transection at different levels. While the course of development is similar in all situations, differences were observed in the way in which some primordia are initiaily formed. The primordium of the new AZM always appears posterior to the old AZM. It develops into an entire new membranellar band in dividing cells and in opimers (posterior fragments from equatorial transections), while it eventually joins with a portion of the old AZM in reorganizers, promers (anterior fragments from equatorial transections) and “large opimers” (cells whose anterior tip has been cut off). The UM-primordium of proters is derived from disaggregation of the kinetosomes of the 2 old UM's, that of opisthes and opimers is formed “de novo” to the right of the AZM-primordium, while the UM-primordium of reorganizers, promers, and “large opimers” is of composite origin, partly “de novo” and partly from the old UM's. The UM primordium differentiates into the new UM's and the 1st frontal cirrus. The primordia of the remaining frontal, ventral, transversal (F-V-T) and marginal cirri originate as “streaks” of cilia, most of which are derived from re-alignment of the constituent cilia of certain pre-existing cirri. New cirri differendiate from the streaks, and replace the remaining old cirri. The streaks are formed similarly in all developmental situations, except for the 1st 3 F-V-T streaks. In proters, reorganizers, and promers, these originate from the posterior 3 frontal cirri, while in opisthes and opimers they are formed “de novo” to the right of the UM-primordium. In the “large opimers” these streaks are formed “de novo” behind the 1st 3 frontal cirri, in spite of the continued presence of these cirri at the anterior tip of the fragments. The site of formation of these streaks thus appears to be determined by an anteriorposterior gradient, rather than by any preformed cortical structure. The new dorsal bristle rows I to III develop from the proliferation of portions of the old rows, while rows IV and V originate from short kineties formed “de novo” on the right margin. New caudal cirri differentiate at the posterior ends of the new rows I to III. The numbers of ventral cirral rows and transversal cirri are variable; these variations are correlated, and related to variations in numbers of developing streaks. A survey of hypotrich developmental patterns revealed extensive parallels, especially in the sites of appearance of primordia. The primordium site appears to be a more constant feature of cortical development than is the “source” of ciliary units. It is concluded that sites of primordia are determined by cellular gradients, with competent preformed structures being utilized if they are appropriately positioned within these gradients.     

OXIDATION OF PHLORIDZIN BY ISOLATED CHLOROPLASTS

Phloridzin was shown to be oxidized by chloroplast fragmentsfrom swiss-chard. From inhibitor studies, kinetics and affinitytoward oxygen, it was inferred that the oxidation was mediatedby a phenolase in a "cresolase" type reaction. Atebrin was foundto inhibit the enzymatic oxidation of phloridzin and of 4-methylcatechol. (Received November 2, 1966; )     

Critical Phases of Oral Primordium Development in Tetrahymena pyriformis GL-C: An Analysis Employing Low Temperature Treatment

SYNOPSIS. The effects of temperatures of 12–18 C on cell division and oral primordium development were investigated in cultures of synchronized Tetrahymena pyriformis GL-C. If exposures to 12 or 15 C were initiated prior to a “transition point,” long delays of cell division were generated. After this transition point, cell division could no longer be substantially delayed by exposure to low temperature. The time of the transition point was somewhat earlier with 15 C than with 12 C treatments. At temperatures higher than 15 C long delays of cell division were not generated regardless of time of treatment. The effects of low temperature on oral morphogenesis were strongly dependent on the stage which was affected. (i) The further development of cells initially in the “anarchic field” stage (stage 1) was immediately blocked at both 12 and 15 C. (ii) Cells initially in the stages of incipient membranelle differentiation (stages 2 and 3) continued to develop at both 12 and 15 C, and formed oral primordia in which all 3 membranelles were clearly differentiated (stage 4). The subsequent progress of these stage 4 primordia depended on the temperature: at 12 C virtually all were resorbed (and cell division was blocked); at 15 C only about 1/3 were resorbed, while the remaining 2/3 completed their development (with the concomitant completion of cell division). (iii) Cells initially in intermediate stages of membranelle differentiation (early stage 4) developed to some extent at 12 C, and then underwent resorpton of oral primordia and blockage of cell division; at 15 C such cells completed their development and division normally. (iv) Cells in which the membranelles and undulating membrane were complete or nearly so (stage 5 and very late stage 4) at the time of the beginning of the cold treatment subsequently finished their development and went thru cell division, even at temperatures as low as 5 C. These results indicate that in addition to a “stabilization point” which occurs shortly before the completion of membranelle development, there is an earlier change in the primordium at the time of the onset of membranelle development, which renders development much less sensitive to direct interference by low temperature.     

Coated Vesicles from the Protozoan Parasite Trypanosoma brucei: Purification and Characterization

ABSTRACT. A procedure was developed to purify a coated vesicle fraction from the protozoan parasite Trypanosoma brucei. Electron microscopy revealed a difference between T. brucei coated vesicles and clathrin-coated vesicles from other eukaryotes: trypanosome vesicles were larger (100 to ISO nm in diameter) and contained an inner coat of electron-dense material in addition to the external coat. Evidence suggests that the internal coat is the parasite's variant surface glycoprotein (VSG) coat. The SDS-PAGE analysis shows the major protein of T. brucei coated vesicles has a molecular mass of 61 kD, similar to VSG; this protein was recognized in an immunoblot by anti-VSG serum. Trypanosome coated vesicles also contain a protein which comigrates with the major protein (clathrin) of coated vesicles purified from rat brains. However, this protein is a minor component and it is not serologically cross-reactive with mammalian clathrin. Immunoblot analysis demonstrated that the parasite vesicles contained host IgG, IgM, and serum albumin.     

The Effect of Temperature on Photosynthesis and Carbon Fluxes in Sunflower and Rape

Sunflower (Helianthus annuusL.) and oilseed rape (Brassica napusL.) were grown at constant temperatures of 30 ?C (warm) and13 ?C (cold). Maximal rates of photosynthesis between 5 ?C and35 ?C were at higher temperatures in sunflower than rape. Photosyntheticrate over 4 h at the growth temperature declined in warm-andcold-grown rape and cold-grown sunflower, but remained constantin warm-grown sunflower. The stimulation of photosynthesis by2.0 kPa O₂ compared to 21 kPa O₂ declined with decreasing temperature.At 10 ?C in warm-grown rape photosynthesis was insensitive to2.0 kPa O₂. However, sensitivity to low O₂ continued at 10 ?Cin warm-grown sunflower. Carbohydrates accumulated in the cold,particularly fructose, glucose and sucrose in warm-grown sunflowertransferred to 13 ?C. By monitoring changes of ¹⁴C in leaves after the assimilationof ¹⁴CO₂, the rates of carbon export from leaves, pool sizesand carbon fluxes between them were estimated. The transferof warm- and cold-grown rape to 13 ?C and 30 ?C, respectively,had little effect on these parameters over 22 h. However, exportof carbon from sunflower leaves at 13 ?C was markedly less thanat 30 ?C, irrespective of the growth temperature, due to slowerexport from the transport pool. The rapid suppression of carbonexport at 13 ?C in warm-grown sunflower may be due to inhibitedtranslocation rather than reduced sink demand in the cold. It is concluded that assimilate utilisation is more depressedin the cold than is photosynthesis; this imposes a greater restrictionon biomass production in sunflower than in rape. Key words: Sunflower, rape, temperature, photosynthesis, carbon fluxes