THE FLAGELLAR APPARATUS OF HYMENOMONAS CORONATA (PRYMNESIOPHYTA)1

The ultrastructure of Hymenomonas coronata Mills was reinvestigated to determine the microarchitecture of the flagellar apparatus. Cell morphology and flagellar apparatus structure are very similar to those of Pleurochrysis. Some important variations occur. First, a crystalline root (= compound root) is absent on microtubular root 1. Second, a two-stranded microtubular root emanates at a right angle from microtubular root 2. Third, a fibrous root emanates from the dorsal region between the basal bodies and extends to the cell's right, paralleling microtubular root 3. These similarities and variations in flagellar apparatus characters are discussed in reference to known variations in the Prymnesiophyta.     

CARBONIC ANHYDRASE AND CARBON FIXATION IN COCCOLITHOPHORIDS1

Rates of carbon fixation in coccolithophorids in culture, unlike many other algae, are carbon limited at ambient levels of dissolved inorganic carbon (DIC). Apparently, plants often rely on activity of carbonic anhydrase (CA) to raise the level of CO₂ in cells and achieve carbon saturation. However, CA activities in the coccolithophorids, Coccolithus (= Emiliania) huxleyi Lohmann and Hymenomonas (=Cricosphaera) carterae Braarud, were either not detectable or very low compared to activities in other systems, including other algae, higher plants, and representative animals. Furthermore, additions of CA to medium with 2 mM DIC at pH 8.1 resulted in nearly 30% enhancement of photosynthesis, but not coccolith formation. Although carbon fixation in coccolithophorids can be suppressed by the CA inhibitor acetazolamide, studies of CaCO₃ nucleation revealed a non-specific effect of the inhibitor. Using a 30 min assay based on pH decreases accompanying loss of dissolved. CO₃^2-, inhibition of crystal formation in the absence of CA at 1 mM acetazolamide was demonstrated for decalcified crab carapace, a tissue with which normal CaCo₃ deposition in vitro has been shown. The results suggest only a minor role for CA in coccolithophorids.     

卡氏膜球藻鞭毛伸缩节律的研究

卡氏膜球藻（Ｈｙｍｅｎｏｍｏｎａｓｃａｒｔｅｒａｅ）是一种单细胞海藻,细胞圆球形,表面覆盖一层球形石（Ｃｏｃｃｏｌｉｔｈｓ）。两条鞭毛稍不等长,着生于细胞前端,鞭毛长约为细胞直径的１．５倍。在２５±℃,光照强度２０００ｌｘ,光暗时间比１４：１０小时条件下,用ＭＥＳⅢ培养基培养卡氏膜球藻,发现细胞在光照条件下伸出鞭毛,活跃游动;在黑暗条件下缩回鞭毛,沉于培养瓶底。进一步试验证明：１．光刺激细胞伸出鞭毛,黑暗刺激细胞缩回鞭毛。２．鞭毛的伸缩与培养中的光暗周期变化严格对应,即光周期开始后２０分钟,细胞开始伸出鞭毛;暗周期一开始,鞭毛就向细胞内收缩。３．在连续光照条件下,鞭毛的周期性伸缩现象消失。所以,卡氏膜球藻鞭毛周期性伸缩是一种受光暗周期调节的外源节律。这种鞭毛伸缩的节律现象在藻类是第一次报道。     

CELL DIVISION PERIODICITY IN 13 SPECIES OF MARINE PHYTOPLANKTON ON A LIGHT: DARK CYCLE1

The division rates of 26 clonal cultures representing 13 species of planktonic marine algae (6 diatoms, 2 flagellated chrysophytes, 2 coccolithophores, 1 cryptomonad flagellate, I dinoflagellate, 1 green alga) were determined every 2 h for 48 h during exponential growth on a 14:10 LD cycle in nutrient-replete batch culture. Cyclic oscillations in the division rate were detectable in 22 of these clones. Of 14 diatom clones examined, four displayed nearly constant division rates throughout the LD cycle and ten showed strong periodicity favoring division during the light periods. In contrast, all other algae (12 clones) exhibited division rate maxima during periods of darkness, and clearly detectable decreases in cell number for time intervals of 4–8 h during periods of illumination. Intraspecific differences in division periodicity were found among eight clones of the diatom Thalassiosira pseudonana (Hustedt) Hasle & Heimdal and six clones of the coccolithophore Emiliania huxleyi (Lohm.) Hay & Mohler.     

EFFECTS OF PHOTOCYCLES AND PERIODIC AMMONIUM SUPPLY ON THREE MARINE PHYTOPLANKTON SPECIES. I. CELL DIVISION PATTERNS1

Cell division patterns in Thalassiosira weissflogii (Grun.), Hymenomonas carterae (Braarud and Fagerl), and Amphidinium carteri (Hulburl) grown in cyclostat culture were analyzed as functions of the periodic supply of light and the limiting nutrient (ammonium) and of combinations of these two factors. In all three species, division patterns were phased by light/dark cycles in N–limited as well as N–replte conditions, and also to ammonium pulses in N–limited growth in continuous light. Both the degree and timing of the cell cycle phasing varied among species. When both stimuli were present, the influence of the photocycle overrode the N–pulse stimulus in H. carterae and A. carteri. while in T. weissflogii, division was always phased by the timing of the N–pulse regardless of the phase angle between the photocycle and the pulse.     

The Inverse Relationship Between Nutrient Nitrogen Concentration and Coccolith Calcification in Cultures of the Coccolithophorid Hymenomonas sp.*

SYNOPSIS Chemical analysis of axenic cultures of Hymenomonas sp. reveals that the degree of coccolith calcification is inversely proportional to the concentration of available nitrogen sources in the medium. This relationship makes possible a useful degree of control over the organism's calcifying activities. In addition, a possible selective advantage of such a relationship in nature is suggested.     

TRACE METAL REDUCTION BY PHYTOPLANKTON: THE ROLE OF PLASMALEMMA REDOX ENZYMES1,2

The phytoplankton cell surface reduces external copper(II) and iron(III) complexes and redox dyes. This reductive activity appears to be mediated by one or more plasmalemma redox enzymes. Trace metal complexes are directly reduced by the redox enzyme, therefore the reduction rate is not regulated by the metal free ion activity in solution. This is in direct contrast to previous measurements of trace metal interactions with the phytoplankton cell membrane. Half-saturation constants for the reduction of Cu(II) complexes with carbonate, phenanthroline and bathocuproinedisulfonate are in the range 2.3–14.7 μM, which suggests that trace metal complexes are not the main electron acceptor in natural waters. In the diatom Thalassiosira weissflogii there is additional reductive activity associated with the cell wall.     

EFFECTS OF PHOTOCYCLES AND PERIODIC AMMONIUM SUPPLY ON THREE MARINE PHYTOPLANKTON SPECIES. II. AMMONIUM UPTAKE AND ASSIMILATION1

The relative influence of the photoperiod and of periodic ammonium pulses in entraining the cell division cycle in nitrogen-limited cyclostat cultures differs dramatically in Hymenomonas carterae Braarud and Fagerl, Amphidinium carteri Hulburt and Thalassiosira weissflogii Grun. We examined how each species processes an NH₄⁺ pulse at various times during the cell cycle and the L/D cycle. Rates of NH₄⁺ uptake and changes in cellular concentrations of NH₄⁺, free amino acids, and protein were examined after the addition of an NH₄⁺ pulse. Depletion of NH₄⁺ from the medium occurred earlier when the pulse was given at the beginning of the light period than at the beginning of the dark period in H. carterae and A. carteri. Depletion took longer in the T. weissflogii cultures and the kinetics were similar during both stages of the photocycle in this species. Similarly, the temporal phasing and maximum pool sizes varied with timing of the NH₄⁺ pulse in H. carterae and A. carteri but complete assimilation was relatively rapid. More persistent pools of NH₄⁺ and free amino acids accumulated in T. weissflogii, and the patterns of assimilation varied little as a function of the timing of the pulse with respect to the photocycle. Although nitrogen metabolism occurred rapidly in nitrogen-limited H. carterae and A. carteri, the entrainment of the cell division cycle by the photoperiod resulted in a large degree of uncoupling between completion of nitrogen assimilation and cell division. It is hypothesized that the strong entrainment of the cell division cycle of T. weissflogii by NH₄⁺ pulses results from a relatively slow rate of nitrogen metabolism.