Zellteilung und Bildung von Innenschalen beiHantzschia amphioxys undAchnanthes coarctata

Before cytokinesis, the identically constructed chromatophores ofHantzschia amphioxys andAchnanthes coarctata are transformed into less effigurated bodies. In normal cytokinesis, the course of mitosis, chromatophore division, and cleavage furrowing are exactly synchronized. The division of the chromatophore appears as a passive process, i.e. intersection by the cleavage furrow. In inequal cell divisions before the formation of inner valves cytokinesis can take place without chromatophore division. Once chromatophore division without mitosis and cytokinesis was observed. InHantzschia there are three types of inner valve formation, inAchnanthes coarctata only two. The inner valves develop under unfavorable growth conditions, the cells possessing them, however, are not resting spores as in some other diatoms. InHantzschia, auxospore formation is suppressed under the cultural conditions used, the cells multiply intensely without diminution.

     

VALVE MORPHOGENESIS AND THE MICROTUBULE CENTER IN THREE SPECIES OF THE DIATOM NITZSCHIA1

The relationship of cell organelles to valve morphogenesis was investigated in three species of Nitzschia. One, N. sigmoidea (Nitzsch) W. Sm., showed consistent ability to generate both nitzschioid and hantzschioid symmetry in daughter cells following cytokinesis; the other two maintained nitzschioid symmetry stably. From previous work with Hantzschia, a certain sequence of events could be anticipated in the cytoplasm. In two significant areas–the behavior of the Microtubule Center (MC) and its microtubule (MT) system, and the central origin of the silicalemma–not only were the results unexpected, but the three species showed fundamental differences among themselves. In N. sigmoidea, the silicalemma (and the future raphe region) arises centrally on the cleavage furrow, and after some lateral expansion, the silicalemmas and their associated organelles move in opposite directions in daughter cells, so that the raphe and the raphe canals end up along the girdle side of the cell as expected. However, the MCs never become associated with their silicalemma, remaining throughout near the girdle bands. In N. sigma (Kütz) W. Sm., the silicalemmas arise centrally and after lateral growth, move in opposite directions to generate nitzschioid symmetry. In this case, the MCs move to the vicinity of but never close to the silicalemmas, and follow them distantly during their lateral movement. In N. tryblionella Hantzsch, the new silicalemmas arise opposite one another, on one side of the daughter cells; each MC soon moves very close to its silicalemma, and remains thus through most of valve morphogenesis. Later, only one silicalemma/MC complex moves laterally, establishing the nitzschioid symmetry in both daughter cells. In all three species, as in Hantzschia, linear arrays of mitochondria aligned along MTs occupy the forming raphe canal, and microfilaments line the outer edge of the expanding silicalemma. The fibulae (the wall struts arching across the raphe canal) in Hantzschia always grow from the valve surface to the girdle surface of the forming valves. In these three Nitzschiae, this invariably happens in only one daughter cell of any pair; in the other, all the fibulae grow from the girdle surface to the valve surface. An explanation of these variations is proposed: that the morphogenetic machinery of Nitzschia and Hantzschia have a common origin, with present Nitzschiae having undergone considerable diversification at the intracellular level, causing the unstable cell symmetry exhibited by several modern species. Perhaps a taxonomic distinction between Hantzschia and Nitzschia lies in whether the morphogenetic machinery associated with valve morphogenesis moves laterally in the same or in opposite directions.     

SILICATE DEFICIENCY AND LIPID SYNTHESIS OF MARINE DIATOMS1,2

Lipid synthesis of three marine diatoms was studied with a ¹⁴CO₂ incorporation technique in silicate limited batch cultures. Growth rates were independent of the silicate concentration but the cellular yields were proportional to the initial amount of silicate. At the beginning of the stationary growth phase, lipid synthesis rates per unit culture volume increased by 1.7 times for Chaetoceros gracilis, 3.1 times for Hantzschia sp., and 2.8 times for Cyclotella sp., respectively compared to those during the exponential growth phase. Lipid carbon accounted for as much as 57% of the carbon in C. gracilis, 71% in Hantzschia sp., and 65% in Cyclotella sp., respectively. Additional enrichment with silicate during stationary growth phase allowed the cultures to grow further. Lipid synthesis rates were reduced during the subsequent growth phase, and the growth rates themselves were dependent on the level of biomass achieved during the previous stationary phase. However, the cellular yields were similar and probably controlled by light.     

菱板藻属（硅藻门）中国新纪录种

报道采自新疆及内蒙古地区的菱板藻属（硅藻门）中国新纪录植物7种,分别为丰富菱板藻（Hantzschia abundans Lange-Bertalot）、喜碱菱板藻（H.alkaliphila Lange-Bertalot）、巴克豪森菱板藻（H.barckhausenii Lange-Bertalot &; Metzeltin）、较长菱板藻（H.longa Lange-Bertalot）、仿密集菱板藻（H.paracompacta Lange-Bertalot）、美丽菱板藻（H.spectabilis(Ehrenberg) Hustedt）和近活跃菱板藻（H.subvivacior Lange-Bertalot）。对其分类学特征进行了详细的描述,并给出了光镜或扫描电镜照片以及生境特征等,为该属种类的世界地理分布提供新资料。     

NANOSTRUCTURE OF THE DIATOM FRUSTULE AS REVEALED BY ATOMIC FORCE AND SCANNING ELECTRON MICROSCOPY

The cell wall (frustule) of the freshwater diatom Pinnularia viridis (Nitzsch) Ehrenberg is composed of an assembly of highly silicified components and associated organic layers. We used atomic force microscopy (AFM) to investigate the nanostructure and relationship between the outermost surface organics and the siliceous frustule components of live diatoms under natural hydrated conditions. Contact mode AFM imaging revealed that the walls were coated in a thick mucilaginous material that was interrupted only in the vicinity of the raphe fissure. Analysis of this mucilage by force mode AFM demonstrated it to be a nonadhesive, soft, and compressible material. Application of greater force to the sample during repeated scanning enabled the mucilage to be swept from the hard underlying siliceous components and piled into columns on either side of the scan area by the scanning action of the tip. The mucilage columns remained intact for several hours without dissolving or settling back onto the cleaned valve surface, thereby revealing a cohesiveness that suggested a degree of cross-linking. The hard silicified surfaces of the diatom frustule appeared to be relatively smooth when living cells were imaged by AFM or when field-emission SEM was used to image chemically cleaned walls. AFM analysis of P. viridis frustules cleaved in cross-section revealed the nanostructure of the valve silica to be composed of a conglomerate of packed silica spheres that were 44.8 ± 0.7 nm in diameter. The silica spheres that comprised the girdle band biosilica were 40.3 ± 0.8 nm in diameter. Analysis of another heavily silicified diatom, Hantzschia amphioxys (Ehrenberg) Grunow, showed that the valve biosilica was composed of packed silica spheres that were 37.1 ± 1.4 nm and that silica particles from the girdle bands were 38.1 ± 0.5 nm. These results showed little variation in the size range of the silica particles within a particular frustule component (valve or girdle band), but there may be differences in particle size between these components within a diatom frustule and significant differences are found between species.