Sperm cell surface characteristics of Plumbago zeylanica L. in relation to transport in the embryo sac

Myosin associated with the male germ cells of angiosperms interacts with actin, promoting transport of the non-motile generative and later sperm cells in the pollen tube. Myosin localizing on the sperm cell plasma membrane seems negligible in Plumbago, as reflected by the absence of: (i) anti-myosin labeling using immunoelectron microscopy, (ii) sperm motility on actin matrices, and (iii) electrophoretic movement changes after addition of antibody. Sperm cells injected directly into actively streaming Nitella internodal cells, however, follow actin bundles and their movement is sensitive to ATP and Mg²⁺. This may be based on simple charge binding since negatively charged latex beads also migrate on actin, whereas neutral or positively-charged latex beads do not. Sperm cells are negatively charged according to capillary microelectrophoresis, whereas killed sperm cells, which are positively charged do not migrate. The sperm cell that normally fertilizes the egg has a higher calculated charge (8.277 × 10³ esu/cm²) compared with the sperm cell that fuses with the central cell (6.120 × 10³ esu/cm²). Received: 15 December 1998 / Accepted: 21 January 1999     

PH-DEPENDENCE OF CHLORTETRACYCLINE(CTC)-INDUCED PLUG FORMATION IN NITELLA FLEXILIS (CHARACEAE)1

The formation of chlortetracycline(CTC)-induced wall appositions (callose plugs) in Nitella flexilis (L.)Ag. was pH-dependent in the range between 4.3-8.3. Plug number and plug diameter increased with the pH of the CTC solution. At pH 4.3 plug formation was light-dependent and occurred below the alkaline regions of the cell surface which form during photo synthetic assimilation of HCO₃^?. Inhibition of photosynthesis by 3–(3′,4′-dichlorophenyl)-1, 1-dimethylurea prevented plug formation in the light. Dark-treated cells could be induced to form plugs by raising the pH of the CTC solution. The formation of large but incomplete plugs in the presence of cytochalasin B is explained by the formation of numerous weak alkaline sites. I suggest that CTC enhances locally the Ca²⁺content at the cytoplasm near the plasmamembrane. The ionophoric character of CTC is probably more pronounced at high pH mainly because of a weaker binding with cations and a closer contact with the membrane.     

A thermodynamic study of Cu++−Zn++ ion exchange in theNitella flexilis cell wall

Summary Exchange isotherms of Cu²⁺ vs Zn²⁺-ions were performed on the cell wall of a fresh water alga,Nitella flexilis. The relevant thermodynamic parameters are calculated. The cell wall absorbs copper selectively. The selectivity is explained by a stronger chelation of the cupric ion, due to the Jahn-Teller effect. The wall acts like a two-site model, based on the nature of the ligands: a first group of aminesites reacts exothermically and a second of hydroxylic-carboxylic sites of lower affinity, reacts endothermically.     

Evolution of temperature responses in the Cladophora vagabunda complex and the C. albida/sericea complex (Chlorophyta)

Differentiation in temperature responses (survival and growth) was investigated among isolates of two tropical to temperate green algal lineages: the Cladophora vagabunda complex and the C. albida/sericea complex. The results were analysed in relation to published data on 18S rRNA and ITS sequence divergence, which have shown that the overall degree of genetic divergence is similar in the two lineages but that very different patterns of radiation have occurred. In the C. vagabunda complex, the two main clades in the well-resolved phylogenetic tree differed mainly in their tolerance to low temperatures. Within-clade variation was no stronger in the Atlantic/Pacific than in the all-Pacific clade. In the C. albida/sericea complex, six distinctive ITS types indicated early radiation. Although distinctive differences were found between some of these types, the thermal responses of others were very similar, indicating physiological stasis. In both lineages there was evidence for some adaptation to local temperature regimes but phylogenetic constraints were generally more important. Isolates with the same ITS sequences showed similar temperature responses even though collected from different climate zones. Evidence was found for a physiological trade-off between growth at high and at low temperatures in the C. albida/sericea complex, whereas, in the C. vagabunda complex, one clade showed more eurythermal growth responses than the other. In the C. vagabunda complex, which is the ancestral lineage of the C. albida/sericea complex, major differentiation was found in cold tolerance but not in heat tolerance, whereas the reverse pattern was found in the derived C. albida/sericea complex. These findings suggest that an acquisition of cold tolerance preceded the loss of heat tolerance during adaptation to colder climates.     

Rapid method to obtain high quality nuclear and chromosome images directly from living cells in the Characeae

This study focused on a method based on the capacity of cationic dyes to stain only the nucleus and chromosomes in cells subjected to either acid or alkaline hydrolysis. The method and the squash were optimized for the Characeae and were described in detail. Nuclei from vegetative shoot apices and antheridial filament cells of unfixed, fixed and herbarium material of Nitella opaca were investigated using the Azure A or Toulidine Blue stains. Comparisons with some other staining methods, used in the previous studies, were also reported. The Azure A/Toulidine Blue method is useful to obtain clear images of chromosome morphology comparable or higher to that obtained with Feulgen or Aceto‐Orcein. It requires little time and a less complicated procedure in comparison with other staining methods.     

Gravity perception requires statoliths settled on specific plasma membrane areas in characean rhizoids and protonemata

Summary. The noninvasive infrared laser micromanipulation technique (optical tweezers, optical trapping) and centrifugation were used to study susception and perception, the early events in the gravitropic pathway of tip-growing characean rhizoids and protonemata. Reorientation of the growth direction in both cell types was only initiated when at least 2–3 statoliths settled on specific areas of the plasma membrane. This statolith-sensitive plasma membrane area is confined to the statolith region (10–35 μm behind the tip) in positively gravitropic rhizoids, whereas in negatively gravitropic protonemata, this area is limited to the apical plasma membrane (0–10 μm). Statolith sedimentation towards the sensitive plasma membrane areas is mediated by the concerted action of actin and gravity. The process of sedimentation, the pure physical movement, of statoliths is not sufficient to initiate graviresponses in both cell types. It is concluded that specific statolith-sensitive plasma membrane areas play a crucial role in the signal transduction pathway of gravitropism. These areas may represent the primary sites for gravity perception and may transform the information derived from the gravity-induced statolith sedimentation into physiological signals which trigger the molecular mechanisms of the opposite graviresponses in characean rhizoids and protonemata. Received September 10, 2001 Accepted November 16, 2001     

TAXONOMIC REEXAMINATION OF 17 SPECIES OF NITELLA SUBGENUS TIEFFALLENIA (CHARALES,CHAROPHYCEAE) BASED ON INTERNAL MORPHOLOGY OF THE OOSPORE WALL AND MULTIPLE DNA MARKER SEQUENCES1

In an attempt to reconstruct the natural taxonomic system for Nitella, 17 species of Nitella subgenus Tieffallenia were reexamined using SEM observations of the internal morphology of the oospore wall (IMOW) and phylogenetic analyses of 4553 base pairs from multiple DNA markers (atpB, rbcL, psaB, and ITS‐5.8S rRNA genes). Our SEM observations identified three types of IMOW: homogeneous (HG), weakly spongy (W‐SG), and strongly spongy (S‐SG) types. Based on differences in the IMOW, species with reticulate or tuberculate oospore wall ornamentation in the external morphology of the oospore wall (EMOW) were subdivided into two distinct groups (characterized by the HG or S‐SG types of IMOW, respectively), which were robustly separated from each other in our molecular phylogenetic analyses. In our molecular phylogeny, the subgenus Tieffallenia consisted of four robust monophyletic groups—three clades of the HG type and a spongy (S‐SG and W‐SG) type clade—that were characterized by differences in the IMOW and EMOW. In addition, our SEM observations and sequence data verified the distinct status of five species (N. japonica Allen, N. oligospira A. Braun, N. vieillardii stat. nov., N. imperialis stat. nov., and N. morongii Allen) that R. D. Wood had assigned as infraspecific taxa. Moreover, our SEM observations of the IMOW also suggested that N. megaspora (J. Groves) Sakayama originally identified by LM includes at least two distinct species, characterized by W‐SG and S‐SG types of IMOW, respectively.     

New finds of charophytes in Iceland with an update on the distribution of the charophyte flora

Charophyte species new to the flora of Iceland are reported and an update on the distribution of the previously known species is given. Four species are new to Iceland; Chara aspera Willdenow, Chara contraria Braun ex Kützing, Tolypella canadensis Sawa and Tolypella glomerata (Desvaux) Leonhardi, while four species were previously known: Chara globularis Thuiller, Chara virgata Kützing, Nitella flexilis (L.) Agardh and Nitella opaca (Agardh ex Bruzelius) Agardh. The finding of the species new to Iceland add to the hitherto known worldwide distribution of those species, including a significant extension to the north.     

ANNUAL GERMINATION WINFOW IN OOSPORES OF NITELLA FURCATA (CHAROPHYCEAE)1

Oospores of Nitella furcata subsp. megacarpa (Allen emend. Wood) were collected from an oospore bank in the sediments of Lake George, New York. Incubated at constant temperatures, all or nearly all of the oospores germinated when exposed to a brief pulse of red light when the annual window of germinability was open. The window seems related to the annual cycle of sediment temperatures. It is open in spring and closes wit the onset of a secondary dormacncy in the summer. Oospores in storage follow a parallel path if held at 18°C, a summer equivalent temperature; the window remains open indefinitely if the oospores are held at 4°C. Attention is drawn to the similarity if the cyclic window of germinability in seeds of summer annuals and oospores of N. furcata.     

Cytoskeletal 10 nm filaments in cells of the algal phyla Chlorophyta,Charophyta, and Chrysophyta and their developmentally regulated and species-specific association with prosomes

Summary.  10 nm diameter filaments were observed in whole-mount preparations of algae of diverse phyla: Acetabularia acetabulum and A. major (Chlorophyta), Chara australis and Nitella flexilis (Charophyta), and Poterioochromonas malhamensis (Chrysophyta). A polyclonal antibody raised against a basic, 50 kDa DNA-binding protein of A. acetabulum stains the filaments of A. acetabulum and A. major as well as of C. australis and N. flexilis. While in the perinuclear region of A. acetabulum and A. major and throughout the cytoplasm of P. malhamensis the 10 nm filaments have a smooth appearance, in the stalk of A. acetabulum and A. major they are densely covered by globular structures; in C. australis and N. flexilis they are less frequently associated with such material. The morphology of a part of the globular particles is quite reminiscent of prosomes. A monoclonal antibody elicited against prosomes isolated from A. acetabulum indeed decorates the globular particles on the A. acetabulum and A. major filaments. The possible role of these filament-particle associations is discussed. Received August 10, 2001; accepted October 30, 2002; published online April 8, 2003 RID="*" ID="*" Correspondence and reprints: Max-Planck-Institut für Zellbiologie, 68526 Ladenburg, Federal Republic of Germany. E-mail: sberger@zellbio.mpg.de RID="**" ID="**" Present address: Long Island University, Southampton, New York, U.S.A. RID="+" ID="+" Present address: Leica Microsystems Wetzlar GmbH, Wetzlar, Federal Republic of Germany