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.     

PHYSIOLOGICAL AND ENVIRONMENTAL CONTROL OF GERMINATION IN SCRIPPSIELLA TROCHOIDEA (DINOPHYCEAE) RESTING CYSTS1

The effects of aging, temperature, and growth medium on germination in culture-produced resting cysts of the marine dinoflagellate Scrippsiella trochoidea (Stein) Loeblich are examined. Cysts undergo a mandatory period of dormancy lasting approximately 25 days, during which germination does not occur. The duration of this period is not affected by temperature. Once the dormancy period is completed, germination is regulated by external factors. Cysts germinate optimally in nutrient replete medium at temperatures greater than approximately 14°C. At lower temperatures or in nutrient-depleted media germination rate is dramatically slowed, although the final germination frequency appears unchanged. The large Q₁₀ of this temperature effect (ca. 11) suggests that the reduction in germination rate at lower temperatures is not merely the reflection of generally reduced metabolic rates, but rather the result of a temperature response specific to germination. At the highest temperatures tested (22-25°C), germination rate remains maximal although vegetative growth is greatly reduced. A shift in temperature or nutrient conditions, per se, is not necessary for germination. The relatively short dormancy period combined with the absence of a requirement for a dramatic shift in environmental conditions could facilitate rapid cycling between resting and vegetative stages in natural S. trochoidea populations. At the same time, the dramatic reduction in germination rate at low temperatures would permit cysts of this species to serve as overwintering cells as well.     

PHYSIOLOGICAL AND ENVIRONMENTAL CONTROL OF GERMINATION IN SCRIPPSIELLA TROCHOIDEA (DINOPHYCEAE) RESTING CYSTS1

The effects of aging, temperature, and growth medium on germination in culture-produced resting cysts of the marine dinoflagellate Scrippsiella trochoidea (Stein) Loeblich ore examined. Cysts undergo a mandatory period of dormancy lasting approximately 25 days, during which germination does not occur. The duration of this period is not affected by temperature. Once the dormancy period is completed, germination is regulated by external factors. Cysts germinate optimally in nutrient replete medium at temperatures greater than approximately 14° C. At lower temperatures or in nutrient-depleted media germination rate is dramatically slowed, although the final germination frequency appears unchanged. The large Q₁₀ of this temperature effect (ca. 11) suggests that the reduction in germination rate at lower temperatures is not merely the reflection of generally reduced metabolic rates, but rather the result of a temperature response specific to germination. At the highest temperatures tested (22–25° C), germination rate remains maximal although vegetative growth is greatly reduced. A shift in temperature or nutrient conditions, per se, is not necessary for germination. The relatively short dormancy period combined with the absence of a requirement for a dramatic shift in environmental conditions could facilitate rapid cycling between resting and vegetative stages in natural S. trochoidea populations. At the same time, the dramatic reduction in germination rate at low temperatures would permit cysts of this species to serve as overwintering cells as well.     

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.     

THE ASSOCIATION OF ROSETTE AND GLOBULE TERMINAL COMPLEXES WITH CELLULOSE MICROFIBRIL ASSEMBLY IN NITELLA TRANSLUCENS VAR. AXILLARIS (CHAROPHYCEAE)1,2

A freeze-fracture investigation of the putative cellulose synthesizing complex (terminal complex) morphology in Nitella translucens var. axillaris (A. Br.) R.D.W. internodal cells revealed single solitary EF globules and PF rosettes on the plasma membrane. The average density of rosettes in elongating internodal cells was 5.6 μm^?2 with slight spatial variation observed. In only three other algal genera (all zygnematalean) have rosette / globule terminal complexes been observed, while this characteristic is common to all vascular plants and one moss thus far investigated. This evidence strongly suggests that the rosette type of terminal complex morphology is an additional characteristic of charophycean algae and lends further support to the hypothesis that this group of algae represents the evolutionary line that gave rise to vascular plants. Observations were also made from the freeze-fracture of Nitella internodal cells concerning the orientation of cell wall microfibrils and cytoskeletal elements near the plasma membrane. The pattern of microfibril orientation in growing internodal cells is initially transverse to the cell long axis, becoming progressively axial presumably due to the strain of elongation. In mature internodal cells, the pattern of microfibril orientation is helicoidal. Microtubules appressed to the inner surface of the plasma membrane are oriented parallel to the most recently formed microfibrils in elongating and mature internodal cells.     

CHLORTETRACYCLINE-INDUCED FORMATION OF WALL APPOSITIONS (CALLOSE PLUGS) IN INTERNODAL CELLS OF NITELLA FLEXILIS (CHARACEAE)1

The formation of chlortetracycline (CTC)-induced wall appositions or plugs in internodal cells of Nitella flexilis (L.) Ag. was studied with light, fluorescence and electron microscopy. These plugs contain callose and pectin. A few minutes after CTC addition plug formation starts by fusion of polysaccharide-containing vesicles (glycosomes) with the plasmalemma. Plug growth is continued by incorporation of glycosome-endoplasmic reticulum (ER) complexes. The cytoplasm near the plug appears dense because of the accumulation of glycosomes and the increased electron density of plasma matrix and organelles. About 1 h after CTC addition plug growth ceases, the cytoplasm recovers to its pretreatment appearance, and a few glycosomes fuse singly with the plug membrane. Crystalline inclusions which consist of hexagonally packed rods are found near the plug. Coated vesicles and coated pits are clearly seen only in very early and late stages of plug formation. Callose is also found in parts of wound plugs produced after mechanical injury. No callose is present in the underlying, highly ordered wound wall. The failure to produce a wound wall beneath CTC-induced plugs appears to be related to the lower number of coated vesicles during plug formation. The possible significance of the partially coated reticulum in plug and wound wall formation is discussed.     

马铃薯晚疫病菌卵孢子萌发的初步研究

描述了马铃薯晚疫病菌卵孢子萌发的方式并研究了菌株组合、卵孢子形成时间、在琼脂培养基上培养时间及光照对卵孢子萌发的影响,结果表明不同菌株组合卵孢子萌发率为0—7.2%,对峙培养20天后形成的卵孢子的萌发率最高达8.7%,在琼脂培养基上培养25-30d 萌发率最高达11.4%,卵孢子形成时黑暗及在琼脂培养基上萌发时光照萌发率最高达11.8%。     

致病疫霉在中国云南的马铃薯田间形成卵孢子*

由致病疫霉Phytophthora infestans (Mont.)de Bary引起的马铃薯和番茄晚疫病是世界性的作物病害,每年均造成巨大的经济损失和社会影响。致病疫霉是异宗配合的卵菌,有两个已知交配型A1和A2,两个相对交配型互作时可进行有性生殖产生卵孢子( Gallegly & Galindo,1958)。过去许多年一直认为致病疫霉在除墨西哥以外的国家中只存在A1交配型,通过产生孢子囊进行无性繁殖。近年来,由于致病疫霉新致病群体的产生以及全球范围的迁移和替代,A2交配型菌株先后在欧洲、美洲、亚洲和非洲的许多国家被发现。A1、A2两种交配型菌株的同时存在,增…     

AUTOINHIBITION OF SPORE GERMINATION IN NOSTOC SPONGIAEFORME (CYANOPHYCEAE)1

Medium in which cultures of Nostoc spongiaeforme Ag. have sporulated contains one or more substances which inhbit the germination of spores (akinetes) of this organism. Germination of spores occurs rapidly in the absence of these substances, but is virtually completely suppressed in their presence.     

散枝猪毛菜的种子多型性及其萌发行为

散枝猪毛菜(Salsola bracchita)主要分布于新疆准噶尔荒漠,具有很强的抗干旱和抗盐碱能力。该文对散枝猪毛菜的果实进行了观察,表明散枝猪毛菜具有4种类型的散布单位和果实,这4种果实在形状、大小、颜色和着生方式上均有显著差异。A型果实绿色、球形、大,着生方式为横生,宿存花被革质,背部有紫红色翅状附属物,直径为(2.161±0.138) mm,单粒重为(3.810±0.113) mg;B型果实绿色、大、扁平、长圆形,着生方式为直立,宿存花被革质,背部有翅状附属物,长为(2.062±0.188) mm,宽为(1.720±0.148) mm,单粒重为(2.665±0.113) mg;C型果实绿色、大、扁平、长圆形,着生方式为直立,宿存花被膜质,背部无翅状附属物,长为(2.239±0.277) mm,宽为(1.844±0.150) mm,单粒重为(2.723±0.559) mg;D型果实黄色、小、扁平、长卵形,着生方式为直立,宿存花被膜质,背部无翅状附属物,长为(1.678±0.163) mm,宽为(1.390±0.110) mm,单粒重为(0.928±0.025) mg。A型、B型和C型种子(果实)在5 ℃/15 ℃、5 ℃/25 ℃、15 ℃/25 ℃(暗12 h/光12 h)变温条件下萌发率>68%,且B型和C型种子比A型种子有较高的萌发率和萌发速率。D型种子在3种变温条件下萌发缓慢,最终萌发率始终维持在较低水平(<20%),划破果皮和种皮能够显著提高D型种子的萌发率和萌发指数,表明D型种子处于生理休眠状态。散枝猪毛菜的种子多型性是对荒漠异质环境的一种适应。     

ENVIRONMENTAL AND ENDOGENOUS REGULATION OF CYST GERMINATION IN TWO FRESHWATER DINOFLAGELLATES

The role of excystment in relation to seasonal succession was investigated in two freshwater dinoflagellates, Ceratium hirundinella (O.F. Müller) Dujardin and Peridinium aciculiferum (Lemmermann). Field studies and laboratory experiments were performed to determine which factors regulate the timing of cyst germination. Environmental factors (temperature, light, nutrients, and anoxia) and endogenous factors (maturation period and biological clock) were investigated. Our main results indicate that temperature and internal maturation period determine when germination can occur. C. hirundinella had a maturation period of 4.5 months and germinated in the laboratory and in the field at temperatures above 6° C. P. aciculiferum had a maturation period of 2.5 months and germinated in the laboratory and in the field at temperatures below 7° C. In addition, our results indicated that both species were regulated by a biological clock. Furthermore, anoxia prevented the germination of C. hirundinella, contrary to results in earlier studies. To conclude, we could explain the appearance in plankton of the two dinoflagellate species through two main factors regulating excystment, that is, temperature and maturation period.     

PHYSIOLOGICAL CHANGES DURING GERMINATION OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AKINETES1

Akinetes of Pithophora oedogonia (Mont.) Wittrock, formed in stationary phase cultures, were induced to germinate by transfer to fresh media. Changes in various physiological parameters were monitored during the first 20 d of germination. Ungerminated akinetes contained a greater percentage of lipid, starch, and dry matter and exhibited lower photosynthetic rates than did vegetative cells. Germination consisted of four phases. Phase I (day-0 to day-1) was marked by a rapid increase in respiratory rates. Phase II (day-2 to day-6) involved protrusion of the germination tube and was insensitive to cyanide, a respiratory inhibitor, and simazine, a photosynthetic inhibitor. Phase III (day-7 to day-14) was marked by rapid elongation of the germination tube, increasing photosynthetic rate, increasing chlorophyll and water content and declining levels of lipid and starch. Germination tube elongation during phase III was not inhibited by simazine, but was cyanide sensitive. Phase IV (day-15 to day-20) was characterized by a reduction in respiratory rate and an abrupt increase in the ratio of photosynthesis to respiration. Germination tube elongation during phase IV was inhibited by simazine. The data indicate that germination in Pithophora oedogonia akinetes consists of an extensive period (phases I, II and III) during which reserve materials are respired. Utilization of internal food reserves apparently permits akinetes to germinate and supports the initial growth of the germination tube in light limited microenvironments.     

LIGHT REQUIREMENTS FOR MONOSPORE GERMINATION IN BANGIA ATROPURPUREA (RHODOPHYTA)1

Monospore germination, in Bangia atropurpurea (Roth) C. Ag. [= B. fuscopurpurea (Dillw.) Lyngb.] is light-dependent. In white light, the percent germination increases with increasing photon fluence rate until the response is saturated at 35 μmol · m^?2· s^?1. At a saturating photon fluence rate in an 18:6 h L:D cycle, 9 days are required for maximum germination. Green light is the most effective spectral region for monospore germination, although the process can occur in red and blue light if sufficiently high photon fluence rates are provided. Monospore germination and photosynthetic oxygen evolution are completely inhibited by DCMU at a concentration of 1 × 10^?6 M. Germination is reduced in a low CO₂ atmosphere and does not occur in the dark when glucose, maltose or inositol are supplied. It is concluded that photosynthesis is required for monospore germination.     

AKINETE GERMINATION IN ANABAENA CIRCINALIS (CYANOPHTA)

Akinetes of a clonal culture of Anabaena circinalis Rabenhorst from Mt. Bold reservoir (eutrophic), South Australia, were isolated and the effects of light, phosphorus, and nitrogen availability on their germination were investigated. Light was required but there was no significant difference in percentage of germination after 72 h if akinetes were incubated in ASM-1 medium at irradiances of 15, 30, or 50 μmol.m^-2.s^-1. Maximum akinete germination occurred by 48 h. Nitrogen was not required, as 88% of akinetes germinated in the flasks without combined nitrogen added to the medium and without N₂ in the air. NH₄⁺-N at 28 mg N.L^-1 completely suppressed germination, whereas 28 mg NO₃ N.L^-1 had no effect relative to the controls without nitrogen. Phosphorus was required, and at 48 h percentage of germination in the flasks with 0.6 mg P.L^-1 added (78%) was significantly greater than in the flasks with 0.06 P.L^-1 (58%) and 0 mgP.L^-1 (24%) added. Germlings in the 0 mg P.L^-1 flasks were only 2–4 cells long and stunted in appearance, whereas germlings at all other P concentrations were 8–16 cells long. It is likely that the isolation process exposed some akinetes to intracellular phosphorus released from lysing vegetative cells, but this was insufficient to allow normal development in the 0 mg P.L^-1 flasks. The plot of percentage of germination vs. initial phosphorus concentration, in the medium showed a relationship analogous to Michaelis-Menten nutrient uptake kinetics, suggesting that a specific membrane-bound enzyme system(s) is involved, with phosphorus as the substrate. The half saturation value (K_S) for germination was 50 μg P.L^-1.     

BIOCHEMICAL COMPOSITION AND METABOLIC ACTIVITY OF SCRIPPSIELLA TROCHOIDEA (DINOPHYCEAE) RESTING CYSTS1

The composition and metabolic activity of cysts of the marine dinoflagellate Scrippsiella trochoidea (Stein) Loeblich were examined during dormancy, quiescence, and germination. On a per cell basis, newly formed cysts contained an order of magnitude more carbohydrate but significantly less protein and chlorophyll a than did exponentially growing vegetative cells. Loss of lipid and carbohydrate from cysts during the initial dormancy period reflected a respiration rate estimated to be 10% of the respiratory activity in vegetative cells. Among older, quiescent cysts the calculated respiration rate decreased further to approximately 1.5% of the vegetative rate and appeared to proceed largely at the expense of carbohydrate reserves. These estimated rates of respiration were in good agreement with direct measurements of cyst oxygen consumption. The transfer of quiescent cysts to conditions permissive for germination resulted in a rapid increase in respiration rate, as evidenced by carbohydrate loss and O₂ consumption. The increased respiratory activity was followed by an increase in protein content and, later, by an increase in chlorophyll a content and photosynthetic capacity. Just prior to germination the P/R ratio became greater than 1, and the estimated chlorophyll-specific photosynthetic activity reached 75% of the rate in vegetative cells. Complete restoration of photosynthetic and respiratory capacity apparently was not achieved until after excystment. These data confirm the common assumption that dinoflagellate cysts represent true “resting” cells, containing extensive energy reserves and displaying greatly reduced metabolic activity.     

DISTRIBUTION OF THE XANTHOPHYLL LOROXANTHIN IN DESMIDS (CHAROPHYCEAE,CHLOROPHYTA)1

Forty-seven species of desmids, representing all four families, were examined for the presence of the xanthophyll loroxanthin by reverse-phase high-performance liquid chromatography. In the Desmidiaceae 28 of the 35 species examined possessed loroxanthin, and in the Mesotaeniaceae two of the six examined had loroxanthin present. All six species of the families Peniaceae and Closteriaceae examined possessed loroxanthin. Although the distribution of loroxanthin appears to be disjunct in the desmids and does not have strict taxonomic significance, it does follow a coherent pattern consistent with current ideas on desmid phylogeny. This pattern suggests that loroxanthin synthesis probably evolved once in the desmid lineage, with one or more subsequent reversals.     

Temperature mediates secondary dormancy in resting cysts of Pyrodinium bahamense (Dinophyceae)

High‐biomass blooms of the toxic dinoflagellate Pyrodinium bahamense occur most summers in Tampa Bay, Florida, USA, posing a recurring threat to ecosystem health. Like many dinoflagellates, P. bahamense forms immobile resting cysts that can be deposited on the seafloor—creating a seed bank that can retain the organism within the ecosystem and initiate future blooms when cysts germinate. In this study, we examined changes in the dormancy status of cysts collected from Tampa Bay and applied lessons from plant ecology to explore dormancy controls. Pyrodinium bahamense cysts incubated immediately after field collection displayed a seasonal pattern in dormancy and germination that matched the pattern of cell abundance in the water column. Newly deposited (surface) cysts and older (buried) cysts exhibited similar germination patterns, suggesting that a common mechanism regulates dormancy expression in new and mature cysts. Extended cool‐ and warm‐temperature conditioning of field‐collected cysts altered the cycle of dormancy compared with that of cysts in nature, with the duration of cool temperature exposure being the best predictor of when cysts emerged from dormancy. Extended warm conditioning, on the other hand, elicited a return to dormancy, or secondary dormancy, in nondormant cysts. These results directly demonstrate environmental induction of secondary dormancy in dinoflagellates—a mechanism common and thoroughly documented in higher plants with seasonal growth cycles. Our findings support the hypothesis that a seasonal cycle in cyst germination drives P. bahamense bloom periodicity in Tampa Bay and point to environmentally induced secondary dormancy as an important regulatory factor of that cycle.     

ENVIRONMENTAL CONTROL OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AKINETE GERMINATION1

Abundance of Pithophora oedogonia akinetes displayed seasonal changes, being greatest in winter and lowest in summer. Akinete abundance showed significant (P < 0.001) negative correlations with photoperiod(r = -0.53) and water temperature (r= -0.75) during the period February 1978 through June 1979. Experiments in which akinete germination was studied in response to manipulations of nutrients (NO₃-N and PO₄-P), photoperiod and temperature indicated that temperature was the primary factor regulating the timing of the vernal flush of akinete germination observed in Surrey Lake.     

THE ULTRASTRUCTURE OF MEIOSPORES OF COLEOCHAETE PULVINATA (CHAROPHYCEAE)1

In view of the relative importance of reproductive cell ultrastructure in phylogenetic and systematic studies of green algae, we investigated the fine structure of germinating zygotes and meiospores of Coleochaete pulvinata Braun. Meiospores have a flagellar apparatus very similar to that of zoospores and spermatozoids of the same species. Meiospores differ from zoospores and spermatozoids of C. pulvinata in having pyramidal body scales similar to those present on zoospores of C. scutata. Meiospores of C. pulvinata had as many as twice the number of spline microtubules as zoospores, and four times the number present in splines of spermatozoids of the same species. Developing meiospores of C.pulvinata, like those of other Coleochaete species, are individually surrounded by chamber walls. These differed from vegetative cell walls in lacking plasmodesmata. Moreover, the chamber walls in germinating zygotes of C.pulvinata stained a cobalt blue color with resorcinal blue, and fluoresced yellow in the presence of aniline blue, thus exhibiting the staining characteristics of callose. In location, morphology and presence of callose, chamberwalls resemble “special walls” of land plants, they may represent a charophycean spore development preadaptation useful in the evolution of walled spores characteristic of land