Photoregulated or energy dependent process of hormogonia differentiation in Nostoc sphaeroides Kutzing (Cyanobacterium)

Hormogonium, which was thought to play an important role in the dispersal and survival of these microorganisms in their natural habitats, is a distinguishable developmental stage of heterocystous cyanobacteria. The present study examined the effects of different light conditions and sugars on the differentiation of Nostoc sphaeroides Kutzing to the hormogonia stage. Results showed that differentiation of hormogonia was light dependent in the absence of sugar, but that close to 100% of cyanobacteria differentiated to hormogonia in the presence of glucose or sucrose, irrespective of the light conditions. This differentiation was inhibited, even in the presence of sugars, upon application of an inhibitor of respiration. Following the testing of different sugars, the effects of different lights were examined. It was found that 5 10 μ mol.m(-2)• s(-1) photon flux density was optimal for hormogonia differentiation. One hundred percent differentiation was obtained with white light irradiation, in contrast with irradiation with green light (80% differentiation) and red light (0-10% differentiation). Although they showed different efficiencies in inducing hormogonia differentiation in N. sphaeroides, the green and red radiation did not display antagonistic effects. When the additional aspect of time dependence was investigated through the application of different light radiations and an inhibitor of protein synthesis, it was found that the initial 6 h of the differentiation process was crucial for hormogonia differentiation. Taken together, these results show that hormogonia differentiation in N. sphaeroides is either a photoregulated or an energy dependent process.

Structure of the phytoplankton community and its relationship to water quality in Donghu Lake, Wuhan, China

The phytoplankton community structure, in terms of species composition, total standing crop, and abundance of the dominant algal species, at four stations in Donghu Lake, Wuhan, China, was investigated monthly from January 1994 to December 1996. A total of 260 taxa was observed, of which Chlorophyta (106 taxa) contributed the highest portion of the total number of taxa, followed by Bacillariophyta (82 taxa) and Cyanophyta (32 taxa). The total standing crop measured by means of chlorophyll a content, cell density, and cell biovolume, as well as the abundance of the dominant species, declined in the order of Station I to Station IV. Seasonal changes of the standing crop varied greatly among the four stations. Although the cell density at the four stations showed a single peak within a year, the peak density varied from July to November, dependent on the sampling year and the station. For chlorophyll a content and cell biovolume, multiple peaks were observed at Stations I and II, but a single peak was found at Stations III and IV. The phytoplankton community structure indicated that the trophic status was the highest at Station I (most eutrophic), followed by Station II; Stations III and IV were the least trophic areas. The long-term changes in phytoplankton community structure further suggested that changes in phytoplankton community structure were correlated with water quality, and eutrophication of Donghu Lake had been aggravated since the 1950s.

Predominant occurrence of apical cell divisions in Oedogoniam pakistanense and its phylogenetic significance

A rare terrestrial species, Oedogonium pakistanense, was first recorded from Hubei Province, south-central China. Morphological characters. including the predominant occurrence of apical cell division and unique lateral apical caps, are described. The growth of the filaments in O. pakistanense from China is usually the result of the repeated divisions of the apical cells and intercalary divisions are rare. It is suggested that this species may represent an evolutionary transition between Oedogonium and Oedocladium, the latter being a terrestrial genus with branched filaments and cell division more often terminal than intercalary.

Cloning and characterization of the gene for UDPGlc dehydrogenase from the cyanobacterium, Microcystis aeruginosa FACHB 905

Using degenerate primers based on conserved regions of the UDP-glucose dehydrogenase (UDPGDH) gene, an initial 476-bp DNA fragment was amplified from the water-bloom forming cyanobacterium, Microcystis aeruginosa FACHB 905. TAIL-PCR and ligation-mediated PCR were used to amplify the flanking regions to isolate an about 2.5-kb genomic DNA fragment. Sequence analysis revealed an ORF encoding a putative 462 amino acid protein, designated Mud for Microcystis UDPGDH. The Mud amino acid sequence is closely related to UDPGDH sequences from cyanobacterium Synechocystis PCC6803 (73% identity, 81% similarity), and bacterium Bacillus subtilis (51% identity and 67% similarity). The cloned mud gene was expressed in Escherichia coli using the pGEX-4T-1 fusion expression vector system to generate a GST-Mud fusion protein that exhibited UDPGDH activity. The cytosolic fraction of M aeruginosa FACHB 905 was subjected to Western analysis with an anti-Mud antibody, which revealed a single band of approximately 49 kD, consistent with the deduced molecular mass of the enzyme. The Mud protein could thus be characterized as a UDP-glucose dehydrogenase, which was a key enzyme for polysaccharide synthesis and has, for the first time, been studied in algae.

Comparative mechanisms of photosynthetic carbon acquisition in Hizikia fusiforme under submersed and emersed conditions

The economic seaweed Hizikia fusiforme (Harv.) Okamura (Sargassaceae, Phaeophyta) usually experiences periodical exposures to air at low tide. Photosynthetic carbon acquisition mechanisms were comparatively studied under submersed and emersed conditions in order to establish a general understanding of its photosynthetic characteristics associated with tidal cycles. When submersed in seawater, H fusiforme was capable of acquiring HCO3- as a source of inorganic carbon (Ci) to drive photosynthesis, while emersed and exposed to air, it used atmospheric CO2 for photosynthesis. The pH changes surrounding the H fusiforme fronds had less influence on the photosynthetic rates under emersed condition than under submersed condition. When the pH was as high as 10.0, emersed H fusiforme could photosynthesize efficiently, but the submersed alga exhibited very poor photosynthesis. Extracellular carbonic anhydrase (CA) played an important role in the photosynthetic acquisitions of exogenous Ci in water as well as in air. Both the concentrations of dissolved inorganic carbon in general seawater and CO2 in air were demonstrated to limit the photosynthesis of H fusiforme, which was sensitive to O-2. It appeared that the exogenous carbon acquisition system, being dependent of external CA activity, operates in a way not enough to raise intracellular CO2 level to prevent photorespiration. The inability of H fusiforme to achieve its maximum photosynthetic rate at the current ambient Ci levels under both submersed and emersed conditions suggested that the yield of aquaculture for this economic species would respond profitably to future increases in CO2 concentration in the sea and air.

Taxonomy of the Lemaneaceae (Batrachospermales, Rhodophyta) in China

Six species, belonging to two genera of Lemaneaceae in China are described. They are Lemanea Bory (including L. sinica Jao, L. crassa S. L. Xie et Z. X. Shi, L. ramosa S. L. Xie et Z. X. Shi and L. simplex Jao) and Paralemanea (Silva) Vis et Sheath (including P catenata (Kutzing) Vis et Sheath and P. parvula (Sirodot) S. L. Xie et Z. X. Shi). Among them L. crassa S. L. Xie et Z. X. Shi and L. ramosa S. L. Xie et Z. X. Shi are new species. Moreover, Paralemanea (Silva) Vis et Sheath and P. catenata (Kutzing) Vis et Sheath, P. parvula (Sirodot) S. L. Xie et Z. X. Shi are newly recorded in China.

Characterization of diurnal photosynthetic rhythms in the marine diatom Skeletonema costatum grown in synchronous culture under ambient and elevated CO2

Photosynthetic performance was examined in Skeletonema costatum (Greville) Cleve. under 12: 12-h light: dark (LD) cycle at ambient CO2 (350 muL L-1) and elevated CO2 (1000 muL L-1). At ambient CO2, the cellular chlorophyll a content, the light-saturated photosynthetic rate (P-m), the initial slope of the light saturation curves ( a), the photochemical efficiency of PSII (F-v/F-m), the apparent carboxylating efficiency (ACE) and the photosynthetic affinity for CO2 [1/K-m (CO2)] all showed rhythmical changes with different amplitudes during the light period. The P-m had similar changing pattern in the light period with the ACE and 1/K-m (CO2) rather than with the alpha and F-v/F-m, indicating that rhythmical changes of photosynthetic capacity may be mainly controlled by the activity of C- reduction associated with CO2 uptake during the light period. The CO2 enrichment reduced the ACE and the affinity to CO2, and increased the a, cellular chlorophyll a content and P m based on cell number. By contrast, the changing patterns of all photosynthetic parameters examined here during the light period had almost the same for cells grown at ambient CO2 and elevated CO2, suggesting that the photosynthetic rhythms of S. costatum are not affected by CO2 enrichment.

Photosynthetic physiology and growth as a function of colony size in the cyanobacterium Nostoc sphaeroides

Algal size can affect the rate of metabolism and of growth. Different sized colonies of Nostoc sphaeroides were used with the aim of determining the effects of colony size on photosynthetic physiology and growth. Small colonies showed higher maximum photosynthetic rates per unit chlorophyll, higher light saturation point, and higher photosynthetic efficiency (a) than large colonies. Furthermore, small colonies had a higher affinity for DIC and higher DIC-saturated photosynthetic rates. In addition, small colonies showed higher photosynthetic rates from 5-45degreesC than large colonies. There was a greater decrease in Fv/Fm after exposure to high irradiance and less recovery in darkness for large colonies than for small colonies. Relative growth rate decreased with increasing colony size. Small colonies had less chl a and mass per unit surface area. The results indicate that small colonies can harvest light and acquire DIC more efficiently and have higher maximum photosynthetic rates and growth rates than large colonies.

Photosynthetic utilization of inorganic carbon in the economic brown alga, Hizikia Fusiforme (Sargassaceae) from the South China Sea

The mechanism of inorganic carbon (C-i) acquisition by the economic brown macroalga, Hizikia fusiforme (Harv.) Okamura (Sargassaceae), was investigated to characterize its photosynthetic physiology. Both intracellular and extracellular carbonic anhydrase (CA) were detected, with the external CA activity accounting for about 5% of the total. Hizikia fusiforme showed higher rates of photosynthetic oxygen evolution at alkaline pH than those theoretically derived from the rates of uncatalyzed CO2 production from bicarbonate and exhibited a high pH compensation point (pH 9.66). The external CA inhibitor, acetazolamide, significantly depressed the photosynthetic oxygen evolution, whereas the anion-exchanger inhibitor 4,4'-diisothiocyano-stilbene-2,2'-disulfonate had no inhibitory effect on it, implying the alga was capable of using HCO3- as a source of C-i for its photosynthesis via the mediation of the external CA. CO2 concentrations in the culture media affected its photosynthetic properties. A high level of CO2 (10,000 ppmv) resulted in a decrease in the external CA activity; however, a low CO2 level (20 ppmv) led to no changes in the external CA activity but raised the intracellular CA activity. Parallel to the reduction in the external CA activity at the high CO2 was a reduction in the photosynthetic CO2 affinity. Decreased activity of the external CA in the high CO2 grown samples led to reduced sensitiveness of photosynthesis to the addition of acetazolamide at alkaline pH. It was clearly indicated that H. fusiforme, which showed CO2-limited photosynthesis with the half-saturating concentration of C-i exceeding that of seawater, did not operate active HCO3- uptake but used it via the extracellular CA for its photosynthetic carbon fixation.

The vertical microdistribution of cyanobacteria and green algae within desert crusts and the development of the algal crusts

Substantial amounts of algal crusts were collected from five different desert experimental sites aged 42, 34, 17, 8 and 4 years, respectively, at Shapotou ( China) and analyzed at a 0.1 mm microscale of depth. It was found that the vertical distribution of cyanobacteria and microalgae in the crusts was distinctly laminated into an inorganic-layer (ca. 0.00 - 0.02 mm, with few algae), an algae-dense-layer ( ca. 0.02 - 1.0 mm) and an algae-sparse-layer ( ca. 1.0 - 5.0 mm). It was interesting to note that in all crusts Scytonema javanicum Born et Flah ( or Nostoc sp., cyanobacterium), Desmococcus olivaceus (Pers ex Ach., green alga) Laundon and Microcoleus vaginatus Gom. ( cyanobacterium) dominated at the depth of 0.02 - 0.05, 0.05 - 0.1 and 0.1 - 1.0 mm, respectively, from the surface. Phormidium tenue Gom. ( or Lyngbya cryptovaginatus Schk., cyanobacterium) and Navicula cryptocephala Kutz.( or Hantzschia amphioxys (Ehr.) Grun. and N. cryptocephala together, diatom) dominated at the depth of 1.0 - 3.0 and 3.5 - 4.0 mm, respectively, of the crusts from the 42 and 34 year old sites. It was apparent that in more developed crusts there were more green algae and the niches of Nostoc sp., Chlorella vulgaris Beij., M. vaginatus, N. cryptocephala and fungi were nearer to the surface. If lichens and mosses accounted for less than 41.5% of the crust surface, algal biovolume was bigger when the crust was older, but the opposite was true when the cryptogams other than algae covered more than 70%. In addition to detailed species composition and biovolume, analyses of soil physicochemical properties, micromorphologies and mineral components were also performed. It was found that the concentration of organic matter and nutrients, electric conductivity, silt, clay, secondary minerals were higher and there were more micro-beddings in the older crusts than the less developed ones. Possible mechanisms for the algal vertical microdistribtion at different stages and the impact of soil topography on crust development are discussed. It is concluded that biomethods ( such as fine species distribution and biovolume) were more precise than mineralogical approaches in judging algal crust development and thus could be a better means to measure the potentiality of algal crusts in desert amelioration.

Primary succession of algal community structure in desert soil

The microbiotic crust study is among new focuses in investigating on the desertification control. Based on determination of algal crusts with different successive ages (4-, 8-, 17-, 34-, 42-year-old) and unconsolidated sand in the desert area, species composition and clustering analyses were carried out in this study. Results on successional orientation revealed that (1) the abundance of Cyanophyta, specially of Scytonema javanicum gradually decreased; (2) the abundance of Chlorophyta, Bacillariophyta and a species of Cyanophyta, Phormidium tenue increased; (3) the biodiversity increased gradually with the community succession; and (4) biomass of microalgae increased at the early stage, but decreased at the later stage due to the abundance of lichens and mosses. But, the speed of natural succession was so slow that the community-building species was still the first dominant species after 42 years, except that its dominant degree decreased just slightly. However, successive speed and trend were affected by water, vegetation coverage, terrain, time and soil physico-chemical properties as well, especially Mn content in the soil appeared to have a threshold effect.

Agrobacterium-mediated transformation of Kentucky bluegrass

Embryogenic calli of Kentucky bluegrass, named Md, were induced from mature seeds and embryos, and proliferated on medium K3 containing 2,4-dichlorophenoxyacetic acid (2,4-D, 10.0 mumol/L), 6-benzylaminopurine (BAR, 0.5 mumol/L) and K5 which was the K3 medium supplemented with cupric sulfa (0.5 mumol/L) under dim-light condition (20-30 mumol.m(-2).s-1, 16 h light) at 24 degreesC. Embryogenic calli were transformed with plasmids pDM805 Carring bar and gus genes, Which was mediated by an Agrobacterium strain AGL1, four transgenic lines were obtained. The important factors that affect the transformation efficiency and obtain desirable number of transgenic plants included: (1) the quality of embryogenic calli; (2) light condition and time of co-cultivation; (3) concentration of antibiotics used for suppressing the overgrowth of Agrobacterium in the course of transformed plant regeneration; (4) selection pressure, etc. The micro nutrient of cupric had significant influence on the quality of embryogenic calli. This presentation is the first successful protocol of Kentucky bluegrass transformation mediated by Agrobacterium.

Cymbellaceae and Gomphonemataceae (Bacillariophyta) from the Hengduan Mountains region (southwestern China)

We present a species list of the Gomphonemataceae and Cymbellaceae occurring in the Hengduan Mountains re-ion. These two families were found to be presented in the area by 117 species, varieties and forms belonging to four genera (Amphora, Cymbella, Didymosphenia and Gomphonema). Size, striae density, habitat and distribution in China are given for each taxon. The common taxa were Cymbella aequalis var. piscicultis. C. affinis, C. cesatii, C. cistula var. gibbosa, C. delicatula. C. gracilis, C. hustedtii, C. minuta f. latens, C. minita var. silesiaca, C. naviculiformis, C. parva. C. turgidida, Gomphonema acuminatum var. acuminatum, G. gracile, G. intricatum, G. olivaceum. G. parvulum and G. truncatum var. capitatum. Some morphological features of Cymbella cistula var. capitata, Cymbella sinica var. miyiensis, Gomphonema hedinii and G. kaznakowii were found to differ from previously published descriptions. Taxa typical of high latitude climates encountered during the present study were Cymbella affinis, C. alpina, C. cistula var. cistida, C. delicatula. C. naviculiformis. Didymosphenia geminata, Gomphonema acuminatum var. pusillum, G. constrictum var. capitatum f. turgidum, G. kaznakowii, G. olivaceum, G. subtile var. subtile, G. tergestinum and G. ventricosum.

Culture of the terrestrial cyanobacterium, Nostoc flagelliforme (Cyanophyceae), under aquatic conditions

Both colonies and free-living cells of the terrestrial cyanobacterium, Nostoc flagelliforme (Berk. & Curtis) Bornet & Flahault, were cultured under aquatic conditions to develop the techniques for the cultivation and restoration of this endangered resource. The colonial filaments disintegrated with their sheaths ruptured in about 2 days without any desiccating treatments. Periodic desiccation played an important role in preventing the alga from decomposing, with greater delays to sheath rupture with a higher frequency of exposure to air. The bacterial numbers in the culture treated with seven periods of desiccation per day were about 50% less compared with the cultures without the desiccation treatment. When bacteria in the culture were controlled, the colonial filaments did not disintegrate and maintained the integrity of their sheath for about 20 days even without the desiccation treatments, indicating the importance of desiccation for N. flagelliforme to prevent them from being disintegrated by bacteria. On the other hand, when free-living cells obtained from crushed colonial filaments were cultured in liquid medium, they developed into single filaments with sheaths, within which multiple filaments were formed later on as a colony. Such colonial filaments were developed at 15, 25, and 30degreesC at either 20 or 60 mumol photons.m(-2).s(-1); colonies did not develop at 180 mumol photons.m(-2).s(-1), though this light level resulted in the most rapid growth of the cells. Conditions of 60 mumol photons.m(-2).s(-1) and 25degrees C appeared to result in the best colonial development and faster growth of the sheath-held colonies of N. flagelliforme when cultured indoor under aquatic conditions.

Effects of desiccation and CO2 concentrations on emersed photosynthesis in Porphyra haitanensis (Bangiales, Rhodophyta), a species farmed in China

The effects on photosynthesis of CO, and desiccation in Porphyra haitanensis were investigated to establish the effects of increased atmospheric CO2 on this alga during emersion at low tides. With enhanced desiccation, net photosynthesis, dark respiration, photosynthetic efficiency, apparent carboxylating efficiency and light saturation point decreased, while the light compensation point and CO2 compensation point increased. Emersed net photosynthesis was not saturated by the present atmospheric CO2 level (about 350 ml m(-3)). and doubling the CO2 concentration (700 ml m(-3)) increased photosynthesis by between 31% and 89% at moderate levels of desiccation. The relative enhancement of emersed net photosynthesis at 700 ml m(-3) CO2 was greater at higher temperatures and higher levels of desiccation. The photosynthetic production of Porphyra haitanensis may benefit from increasing atmospheric CO2 concentration during emersion.