BACTERIA THAT INDUCE MORPHOGENESIS IN ULVA PERTUSA (CHLOROPHYTA) GROWN UNDER AXENIC CONDITIONS1

Marine foliaceous green macroalgae such as Ulva lose their typical morphology when cultured aseptically in defined synthetic media. However, after reinfection by certain marine bacteria (isolated from unialgal cultures of Ulva pertusa Kjellman), the organisms regain their typical foliaceous or tubular morphology. To investigate the morphogenesis (MG) induced in U. pertusa by bacteria, we isolated and identified bacteria with MG activity on U. pertusa and studied the distribution of such bacteria in seawater and on various marine macroalgae. We isolated 1555 bacterial strains from 18 species of marine macroalgae (six Chlorophyta, five Phaeophyta, and seven Rhodophyta), from seawater and from sediment collected at the beach at Omaezaki, Shizuoka Prefecture; Japan. Of these, 676 bacterial strains (43.5%) showed MG activity. They were classified into six bacterial groups, Flavobacterium, Vibrio, Pseudomonas, Deleya, Escherichia, and gram-positive cocci. These bacteria were ubiquitous among the samples and were not specific to U. pertusa. Several plant growth regulators had no MG activity. Filter-sterilized supernatants of culture media of MG-active bacteria strains did not induce MG. Cocultivation of Ulva with active bacterial strains is so far the only way to induce the MG effect, which suggests that for MG direct contact between Ulva and the bacterial strain is necessary.     

Abiotic factors affecting the development of <Emphasis Type="Italic">Ulva</Emphasis> sp. (Ulvophyceae; Chlorophyta) in freshwater ecosystems

The influence of physicochemical factors on the development of Ulva species with distromatic tubular morphology was studied in three streams located in Poznan, Poland. The study evaluated key environmental factors that may influence the colonisation and growth of Ulva populations in freshwater systems. In total, nine environmental parameters were included: temperature, water depth, pH, oxygen (O₂), ammonium (NH₄ ⁺), nitrate (NO₃ ⁻), phosphate (PO₄ ³⁻), sodium chloride (NaCl) and total iron (Fe). Morphometric features of thalli (length and width, percentage of furcated and young thalli) and surface area of free-floating mats formed by the freshwater populations of Ulva were compared at all sites. Principal components analysis indicated the most important factors influencing Ulva development were sodium chloride concentrations and water depth. Two other key chemical factors affecting the freshwater form of Ulva were phosphate and nitrite concentrations. High concentrations of sodium chloride inhibited the development of Ulva, leading to a lower number of thalli in the Ulva mats. At the sites with stable and deeper water, the surface area of the mats was larger. Both phosphate and nitrite concentrations were positively correlated with an increase in the number of thalli in the mats and the thalli length.     

Some aspects of decomposition of leaf litter of the seagrass Halophila stipulacea from the gulf of Aqaba (Jordan)

Decomposition of the seagrass Halophila stipulacea (Forsk.) Aschers. followed in situ over 340 days showed that the plant lost 40.8% of its initial weight during the first 85 days and only 21.2% over the remaining 255 days of the incubation period. The observed overall rate of decay of 0.18% day^?1 indicates the high resistance of Halophila tissue to decomposition.An exponential model showing a regularly decreasing decay coefficient was fitted to the data of weight loss. The correlation between observed and calculated weight remaining was highly significant (r = 0.9881, P < 0.0001).The samples of decomposing leaf litter harboured 2.2 × 10¹¹ bacteria g^?1 dry wt. on average and consumed 0.25?1.07 mg O₂^?1 dry wt. h^?1. The early colonizing bacteria of the detritus were mostly non-sporogenous forms. The most prominent genera involved in decomposition were Actinomyces, Arthrobacter, Bacillus and Pseudomonas, all of which are capable of degrading structural carbohydrates.     

Changes in nitrogen assimilation, metabolism, and growth in transgenic rice plants expressing a fungal NADP(H)-dependent glutamate dehydrogenase (gdhA)

In plants, glutamine synthetase (GS) is the enzyme that is mainly responsible for the assimilation of ammonium. Conversely, in microorganisms such as bacteria and Ascomycota, NADP(H)-dependent glutamate dehydrogenase (GDH) and GS both have important roles in ammonium assimilation. Here, we report the changes in nitrogen assimilation, metabolism, growth, and grain yield of rice plants caused by an ectopic expression of NADP(H)-GDH (gdhA) from the fungus Aspergillus niger in the cytoplasm. An investigation of the kinetic properties of purified recombinant protein showed that the fungal gdhA had 5.4–10.2 times higher V _max value and 15.9–43.1 times higher K _m value for NH₄ ⁺, compared with corresponding values for rice cytosolic GS as reported in the literature. These results suggested that the introduction of fungal GDH into rice could modify its ammonium assimilation pathway. We therefore expressed gdhA in the cytoplasm of rice plants. NADP(H)-GDH activities in the gdhA-transgenic lines were markedly higher than those in a control line. Tracer experiments by feeding with ¹⁵NH₄ ⁺ showed that the introduced gdhA, together with the endogenous GS, directly assimilated NH₄ ⁺ absorbed from the roots. Furthermore, in comparison with the control line, the transgenic lines showed an increase in dry weight and nitrogen content when sufficient nitrogen was present, but did not do so under low-nitrogen conditions. Under field condition, the transgenic line examined showed a significant increase in grain yield in comparison with the control line. These results suggest that the introduction of fungal gdhA into rice plants could lead to better growth and higher grain yield by enhancing the assimilation of ammonium.     

Anaerobic digestion of Ulva sp. 1. Relationship between Ulva composition and methanisation

Ulva often represents the main component of mass algal growths, and its composition and degradability make it a relatively good methanisation substrate. In ‘green tides’ Ulva sp. from Brittany, the low content oflignin-type components (polyphloroglucinols: 1.3% dry weight), and the large hemicellulosic fraction (9% dry weight) favour the substrate's accessibility to enzymes. Anaerobic degradation with a batch orcompletely stirred system is technically possible. However, the methane yield reached only 0.20 m³ kg⁻¹ volatile solids and the epuration rate 50% volatile solids in experiments in batch or completely stirred reactors. More generally, methanisation comes up against various practical obstacles: seasonal growth of Ulva, low density of alga in suspension for loading the digester, high S concentration leading to the production of a biogas with a high H2S content, and, finally, the existence of a refractory or slowly degradable part, which requires a compromise between productivity and biological yield. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of diet and heavy metals on growth rate and fertility in the deposit-feeding snail Potamopyrgus jenkinsi (Smith) (Gastropoda: Hydrobiidae)

Evidence for the influence of food type and heavy metals on shell growth and fertility is presented for a freshwater population of the snail P. jenkinsi. When fed an excess of lettuce or lamb heart (protein source), growth rates were higher for lettuce. Highest growth rates occurred at a diet of lettuce plus lamb heart. Fertility was favoured by a diet of lamb heart. When fed an excess of lettuce, the EC₅₀ growth values were 16 µg Cd l^–1, 13 µg Cu l^–1, and 103 µg Zn l^–1 in lake water; snail fertility was inhibited at 25 µg Cd l^–1 and 30 µg Cu l^–1. A diet of lake detritus spiked with Cd or Cu resulted in a decrease of approximately 50% in growth rates, when compared with growth on non-spiked detritus. Spiked detritus lost metals into lake water. Food type positively interacted with metal stress, both for growth rate and fertility. The assessment of inhibitory effects of detritus contaminated either in the field or, notably, by spiking, and serving as food source for deposit feeders is hampered by sampling problems in the field and by redistribution processes of pollutants between particles and water in laboratory-scale experiments.     

Hormonal regulation of cotton ovule and fiber growth: Effects of bromodeoxyuridine,AMO-1618 and p-chlorophenoxyisobutyric acid

The effects of 5-bromo-2-deoxyuridine (BUdR, thymidine analogue), AMO-1618 (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride), a growth retardant, and p-chlorophenoxyisobutyric acid (PCIB, an antiauxin) on growth (dry weight increase) and fiber development in unfertilized cotton (Gossypium hirsutum L.) ovules grown in vitro have been studied. BUdR (5 M) causes about 70% inhibition of fiber production, with little effect on ovule growth, if applied during the first 6 d of culture in the presence of GA₃ and IAA. AMO-1618, when used with GA₃ alone, causes only a small reduction in both dry weight and fiber production, but when used with IAA alone reduces both fiber production and dry weight, the effect on the latter being predominant. In the presence of both IAA and GA₃, AMO-1618 causes a small decrease in fiber production but a major decrease in dry weight. PCIB completely inhibits fiber growth but has little effect on dry weight, especially when GA₃ is present. These results indicate that GA₃ mainly promotes ovule growth while IAA is largerly responsible for fiber growth.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride - BUdR 5-bromo-2-deoxyuridine - GA₃ gibberellic acid - IAA indole-3-acetic acid - PCIB p-chlorophenoxyisobutyric acid - TFU total fiber units     

Isolation,partial characterization,and the effect of plant growth-promoting bacteria (PGPB) on micro-propagated sugarcane in vitro

We report the isolation of nitrogen fixing, phytohormone producing bacteria from sugarcane and their beneficial effects on the growth of micropropagated sugarcane plantlets. Detection of the nitrogen fixing bacteria by ARA-based MPN (acetylene reduction assay-based most probable number) method indicated the presence of up to 10⁶ bacteria per gram dry weight of stem and 10⁷ bacteria per gram dry weight of root of field-grown sugarcane. Two nitrogen fixing bacterial isolates were obtained from stem (SC11, SC20) and two from the roots (SR12, SR13) of field-grown plants. These isolates were identified as Enterobacter sp. strains on the basis of their morphological characteristics and biochemical tests. The isolate SC20 was further characterized by 16S rRNA sequence analysis, which showed high sequence similarity to the sequence of Enterobacter cloacae and Klebsiella oxytoca. All the isolates produced the phytohormone indoleacetic acid (IAA) in pure culture and this IAA production was enhanced in growth medium containing tryptophan. The bacterial isolates were used to inoculate micro-propagated sugarcane in vitro where maximum increase in the root and shoot weight over control was observed in the plantlets inoculated with strain SC20. By using the¹⁵N isotope dilution technique, maximum nitrogen fixation contribution (28% of total plant nitrogen) was detected in plantlets inoculated with isolate SC20.     

Gracilaria conferta and its epiphytes: 3. Allelopathic inhibition of the red seaweed byUlva cf.lactuca

In a previous study (Svirski et al., 1993), it was found that growth inhibition ofGracilaria spp., when cultured in the presence ofUlva cf.lactuca, was not due to shading or nutrient depletion, but seemed to be caused by competition for inorganic carbon or some type of allelopathy. In the present study, we attempted to differentiate between these two possible influences by (1) growing the two algae in biculture under various conditions, but keeping inorganic carbon levels constant and measuring net photosynthesis, respiration and growth rates, and by (2) measuring growth rates ofGracilaria spp. in the presence of extracts derived from media previously used to growUlva cf.lactuca.Both net photosynthesis and growth rates ofGracilaria spp. in biculture were inhibited, despite CO₂ (and also HCO₃ ^–) levels being kept constantly high in the culture media. It is likely that these responses were due to markedly enhanced rates of dark respiration inGracilaria spp. when grown together withUlva cf.lactuca. Growth ofGracilaria spp. was also inhibited by extracts derived from seawater in whichUlva cf.lactuca had previously been grown. The strong inhibition by ethyl acetate and chloroform extracts indicate an allelopathic effect onGracilaria spp.     

Differential toxic effects of Ulva lactuca (Chlorophyta) on the herbivorous gastropods,Littorina littorea and L. obtusata (Mollusca)

Members of the genus Ulva are widespread and abundant in intertidal and shallow subtidal areas but there are conflicting data regarding susceptibility to herbivory. While some studies have documented that Ulva spp. were favored by a diversity of marine herbivores, other work has revealed herbivore deterrence. We investigated grazing and growth rates of the littorinid species, Littorina littorea and L. obtusata, when offered Fucus vesiculosus, Ascophyllum nodosum, Ulva lactuca, and Chondrus crispus, highlighting distinctive vulnerabilities to toxic effects of U. lactuca. Ulva lactuca was the preferred food of L. littorea, while L. obtusata showed no grazing on this ephemeral algal species. In contrast, F. vesiculosus was highly preferred by L. obtusata. Although L. littorea demonstrated a grazing preference for U. lactuca, growth rate of this gastropod species was nearly 3× greater when fed F. vesiculosus, suggesting a non‐lethal, negative effect of U. lactuca on L. littorea with long‐term exposure. Mortality of L. obtusata ranged from 0% to 100% when held in the presence of various Ulva densities for 1 week, and Ulva exudate depressed herbivory of this gastropod. We conclude that the water‐soluble, toxic exudate produced by U. lactuca in response to herbivory had allelochemical properties, and may contain a cleavage product (acrylic acid) of dimethylsulfoniopropionate or reactive oxygen species (i.e., H₂O₂). Observed differences in susceptibility to Ulva toxicity by the littorinid species may be related to generalist versus specialist feeding and habitat strategies.     

Growth, dry weight partitioning and wood properties of Pinus radiata D. Don after 2 years of CO2 enrichment

Abstract Advanced selections (families 20010 and 20062) of P. radiata D. Don were exposed to either 340 or 660 μmol CO₂ mol ¹ for 2 years to establish if growth responses to high CO₂ would persist during the development of woody tissues. The experiment was carried out in glasshouses and some of the trees at each CO₂ concentration were subjected to phosphorus deficiency and to periodic drought. CO₂ enrichment increased whole-plant dry matter production irrespective of water availability, but only when phosphorus supply was adequate. The greatest increase occurred during the exponential period of growth and appeared to be tied to increased rates of photosynthesis, which caused accelerated production of leaf area. The increase in whole-plant dry matter production was similar for both families; however, family 20010 partitioned larger amounts of dry weight to the trunks than family 20062. which favoured the roots and branches. Wood density was generally increased by elevated CO₂ and for family 20010 this increase was due to thickening of the tracheid walls. Tracheid length was similar at both CO₂ levels but differed between families. These results suggest that, as the atmospheric CO₂ concentration rises, field-grown P. radiata should produce more dry weight at sites where phosphorus is not acutely deficient, even where drought limits growth; however, increases in wood production are likely only for genotypes which continue to partition at least the same proportion of dry weight to wood in the trunk.     

灵芝胞外多糖分批发酵动力学模型

利用分批发酵研究了灵芝（Ganoderma lucidum）胞外多糖的合成特性,结果表明Ganoderma lucidum多糖合成和菌体生长呈部分生长关联型。菌体干重、胞外多糖分别达到15.56g·L^-1<、3.02g·L^-1<,胞外多糖对细胞干重得率系数(Y_p/x）为0.19。根据分批发酵试验结果采用Logistic方程、Luedeking-Piret方程和类似Luedeking-Piret方程,得到了描述灵芝生长、胞外多糖以及葡萄糖底物消耗分批发酵动力学模型。同时在初始葡萄糖变化较大范围内,试验数据与模型预测值进行了比较拟合,平均相对误差小于5％,表现出很好的适用性。表明该动力学模型对指导灵芝胞外多糖的发酵生产具有实际意义。     

Interaction mechanisms between Gracilaria chilensis (Rhodophyta) and epiphytes

Epiphytes can have a considerable effect on Gracilaria production, and Ulva is one of the commonest algal species identified as an epiphyte, reaching loads of 60% (g of epiphytes per g of Gracilaria) in the intertidal cultures of southern Chile. This study evaluates the relative importance of light reduction, addition of weight to the host thalli and nutrient depletion, as mechanisms determining the interaction effects of Ulva epiphytes on Gracilaria cultivation. Using field experiments undertaken during the main Gracilaria growth season (spring), we evaluate the mechanisms of epiphyte-host algae interaction by manipulating artificial epiphytes. The results indicate that Ulva can significantly depress Gracilaria biomass production and that the addition of weight to the host algae and the consequent dislodgement increase, appear to be the main mechanisms involved in the Ulva-Gracilaria interaction. However, the light reduction caused by the epiphytes can also partially explain the reduction in Gracilaria production. Nutrients depletion would not appear to fully account for the detrimental effects of Ulva over Gracilaria in intertidal farming areas of southern Chile.     

Effects of seasonal changes of soil salinity and soil nitrogen on the N-metabolism of the halophyteArthrocnemum fruticosum (L.) Moq.

Summary The N-metabolism ofArthrocnemum fruticosum (L.) Moq., growing in a saline area north-east of the Dead Sea in Jordan, was studied over its vegetative growth period from March to September 1981. Plant and soil samples were taken at monthly intervals. Water content, Na⁺, K⁺, Cl⁻, NH ₄ ⁺ , NO ₂ ⁻ and NO ₃ ⁻ concentrations were determined in the soil extracts, and the same determinations plus ash weight, soluble carbohydrates, proline, proteins andin vivo nitrate reductase in the plant roots and shoots. Soil humidity decreased and salinity increased from March to August, with re-wetting occurring in late July. K⁺ and Cl⁻ were much lower in the soils than Na⁺. Plant relative dry weight increased during summer due to the absorption of Na⁺ in addition to increased organic dry weight. The uptake of Na⁺ was not balanced by a similar uptake of Cl⁻. Ammonium and nitrate decreased in soil and plants in parallel with increasing salinity. Nitrite was only found in the roots and always in very low quantities. Proline was found only in March. The total soluble carbohydrates in the roots showed a short increase in June when the sodium in the plants also increased. It was concluded that carbohydrates may be used to balance osmotic shocks, but that another compatible compounds is necessary to maintatin long-term osmotic equilibrium. The nitrate reductase activity, measuredin vivo, and the soluble protein changed roughly in parallel with the internal nitrate from May to August, suggesting that nitrogen uptake and reduction in the plant is inhibited during summer when the soil is dry and very saline. This could be a direct effect of drought and/or salinity on the plants, or an indirect onevia an inhibition of nitrifying bacteria.     

Utilisation of Ulva rigida biomass in the Venice Lagoon (Italy): biotransformation in compost

In the Venice Lagoon (Italy), about 10⁶ t (wet weight) of Ulva rigida biomass are produced annually as one of the major results of eutrophication. Harvests have been initiated to reduce negative impacts of this biomass, however, due to the high costs of such effort, only 40 000 t yr^-1 are currently being collected. At the moment, biotransformation into compost seems to be the only feasible technology for utilising large quantities of Ulva biomass. We describe and discuss here a successful composting strategy together with the chemico-physical and microbiological characteristics of the resultant composts. Our composting experiments were conducted at a scale of 20 t. The composting technology utilises large proportions (70–90%) of Ulva biomass and results in a valuable, high-quality end product (compost and compost-based products). This process and the resulting products represents a relatively simple way of utilising the Ulva biomass produced annually in the Venice Lagoon.     

Effect of salinity on tomato (Lycopersicon esculentum Mill.) during seed germination stage

A study was conducted using ten genetically diverse genotypes along with their 45F₁ (generated by diallel mating) under normal and salt stress conditions. Although, tomato (Lycopersicon esculentum Mill.) is moderately sensitive to salinity but more attention to salinity is yet to be required in the production of tomato. In present study, germination rate, speed of germination, dry weight ratio and Na⁺/K⁺ ratio in root and shoot, were the parameters assayed on three salinity levels; control, 1.0 % NaCl and 3.0 % NaCl with Hoagland’s solution. Increasing salt stress negatively affected growth and development of tomato. When salt concentration increased, germination of tomato seed was reduced and the time needed to complete germination lengthened, root/shoot dry weight ratio was higher and Na⁺ content increased but K⁺ content decreased. Among the varieties, Sel-7 followed by Arka Vikas and crosses involving them as a parent were found to be the more tolerant genotypes in the present study on the basis of studied parameters.     

BIOMASS AND DYNAMICS OF GROWTH OF ULVA SPECIES IN PALMONES RIVER ESTUARY1

During the last decade, the Palmones River estuary has undergone severe eutrophication followed by a green tide episode; two species of Ulva, rotundata Blid. and Ulva curvata (Kütz.) De Toni, were the main macroalgae responsible for this bloom. From November 1993 to December 1994, we followed the biomass, the growth dynamics, and tissue elemental composition (C:N:P)of Ulva species, as well as some physicochemical variables in the estuary. Maximum biomass (up to 375 g dry wt·m^?2 in some spots, corresponding to a thallus area index of nearly 17 m²Ulva·m^?2 sediment) were observed in June and December. However, the biomass varied among the sampling stations. Water nitrate, ammonia, and phosphate showed high concentrations throughout the year, with extremely high transient pulses, sustaining the high growth rates observed. Growth rates were estimated directly in the field. The rates were generally higher in Ulva discs maintained in net cages than those estimated by changes in biomass standing stock between two consecutive samplings. The difference between both estimates was used to quantify the importance of the processes causing loss of biomass, which were attributable to grazing, exported biomass, and thallus decomposition under anaerobic conditions resulting from extreme self-shading. Maximum chlorophyll content was found in winter, whereas the minimum was in spring. Atomic N:P ratios were generally higher in the algae than in the water. However, the absolute concentrations of tissue N and P were always higher than the critical levels for maximum growth, which suggests that growth was not limited by inorganic N or P availability. The results suggested that the increase in nutrient loading in the river may have triggered the massive development of green algae and that light limitation and temperature stress in summer seem to be the main factors controlling the abundance of Ulva in the estuary. In addition to light availability and thermal stress, the different loss processes may have a decisive role in the dynamics of Ulva biomass.     

Influence of auxins on growth ofClaviceps purpurea (Fries) tulasne in saprophytic cultures

A 10⁻³ m β-indolebutyric and 2,4-dichlorophenoxyacetic acid concentration stimulated the fresh weight increase and dry matter production in the mycelium of staticClaviceps purpurea cultures to 170–180% of the control value. Higher concentrations severely inhibited growth. α-Naphthylacetic acid was less active. β-Indoleacetic acid differed markedly from the other auxins, as it stimulated the fresh weight increase, but at the same time inhibited dry matter production. In submerse cultivation, the differences between the test auxins disappeared; none of them stimulated growth and only inhibition of growth, by concentrations of over 10⁻⁵–10⁻⁴ m, was observed. The used strain did not produce alkaloids in saprophytic cultures, even in the presence of auxins.     

Dynamics of phytoplankton detritus in a shallow,eutrophic lake (Lake Loosdrecht,The Netherlands)

A study was made of the mortality and aerobic decomposition of light- and phosphorus-limited cultures of Oscillatoria limnetica, a dominant phytoplankton species in shallow, eutrophic Lake Loosdrecht (The Netherlands). When placed in the dark at 20 °C, most cells died and lysed within twelve days. The labile organic matter was completely decomposed within three weeks. Absorbance spectra indicated that blue green algae may contributed significantly to the refractory dissolved substances in the lake. Refractory particulate matter constituted from 7 to 24% of the biomass of O. limnetica, depending on the growth rate before incubation in the dark. The decomposition rate of this fraction was 0.005 d^–1. On a basis of a steady-state model of the dynamics of phytoplankton detritus, the areal organic dry weight concentration of the detritus in the lake is ca. 60 g m^–2. This means the quantities of detritus in the seston and epipelon are about equal.     

An Experimental Study on the Food Chain Among Bacteria,Paramecium and Daphnia

A quantitative study is made of the feeding of Paramecium caudatum on bacteria and of the feeding of Daphnia pulex on Paramecium and bacteria. The growth yield of P. caudatum on a diet of an unidentified yellow-colored bacterium was about 55% on a dry weight basis. Paramecium would not grow if the concentration of bacteria is less than 1 . 10₇ cells ml. Several other bacterial species were tested. Paramecium could not grow successfully on all of them, but could on Rhodopseudomonas spheroides. Adults of Daphnia pulex could grow and reproduce on a diet of P. caudatum alone, but young grew successfully only when bacteria were present.