Collection and Germination of Sporocarps of Azolla caroliniana

Azolla caroliniana Willd. with matured mega- and microsporocarpswere harvested from the field, sun dried and sieved to formballs of megasporocarps and massulae. The separated sporocarpswere tested for germination in different media in Petri dishesunder laboratory/greenhouse conditions. Only the swollen, greenmegasporocarps germinated. Nutrient medium was superior to asoil solution. The observed percentage germination was betteron a solid surface than in a liquid medium. Germination didnot occur with dark incubated sporocarps. The addition of phosphorusstimulated sporocarp germination and at a concentration of 30ppm, an 86% increase in germination was noted against the control.Percentage germination varied widely with pH, and optimum germinationwas recorded at a neutral pH. The effect of nitrogen sourceson sporocarp germination indicated that 70 ppm of nitrate, 7.5ppm of ammonium, 15 ppm of nitrite and 15 ppm of urea increasedgermination by 51, 66, 44 and 63%, respectively; further increasesin concentration inhibited germination. Treatment with 100 ppmof either kinetin or gibberellic acid, or a mixture of both,enhanced germination by 67, 55 and 84%, respectively. Azolla caroliniana Willd., sporocarp collection, germination     

Effect of chilling on growth and nitrogen assimilation in Azolla caroliniana

Azolla caroliniana was exposed to 5 °C in darkness for 1, 2, 3, 5 or 7 d and then recovered for 7 d. Plants previously chilled for 2 or 3 d exhibited higher growth rates when transferred to normal temperature than either the control plants or those previously chilled for 5 or 7 d. Increased plant growth may be related to increased contents of chlorophyll, sucrose, and reducing sugars, due to increased photosynthetic capacity. In another experiment Azolla plants were chilled at 5 °C for 7 d and then transferred for 0, 4, 8, 12, or 16 d recovery to the N-free Hoagland solution or Hoagland solution containing 5 mM KNO₃. In previously chilled plants, the growth rate was decreased. In the medium supplemented with nitrogen, the growth rate was greater than in the N-free medium in both chilled and nonchilled plants. In chilled plants the decrease in growth rate may be related to the disturbance of Anabaena azollae cells where the protecting envelope of the heterocysts was deorganized. During the recovery the rate of N₂-fixation increased in both chilled and nonchilled plants up to 12 d after which both rates were similar. However, during the first 4 d the rate of the nonchilled plants was approximately 4-fold that of the previously chilled plants. Nitrate reductase and nitrite reductase activities in control plants were higher than in those previously chilled for 7 d. Both activities increased in nonchilled and previously chilled plants up to 12 d then decreased. The total protein content increased up to 12 d in chilled and nonchilled plants after which it decreased. Under all treatments, the values were higher in nonchilled plants than in those previously chilled ones and were also higher in presence of N than in its absence. Thus the presence of N-source in the medium counteracts the effect of chilling injury particularly during prolonged recovery.     

Salinity Induced Alterations in the Growth and Cellular Ion Content of Azolla caroliniana and Azolla microphylla

Journal of Plant Growth Regulation - The nitrogen fixing aquatic pteridophyte Azolla is often found in the rice fields and is responsible for maintaining the soil fertility and productivity....     

Response of growth and antioxidant enzymes in Azolla plants (Azolla pinnata and Azolla filiculoides) exposed to UV-B

Effect of ultravilolet-B (0.4 Wm(-2)) irradiation on growth, flavonoid content, lipid peroxidation, proline accumulation and activities of superoxide dismutase and peroxidase was comparatively analysed in Azolla pinnata and Azolla filiculoides. Growth measured as increment in dry weight reduced considerably due to all UV-B treatments. However, the reduction was found to be severe in A. filiculoides as compared to A. pinnata. The level of UV-absorbing compound flavonoids increased significantly in A. pinnata plants whereas only a slight increase in the flavonoid content was observed in A. filiculoides. UV-B exposure led to enhanced production of malondialdehyde (MDA) and electrolyte leakage in A. filiculoides than A. pinnata. Proline accumulation also showed a similar trend. Marked differences in the activity of antioxidant enzymes such as superoxide dismutase (SOD) and peroxidase (POD) was noticed in both the plants exposed to UV-B. Our comparative studies indicate A. pinnata to be better tolerant to UV-B as compared with A. filiculoides which appears to be sensitive.     

The oxidative stress caused by NaCl in Azolla caroliniana is mitigated by nitrate

In order to assess the role of the antioxidant defense system against salt treatment, the activities of some antioxidative enzymes and levels of some nonenzymatic antioxidants were estimated in Azolla caroliniana subjected to NaCl treatment (50 mM) for 10 days in absence or presence of nitrate. In A. caroliniana, salt treatment in absence of nitrate preferentially enhanced electrolyte leakage, lipid peroxidation, and H₂O₂ content. Also, the specific activitiy of guaiacol peroxidase (POX), glutathione reductase (GR), catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) increased. In addition, reduced glutathione level increased and consequently, glutathione/oxidized glutathione (GSH/GSSG) ratio increased. Accumulation of Na⁺ increased significantly by salinity stress which resulted in a significant decrease in K⁺ accumulation, accordingly, K⁺/Na⁺ ratio decreased. Replacement of potassium chloride by potassium nitrate in nutrient solution under salt stress (50 mM NaCl) exhibited a reduction in electrolyte leakage, lipid peroxidation, and H₂O₂ contents. Conversely, the specific activity of APX, POX, GR, CAT, and SOD increased. The content of total ascorbate decreased, in contrast, reduced and GSSG increased and the ratio of GSH/GSSG increased 2.3-fold compared to the control value. Sodium ion accumulation was minimized in the presence of nitrate, potassium ion accumulation increased and as a result, K⁺/Na⁺ ratio increased when compared with the corresponding salinized plants. The differential changes in the specific activity of antioxidant enzymes due to NaCl treatment and nitrate may be useful as markers for recognizing salt tolerance in A. caroliniana.     

Glutamine synthetase specific activity and protein concentration in symbiotic Anabaena associated with Azolla caroliniana

Glutamine synthetase (GS) is the primary NH₄ ⁺ assimilating enzyme of cyanobacteria. The specific activities and cellular protein concentration of GS in symbiotic cyanobacteria associated with the water fern Azolla caroliniana were determined and compared to free-living cultures of Nostoc sp. strain 7801, a strain originally isolated from symbiotic association with the bryophyte Anthoceros punctatus. Both the in vitro specific activity and concentration of GS in symbiotic cyanobacteria separated from A. caroliniana were approximately 3-fold lower than the free-living Nostoc sp. strain 7801 culture. These results imply depressed synthesis of GS by the symbiont associated with A. caroliniana.     

Occurrence and ultrastructural characterization of bacteria in association with and isolated from Azolla caroliniana.

The occurrence and ultrastructure of bacteria in leaf cavities of symbiotic Azolla caroliniana were examined by transmission electron microscopy. Bacteria were observed in all leaf cavities of Azolla cultures. Five ultrastructurally distinct types of bacteria were observed in each individual leaf cavity. Features used to characterize the bacteria included morphology, cell wall structure, and cytoplasmic organization. At least one gram-positive and as many as four gram-negative types of bacteria reside in leaf cavities of A. caroliniana. The morphological and ultrastructural characteristics of the gram-positive bacterium suggest that it is an Arthrobacter sp. The gram-negative bacteria could not be cultured; therefore, they have not been classified further. Bacterial cell shape and cell wall structure were similar in leaf cavities of different ages, but cell size and cytoplasmic composition varied. The relative contributions of each bacterial type to the total community within individual leaves was determined. Ultrastructural characteristics of bacterial isolates cultured from A. caroliniana in a free-living state were also examined.     

Uptake and Toxicity of Arsenic,Copper, and Silicon in Azolla caroliniana and Lemna minor

Here we report on the analysis of two aquatic plant species, Azolla caroliniana and Lemna minor, with respect to tolerance and uptake of co-occurring arsenic, copper, and silicon for use in engineered wetlands. Plants were cultured in nutrient solution that was amended with arsenic (0 or 20 μM), copper (2 or 78 μM), and silicon (0 or 1.8 mM) either singly or in combination. We hypothesized that arsenic and copper would negatively affect the uptake of metals, growth, and pigmentation and that silicon would mitigate those stresses. Tolerance was assessed by measuring growth of biomass and concentrations of chlorophyll and anthocyanins. Both plant species accumulated arsenic, copper, and silicon; L. minor generally had higher levels on a per biomass basis. Arsenic negatively impacted A. caroliniana, causing a 30% decrease in biomass production and an increase in the concentration of anthocyanin. Copper negatively impacted L. minor, causing a 60% decrease in biomass production and a 45% decrease in chlorophyll content. Silicon augmented the impact of arsenic on biomass production in A. caroliniana but mitigated the effect of copper on L. minor. Our results suggest that mixtures of plant species may be needed to maximize uptake of multiple contaminants in engineered wetlands.     

The effect of Azolla on mosquito breeding

Surface agents to smother mosquito breeding sites have been used extensively for mosquito larval control. Such agents range from oil films and chemical monolayers, to expanded polystyrene beads(1,2). Here, Lu Bao-lin discusses the use of Azolla - a floating fern - for a similar effect. The fern has the additional advantage of providing a useful source of green manure as a crop fertilizer.     

Nutritive value of maygrass,Phalaris caroliniana

Maygrass, Phalaris caroliniana,a native annual grass used as a food resource by prehistoric Indians of the eastern United States, was analyzed for nutritive value. Protein nutrient density of maygrass grains is higher than that for other starchy seeds, oily seeds, and nuts commonly found in paleoethnobotanical samples from the region. Maygrass grains are a good source of several vitamins and minerals, especially thiamin and dietary iron. The amino acid in shortest supply is lysine. Nutritional quality of the grains may have served as an inducement for its protection or cultivation.     

Species-specific effect of UV-B radiation on the temporal pattern of leaf growth

Recent molecular and physiological studies have demonstrated that ultraviolet‐B radiation (UV‐B) can affect some of the processes involved in leaf growth, but the phases of leaf growth affected have not been clearly delimited. We used functional growth analysis to assess the effects of UV‐B radiation on the time course of leaf growth in seedlings of two birch species (Betula pendula and Betula pubescens). Our aim was to identify the phase(s) of leaf development affected by UV‐B radiation. In a greenhouse study, 1‐year‐old birch seedlings were subjected to three daily doses of supplemental UV‐B radiation treatments (UV‐B⁺) and no UV‐B radiation controls (UV‐B^?). Leaf growth measurements every 2 days were complemented by assessment of other functional traits over a 4‐week period at the start of the growing season. Using fitted curves, we were able to determine that the rate of leaf expansion was slowed by the UV‐B⁺ treatment in leaves of B. pendula because of a slower maximum leaf growth rate compared with plants under the UV‐B^? controls, but that compensation toward the end of the period of expansion negated this difference when leaves reached their final size. UV‐B⁺ had little effect on the rate of B. pubescens leaf growth despite a larger reduction in leaf final size due to UV‐B⁺ than occurred in B. pendula leaves. In conclusion, effective regulation ameliorated the effects of UV‐B radiation on leaf and seedling growth in B. pendula, whereas in B. pubescens, reductions in leaf final size under UV‐B⁺ were consistent with a slightly reduced rate of height growth.     

Studies on Nitrogen Fixation and Photosynthesis in Azolla imbricata Roxb and Azolla fiticuloides Lam.

Azolla imbricata and Azolla filieuloides were studied in regard to the nitrogenase- catalyzed reactions of C2H2 reduction and H2 production, employing gas chromatography; and photosynthetic CO2 uptake as well as simultaneous determinations of C2H2 reduction, photosynthesis and respiration in a closed system. Photosynthetic CO2 uptake and respiratory C02 production were determined using an infrared gas analyzer. These studies have indicated the following 1. Nitrogenase-catalyzed C2H2 reduction is largely light dependent. About 10,000 lux were required for saturation in A imbricata. A concentration of 10% C2H2 in the gas phase is saturating for C2H2 reduction and 1% CO inhibits C2H2 reduction with concomitant H2 production. 2. A determination of C2H2 reduction activity as a function of leaf age established a develop mental gradient in both A. imbricata and A. fgliculaides. In both species activity is negligible in the apex, increases markedly in progressively older leaves, plateaus, and decreases as leaves senesce. The developmental gradient of activity is much steeper in A. imbricate than in A. filiculoieds due to differences in their gross morphology. 3. Nitrogenase-eatalyzed H2 production in A. imbricata was not detectable under Ar but was appreciable under Ar containing 15% C2H2 and 2% CO. H2 production was also determined under the latter gas phase as a function of leaf. These studies implicate the occurrence of an uptake hydrogenase. 4. The photosynthetic compensation points in air are approximately 30 ppm CO2 for A. imbricata and A. filiculoides. 5. Simultaneous measurements of photosynthesis, respiration and C2H2 reduction in A. imbricata demonstrated the immediate dependence of nitrogenase on photosynthetically captured radiation for energy but an indirect dependence on CO2 fixation.     

Modelling spread of the invasive macrophyte Cabomba caroliniana

1. Predicting spread of non-indigenous species requires an understanding of where propagules are being transported, and whether these propagules can survive in the novel habitat and successfully integrate into the recipient community. In this study, we model potential spread of invading Cabomba caroliniana in Ontario, Canada, using a combination of passive and active dispersal models coupled with an environmental suitability model, thereby considering the first two stages of the invasion process.
2. Measures of propagule pressure incorporated both human-mediated dispersal via trailered boats, and advective flow from invaded to non-invaded systems, while habitat suitability was forecasted by combining native and global data sets and using boosted regression trees.
3. Risk of invasion differed depending on the combination of approaches used and the time period considered. Three lakes appear to be at greatest risk owing to a combination of high boater and water movement from invaded sources, and high environmental suitability. The best predictors of lake suitability were pH, mean lake temperature and dissolved calcium concentration. Hundreds of lakes in Ontario may be suitable for establishment of Cabomba , highlighting the need for vector management.     

Differential response of antioxidant enzymes to salinity stress in two varieties of Azolla (Azolla pinnata and Azolla filiculoides)

The activity and modulation of antioxidant components were comparatively analyzed in two varieties of Azolla (Azolla pinnata and Azolla filiculoides) under different concentrations of NaCl. The total superoxide dismutase (SOD) and ascorbate peroxidase (APX) activity increased in A. pinnata, whereas both enzyme activities decreased in A. filiculoides. The plants of A. pinnata exposed to 30 mM NaCl contained a lower amount of Na⁺ ions and showed a lower electrolyte leakage than A. filiculoides. Our studies indicate a differential response of antioxidant enzymes in relation to salt tolerance in Azolla plants. On the basis of our comparative analysis, A. pinnata has been ranked salt tolerant as compared with A. filiculoides, which is salt sensitive.     

The effect of exposure to enhanced UV-B radiation on the penetration of monochromatic and polychromatic UV-B radiation in leaves of Brassica napus

Using quartz optical fibres, penetration of both monochromatic (310 nm) and polychromatic UV-B (280–320 nm) radiation in leaves of Brassica napus L. (cv. Ceres) was measured. Plants were grown under either visible light (750 μmol m⁻² s⁻¹ photosynthetically active radiation) or with the addition of 8. 9 KJ m⁻² day⁻¹ biologically effective UV-B (UV-B_BE) radiation. Results showed that of the 310 nm radiation that penetreated the leaf, 90% was within the intial one third of the leaf with high attenuation in the leaf epidermis, especially in UV-treated plants. Polychromatic UV-B radiation, relative to incident radiation, showed a relatively uniform spectral distribution within the leaf, except for collimated radiation. Over 30% of the UV-screening pigments in the leaf, including flavonoids, were found in the adaxial epidermal layer, making this layer less transparent to UV-B radiation than the abaxial epidermis, which contained less than 12% of the UV-screening pigments. UV-screening pigments increased by 20% in UV-treated leaves relative to control leaves. Densely arranged epicuticular wax on the adaxial leaf surface of UV-treated plants may have further decreased penetration of UV-B radiation by reflectance. An increased leaf thickness, and decreases in leaf area and leaf dry weight were also found for UV-treated plants.     

增强的UV-B辐射对植物影响的研究

综述了国内外有关UV－B辐射对植物影响的研究现状与动态,讨论了增强的UV－B辐射对植物生长及形态结构、植物生理生化代谢、植物遗传物质、UV－B吸收物质及某些基因表达和种群及生态系统的影响。展望了增强的UV－B辐射对植物影响领域中值得深入探讨的问题。     

Effects of Light on Transport by Azolla pinnata

Effects of light flux density (LFD) during growth and uptakeassay on induction of transport system and kinetics of transport were studied using the Azolla pinnata-Anabaena azollae association (Azolla). Theinduction and uptake kinetics of the transport system were determined using an automated system that measuredthe NO₃ concentration in the growth medium as a function oftime, using an on-line high performance liquid chromatograph(HPLC) with a UV-VIS detector. Full induction of the transport system required about 1.5 to 2.0 h and occurred without any apparent lag phase,regardless of the LFD provided. The level of induction of transport of Azolla grown at 600 µmol m^–2s^–1 LFD was higher than for that grown at 100 µmolm^–2 s^–1. Similarly, 600 µmol m^–1 s^–1LFD during the assay resulted in a higher level of inductionthan did 100 umol m^–2 s^–1. An increase in the LFDeither during the growth or the assay period increased the uptake rate; however, an increase in LFD duringthe latter period had greater effect. Azolla grown and assayedat 600 umol m^–2 s^–1 had the highest uptake rate. The uptake rate at 50 cm³ m^–3ambient CO₂ concentration was initially higher than at 305 cm³m^–3, but the uptake rate decreased rapidly with time andeventually dropped below that at 305 cm³ m^–3 CO₂. Thesedata suggest that the energy required for transport in Azolla may bypass the photosynthetic CO₂ fixationand carbon-cycling. Key words: carbon dioxide, concentration dependence, light flux density, uptake