Photosynthetic carbon sources in somepotamogeton species

The ability of somePotamogeton species to use bicarbonate for photosynthesis was assayed by means of relative net photosynthetic rates in alkaline (bicarbonate) and acid (free CO₂) solutions with an equivalent amount of inorganic carbon. The results showedPotamogeton crispus, P. oxyphyllus, P. maackianus, P. perfoliatus, P. malaianus and the submerged leaves ofP. distinctus to be able to use bicarbonate ions for photosynthesis. To the contrary, the submerged leaves ofP. fryeri, which is an inhabitant of soft and acid waters, and the floating leaves ofP. distinctus were proven to be ‘non-users’ of bicarbonate ions. Furthermore, the relative photosynthetic rates were determined using natural waters with various carbon conditions. The dependence of photosynthetic performance on the free CO₂, pH and alkalinity of the waters is discussed in relation to carbon metabolism. Further it is suggested that the carbon conditions are ecologically significant in relation to the productivity and success of macrophyte species in natural habitats.     

Nitrogen and sulphur requirements of Colletotrichum inamdarii Lal

Summary Nitrogen and sulphur requirements ofColletotrichum inamdarii Lal isolated from the leaves ofCarissa carandas L. have been studied. DL-serine, L-asparagine and L-phenylalanine have been found to be of good nitrogen source followed by potassium nitrate, calcium nitrate, magnesium nitrate, DL-alanine, ammonium nitrate, glutamic acid, ammonium sulphate, DL-valine, aspartic acid, ammonium chloride, ammonium hydrogencarbonate, L-histidine and potassium nitrite. There was no growth in the absence of nitrogen.Sporulation was excellent on calcium nitrate and sodium nitrate, Very good on DL-serine, potassium nitrate, and magnesium nitrate. Good on L-asparagine, L-phenylalanine and ammonium oxalate. Fair on DL-alanine, DL-leucine, ammonium sulphate, DL-valine, ammonium chloride and L-histidine whereas poor on glutamic acid, aspartic acid, ammonium tartarate and ammonium nitrate. Few spores were observed on ammonium hydrogencarbonate but potassium nitrite did not show any sporulation.Amongst the sulphur compounds sodium bisulphate gave the best growth and good sporulation, followed by sodium thiosulphate, magnesium sulphate, ammonium sulphate and potassium sulphate. Thiourea gave negligible growth whereas it failed to grow on zinc sulphate and potassium persulphate.     

Heterotrophic nitrification in a health soil demonstrated by anin situ method

Summary Nitrate reductase activity (NRA) in the leaves of two subspecies ofHypochaeris radicata was taken as a parameter for nitrate production in the soilin situ. Ammonium addition to the soil ofH. radicata ssp.radicata (soil pH 6.2) resulted in an increase of NRA, thus indicating nitrate formation by chemolithotrophic nitrifiers after a certain time-lag. Addition of ammonium to the soil ofH. radicata ssp.ericetorum (soil pH 4.3) dit not affect NRA in the leaves. Tests based on the MPN method failed to demonstrate the occurrence of chemolithotrophic nitrifiers in this soil. However, the addition of peptone led to an increase of NRA within seven days, which indicates the presence of heterotrophic nitrifying organisms. The results obtainedin situ were confirmed in a laboratory experiment, where soil samples were incubated in the presence and absence of (NH₄)₂SO₄ or peptone. The addition of ammonium led to a decrease in the production of nitrate to zero as compared with the control in the acid soil of ssp.ericetorum, whereas the addition of peptone resulted in nitrate levels amounting to about twice the control value. In the soil of ssp.radicata nitrate formation showed a rapid increase, compared with the control, after the addition of ammonium as well as after the addition of peptone.Grassland species research group, publication no27     

Phenolic content of daylight-exposed and shaded floating leaves of water lilies (Nymphaeaceae) in relation to infection by fungi

Under suboptimal growing conditions (e.g. a lack of sunshine), floating leaves of Nymphaea alba and Nuphar lutea can become heavily infected with the fungi Colletotrichum nymphaeae and Pythium F, respectively. These fungi normally act as decomposers of senescent leaves. Mature leaves of Nymphaea alba and Nuphar lutea contain high concentrations of phenolics, secondary substances known for their fungistatic properties. The production of these compounds requires energy and primary metabolites. The hypothesis that suboptimal growing conditions reduce the ability of nymphaeids to maintain a sufficiently high level of phenolics, thereby making them more vulnerable to infection by fungi, was tested. Outdoor mesocosm experiments were used to examine the response of floating leaves of Nymphaea alba and Nuphar lutea to reduced light availability. Shading significantly reduced the phenolic content of the leaves. This was accompanied by higher disease severity. The outcome of this experiment is also discussed in relation to the higher nitrogen content measured in shaded leaves. Received: 8 February 1997 / Accepted: 12 July 1997     

The influence of selected water quality parameters on the decay rate and exoenzymatic activity of detritus of Nymphaea alba L. floating leaf blades in laboratory experiments

Summary A chemostat study was conducted to investigate the influence of water quality parameters related to acidification processes on the decomposition of floating leaves of Nymphaea alba L. HCO _inf3 ^sup– and total Al concentration and pH influenced the decay rate. The activity of four cell-wall decaying exoenzymes was measured in the detritus. The activity of two types of pectic enzyme and xylanase was low under acid conditions. Cellulase activity was little affected. The exoenzyme activity seemed to be influenced by the pH of the water within the detritus. Inhibition of pectic enzymes under acid conditions may be an important factor causing the slow decay of macrophyte remains in acid waters.     

Some physiological studies in two species of phytophthora

Summary The paper deals with some physiological studies viz., (1) Production of enzymes (2) Effect of chemicals and sugar solutions and (3) Utilization of amino acids, by two species ofPhytophthora i.e.,Phytophthora palmivora Butler andP. parasitica Dast. var.macrospora Ashby., isolated from rotten fruits ofAchras sapota andAnona squamosa respectively.In the study of production of extra-cellular enzymes, it was found that both the isolates ofPhytophthora produced enzymes like inulase, amidase, emulsin and diastase in small quantity.Among the various chemicals and salt solutions used to study their effects in the formation of sporangia; it was observed that these were remarkably produced in abundance by both the species ofPhytophthora specially in the chemical solutions like sodium chloride, potassium nitrate, sodium thiosulphate and potassium permanganate. On the other hand, chemical solutions like strontium sulphate, potassium chromate, ammonium oxalate, zinc sulphate, copper sulphate, potassium sulphate, strontium nitrate and ferrous sulphate completely ceased the sporangial development. Among the various sugar solutions tried, dextrose, galactose, glucose, laevulose and fructose accelerated sporangial formation.An attempt was also made to study the effect of various amino acids singly or in combination on growth and sporulation. Both the isolates under study, utilized L-Arganine monohydrochloride and DL-Aspartic acid, hence these were growth promoters. It is interesting to note that the growth of the isolates was good, only when DL-Norleucine and DL-Methionine (both growth inhibitors) were provided in combination.Forms a part of Senior author's M.Sc. (Agriculture) Thesis, University of Poona, (Poona) India.Respectively, Ex-Jr. Res. Fellow, I.C.A.R. New Delhi; Professor of Plant Pathology and Principal, College of Agriculture, Junagad (Gujarat); and Plant Pathologist, Wheat Rust Research Station, Mahabaleshwar (Poona), India.     

Decomposition and macroinvertebrate colonization of aquatic and terrestrial leaf material in alkaline and acid still water

• 1 Decomposition of the leaves of Nymphaea alba L. and Betula pubescens Ehrh. was studied in two ponds of contrasting pH, buffering capacity and trophic level. Rates of carbon loss, concentrations of nitrogen, protein and phenolics and colonization of the leaf material by macroinvertebrates were studied.
• 2 Decomposition of B. pubescens leaves was slower than that of N. alba in both ponds. Protein and phenolic concentrations were higher in the decomposing N. alba material, whereas no significant difference was found for nitrogen concentrations.
• 3 Decomposition of both species was slower in the acid water. The effect of acid water on decomposition rate was similar for both species. Both nitrogen and protein concentrations of N. alba remained higher under acid conditions, whereas no effect of study site was observed on the protein and nitrogen concentrations in B. pubescens litter. The concentration of phenolic compounds was higher in N. alba litter from the acid pond; no such difference was observed for B. pubescens litter. The high concentrations of phenolic compounds in N. alba litter from the acid pond probably induced chemical immobilization (tanning reaction), yielding high concentrations of nitrogen and protein in the litter.
• 4 Diversity of the detritivorous macroinvertebrate fauna on the litter of both species was extremely low in the acid pond, while a relatively high diversity occurred in the alkaline water. Exclusion of large macrofauna inhibited decomposition in the alkaline water, while there was no comparable influence in the acid water.
• 5 The effects of low pH on the decomposition of both terrestrial and aquatic macrophyte litter appeared to be caused by interactive effects of low pH on the microbial decomposition, on the detritivorous macroinvertebrates and, in the case of N. alba, on the resource quality of the detritus.

     

Localization of the beet mild yellowing virus inSinapis alba L.

Virus particles of isometric shape with a diameter of 26 nm were found in the sieve tubes and accompanying phloem cells in ultrathin sections prepared from the nerves of white mustard (Sinapis alba L.) leaves and roots infected with the beet mild yellowing virus (BMYV). BMYV particles were much more frequent in the roots ofSinapis alba plants. Isometric particles were not found in the leaves and roots of healthy mustard plants.     

Sulphur requirements of certain isolates ofAlternaria tenuis Auct

The sulphur nutrition of three isolates ofAlternaria tenuis Auct., isolated from the diseased leaves ofMangifera indica L.,Musa paradisiaca L. andPsidium guajava L., was studied. They were grown on the medium devoid of sulphur as well as on media containing various sources of sulphur viz., ammonium sulphate, sodium hyposulphite, sodium thiosulphate, magnesium sulphate, potassium sulphate, potassium metabisulphite, zinc sulphate and thiourea. Sodium hyposulphite, sodium thiosulphate, magnesium sulphate, potassium sulphate and zinc sulphate were generally found to be satisfactory sources for the growth of all the isolates under study. Poor growth of the different isolates was observed on the medium devoid of sulphur.     

Nitrogen requirements of certain isolates of alternaria tenuis auct

Three isolates ofA. tenuis isolated from the diseased leaves ofMangifera indica l. Musa paradisiaca l. andPsidium guajava l. were investigated. They were grown on different sources of nitrogen viz., potassium nitrate, sodium nitrate, calcium nitrate, ammonium nitrate, sodium nitrite, ammonium sulphate, ammonium chloride, glycine, DL-valine, L-glutamic acid, urea, thiourea, L-asparagine and peptone. They were also grown on the medium lacking nitrogen. A wide variation was observed in the growth and reproduction of the different isolates. The growth of all of them was good on potassium nitrate, calcium nitrate, glycine, DL-valine, L-glutamic acid, L-asparagine and peptone but the sporulation was satisfactory on calcium nitrate only. Sodium nitrite supported moderate growth of banana leaf isolate whereas there was no growth of the other two isolates. None of the organisms could grow on the medium lacking nitrogen as well as on thiourea. The results obtained with the isolates under study have been compared with those of earlier investigators and it has been clearly established that the different isolates ofA. tenuis could show marked differences in their nitrogen requirements.     

A newHalophytophthora species,H. porrigovesica, from subtropical and tropical mangroves

A new oomycete was found from intertidal fallen leaves of mangroves in Japan and Thailand and is described here asHalophytophthora porrigovesica. This species is characterized by having an epapillate, ovate zoosporangium with a lens-shaped dehiscence plug-like material at the apex, and by forming an expanding long cylindrical vesicle prior to zoospore release. A key to 14 species and 2 varieties ofHalophytophthora including the new species is proposed. The subtropical (Iriomote is., Japan) strains and tropical (Thailand) strains were different in physiological properties and especially in the asexual reproduction. The subtropical strains showed a lower optimal temperature and wider range of suitable temperature and salinity for zoosporangium formation, whereas the tropical strains showed a higher optimal temperature and narrower range of temperature and salinity. These differences are explained as adaptations of the strains to the environmental conditions of their respective habitats. From the subtropical mangroves, six strains of the new species have been isolated only from submerged leaves ofSonneratia alba, while several strains have been isolated from tropical mangroves from the leaves of three species of mangrove trees,S. alba, Bruguiera gymnorrhiza andAvicennia alba. This indicates a change of taxon selectivity (host specificity) with the geographical distribution.     

Effects of ammonium-N on development and infectivity of the take-all fungus

Effects of applications of a mixture of ammonium sulphate and mono-ammonium phosphate and of ammonium nitrate on the incidence of take-all disease of wheat (caused by Gaeumannomyces graminis var. tritici) and on subsequent inoculum levels were studied in field and glasshouse experiments. In a field experiment in Western Australia, on a sandy soil at pH 5·4, nitrogen applications had no detectable effect on disease severity at anthesis, but ammonium sulphate treatment increased the number of propagules of the pathogen in the soil. In a pot experiment, in which seed was sown in the field experiment soils, disease was greater in soil from plots treated with ammonium sulphate and least in soil from the nil-nitrogen plots, reflecting the respective inoculum levels in the field plot. However, treatment of the soils of lower inoculum with ammonium sulphate and ammonium nitrate during this pot experiment decreased disease. A second pot experiment confirmed the effectiveness of ammonium sulphate and ammonium nitrate in reducing take-all at lower inoculum levels, and their ineffectiveness at higher inoculum levels.     

Bulk soil pH and rhizosphere pH of peach trees in calcareous and alkaline soils as affected by the form of nitrogen fertilizers

One-year old nectarine trees [Prunus persica, Batsch var. nectarina (Ait.) Maxim.], cv Nectaross grafted on P.S.B2 peach seedlings [Prunus persica (L.) Batsch] were grown for five months in 4-litre pots filled with two alkaline soils, one of which was also calcareous. Soils were regularly subjected to fertigation with either ammonium sulphate or calcium nitrate providing a total of 550 mg N/tree. Trees were also grown in such soils receiving only deionized water, as controls. Rhizosphere pH, measured by the use of a microelectrode inserted in agar sheet containing a bromocresol purple as pH indicator and placed on selected roots, was decreased by about 2–3 units compared to the bulk soil pH in all treatments. This decrease was slightly less marked when plants were supplied with calcium nitrate rather than ammonium sulphate or control. Measurements conducted during the course of the experiment indicated that ammonium concentration was similar in the solution of soils receiving the two N fertilizers. During the experiment, soil solution nitrate-N averaged 115 mg L^–1 in soil fertilized with calcium nitrate, 68 mg L^–1 in those receiving ammonium sulphate and 1 mg L^–1 in control soils. At the end of the experiment nitrate concentrations were similar in soils receiving the two N sources and bulk soil pH was decreased by about 0.4 units by ammonium sulphate fertigation: these evidences suggest a rapid soil nitriflcation activity of added ammonium. Symptoms of interveinal chlorosis in apical leaves appeared during the course of the experiment in trees planted in the alkaline-calcareous soil when calcium nitrate was added. The slightly higher rhizosphere pH for calcium nitrate-fed plants may have contributed to this. The findings suggest that using ammonium sulphate in a liquid form (e.g. by fertigation) in high-pH soils leads to their acidification and the micronutrient availability may be improved.     

六种阔叶树种叶片水浸提液对云南松种子萌发生长的化感作用

为了筛选营建云南松抗虫混交林的树种,该研究观察了云南切梢小蠹非寄主植物川滇桤木、缅桂、滇朴、樟树、麻栎和山茶六种阔叶树种叶片不同浓度的水浸提液对云南松种子萌发及幼苗生长的化感作用。结果表明:(1)川滇桤木、滇朴、麻栎和山茶四种阔叶树种叶片的水浸提液对云南松种子萌发和幼苗生长表现出低浓度促进,高浓度抑制效应。(2)在测试浓度范围内,樟树和缅桂叶片水浸提液对云南松种子萌发和幼苗生长存在抑制作用。综上所述,六种阔叶树种对云南松的化感作用敏感性不同,低浓度范围内的川滇桤木、滇朴、麻栎和山茶树叶片水浸提液对云南松生长表现出促进作用,樟树和缅桂叶片水浸提液对云南松生长具有抑制作用。因此,结合营林技术,可选用川滇桤木、滇朴、麻栎等阔叶树种与云南松混交,营建云南松抗虫混交林。     

Long-term effects of SO2 on plants,SO2 metabolism and regulation of intracellular pH

The impact of SO₂ on the ionic balance of plants and its implications for intracellular pH regulation was studied to find explanations for long-term effects of SO₂. When sulphur, taken up as SO₂ by the shoots of plants, is not assimilated in organic compounds, but stored as sulphate, an equivalent amount of H⁺ is produced. These H⁺ ions are not buffered chemically, but removed by metabolic processes.On the basis of knowledge on metabolic buffering mechanisms a conceptual model is proposed for the removal of shoot-generated H⁺ by (i) OH^- ions, produced in the leaves when sulphate and nitrate are assimilated in organic compounds and/or by (ii) OH^- ions produced by decarboxylation of organic anions (a biochemical pH stat mechanism). The form in which nitrogen is supplied largely determines the potential of the plant to neutralize H⁺ in the leaves during SO₂ uptake by the proposed mechanisms.In field experiments with N₂ fixing Vicia faba L. crops, the increase of sulphate in the shoots of SO₂-exposed plants was equivalent in charge to the decrease of organic anion content, calculated as the difference between inorganic cation content (C) and inorganic anion content (A), indicating that H⁺ ions produced in the leaves following SO₂ uptake were partly removed by OH^- from sulphate reduction and partly by decarboxylation of organic anions.The appearance of chronic SO₂ injury (leaf damage) in the field experiment at the end of the growing period is discussed in relation to the impact of SO₂ on the processes involved in regulation of intracellular pH. It is proposed that the metabolic buffering capacity of leaf cells is related to the rates of sulphate and nitrate reduction and the import rate of organic anions, rather than to the organic anion content in the vacuoles of the leaf cells.     

The response ofPlantago lanceolata L. andP. major L. spp.major to nitrate depletion

To study aspects of the ecology of grassland species, in a comparative experiment, plants ofP. lanceolata andP. major were grown in pots in a greenhouse, and subjected to a gradual nitrate depletion for several weeks. Control plants were weekly supplied with nitrate. Growth, leaf appearance and disappearance, concentrations of cations and inorganic anions, soluble and insoluble reduced nitrogen concentrations,in vivo nitrate reductase activity (NRA) and the concentration of non-structural carbohydrates in several parts of the plants were followed. Depletion of nitrate caused a reduction of shoot growth, both in biomass and number of leaves. Withering of leaves increased. Accumulation of root dry matter was little (P. lanceolata), or not (P. major) affected. The concentration of reduced nitrogen in all tissues also decreased, both that of the soluble and that of the insoluble fraction. As a result, nitrogen use efficiency (NUE, g dry matter produced per mmol N incorporated) increased by nitrate depletion. NRA was higher in the roots than in the leaves, and decreased with increasing nitrate depletion. In control plants, nitrate became also limiting. This resulted in decreasing nitrate concentrations in leaves and roots. In the leaves, the decrease in nitrate concentration was preceded by a decrease in NRA. The decrease of the nitrate concentration was parallelled by an increase in the concentration of soluble sugar. No major differences in the response towards nitrate depletion were observed between the two species. Grassland Species Research Group, publication no. 129     

Mitodepressive effects ofChelidonium alkaloids on root tip cells ofAllium cepa L

A comparison of the effects of a water extract of the fresh vegetation apex ofChelidonium majus L. var.majus, with those of berberine sulphate and of chelidonine hydrochloride is reported. The water extract of fresh stems and leaves ofChelidonium majus and the berberine sulphate solution had marked mitodepressive effects on onion root tip cells. Chelidonine hydrochloride had similar but less marked effects. On the basis of the results obtained it can be assumed that the most active group of substances with cytostatic effects, hindering the cells from entering mitosis, are protoberberine bases contained in the latex ofChelidonium majus. Within the range of the investigated concentrations the extract of fresh stems and leaves was less toxic for the cells than berberine sulphate. The data ascertained provide evidence that the mechanism of the cytostatic action of chelidonine, of berberine, as well as of the extract of fresh stems and leaves ofChelidonium, majus differs from the mechanism of the action of colchicine. Of the testedChelidonium alkaloids only chelidonine produced a partial inactivation of the mitotic spindle.     

Sulphate can induce differential expression of thioglucoside glucohydrolases (myrosinases)

Thioglucoside glucohydrolase (EC 3.2.3.1; myrosinase) hydrolyses glucosinolates and thereby liberates glucose and sulphur and nitrogen compounds. To examine the hypothesis that the myrosinase-glucosinolate system is influenced by environmental factors, the effect of sulphate on the expression of myrosinases was examined. On examining different plant organs at various stages, it was observed that sulphate induces a differential expression of myrosinase polypeptides in plants ofSinapis alba L. (white mustard). Specific myrosinase polypeptides, dependent on sulphate in the growth medium, were detected on immunoblots. Without sulphate a maximum of three polypeptides was detected in buds, two in cotyledons and one in stems and roots. In plants cultured on medium with sulphate up to four polypeptides could be observed in cotyledons, five polypeptides in buds, two in stems and one in roots. Expression of myrosinases was, in general, high in plants cultured on a medium supplemented with sulphate. In floweringS. alba plants, sulphate-starved plants showed a higher expression of myrosinase in cotyledons and stems compared to plants fed with sulphate. Sulphate-fed plants had a high expression in inflorescences and roots. The organ- and time-specific induction of the myrosinase expression is discussed in relation to sulphate metabolism and availability of sulphate under normal conditions of cultivation and in relation to protection of Brassicaceae species. This is the first evidence for a specific induction of individual myrosinase proteins.     

Production,nutrient dynamics and initial decomposition of floating leaves of Nymphaea alba L. and Nuphar lutea (L.) Sm. (Nymphaeaceae) in alkaline and acid waters

Production, turnover and nutrient dynamics of floating leaves of Nymphaea alba L. and Nuphar lutea (L.) Sm. were studied in four aquatic systems in The Netherlands, differing strongly in water quality. Production was 108–447 g AFDW.m⁻² for N. lutea and 319–348 g AFDW.m⁻² for N. alba. Turnover ranged from 3.6 to 4.4 without much difference between the sites and the species. During senescence 60–70% of the N and P from the leaves was resorbed by both of the plant species. The nutrient flow from the floating leaves into the detritus food chain differed considerably between the species and sites studied, mainly because of the differences in production. The data suggest that production is strongly influenced by the environment, whereas turnover and nutrient resorption during senescence seem to be plant characteristics. There was little difference in dynamics of the chlorophyll-α concentration in the leaves of the two species, irrespective of the growing site. Floating leaves of both species lost about 70% of their area due to fragmentation in the alkaline waters, whereas in the acid water very little fragmentation was observed.     

Spirulina culture in sea-water

Summary Laboratory experiments using small raceway ponds have shown that Spirulina maxima can be adapted easily to grow in sea-water supplemented with nitrate, phosphate, bicarbonate, and Fe-EDTA. To prevent precipitate formation, phosphate was supplied by diffusion through a dialysis membrane; the amount of Na-bicarbonate added was low (100 ppm) and the pH was kept in the range 8.6–8.8 by bubbling CO₂ into the culture.No significant differences have been noticed in productivity or in the chemical composition of the biomass between cultures in sea-water and in the standard bicarbonate medium. Cultures subjected to light/dark cycles of 12/12 h showed a higher respiration rate in sea-water than in the bicarbonate medium.The higher weight loss in the sea-water medium in the dark was counterbalanced by an increased synthesis of carbohydrates during the light period.