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     

Ammonium and nitrate nutrition inPlantago lanceolata andPlantago major L. ssp.major

P. lanceolata andP. major were grown in culture solutions with nitrate or ammonium as the nitrogen source. Dry matter accumulation in the shoot was faster with nitrate than with ammonium, whilst that of the roots was not affected by the nitrogen source. As a consequence, the shoot-to-root ratio was lower with ammonium than with nitrate. InP. lanceolata, dry matter percentage of shoot and root tissue was lower with nitrate nutrition, suggesting better elongation growth than with ammonium. However, in shoot tissue ofP. major the opposite was found. The rate of root respiration declined with time, and this was almost completely due to a declining activity of the alternative path, which amounted to about 30–60% of total root respiration. Respiration via the cytochrome path was for a part of time slightly increased by ammonium, whereas the activity of the alternative path was strongly enhanced. The concentration of ethanol-soluble carbohydrates (SC) in the roots of both species was higher when nitrate was used, but no difference in the concentration of starch was found. When the plants were transferred from one nitrogen source to the other, many parameters, including the concentration of nitrate and chloride, and the shoot to root ratio, adjusted to the new situation in both species. Grassland Species Research Group, Publication no. 116.     

Nitrate reduction in the leaves and numbers of nitrifiers in the rhizosphere ofPlantago lanceolata growing in two contrasting sites

Summary Numbers of autotrophic nitrifiers in the rhizosphere, and thein vivo nitrate reductase activity (NRA) in the leaves of individual plants ofPlantago lanceolata were determined in plants at two contrasting sites. In a dune grassland, high numbers of nitrifiers were present in the rhizosphere, and significant NRA was detected in the leaves. During dry periods nitrate utilization sometimes was depressed. In a wet hayfield, on peat soil, very low numbers of nitrifiers were found in the rhizosphere. Also the NRA was low. In the wet habitat, the NRA in the leaves of some fen species, containing aerenchyma in the roots, was higher than that ofP. lanceolata, not containing aerenchyma.Grassland Species Research Group. Publication No. 105.     

Nitrate reductase activity in leaves and roots ofAlnus glutinosa (L) Gaertner

Summary Thein vivo nitrate reductase activity (NRA) was determined inAlnus glutinosa plants grown nonsymbiotically on ammonium, nitrate, a combination of both, or symbiotically with atmospheric nitrogen as the only nitrogen source. Root NRA was absent when ammonium or atmospheric nitrogen was the nitrogen source. With nitrate in the culture solution the roots showed a high NRA. However, the leaf NRA behaved quite differently: with negligible activities on all nitrogen sources except atmospheric nitrogen. The foliar NRA measured, however, is likely not due to the activity of the plant but of microbial origin. Methods commonly used to facilitate produced nitrite to leak out of the tissue, such as addition of propanol and cutting the plant material, did not increase the nitrite release from the leaves. A turbidity developed when testing the samples for nitrite which was positively correlated with the NRA. Populations of microorganisms in the phyllosphere did not differ between the nutritional treatments. Bacteria, able to grow on a low-nitrogen medium, were present on the leaves. Nitrifiers could not be detected. The bacteria on the leaves appear to produce nitrite when incubated with leaf material. Grassland Species Research Group, Publication no. 106     

The effect of nitrate concentration in a flowing solution system on growth and nitrate uptake of twoPlantago species

Summary Juvenile plants ofPlantago lanceolata andP. major ssp.major were grown in a flowing solution system at 7.5 mM or 9.5 M NO₃. The parameters investigated were: RGR, shoot weight percentage, leaf length, length of main root axis, shoot concentrations of major ions and organic N, and the specific uptake rate for NO₃. At 9.5 M NO₃ growth ofP. major was not hampered, whereas shoot growth and leaf length ofP. lanceolata were reduced. The NO₃ concentration ofP. lanceolata decreased more than that ofP. major. The different performances of the species at 9.5 M NO₃ were associated with different specific uptake rates. In both treatments the root system ofP. major was shorter than that ofP. lanceolata. P. lanceolata accumulated more NO₃ in the leaves. The performance of thePlantago species is discussed in relation to the availability of nutrients in their habitats.Grassland Species Research Group. Publication no. 37.     

Establishment of Plantago lanceolata L. and Plantago major L. among grass

Summary Establishment of Plantago lanceolata and P. major ssp major among grass was studied in a field experiment in which survival and selection on date of seedling emergence and plant size was investigated in relation to the vegetation structure. P. major — in contrast to P. lanceolata — was not able to establish itself in grass because of its lower competitive ability caused by later germination, smaller seedling size, and shorter leaves. In both species there was selection for early germination. For P. lanceolata a significant correlation was found between the strength of selection and the light climate, determined by the structure of the grass sward. Plants that germinated early were at an advantage because they were larger, especially the leaves, when compared with plants that germinated late. It seems likely that selection was mainly by competition for light. Contrary to expectation P. major-seedlings had a higher shade tolerance than those of P. lanceolata. The performance of both species is discussed in relation to their different life strategies.Grassland species research group publication no 142     

Influence of NO3 - and NH4 + nutrition on fermentation,nitrate reductase activity and adenylate energy charge of roots of Carex pseudocyperus L. and Carex sylvatica Huds. exposed to anaerobic nutrient solutions

The adenylate energy charge, production of ethanol and lactate, and nitrate reductase activity were determined in order to study the influence of different nitrogen sources on the metabolic responses of roots of Carex pseudocyperus L. and Carex sylvatica HUDS. exposed to anaerobic nutrient solutions. Determination of adenylates was carried out by means of a modified HPLC technique. Total quantity of adenylates was higher in Carex pseudocyperus than in Carex sylvatica under all conditions. In contrast, the adenylate energy charge was only slightly different between the species and decreased more or less in relation to the applied nitrogen source under oxygen deficiency. The adenylate energy charge in roots of plants under nitrate nutrition showed a smaller decrease under anaerobic environmental conditions than plants grown with ammonium or nitrate/ammonium. Roots of nitrate-fed plants showed a lower ethanol and lactate production than ammonium/nitrate- and ammonium-fed plants. Ethanol production was higher in C. pseudocyperus, formation of lactate was lower compared to that in Carex sylvatica. The activity of enzymes involved in fermentation processes (ADH, LDH and PDC) was enhanced significantly after 24 hours of exposure to anaerobic nutrient solutions in roots of both species. The induction of these enzymes was only slightly influenced by different nitrogen supply. In vivo nitrate reductase activity increased almost 3-fold compared to the aerobic treatment in both species and overcompensated loss of NADH reoxidation capacity caused by decrease of ethanol and lactate development. Induction of in vitro nitrate reductase activity was enhanced 313% in C. pseudocyperus and 349% in C. sylvatica under anaerobic environmental conditions and nitrate supply. These results indicate that nitrate may serve as an alternative electron acceptor in anaerobic plant root metabolism and that the nitrate-supported energy charge may be due to an accelerated glycolytic flux resulting from a more effective NADH reoxidation capacity by nitrate reduction plus fermentation than by fermentation alone.Abbreviations ADH alcohol dehydrogenase - AEC adenylate energy charge - DMSO dimethyl sulfoxide - EDTA ethylen diamine tetraacetic acid - HPLC high performance liquid chromatography - LDH lactate dehydrogenase - NRA nitrate reductase activity - PCA perchloric acid - PDC pyruvate decarboxylase - PVP polyvinylpyrrolidone - PVPP polyvinylpolypyrrolidone - TCA trichloroacetic acid, Tris-tris(hydroxymethyl)aminomethane     

Nitrate production in the rhizosphere of Plantago species

Summary The production of nitrate in an old established dune grassland soil and its uptake by plants was studied by comparing amounts of mineral nitrogen and numbers of nitrifying bacteria in the rhizosphere on the one hand, and on the other accumulated nitrate and levels of nitrate reductase (NaR) of individual plants of three Plantago species,i. e., P. major, P. lanceolata andP. coronopus. For these three Plantago species andP. media basal levels of NaR in the absence of nitrate were determined in plants grown in culture solutions. The basal NaR levels ofP. major andP. media (species occurring on nutrient-rich soils) were significantly higher than those ofP. lanceolata andP. coronopus (species found on nutrient-poor soils). NaR activity increased in the presence of nitrate and was suppressed by ammonium.From the numbers of nitrifying bacteria in the rhizosphere and NaR activity in the leaves it was concluded that nitrate was produced in the root environments of the three Plantago species and that the compound was taken up by the plants. NaR activities and numbers of nitrifying bacteria were higher for individuals ofP. major than for those ofP. lanceolata andP. coronopus. No correlation was found between the ammonium levels and the numbers of nitrifying bacteria in the soil, and no indications of inhibition of nitrifying bacteria in the rhizosphere were obtained. For individuals ofP. lanceolata a correlation was found between the numbers of nitrifying bacteria in the soil and NaR activity in the leaves. The results are discussed in relation to the ecological habitats of the three species.Grassland Species Research Group Publication No.38.     

How does glutamine synthetase activity determine plant tolerance to ammonium?

The wide range of plant responses to ammonium nutrition can be used to study the way ammonium interferes with plant metabolism and to assess some characteristics related with ammonium tolerance by plants. In this work we investigated the hypothesis of plant tolerance to ammonium being related with the plants’ capacity to maintain high levels of inorganic nitrogen assimilation in the roots. Plants of several species (Spinacia oleracea L., Lycopersicon esculentum L., Lactuca sativa L., Pisum sativum L. and Lupinus albus L.) were grown in the presence of distinct concentrations (0.5, 1.5, 3 and 6 mM) of nitrate and ammonium. The relative contributions of the activity of the key enzymes glutamine synthetase (GS; under light and dark conditions) and glutamate dehydrogenase (GDH) were determined. The main plant organs of nitrogen assimilation (root or shoot) to plant tolerance to ammonium were assessed. The results show that only plants that are able to maintain high levels of GS activity in the dark (either in leaves or in roots) and high root GDH activities accumulate equal amounts of biomass independently of the nitrogen source available to the root medium and thus are ammonium tolerant. Plant species with high GS activities in the dark coincide with those displaying a high capacity for nitrogen metabolism in the roots. Therefore, the main location of nitrogen metabolism (shoots or roots) and the levels of GS activity in the dark are an important strategy for plant ammonium tolerance. The relative contribution of each of these parameters to species tolerance to ammonium is assessed. The efficient sequestration of ammonium in roots, presumably in the vacuoles, is considered as an additional mechanism contributing to plant tolerance to ammonium nutrition.     

Biomass production and nitrate metabolism of Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L. (C4 plant) in cultures at different levels of nitrogen supply

Summary Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C₃ plant) and Amaranthus retroflexus L. (C₄ plant) were maintained under open air conditions in standard soil at low and high nitrogen supply levels.A comparison of shoot dry weight and shoot length in the various series shows that the growth of the aboveground parts of both species was severely reduced under low N conditions. In both pure and mixed cultures the differences resulting from low N vs. high N conditions was less pronounced with Atriplex (C₃ plant) than with Amaranthus (C₄ plant). The root dry weight of the two species was not reduced so much under low N conditions as was the shoot dry weight. The low N plants were found to contain a larger proportion of their biomass in the roots than did the high N plants. In general the root proportion of Atriplex was greater than that of Amaranthus. The contents of organic nitrogen and nitrate and the nitrate reductase activity (NRA) per g dry weight of both species decreased continually throughout the experiments. With the exception of young plants, the low N plants always had tower contents of organic nitrogen and nitrate and nitrate reductase activities than did the high N plants. The highest values of NRA were measured in the leaf laminae. The eaves also exhibited the highest concentrations of organic nitrogen. The highest nitrate concentrations, however, were observed in the shoot axis, and in most cases the lowest nitrate values were found in the laminae. At the end of ne growing season this pattern was found to have been reversed with Atriplex, but not with Amaranthus. Thus Atriplex was able to maintain a higher NRA in the laminae than Amaranthus under low N conditions.The transpiration per leaf area of the C₄ plant Amaranthus during the course of a day was substantially lower than that of the C₃ plant Atriplex. There were no significant differences in transpiration between the low N and high N series of Amaranthus. The low N plants of Atriplex, however, clearly showed in most cases higher transpiration rates than the corresponding high N plants. These different transpiration rates of the high N and the low N Atriplex plants were also reflected in a distinct ¹³C discrimination.The sum of these results points to the conclusion that the C₃ plant Atriplex hortensis can maintain a better internal inorganic nitrogen supply than the C₄ plant Amaranthus retroflexus under low N conditions and an ample water supply, due to the larger root proportion and the more pronounced and flexible transpiration of the C₃ plant.Dedicated to Prof. Dr. Karl Mägdefrau, Deisenhofen, on the ocasion of his 80th birthday     

Nitrate reduction and nitrate content in ash trees (Fraxinus excelsior L.): distribution between compartments,site comparison and seasonal variation

Summary Nitrate reductase activity (NRA), nitrate content and biomass components of leaflets, leaf stalks, old stem, current-year stem and roots of ash trees (Fraxinus excelsior L.) growing in their natural habitats were investigated. In addition, NRA, total nitrogen and nitrate concentration were analyzed in the leaves and roots of ash trees from four different field sites. The highest NRA per gram biomass and also per total compartment biomass was found in the leaflets, even though root biomass was much higher than total leaflet biomass. The highest nitrate concentrations were found in the leaf stalks. Correlations between nitrate availability in the soil and NRA in leaves were not significant due to high variability of the actual soil nitrate concentrations. The seasonal variation in foliar NRA, nitrate concentration and total nitrogen concentration is much smaller in F. excelsior than reported for herbaceous species and is mainly caused by changes in the actual soil nitrate availability and by senescence of the leaves.     

Effects of NaCl salinity on 15N-nitrate fluxes and specific root length in the halophyte Plantago maritima L.

The effect of salinity on nitrate influx, efflux, nitrate net uptake rate and net nitrogen translocation to the shoot was assessed in a ¹⁵N steady state labelling experiment in the halophyte Plantago maritima L. raised for 14 days on solution supplied with 50, 100 and 200 mol m^–3 sodium chloride or without sodium chloride. Additionally, salinity induced changes in root morphology were determined. Specific root length increased upon exposure to elevated sodium chloride concentrations due to variations in biomass allocation and length growth of the tap root. Changes in root morphology, however, had a minor effect on nitrate fluxes when expressed on a root fresh weight basis. The decreased rate of nitrate net uptake in plants grown on elevated levels of sodium chloride was almost entirely due to a decrease in nitrate influx. Expressed as a proportion of influx, nitrate efflux remained unchanged and was even lower at the highest salinity level. At all sodium chloride concentrations applied the initial rate of nitrogen net translocation to the shoot decreased relative to the rate of nitrate net uptake. It is concluded that under steady state conditions the negative effect of sodium chloride on the rate of nitrate net uptake at non growth-limiting salinity levels was due to the interaction between sodium chloride and nitrate transporters in the root plasma membrane and/or processes mediating the translocation of nitrogen compounds, possibly nitrate, to the shoot.     

Kinetics of nitrate uptake by different species from nutrient-rich and nutrient-poor habitats as affected by the nutrient supply

The species Urtica dioica L., Plantago major ssp. major L., Plantago lanceolata L., Hypochaeris radicata L. ssp. radicata and Hypochaeris radicata ssp. ericetorum Van Soest were grown under high and low nutrient conditions (1/4 Hoagland and 2% of 1/4 Hoagland further called the 100% and 2% treatment, containing 3.75 mM NO^-₃ and 0.075 mM NO^-₃, respectively). After a certain period half of the plants were transferred from low to high or high to low nutrients, yielding the 100%/2% and the 2%/100% treatments. The kinetics of nitrate uptake in the range of system I of the five species grown under the different nutrient conditions were measured during a three week experimental period. The nitrate uptake of all the species showed the characteristic features of Michaelis-Menten kinetics. Under low nutrient conditions the apparent V_max of U. dioica expressed per g dry root was lower than under high nutrient conditions. For H. radicata ssp. radicata and for H. radicata ssp. ericetorum the reverse was found. The V_max values of P. major ssp. major were almost the same for the two treatments. The apparent V_max in young plants of P. lanceolata was higher in the 100% treatment than in 2%; whereas the reverse was found in mature plants. The results are explained in relation to the relative growth rate, the shoot to root ratio and the natural environment of the species. The apparent K_m values were not influenced by the different treatments. Differences in K_m between the species, if any, were very small. It is suggested that the V_max is a more important parameter for the distribution of plant species in the field than the K_m. The rate of nitrogen accumulation was calculated from growth data and the contents of nitrate and reduced nitrogen. It is concluded that the V_max of system I for nitrate uptake in most cases was sufficient to explain the observed growth rates.     

Importance of seed Zn content for wheat growth on Zn-deficient soil

Eggplants (Solanum melongena L. cv. Bonica) were grown in a glasshouse during summer under natural light with one unbranched shoot or one shoot with 3 to 4 branches and with or without fruit in quartz sand buffered and not buffered with 0.5% CaCO₃ (w : v), respectively. Nutrient solutions supplied contained nitrate or ammonium as the sole nitrogen source. Compared with nutrient solutions containing nitrate (10 mM), solutions containing ammonium (10 mM) caused a decrease in net photosynthesis of eggplants during early stages of vegetative growth when grown in quartz sand not buffered with CaCO₃. The decrease was not observed before leaves showed interveinal chlorosis. In contrast, net photosynthesis after bloom at first increased more rapidly in eggplants supplied with ammonium than with nitrate nitrogen. However, even in this case, net photosynthesis decreased four weeks later when ammonium nutrition was continued. The decrease was accompanied by epinasty and interveinal chlorosis on the lower leaves and later by severe wilting, leaf drop, stem lesions, and hampered growth of stems, roots, and fruits. These symptoms appeared later on plants not bearing fruits than on plants bearing fruits. If nutrient solutions containing increasing concentrations of ammonium (0.5–30 mM) were supplied after the time of first fruit ripening, shoot growth and set of later flowers and fruits were promoted. In contrast, vegetative growth and reproduction was only slightly affected by increasing the concentration of nitrate in the nutrient solutions. In quartz sand buffered with CaCO₃ ammonium nutrition caused deleterious effects only under low light conditions (shade) and on young plants during rapid fruit growth. If eggplants were supplied with ammonium nitrogen before bloom, vegetative growth was promoted, and set of flowers and fruit occurred earlier than on plants supplied with nitrate. Furthermore, the number of flowers and fruit yield increased. These effects of ammonium nutrition were more pronounced when plants were grown with branched shoots than with unbranched shoots. The results indicate that vegetative and reproductive growth of eggplants may be manipulated without causing injury to the plants by supplying ammonium nitrogen as long as the age of the plants, carbohydrate reserves of the roots, quantity of ammonium nitrogen supplied, and pH of the growth medium are favourable. T W Rufty Section editor     

Nitrate assimilation in the forage legume Lotus japonicus L.

Nitrate assimilation in the model legume, Lotus japonicus, has been investigated using a variety of approaches. A gene encoding a nitrate-inducible nitrate reductase (NR) has been cloned and appears to be the only NR gene present in the genome. Most of the nitrate reductase activity (NRA) is found in the roots and the plant assimilates the bulk of its nitrogen in that tissue. We calculate that the observed rates of nitrate reduction are compatible with the growth requirement for reduced nitrogen. The NR mRNA, NRA and the nitrate content do not show a strong diurnal rhythm in the roots and assimilation continues during the dark period although export of assimilated N to the shoot is lower during this time. In shoots, the previous low NR activity may be further inactivated during the dark either by a phosphorylation mechanism or due to reduced nitrate flux coincident with a decreased delivery through the transpiration stream. From nitrate-sufficient conditions, the removal of nitrate from the external medium causes a rapid drop in hydraulic conductivity and a decline in nitrate and reduced-N export. Root nitrate content, NR and nitrate transporter (NRT2) mRNA decline over a period of 2 days to barely detectable levels. On resupply, a coordinated increase of NR and NRT2 mRNA, and NRA is seen within hours.     

Polymorphic microsatellite loci in Plantago lanceolata

The genus Plantago is particularly interesting for evolutionary studies because of its wide range of mating systems. We have developed primers for five highly polymorphic microsatellite loci isolated from P. lanceolata. All five loci amplified and were polymorphic in the two populations examined, Lowsteads Beach in the United Kingdom and Duke in the United States. These new markers will allow a comparison of population structure between the outcrossing species P. lanceolata, and the highly selfing species P. major.     

Genetic differentiation in Plantago major L. in growth and P uptake under conditions of P limitation

To study possible adaptive mechanisms inbred lines from three populations of Plantago major from sites that were found to differ in P availability were compared. In a pot experiment the growth and P uptake either in the presence or absence of Glomus fasciculatum was determined. Under these P-limited conditions it was shown by partitioning the relative growth rate (RGR, in mg g^-1 day^-1) in the components root weight ratio (RWR, in g_roots g_plant ^-1), specific P uptake rate (SPUR, in mol P g_roots ^-1 day^-1), and P-efficiency (PEFF, in mg mol P^-1), that the increase in RGR of mycorrhizal infected plants was related to an increase in SPUR, and a decrease in RWR and PEFF. P. major ssp. major had a lower RGR (related to a lower PEFF and SPUR) and a higher RWR than P. major ssp. pleiosperma. In a second experiment three inbred lines were compared upon P depletion in a nutrient solution. The P. major ssp. major line had a lower RGR and higher RWR, and a higher accumulation of P in the roots than the P. major ssp. pleiosperma lines under optimal growing conditions. There were no differences among the inbred lines in the relative contribution of inorganic P to the total P concentration in the shoot. The results are discussed in relation to the characteristics of the habitats of the investigated P. major populations.     

Partitioning of inorganic nitrogen assimilation between the roots and shoots of cerrado and forest trees of contrasting plant communities of South East Brasil

Summary Woody plants growing in cerrado and forest communities of south-east Brasil were found to have low levels of nitrate reductase activity in their leaves suggesting that nitrate ions are not an important nitrogen source in these communities. Only in the leaves of species growing in areas of disturbance, such as gaps and forest margins, were high levels of nitrate reductase present. When pot-grown plants were supplied with nitrate, leaves and roots of almost all species responded by inducing increased levels of nitrate reductase. Pioneer or colonizing species exhibited highest levels of nitrate reductase and high shoot: root nitrate reductase activities. Glutamine synthetase, glutamate synthase and glutamate dehydrogenase were present in leaves and roots of the species examined.¹⁵N-labelled nitrate and ammonium were used to compare the assimilatory characteristics of two species:Enterolobium contortisiliquum, with a high capacity to reduce nitrate, andCalophyllum brasiliense, of low capacity. The rate of nitrate assimilation in the former was five times that of the latter. Both species had similar rates of ammonium assimilation. Results for eight species of contrasting habitats showed that leaf nitrogen content increased in parallel with xylem sap nitrogen concentrations, suggesting that the ability of the root system to acquire, assimilate or export nitrate determines shoot nitrogen status. These results emphasise the importance of nitrogen transport and metabolism in roots as determinants of whole plant nitrogen status.     

Effects of rhizosphere soil,vesicular-arbuscular mycorrhizal fungi and phosphate onPlantago major L. ssp.pleiosperma Pilger

Biotic factors in the rhizosphere and their effect on the growth ofPlantago major L. ssp.pleiosperma Pilger (Great plantain) were studied. In a pot experiment the effect on shoot growth of the addition of 2.5% rhizosphere soil at four levels of phosphate was highly dependent on the availability of phosphate: a promoting effect at low phosphate levels was observed while a reducing effect occurred at higher phosphate levels. As the roots were infected with vesicular-arbuscular mycorrhizal (VAM) fungi in the treatment with rhizosphere soil, two other experiments were set up to separate effects of the indigenous VAM fungi from effects of the total rhizosphere population. The uptake of phosphate and shoot growth was not decreased at higher phosphate availability when VAM inoculum was added alone or in combination with rhizosphere soil. The growth reducing effect of the rhizosphere soil could therefore not be ascribed only to mycorrhizal infection. The results suggest that biotic factors in the rhizosphere soil affect the phosphate uptake ofPlantago major ssp.pleiosperma. This may, under conditions of phosphate limitation, lead to an increase of phosphate stress and, subsequently, a growth reduction. Futhermore, it is concluded that VAM fungi, as part of the rhizosphere population, may compensate this phosphate stress by enhancing the phosphate uptake.Grassland Species Research Group Publication No. 148.     

Anti-mitotic and anti-genotoxic effects of Plantago lanceolata aqueous extract on Allium cepa root tip meristem cells

Plantago is the most important genus of Plantaginaceae family and is used in traditional medicine around the world for different purposes. Plantago coronopus L., Plantago major L., Plantago media L. and Plantago lanceolata L. are most commonly used species of Plantago in traditional medicine in Turkey. The main goal of this study was to investigate the eventual anti-mitotic and anti-genotoxic effects of P. lanceolata L. leaf aqueous extracts (15 g/L and 30 g/L) on Allium cepa L. root tip meristem cells which were treated with 0.7% hydrogen peroxide. For this purpose, two different experiments were performed under the same conditions. In the first experiment, Allium cepa onion bulbs were treated with 0.7% H₂O₂ for 1 h. After the H₂O₂ treatment, the onion bulbs were treated with two different concentrations (15 g/L and 30 g/L) of P. lanceolata extracts for 24 h. In the second experiment, A. cepa onion bulbs were treated with two different extract concentrations (15 g/L and 30 g/L) for 24 h and then with 0.7% H₂O₂ for 1 h. The test concentrations were determined according to doses which are recommended in alternative medicinal usage by people. As positive and negative control 0.7% H₂O₂ and tap water was used, respectively. As a result, it was determined that aqueous extracts reduced mitotic index and chromosome aberrations in treatment groups in comparison with controls. These results showed that P. lanceolata aqueous extracts have anti-mitotic and anti-genotoxic effects.