Symbiotic Performance of Supernoclulating Soybean (Glycine max (L.) Merrill) Mutants during Development on Different Nitrogen Regimes

Growth and symbiotic performance of soybean (Glycine max (L.)Merrill) cv. Bragg and three of its induced nodulation mutants(nod49, non-nodulating; ntsl 116, intermediate supernodulator;nts1007, extreme supernodulator) were compared throughout developmentunder different nitrogen regimes (0, 2, 5 and 10 mol nitratem^–3). Nitrogen fixation was assessed using ¹⁵N-isotopedilution and xylem sap analysis for ureide content. Both techniquesconfirmed a complete lack of N₂ fixation activity in nod49.Plant reliance on nitrogen fixation by the other genotypes wasdependent on the nitrate regime and the developmental stage.The ntsl007 and ntsl 116 mutants fixed more nitrogen than theparent cultivar in the presence of 10 mol m^–3 nitratein the nutrient solution, but higher input of symbioticallyderived nitrogen was still insufficient to offset the amountof nitrogen removed in the harvested seed. However, the mutantsutilized less nitrate for growth than Bragg. Comparison of estimatesof N₂ fixation derived from the ¹⁵N-dilution technique withthose based on relative ureide content of xylem sap indicatedthat the latter offered a simple and reliable procedure forevaluating the symbiotic performance of supernodulating plants. Key words: ¹⁵N-isotope dilution, supernodulation, ureides     

Further Evidence for the Relationship between Light-Induced Changes of Plasmalemma Transport and Transthylakoid Proton Uptake

The simultaneous measurement of the induction curves of chlorophyllfluorescence, its responses to saturating flashes, light-scatteringat 532 nm, and plasmalemma voltage supports previous findings(Hansen, Kolbowski, and Dau, 1987), that light-induced uptakeof protons into the inner thylakoid space causes the rapid (5to 20 s) light-induced depolarization at the plasmalemma viasubstrate depletion of the electrogenic H⁺-pump. These conclusionsare based on kinetic studies which enable the separation ofindividual components in complex signals by means of their assignmentto different time-constants. In contrast to the previous investigation,binary noise was used for modulation of the actinic light. Thenew input signal not only increased the reliability of the previousresults obtained by sine-waves, but also led to the detectionof three additional time-constants. One of these is probablyrelated to the action of light on the potassium channel of theplasmalemma. The others are assigned to the quencher Q and toa still unknown process. Key words: Chlorophyll fluorescence, plasmalemma potential, proton fluxes, noise, scattering, spinach, state-transitions, thylakoid membrane     

Synthesis of Carcinoembryonic Antigen <Emphasis Type="Italic">in vitro</Emphasis>

NORMAL and neoplastic mammalian cells cultivated in vitro retain a number of functions that characterize their cellular origin, even after extensive passage¹. It therefore seems reasonable to expect that cell products such as tumour-associated antigens could, if present from the outset, be retained in a demonstrable state when the tumour cells are cultivated outside the original host organism. The discovery by Gold and Freedman² of an antigenic substance specific for entodermally-derived cancers of the digestive system, carcinoembryonic antigen (CEA), provides a suitable candidate for studying one such property related to a particular type of human cancer. It has been proposed, however, that tumour-specific antigens such as CEA are not indigenous to the tumours, but are glycoproteins produced elsewhere in the body and coating the tumour cells secondarily³. If this were the case, then human colonic cancer cells in long-term propagation in vitro should not synthesize this material. We now present evidence to the contrary.     

Morphactin and Adventitious Root Formation in Pea Cuttings

Stock plants of pea (Pisum sativum L. cv. Alaska) were grown at different controlled levels of irradiance (4, 16 or 38 W m^?2) for 11 days from sowing. Morphactin (CFM, methyl-2-chloro-9-hydroxy-fluorene-9-carboxylate) was applied to the apex of the stock plants 3 days before cuttings were excised. The cuttings were rooted at 16 W m^?2. High levels of morphactin (>5 × 10^?3 mg l^?1) inhibited root formation in the cuttings. Low concentrations of CFM (5 × 10^?5 mg l^?1) promoted the formation of adventitious roots in cuttings from plants grown at all three levels of irradiance, with the most pronounced effect in cuttings from 4 W m^?2. Measurements of ethylene evolution by CFM-treated plants 3 days after application, revealed a stimulatory effect on ethylene production by high CFM concentrations.     

Seasonal pattern in nutrient limitation and grazing control of the phytoplankton community in a non-stratified lake

1. The relative importance of zooplankton grazing and nutrient limitation in regulating the phytoplankton community in the non-stratified Lake Kvie, Denmark, were measured nine times during the growing season.
2. Natural phytoplankton assemblage bioassays showed increasing importance of nutrient limitation during summer. Growth rates at ambient nutrient concentrations were continually below 0.12 per day, while co-enrichment with nitrogen (N) and phosphorus (P) to above concentration-saturated conditions enhanced growth rates from May to the end of July.
3. Stoichiometric ratios of important elements in seston (C : N, C : P, N : P), in lake water (TN : TP), in external loading (TN : TP) and in internal loading (DIN : DIP) were measured to determine whether N or P could be the limiting nutrient. TN : TP molar ratio of both lake water, benthic fluxes and external loading suggested P limitation throughout the growing season. However, seston molar ratios suggested moderate P-deficiency only during mid-summer.
4. Abundance and community structure of the zooplankton varied considerably through the season and proved to be important in determining the responses of algal assemblages to grazing. High abundance of cladocerans and rotifers resulted in significant grazing impact, while cyclopoid copepods had no significant effect on the phytoplankton biomass.
5. Regeneration of ammonium and phosphate by zooplankton were periodically important for phytoplankton growth. A comparison of nutrient regeneration by zooplankton with nutrient inputs from sediment and external sources indicated that zooplankton may contribute significantly in supplying N and P for the growth of phytoplankton.     

Avian rarity in ten cloud-forest communities in the Andes of Ecuador: implications for conservation

Avian rarity was investigated in ten high-altitude cloud forests in the Andes of Ecuador. Data on species compositions and abundances were obtained by a fully standardized method (standardization for area, altitude, habitat, effort and seasonality). The rare species were isolated from rank-abundance plots on the basis of the quartile definition of rarity. A positive correlation between mean abundances of species and number of sites occupied suggests that high-altitude bird species classified rare by abundance generally can also be classified rare by range. However, it is necessary to be cautious using this result in ranking conservation priorities since the generality is not obeyed by all species. Within the two abundance classes (contains one and two individuals, respectively) represented among the rare species, the one-individual class had significantly more species than the two-individual class. The quantitative rarity of taxa and ecological groupings produced similar results for all sites, while pairwise similarity of rare species between sites was very low. Together with the difficulty of identifying species that are truly rare by abundance, these results imply that sites selected for conservation preferably should be based upon a qualitative evaluation of lists of species referred to vulnerability categories such as endemic, restricted-range, CITES or IUCN threatened/near-threatened species. However, it is necessary also to incorporate other aspects of biodiversity to cover a full range of biotic diversity.     

Nitrogen Economy of Post-fire Stands of Shrub Legumes in Jarrah (Eucalyptus marginata Donn ex Sm.) Forest of S.W. Australia

Hansen, A. P., Pate, J. S., Hansen, A. and Bell, D. T. 1987.Nitrogen economy of post-fire stands of shrub legumes in jarrah(Eucalyptus marginata Donn ex Sm.) forest of S.W. Australia.—J.exp. Bot. 38: 26–41. Growth, demography and N economy of 1–6-year-old standsof Acacia pulchella, A. alata, A. extensa and Bossiaea aquifoliumwere examined using population sampling to assess annual incrementsof N as living biomass, and returns of N as litter, seed anddead plants. Dependence on nitrogen fixation was assessed fromseasonal profiles of acetylene reduction, employing data fromprevious calibrations to convert C₂H₂ reduced to N₂ fixed. After2 years of slow growth and minimal reproduction all speciesgrew rapidly to achieve maximum or near maximum size and seedproduction. Intense self-thinning of stands occurred in thesecond and third years, especially in the highly dense standsof the smallest species, A. alata. Annual turnover in standsranged from 0?3 to 127 kg N ha^–1 year^–1, dependingon species current age and density of a stand. Returns of Nas litter and shed seed comprised small proportions of the annualbudgets, but returns due to plant death equalled or exceededincrements of living biomass in years when stands were thinningrapidly. Proportional dependencies of the species on fixed N₂were relatively high (13–61%) in first year seedlings,and then declined markedly to 1?1–3?4percnt; in the second,0?3–1?6% in the third, and, with one exception, to wellbelow 1% in the fourth and sixth year stands. Mean annual ratesof N₂ fixation over the 6-year post-fire period were 1?6 kgN ha^–1 year^–1 for A. alata, 0–49 for A. pulchella,0?19 for B. aquifolium and 0-10 for A. extensa Key words: Shrub legumes, post-fire N economy     

Exclusion Errors in Pressure Chamber Estimates of Leaf Water Potential

The common practice of having between 8 and 20 mm of plant samplesexcluded from pressure chambers during determinations of xylemsap pressure potential can produce ‘exclusion’ errorsas large as –1300 kg–1. These may be minimized bysimple improvements in methodology which also facilitate operationand permit determinations with samples of different size, shape,and rigidity.