The effects of seed weight on growth and competitive ability of Rumex acetosella from two successional old-fields

Summary The effects of seed size on growth, biomass allocation and competitive ability of Rumex acetosella plants grown either individually or in competition were studied in two populations (6 months and 15 years old respectively) sampled from a postcultivation successional gradient. For plants grown individually there were highly significant effects of seed weight on growth after 43 days, with a higher relative growth rate (RGR) observed for plants raised from heavier seeds. However at the end of the experiment, seedlings developed from lighter seeds had a RGR 2 times greater than those from heavier seeds. Final biomass of the two types was not significantly different after 73 days of growth. When plants were grown individually, there were only slight differences between populations, but when grown in monocultures of 4 plants per pot, plants from the old population had higher root and leaf biomass per pot whereas those from the young population had a higher reproductive effort per pot. This suggests that a trade-off between allocation to sexual and vegetative reproduction occurs over successional time. In mixtures of light and heavy seeds, plants from light seeds were shorter, had fewer leaves and lower biomass than plants from heavy seeds, which were also taller and produced more dry matter than plants grown from heavy seeds in monoculture. The significant effects of seed weight and population on biomass parameters persisted unit the end of the experiment. Seedlings from heavy seeds were strong competitors: those from the young population grew better in the presence of neighbors than in monoculture and those from the late successional population suppressed the more the growth of their partners. Seedlings from light seeds were subordinate competitors. These results suggest that seedlings from seeds of different sizes benefit from contrasting ecological conditions and that selection acts on reproductive output along successional gradients.     

Purification and characterization of sulfatases from Haliotis rufescens: evidence for changes in synthesis and heterogeneity during development

Summary The digestive glands of many marine molluscs are rich sources of arylsufatase enzymes which may function in the catabolism of sulfated polysaccharides in the diets of herbivorous species. Arylsulfatases, partially purified from the hepatopancreas of the red abalone, Haliotis rufescens, were investigated with respect to heterogeneity, catalytic requirements, and timing of induction during development. Four hepatopancreatic enzymes were purified from adult animals using a combination of hydrophobic interaction and anion-exchange chromatography. Zymograms of the four partially-purified enzymes produced by electrophoresis under nondenaturing conditions revealed a fifth, relatively more basic isozyme. All four partially-purified enzymes appear to be monomeric, with molecular weights of approximately 43 000 Da each, as measured by gel filtration. The affinities for p-nitrocatechol sulfate, pH optima, and strengths of inhibition by anions displayed by these enzymes are similar to the values reported for other molluscan arylsulfatases. Three of the four enzymes have K _m values between 0.8 and 2.0 mM for p-nitrocatechol sulfate; the remaining enzyme (A₂) has a K _m of 6.7 mM. All four enzymes have pH and temperature optima of 5.5 and 45°C, respectively. Three of the four enzymes have-t_1/2(50°C) values of 3.5 min; the enzyme A₄ has a t_1/2 has a t_1/2(50°C) of 8.5 min. A monoclonal antibody directed against form A_1b does not cross react with any of the other hepatopancreatic arylsulfatases when assayed by Western blot, confirming the structural heterogeneity of the adult enzymes.Total arylsulfatase activity increases in a biphasic manner during early abalone development, with the first increase occurring early in larval maturation. The secoad phase of enzyme expression is dependent upon the induction of settlement and metamorphosis of the competent veliger larvae, strongly suggesting that the expression of arylsulfatase synthesis (and the maturation of the digestive gland, the hepatopancreas) is controlled by genetic events which occur as a result of metamorphosis. Competent veliger larvae express only two arylsulfatase forms, which share many physicochemical and kinetic characteristics with the adult hepatopancreatic enzymes. However, neither of the larval arylsulfatases is recognized by the monoclonal antibody to form A_1b from adult hepatopancreas. Endogenous enzyme inhibitor levels in larvae remain constant throughout the period of arylsulfatase induction, and therefore do not contribute to the control of arylsulfatase activity levels during development.These results are the first documentation of the developmental induction of a specific protein(s) in abalone as a result of metamorphosis. The significance of the timing of arylsulfatase expression is discussed in relation to potential physiological substrates and the dietary switching which occurs at metamorphosis. Possible genetic events which are consistent with the observed patterns of expression of these enzymes also are considered.Abbreviations BSA bovine serum albumin - C centigrade - Da daltons - DEAE diethylaminoethyl - ELISA enzyme-linked immunosorbent assay - FPLC fast protein and polynucleotide liquid chromatography - GABA -aminobutyric acid - HAT hypoxanthine, aminopterin, thymidine - Hepes N-(2-Hydroxythyl)piperazine-N'-(2-ethanesulfonic acid) - HPLC high pressure liquid chromatography - KBS Kantor's balanced salt solution - K _m Michaelis constant - PBS phosphate buffered saline - R _m relative mobility - RPMI Roswell Park Memorial Institute - SDS sodium dodecyl sulfate - T time - TBS TRIS buffered saline - V _max maximal velocity     

Effects of photoperiodicity and light irradiance on phosphate-limited Oscillatoria agardhii in chemostat cultures

The cyanobacterium Oscillatoria agardhii was grown in continuous culture under various light conditions in order to study the interactions of light on phosphorus-limited growth. Under severe P-limiting (light-saturating) conditions, a low chlorophyll a and C-phycocyanin content was found. In addition, the light-harvesting capacity, reflected in the values of P _max (maximum light-saturated oxygen production rate) and (photosynthetic affinity), were low compared to light-limited cultures.Reduction of the light climate, either by reduction of the length of the photoperiod or light-intensity, resulted in an increase in light-harvesting capacity (higher pigment content, P _m and ) during growth under P-limiting conditions. Light-induced changes in P _max and could be related to the relative growth rate, being the actual growth rate as a fraction of the growth rate which would be observed under light-limiting conditions.Under P-limiting conditions, reduction of the light-climate caused a reduction in dry weight of the culture. This decrease was mainly due to a decrease in carbohydrate content of the cells. Under all conditions tested, carbohydrates were found to accumulate during the light-period and to be consumed during the dark-period.Evaluation of carbohydrate consumption in the dark yielded a specific maintenance rate constant of 0.001 h^-1. This observation leads to the conclusion that the specific maintenance rate constant is independent on the character of the growth rate limiting nutrient for O. agardhii.     

Stand microclimate and physiological activity of tree leaves in an oak-hornbeam forest

Summary In an uneven-aged, multi-species oak-hornbeam forest at Báb, SW Slovakia (former IBP Forest Research Site), a series of micrometeorological and ecophysiological measurements started in 1985. The aims of the work are to improve understanding of physiological processes (photosynthesis, respiration, and transpiration) of adult trees and stand microclimate, to collect data for simulation of the canopy (stand) photosynthesis and for ecological synthesis of the functioning of the forest ecosystem. In this paper, photosynthetically active radiation (PAR), air temperature (AT) and relative humidity (RH), wind speed (WS), and CO₂ concentration ([CO₂]) in and above the forest are characterized for the fully leaved season, using diurnal courses, vertical profiles and isodiagrams (isopleths). Approximately 50% of incident PAR was absorbed by the upper 4–5 m layer of leaves and only approximately 5% or less penetrated to the forest floor. Vertical gradients of AT and RH were generally low, but large differences in diurnal ranges of AT and RH were observed between vertical levels. The upper leaf canopy greatly reduced WS, and at a height of about 14 m above the ground it was close to zero. The highest diurnal [CO₂] maximum and variations occurred at 1 m above the ground, and the lowest above the forest. In good light conditions in the forest, the entire leaf canopy (overstorey and understorey canopy) is a large sink of CO₂. At night the forest stand is a source of CO₂, the largest internal source being the soil and forest floor.     

A revision of coregonine fish distribution and abundance in eastern James-Hudson Bay

Synopsis Recent sampling programs conducted in the estuaries of the Eastmain and La Grande rivers (James Bay) and the Great Whale, Little Whale, Innuksuac and Povungnituk rivers (Hudson Bay) revealed patterns of coregonine fish distribution that differ from previous observations. The relative abundance of cisco, Coregonus artedii, and lake whitefish, C. clupeaformis, varied among rivers but did not reveal a latitudinal cline. Previous sampling programs underestimated the abundance of cisco in the Little Whale River. In addition, cisco was the third most abundant species captured in the Povungnituk River, situated 200 km to the north of the previously proposed northern limit at Innuksuac River. As such, the low abundances of cisco in the Great Whale and Innuksuac rivers cannot be attributed to a physiological inability to cope with a reduced growing season. Immature cisco were almost totally absent from the estuaries of the Hudson Bay rivers following spring breakup whereas immature lake whitefish made up 100% of the catch in the Innuksuac River at the same time of year. Species-specific migration patterns in Hudson Bay that differ from those observed in James Bay and the existence of unique juvenile overwintering rivers are 2 hypotheses proposed to explain the discontinuous age-class distribution of cisco and lake whitefish observed in Hudson Bay.Contribution to the program of GIROQ (Groupe Interuniversitaire de Recherche Océanographique du Québec).     

Components of relative growth rate and sensitivity to nitrogen availability in annual and perennial species of Bromus

Summary Two grass species, the annual Bromus sterilis and the perennial Bromus erectus, were grown from seeds for 28 days in a hydroponic culture system at 1 and 100 M NO₃ ^- in the nutrient solution. At 100 M NO₃ ^-, the relative growth rate (RGR) of the perennial was 30% lower than that of the annual. This was only the consequence of the higher specific mass of its leaves, since its leaf mass ratio was higher than that of the annual and the unit leaf rates (ULR), calculated on an area basis, were similar for the two species. At 1 M, the RGR of the annual was 50% lower than at 100 M, while that of the perennial was not significantly lower. This was due mainly to a lower ULR for the annual. while for the perennial ULR was the same in both treatments. These differences between the two species were all the more striking in that the differences in total nitrogen concentrations and nitrate reductase activities between the two treatments were very similar for both species. These different responses together with differences in the nitrogen productivity of the two species suggest that the level of nutrient availability may play an important role in the distribution of these Bromus species in natural habitats. Scope: Components of growth and response to nitrate availability in annual and perennial grasses     

Primary structure of a pheromone-binding protein from Antheraea pernyi: homologies with other ligand-carrying proteins

Summary An antennal cDNA clone encoding the complete sequence (163 amino acids) of a pheromone-binding protein precursor from the male silk moth, Antheraea pernyi, was isolated using oligonucleotide probes. The cloned cDNA was expressed and the translation product detected by specific antibodies. The deduced protein sequence consists of a signal peptide of 21 amino acids and a mature binding protein of 142 amino acid residues. The predicted structure of this protein is homologous to binding-proteins from different insect species which have previously been identified, but shows no similarities to odorant-binding proteins from vertebrates, suggesting that soluble odorant-binding proteins in insects and vertebrates represent an evolutionary convergence.Abbreviations PBP pheromone-binding protein - OBP odorant-binding protein - cDNA complentary DNA - poly(A ⁺) RNA polyadenylated RNA - SSC 0.15 M sodium chloride+0.015 M sodium citrate - SDS-PAGE sodium dodecylsulfate polyacrylamide gelelectrophoresis