Plant availability of cadmium in presence of organic acids: an interactive aspect

The present communication reports the effect of various carboxylic and amino acids on the uptake and translocation of root-absorbed Cd by maize (Zea mays). Statistically significant increases in Cd accumulation in various plant tissues with increasing supplementation of organic acids suggested the existence of Cd-organic acid interaction in soil-rhizosphere environment of the plant. The potentiality of phytochelators (organic acids) to form plant available organically bound Cd is discussed.     

Cellular dynamics of in vitro allogeneic reactions of<Emphasis Type="Italic"> Hymeniacidon heliophila</Emphasis> (Demospongiae: Halichondrida)

Allograft reactions of the sponge Hymeniacidon heliophila Parker, 1910 have been studied and quantified at the cellular level in vitro. Cell-layer assays were used to record the timing of rejection between allogeneic individuals and to investigate changes in the cellular subpopulations of primmorphs belonging to different individuals and placed in direct contact. The initial contact on both cell layers and primmorphs was followed by partial fusion and ended by their isolation with formation of a defined barrier but without marked collagen deposition. Using cytospins, cellular subpopulations from primmorphs were morphologically distinguished based on overall shape and on nuclear and cytoplasmic characteristics. In the beginning of the cultures up to 17 cell types could be recognized. Within 5 days, following reaggregation and primmorph formation, populations of eight of these types suffered marked reduction, whereas nine other cell types were either maintained or reduced at a slower pace. When submitted to allogeneic contact, the cellular dynamics of the four remaining types were altered. Surprisingly, the percentage of archeocytes is reduced, probably depleted by differentiation into other, differentiated cell populations. Cellular responses to allogeneic contact were characterized mainly by a transient increase in globoferous cells, a larger participation of presumed collagen-secreting cells, and by a remarkable expansion of the collencyte population. The collencyte population remained altered after the isolation of the individuals by a collagen barrier, and this can represent a mechanism of short-term immune memory.Communicated by O. Kinne, Oldendorf/Luhe     

Pitch shifts and song structure indicate male quality in the dawn chorus of black-capped chickadees

The fee-bee song of male black-capped chickadees (Poecile atricapillus) is considered a single-type song that singers transpose up and down a continuous frequency range. While the ability to shift song pitch in this species provides a mechanism for song matching as an aversive signal in male-male territorial song contests, the functional significance of this behaviour during the MIDDLE" BORDER="0">soloMIDDLE" BORDER="0"> performances of males during the dawn chorus is unclear. We analysed the dawn chorus songs and singing behaviour of males whose winter-flock dominance status we determined. We used correlation analysis to show that pitch shifts were accompanied by changes to other fine structural characteristics in song, including temporal and relative amplitude parameters. We also found that songs of socially dominant males and songs of their most subordinate flockmates could be distinguished using these methods by the way they performed a between-note frequency measure accompanying pitch shifts. That is, a ratio measure of the internote frequency interval remained constant for songs of high-ranking birds despite changes in absolute pitch, while low-ranking males sang a smaller ratio as they shifted to higher absolute pitches. These findings identify previously unrecognised variation in the songs of black-capped chickadees. More importantly, they indicate a mechanism by which pitch shifting during the dawn chorus of black-capped chickadees could provide a reliable indicator of relative male quality.Communicated by I. Hartley     

Dichlorvos degradation studied by 31P-NMR

We studied the hydrolysis and TiO₂ photocatalysis of the pesticide dichlorvos at pH 2.6–9 using phosphorus-31 nuclear magnetic resonance (³¹P NMR). We found that the hydrolysis of dichlorvos led to the formation of dimethyl phosphate at pH 5.6–9. On the other hand, TiO₂ photocatalysis decomposed dichlorvos into dimethyl phosphate, which further reacted to form monomethyl phosphate at pH 2.6 and 9. Monomethylphosphate was hydrolysed into phosphate at pH 2.6. ³¹P NMR is therefore a promising tool to study the degradation of organophosphorus pesticides.     

Photosynthetic carbon dioxide fixation in zooxanthellae

The carbon-fixation patterns of freshly isolated zooxanthellae from the hermatypic coral Acropora formosa were examined during a 15 min exposure to sodium mosa were examined during a 15 min exposure to sodium [¹⁴C]bicarbonate. The labelling pattern during the first 60 s exposure showed that the C₃ carbon-fixation pathway is the major route for photosynthetic carbon fixation in Symbiodinium sp. 3-Phosphoglyceric acid, which constituted >50% of the label after 5 s, steadily decreased over the first 60 s. Hexose phosphates, aspartate, malate and glucose were the other main products during the first 60 s. Over longer periods, significant amounts of the organic acids succinate, aspartate and glutamate were found in the extract along with glucose; but no glycerol.     

Effects of feeding history on the growth characteristics of a reef fish at settlement

A feeding experiment was conducted on the pelagic stages of the tropical goatfish Upeneus tragula (family Mullidae) to examine how food quantity affects growth characteristics and potential success at settlement. Pelagic goatfish were collected from aggregation rafts 3 nautical miles west of Lizard Island on the northern Great Barrier Reef during December 1990. Three tanks in each of four feeding regimes were stocked with 25 pelagic goatfish between 20 and 23 mm standard length (SL). The four feeding regimes were: fed ad lib. (fed): fed once per day (f1pd); starved every second day (stld); starved for 3 d and re-fed (st3d). Fishes were fed 36 to 48 h old Artemia sp. nauplii (Ocean Star strain). Fish were removed from tanks when they underwent metamorphosis, changed pigmentation and settled to the bottom of the tanks. Morphology, muscle development, time taken to settle and biochemical condition were examined. Growth attributes of the treated fish were compared to fish which settled within 24 h of capture (field). All attributes examined were significantly influenced by the feeding treatments. Fish within the fed and st3d treatments were significantly larger and heavier than fish in the less well-fed treatments (f1pd, st1d). Similarly, concentrations of total lipid, carbohydrate and protein in the settled fish were significantly higher in the fed and st3d treatments compared with the st1d and f1pd treatments. For all these morphological and biochemical attributes the st1d and f1pd fish did not significantly differ from the field fishes, but did differ from the fed and st3d fishes. Water content was significantly higher in the f1pd, st1d and field fishes compared with the fed and st3d fish. Furthermore, the average time taken to settle followed the pattern: fed (14d)Muscle development mirrored the patterns in fish length between treatments, being more developed in the fed treatment and least well developed in the st1d treatment. Feeding rate differed significantly between treatments and changed through the experiment for all but the fed treatment. Feeding rate decreased slightly for the f1pd and st1d treatments over the experimental period, but increased rapidly for the st3d treatment. The experiment suggests that U. tragula are physiologically well suited to exploiting a patchy food source, and that food availability within the pelagic stages can have a major influence on the growth characteristics of this reef fish at settlement. The ramifications of this finding are discussed in relation to survival and success once fish have recruited to the reef population.     

Phaeocystis blooms and eutrophication of the continental coastal zones of the North Sea

It is suggested that novel nuisance algal blooms can result from major shifts in N/P or NH₄ ⁺/NO₃ ^- ratios. Inland hydraulic engineering caused a shift from P-limitation (before 1977) towards N-limitation (after 1977) in the Marsdiep area (Dutch coastal waters). Following this shift the colonial flagellate Phaeocystis sp. became more abundant and started to bloom during the nutrient-controlled period (later spring to autumn). Competition experiments showed that the N/P ratio can influence the species composition of marine phytoplankton. In addition, the natural distribution of some species like Rhodomonas sp. and Emiliania huxleyi may be affected by the frequency of nutrient pulses in the system. Phaeocystis was a poor competitor under P-limitation and a good competitor under N-limitation. Colony formation was absent under P- and NH₄ ⁺-limitation. Colonies were formed under NO₃ ^--limitation. These preliminary results suggest that colony-forming Phaeocystic blooms may be restricted (besides light-controlled environments) to those N-controlled environments where nitrate is consumed by Phaeocystis. The distribution of Phaeocystis along the European continental coast is evaluated on the basis of its ability to compete for nutrients and to form colonies when nitrate is the major N-source.     

Effects of eutrophication and sedimentation on juvenile corals

Settlement of juvenile scleractinian corals was investigated from 1987 to 1990 on eutrophic and less eutrophic fringing reefs on the west coast of Barbados, West Indies. The number of coral recruits and number of recruiting coral species on cement blocks decreased with increasing eutrophication of the reefs. This may suggest lower settlement rates on eutrophic reefs, but could also liave resulted from higher post-settlement mortality, since blocks were examined only once after 3 yr of immersion. Coral settlement rates to artificial plates that were checked monthly were also lower on the more eutrophic reefs. This could result from lower local availability of larvae caused by fewer adult corals and/or lower reproductive rates of corals on eutrophic reefs. However, the ratio of coral recruits to adult coral abundance was considerably lower on eutrophic reefs, suggesting that local coral abundance alone can not explain lower settlement rates on eutrophic reefs. The lower rates on eutrophic reefs may result from a lower probability of coral larvae settlin when present, perhaps because of a limited availability of suitable settlement substrate. Colonization of settlement plates by non-coralline organisms was heavier on eutrophic reefs, and unoccupied space was lower, supporting the suggestion that suitable coral settlement substrate may be limiting on eutrophic reefs. Moreover, coralline algae, which facilitate metamorphosis and settlement of coral larvae, were less abundant on settlement plates on eutrophic reefs.     

Increased metabolic cost of maintenance in hybrids of the stone crabs Menippe mercenaria and M. adina

Three recently emerging genotype classes of the genus Menippe (M. mercenaria, M. adina, and their hybrids) were examined for potential physiological correlates of gene mixing over a salinity range of 5 to 35‰. Resting metabolic rate (RMR), as measured by oxygen uptake (V˙ _O2), was highest in the hybrids. Differences in V˙ _O2 could not be accounted for by differences in systemic adaptations (e.g. heart rate or scaphognathite frequency); therefore it was concluded that they were based on potential underlying differences in carbohydrate metabolism. The higher RMR in the hybrids was attributed to a higher metabolic cost of maintenance, resulting from the breakup of coadapted gene complexes as a result of introgressive hybridization. Received: 22 July 1996 / Accepted: 17 October 1996     

The hydrolytic products of aluminum and their biological significance

The relative distribution of Al between its various organic and inorganic complexes dictates its mobility in the environment, bioavailability, and toxicity. In recent years, there has been significant progress made in understanding the differential bioavailability and toxicity of various chemical species of Al to plants and certain aquatic organisms. Far less information concerning chemical speciation and differential uptake and transport of Al in humans is available. Among the important inorganic complexes of interest are the hydrolyzed-Al species, particularly the nonequilibrium, metastable polynuclear complexes, which form readily, have a fairly wide stability range, and have been demonstrated toxic to plants and fish. In recent years²⁷Al NMR spectroscopy has provided significant direct information on the polynuclear complexes existing in a wide range of aqueous solutions. The [Al₁₂O₄(OH)_24+n(H₂O)_12–n]^(7–n)+ polynuclear complex is often found to be the predominant species in partially neutralized Al solutions and has recently been demonstrated to be more toxic to certain plants than the hexaaqua Al cation. It is also the principal component of Al-chlorohydrate, a highly soluble antiperspirant, present in many hydrolyzed Al solutions utilized in water and waste water treatment, and, as hypothesized herein, a primary constituent of many hydroxide gels utilized as antacids. This polynuclear has a wide pH stability range, reportedly forms copolynuclears with Si, and contains tetrahedrally coordinated Al within its structure, all features that may be relevant to the recently reported properties of Al associated with neuritic plaque cores.