Growth control in cultured 3T3 fibroblasts : III. Binding interactions of a growth inhibitory activity with target cells

A Fibroblast Growth Regulator (FGR), which inhibits the growth and division of proliferating fibroblasts, has been isolated from medium conditioned by exposure to density-inhibited 3T3 cells. The binding of this FGR to its target cells has been analysed using [³⁵S]methionine-labeled inhibitor. The key features of this interaction are (a) there are approx. 3–4 × 10⁵ binding sites/cell; (b) more ligand is bound at 37 than at 4 °C, possibly due to internalization of the molecule at the higher temperature; (c) on a per cell basis, approximately the same amount of ligand is bound at high cell density as at low cell density; (d) there is no evidence of target cell heterogeneity in the binding of the inhibitor; and (e) the binding can be inhibited partially by calf serum. The results suggest that modulation of cell surface receptor binding by serum and growth inhibitory factors may be an important feature in growth regulation.     

The effects of temperature on photophosphorylation and on the two forms of cytochrome 559 in subchloroplast particles

Two forms of cytochrome 559 have been demonstrated in chloroplasts, one of which is reducible by ascorbate (the A-form) and one of which cannot be reduced by ascorbate (the D-form). Analysis of the effects of temperature on the reduction of the cytochromes by light showed that the D-form was only observed between 20 and 40 °C. Below this range, only the A-form of the cytochrome was affected by light; the D-form remained oxidized. Also both electron transport and PMS⁺-photophosphorylation rates showed a sharp temperature transition at about 20 °C. Both electron transport and photophosphorylation are most sensitive to the inhibitor, CMU, at temperatures above 20 °C, and this coincides with the reduction of cytochrome 559 (D) which is extremely sensitive to CMU. Also, a transition temperature at 18 °C for fluorescent quenching was demonstrated.     

Theoretical contributions to biological control success

Ecologists have long tried, with little success, to develop ecological theory for biological control. Biological control illustrates how science often follows, rather than precedes, technological advances. A scientific theory of biological control remains a worthy and achievable goal. We need to (1) combine deductions from mathematical models with rigorous empiricism measuring and modeling the effects of abiotic and biotic environmental drivers on demography and population dynamics of real biological control systems in the field, (2) use a wider range of model systems to explore how population structure, movement, spatial heterogeneity, and external environmental conditions influence population and community dynamics, and (3) combine deductive and inductive approaches to address the day-to-day concerns of biocontrol scientists including how to rear and release a control organism, suppress the target organism, and minimize harm to non-target organisms. Further progress will require more fundamental research in population and community ecology directly relevant to biological control.     

Towards diagnostic biotic indices for river macroinvertebrates

The construction of biotic indices that use macroinvertebratesto assess pollution and other anthropogenic disturbances ofrivers and streams often requires that each taxon be assigned anumber indicating its level of sensitivity. A problem inconstructing such indices is that individual taxa may varyquite widely in sensivity, depending on the nature of theparticular disturbance. One possible means of overcoming thisproblem is to construct a suite of indices, each assembledusing sensitivity numbers targeted to a particular impact.In order to test this idea, we sampled macroinvertebrates fromrivers in south-eastern Australia subjected to three differenttypes of anthropogenic disturbance: operation of large dams,discharge of effluent from municipal sewage treatment plants,and contamination by metals originating from historical mining.Using macroinvertebrate data from sampling sites with varyinglevels of exposure to disturbance, we developed sensitivitynumbers for macroinvertebrate families for individual riversand combinations of rivers with the same disturbance type.Sensitivity numbers calculated for individual families differedsignificantly according to disturbance type in several cases.Gastropod molluscs (family Thiaridae) were tolerant of dameffects but sensitive to sewage and metals, whereascoenagrionid damselfly nymphs, elmid beetles and ostracods weremost tolerant of sewage. Corydalid alderfly larvae,leptophlebiid mayfly nymphs, lestid damselfly nymphs,libellulid dragonfly nymphs and scirtid beetle larvae weremost tolerant of metals. Indices constructed using sensitivitynumbers for a particular disturbance were generally mostresponsive to that disturbance, but there was considerablegenerality in responses as well as substantial variabilitybetween different rivers with the same disturbance type. Inparticular, macroinvertebrate communities at sites downstreamof dams responded quite variably, probably because ofsubstantial differences in release regimes. We conclude thatthe approach has merit but requires considerable furtherdevelopment and testing, as well as consideration of the levelsof specificity and diagnostic strength that are appropriate orachievable.