A quantitative theory of expected volume changes of the mouth during feeding in teleost fishes

The mechanism of mouth expansion in fish, consisting of jaws, suspensoria (j) and hyoids (h) has been modelled by a four-bar isosceles linkage. This model provides insight into limitations and demands of the expansion system used in feeding, as it can be optimized with regard to maximum mouth volume increase. The optimum length ratio of hyoids and jaws was found to be h/j = 0–7. This optimum is modified by mouth bottom depression, jaw protrusion and swimming.
To expand the mouth, at least two forces are required; one exerted by the sternohyoid and ventral body muscles, the other by the epaxial muscles through transmission in the quadrato-articular joints. (Data from EMG experiments confirm the synchronous activity of these muscle groups.) Force transmission and mouth volume increase are constraining quantities, which can be compromised. This leads to a model of the initial mouth shape which is actually found in many 'generalized' fishes, and to demands concerning volume and physiological cross-sectional area of the muscles involved.
Options for specific relative lengths of jaws and hyoids (h/j-ratios) are, for various fish species, compared with model predictions. The applicability of the model approach is shown by the obtained results.     

Contribution of space remote sensing to river studies

• 1 A review is presented of types of satellite remote-sensing data currently available, and their recent uses in studies of river systems.
• 2 Broad-scale assessments of relative water quality may be carried out, although precise indication of water quality requires samples to be taken in situ.
• 3 In the event of flooding, the extent of inundation may be determined and damage assessed quickly. Some radar data allow measurements of flood water even when obscured by vegetation.
• 4 Riparian vegetation may be mapped over large areas, although the recognition of specific tree species remains difficult.
• 5 One of the most basic and widely used applications of remote-sensing data for rivers is that of mapping, both as a single event and over time to follow changes, e.g. channels in a delta. Entire catchments may be mapped, although the efficiency of detection of low-order streams is dependent upon the characteristics of the system used.
• 6 Remote-sensing data has been widely used in all of the above types of study, but is rarely employed on a long-term basis. Several factors can explain this situation, including, for example, the absence of reliable absolute relationships between spectral data and ecological parameters.
• 7 A clear definition of observational needs (e.g. spectral bands, ground resolution, acquisition frequency) of stream ecologists, together with the identification of ecological parameters that may be collected relatively easily from space, will improve remote sensing as an ecological tool in many restoration and management situations.

     

Early Release of ABA from Cell Walls During Rose Petal Protoplast Isolation

During the isolation of rose petal protoplasts, two successivetransient abscisic acid (ABA) accumulations were detected whendigest medium and tissue slices were assayed simultaneously,using polyclonal antibodies raised against (+)-ABA. Late accumulation,occurring after more than 1 h of incubation, was observed, whetherenzymes were present or not, in a hyperosmotic medium. Veryearly accumulation, occurring at a maximum of 15 min after thebeginning of incubation, was observed only in the presence ofcellulolytic and pectinolytic enzymes. The ABA level could beincreased by the addition of tetcyclacis, an inhibitor of mono-oxygenaseknown to delay ABA oxidation. The need for cell wall digestingenzymes to observe this first ABA increase suggested that itwas due to a release from the cell wall. Analysis by radioimmunoassay(RIA) and high performance liquid chromatography (HPLC) showedthat ABA and another non-acidic immunoreactive compound werereleased from purified cell walls by the same enzymes. Key words: ABA, cell wall, protoplast, rose petal     

Atmospheric Ozone Interacts with Stress Ethylene Formation by Plants to Cause Visible Plant Injury

Ozone toxicity was studied in peas, beans, and tobacco (BelB and Bel W3). These experiments showed that ozone toxicitywas related to the rates of ethylene biosynthesis. Sensitivityto ozone was reduced if ethylene biosynthesis was inhibitedafter treatment with aminoethoxyvinylglycine (AVG). Similarly,plants that were able to reduce or prevent stress ethylene formationwere less sensitive after both short- and long-term exposureto ozone. Plants conditioned by longer exposures to ozone havelow rates of ethylene formation and this may be why brief ozoneexposures may be more phytotoxic than prolonged fumigations. Key words: Nicotiana tabacum, Phaseolus vulgaris, Pisum sativum, lipid peroxidation, peas, Pinto beans, tobacco