Response of transpiration and photosynthesis to a transient change in illuminated foliage area for a Pinus radiata D. Don tree

Sudden but transient changes in the fraction or illuminated foliage area in a well-watered 7-year-old Pinus radiata D. Don tree were imposed by completely covering either the upper 22% or the lower 78% of the foliage for periods of up to 36 h. Measurements of transpiration flux density (E), tree conductance (g_t), stomatal conductance (g_s) and net photosynthesis (A) were made to test the hypothesis that compensatory responses would occur in the remaining illuminated foliage when the cover was installed. When the lower foliage was covered there was an immediate decrease in g_t. However, when tree conductance was normalized with respect to the illuminated leaf area (g_t'), it increased between 50 and 75%, depending on the value of air saturation deficit (D). The effect was also apparent from concurrent measurements of increases in g_s and A up to 59 and 24%, respectively, for needles in the top third of (he crown. When the cover was removed these effects were reversed. The changes in the lower foliage when the upper foliage was covered were much smaller. Changes in bulk needle water potential were small. It is suggested that the observed responses occurred because of a perturbation to the hydraulic pathway in the xylem that could have triggered the action of a chemical signal to regulate stomatal conductance and photosynthesis.     

Genbank accession #: AF139098

Plant Molecular Biology -     

Geographical and temporal variation in the diet of Bank Cormorants Phalacrocorax neglectus in South Africa

The Bank Cormorant Phalacrocorax neglectus is endemic to the Benguela upwelling ecosystem off southwest Africa and is classified as Endangered owing to a recent large reduction in its number. It is thought that food scarcity, including a decreased abundance of West Coast rock lobster Jasus lalandii, has been a major driver of the decrease, yet its diet in South Africa is poorly known. We collected 941 pellets regurgitated by Bank Cormorants, at 18 South African breeding colonies during 1975–1985, and 1 523 pellets at 17 colonies during 1995–2002. The species composition of the diet (% numbers) was significantly different between the two periods, with widespread decreases in proportions of rock lobster in the west and of octopus and cuttlefish Sepia spp. at most localities. These taxa were replaced in the diet by fish, including Gobiidae and Clinidae. The pelagic goby Sufflogobius bibarbatus, an important prey of Bank Cormorants in Namibia, was absent from pellets collected in 1975–1985 but common at northern localities from 1995–2002. Composition of the diet by frequency of occurrence was only determined for 1995–2002, when rock lobster was present in 67% of all samples collected, cuttlefish in 39%, and Clinidae in 32%. Data for 1975–1985 and 1995–2002 showed that carapace lengths of rock lobsters eaten by Bank Cormorants averaged 56 mm (range 22–82 mm) and 50 mm (range 22–75 mm), respectively, which compares to the minimum legal size of 75 mm for fisheries in South Africa. This energy- rich prey item was an important constituent of the diet in the winter breeding period.     

Calcium control of waveform in isolated flagellar axonemes of chlamydomonas

The effect of Ca(++) on the waveform of reactivated, isolated axonemes of chlamydomonas flagella was investigated. Flagella were detached and isolated by the dibucaine procedure and demembranated by treatment with the detergent Nonidet; the resulting axomenes lack the flagellar membrane and basal bodies. In Ca(++)-buffered reactivation solutions containing 10(-6) M or less free Ca(++), the axonemes beat with a highly asymmetrical, predominantly planar waveform that closely resembled that of in situ flagella of forward swimming cells. In solutions containing 10(-4) M Ca(++), the axonemes beat with a symmetrical waveform that was very similar to that of in situ flagella during backward swimming. In 10(-5) M Ca(++), the axonemes were predominantly quiescent, a state that appears to be closely associated with changes in axomenal waveform or direction of beat in many organisms. Experiments in which the concentrations of free Ca(++), not CaATP(--) complex were independently varied suggested that free Ca(++), not CaATP(--), was responsible for the observed changes. Analysis of the flagellar ATPases associated with the isolated axonemes and the nonidet- soluble membrane-matrix fraction obtained during preparation of the axonemes showed that the axonemes lacked the 3.0S Ca(++)-activated ATPase, almost all of which was recovered in the membrane-matrix fraction. These results indicate that free Ca(++) binds directly to an axonemal component to alter flagellar waveform, and that neither the 3.0S CaATPase nor the basal bodies are directly involved in this change.     

Histiostoma papillata sp. n. (Acari: Histiostomatidae), a mite attacking fish in Australia

Histiostoma papillata sp. n. (Acari: Histiostomatidae) is described from Victoria, Australia. It was found in the fins and gills of juvenile Murray cod, Maccullochella peelii peelii (Mitchell), where it appeared to inflict injuries thought to be responsible for the mortality of fish in a diet trial.