Calcification in the bivalve periostracum

The periostracum in certain bivalves is imbedded with calcified, spiculelike structures analogous if not homologous to cuticular spicules found in the Aplacophora and Polyplacophora (chitons). Although rare or absent in most living bivalves, calcified periostracal structures are apparently an ancestral feature in some bivalve groups, i.e. the Mytilacea, Permophoridae, Myoida. and Anomalodesmata. Ancestors of the Bivalvia and Polyplacophora may have been covered with a flexible, spiculestudded cuticle. Shell plates in these two classes may have originated through a modification of the mechanism of spiculelike cuticular calcification. resulting in a primordial shell with simple prismatic structure.     

X-Ray Micro-Analysis of Cells and Cell Compartments of A triplex spongiosa: I. LEAVES

Atriplex spongiosa was grown in hydroponic culture with additionsof 0, 200, 400 and 600 mM NaCl. Frozen, hydrated cells and cellcompartments of young and mature leaf tissue were analysed byX-ray micro-analysis. Evidence for low K + Na and Cl content,and high K selectivity in the bundle sheath cytoplasm was obtainedfrom data on X-ray count ratios and on total X-ray counts. Vacuolesof the major cell types of the mature leaf had either high Kor high Na and Cl contents when grown in the absence or presenceof NaCl. Comparison of K, Na and Cl content of different cell types inthe mature leaf showed gradients in selectivity for K. relativeto Na between the bundle sheath cells and the bladder cells.In the young expanding leaves salt was sequestered in the numeroussalt bladders on the leaf surface, while the cytoplasm and developingvacuoles of undifferentiated cells contained largely K and littleNa or Cl. The results support general views on the compartmentation ofsalt in plants cells in relation to osmotic or saline stress. Key words: Atriplex spongiosa, X-ray analysis, Salinity, Compartmentation, Leaf     

The relationships among three habitat scales and stream benthic invertebrate community structure

1. The relationships between three habitat scales and lotic invertebrate species composition were investigated for the 15 540 km² Yakima River basin in south-central Washington, U.S.A.
2. The three spatial scales were sample (the sampled riffle), reach (a length of ten–twenty stream widths) and segment (a length of stream of nearly uniform slope and valley form having no change in stream order).
3. Physical variables were highly correlated between scales and expressed a relationship between altitude, basin form and small-scale physical structure.
4. Multiple discriminant function analyses indicated that segment- and reach-scale variables discriminated among species-defined groups better than sample-scale variables.
5. Species composition varied along a complex altitudinal gradient of changing basin form and resultant land use.
6. There was no clear relationship between species richness and altitude on a site basis. However, when viewed at the basin scale, maximum richness was observed at the transition between montane and valley sites.     

Nesting activity,breeding success and colony size for the Wedge-tailed Shearwater Puffinus pacificus on Heron Island

Abstract The Capricorn Group of islands in Australia's Great Barrier Reef Marine Park sustains one of the world's largest breeding populations of the Wedge-tailed Shearwater Puffinus pacificus. Heron Island, a 13.5 ha coral cay which supports tourist and research station leases as well as a national park, is the third largest nesting island in the group. Sample censuses of breeding burrows were conducted each year between 1985 and 1990 and a further survey was completed in 1993. These returned estimates of between 13 264±1387 and 16 337±1545 active burrows (Y±SE). Burrow densities within each of the habitats monitored showed no significant trends between years, although there were large differences in burrow density between habitats. There were roughly the same number of burrows in the developed (west) and national park (east) halves of the cay. A miniature video camera system (burrowscope), which allowed nesting chambers at the ends of burrows to be inspected, was used in 1989, 1990 and 1993. This demonstrated that around half the burrows were occupied by incubating birds. Variations were found in the distribution of incubating birds between habitats, although this did not remain constant between the years. In the 1993 season, breeding activity was traced from the burrow establishment to fledging stage. Fifty-one per cent of burrows were used for breeding (eggs laid), 77% of eggs hatched and 80% of chicks produced a fledgling. Overall breeding success for the island was estimated at 61%. In 1993 the area designated as Buildings was found to have significantly lower hatching success compared with natural habitats. Most mortality occurred at the egg stage; however, in the Fringe habitat, mortality was highest at the chick stage. Previous surveys have estimated the breeding population from burrow counts. It now appears that only about 30% of such burrows produce fledglings.     

Sensitivity to metalaxyl of Phytophthora infestans populations in potato crops in south-west England in 1980 and 1981

A laboratory test was developed to assess the sensitivity of field populations of Phytophthora infestans to metalaxyl. Discs of potato leaf tissue were floated upon solutions of the fungicide at different concentrations and inoculated with spores. The extent of symptom development was noted after incubation under standard conditions for 5–6 days. In preliminary experiments growth of isolates of P. infestans obtained from culture collections was severely inhibited in discs treated at 2 μg/ml. By contrast the development of an isolate obtained from a crop in Eire in which blight control with metalaxyl had failed, and known to be markedly less sensitive in vitro, was unaffected in discs treated at 100 μg/ml. During the summer of 1980, 234 samples of P. infestans were obtained from 20 sites in south-west England, 10 of which had received sprays containing metalaxyl and 10 of which had not. All samples were sensitive to metalaxyl applied at 2 μg/ml. In 1981, 35 sites within the same area, 30 of which had received sprays containing either metalaxyl or ofurace (a related fungicide), were similarly surveyed. Most of the 79 samples of P. infestans examined proved sensitive and at all sites the amount of blight was small. However, at three sites, including one not treated with acylalanine fungicides, strains were found which were unaffected by 100 μg/ml metalaxyl in leaf disc tests. These findings are discussed in relation to the development of resistant blight in other areas and to the use of fungicide mixtures.     

Depolymerization of cortical microtubules is not a primary cause of chilling injury in corn (Zea mays L. cv Black Mexican Sweet) suspension culture cells

Cold-induced depolymerization of cortical microtubules were examined in suspension culture cells of corn (Zea mays L. cv Black Mexican Sweet) at various stages of chilling. In an attempt to determine whether microtubule depolymerization contributes to chilling injury, experiments were carried out with and without abscisic acid (ABA) pretreatment, since ABA reduces the severity of chilling injury in these cells. Microtubule depolymerization was detectable after 1 h at 4°C and became more extensive as the chilling was prolonged. There was little chilling injury after 1 d at 4°C in either ABA-treated or non-ABA-treated cells. After 3 d at 4°C, there was about 26% injury for ABA-treated and 40% injury for non-ABA-treated cells, as evaluated by 2,3,5-triphenyl-tetrazolium chloride reduction and by regrowth. After 1d at 4°C, less than 10% of cells retained full arrays of microtubules in both ABA-treated and non-ABA-treated cells, the remainder having either partial arrays or no microtubules. After 3d at 4°C, about 90% of cells showed complete or almost complete depolymerization of microtubules in both ABA-treated and non-ABA-treated cells. ABA did not stabilize the cortical microtubules against cold-induced depolymerization. In about 66% of ABA-treated cells and 57% of non-ABA-treated cells that had been held at 4°C for 3d, repolymerization of cortical microtubules occurred after 3h at 28°C. These results argue against the hypothesis that depolymerization of cortical microtubules is a primary cause of chilling injury.