Heat shock and the protection against metal toxicity in wheat leaves1

Abstract. Wheat (Triticum aestivum L. var. TAM-W101) leaf segments exhibited an acquired protection against metal toxicity following exposure of the seedlings to heat shock temperatures in the dark. The acquired protection of the leaf segments to cadmium was 400-fold greater than leaf segments from seedlings kept at 25°C and exhibited the greatest change in protection of the five metals tested. Increased protection against aluminium and iron toxicity was also detected in the leaf segments from heat shocked seedlings. The concentration of aluminium at which a 50% loss of 2,3,5-triphenyltetrazolium chloride reduction occurred was 5.5 mol m^?3 in control leaf segments and 20 mol m^?3 in the leaf segments from heat shocked seedlings. The 50% loss of 2,3,5-triphenyltetrazolium chloride reduction in the leaf segments from heal shocked seedlings was four-fold higher for iron. A small, yet reproducible change in the 2,3,5-triphenyltetrazolium chloride reduction was observed for copper and no change in reduction was observed for zinc treatments in the leaf segments from heat shocked seedlings. These data indicate that exposure of wheat seedlings to heat shock temperatures results in the acquisition of protection against metal toxicity to otherwise lethal concentrations of aluminium, cadmium, and iron.     

Temporal Hierarchies of Variation and the Maintenance of Diversity

Abstract A general model shows how the long-term growth rate of a population can be partitioned into components representing various mechanisms of maintenance of species diversity. One component summarises the effects of fluctuation-independent mechanisms, which include classical resource partitioning and frequency-dependent herbivory. Two other components represent fluctuation-dependent mechanisms, the storage effect and relative nonlinearity of competition.
The general model shows how a community will track an equilibrium set by fluctuation-independent mechanisms and the environmental state when community dynamics are faster than the rate of environmental change. Fluctuation-dependent mechanisms can be important for diversity maintenance with or without such tracking, but on long timescales their effects are indistinguishable from those of fluctuation-independent mechanisms.
These considerations lead to a hierarchical view of mechanisms of diversity maintenance where the effects of different timescales are partitioned or merged depending on the timescale of observation. These issues are illustrated with model examples involving various combinations of resource partitioning, fluctuations in recruitment rates, variation in the timing of germination, and seasonality. The very long timescales associated with climate change contain many complexities but nevertheless many ideas applicable to shorter timescales may be useful in a modified form.     

The upstream/downstream movement paradox of lotic invertebrates: quantitative evidence from a Welsh mountain stream

• 1 This study attempts to determine the mechanisms by which the downstream displacement of lotic invertebrates is compensated by the upstream movements of immatures and adults. To this end, submerged and aerial traps were set up at three sites, each 100 m apart on a small mountain stream (Yr Ogof) in North Wales and operated for 12 months.
• 2 At Site 1 (the source), 19.3% of the benthic invertebrates lost as drift were replaced by the upstream movement of aquatic stages. At Site 2, the average upstream compensation was 51.1% (although there was a marked difference between the two traps at the site). At downstream Site 3 the average compensation was 55.4%. The net loss of benthos downstream over 1 year was estimated to be 261920 individuals from Site 1, 41891 from Site 2, and 40470 from Site 3.
• 3 At Sites 1 and 2, the numbers of invertebrates drifting were positively correlated with both current speed and water depth. At Sites 2 and 3, the numbers moving upstream were positively correlated with water temperature. At all three sites, the numbers of animals drifting were positively correlated with the numbers moving upstream, under water.
• 4 In none of the eight common species of stoneffy did females show a strong overall upstream flight preference—however, two species, Leuctra nigra and Nemoura erratica, showed a significant downstream preference.
• 5 As with the stonefly nymphs, most of the caddisfly larvae showed a longitudinal distribution. Agapetus fuscipes larvae were most abundant at Site 1, yet females showed no preferred flight direction—this would seem to be inappropriate for maintaining this larval distribution pattern. However, females caught moving upstream at Site 2 were bigger and contained twice as many eggs, which were also larger, than females moving upstream at Site 1. The flight patterns of the other Trichoptera also seemed inappropriate for maintaining their respective larval distributions. Immature insects moved upstream at certain sites and times, but trends were not consistent. There was no correlation between female flight direction and local wind speed and direction.
• 6 Downstream displacement of the most abundant non-insect species, Gammarus pulex, was quite considerable at all three sites. However, at several times during the year the numbers moving upstream approached or exceeded those drifting. Maintenance of benthic population densities in this species is thought to be through a combination of upstream movement (which was highly correlated with benthic density at Sites 1 and 3) and production of young over a long (10 month) reproductive period. Maintenance of the benthic populations of the immature stages of the majority of insect species in Yr Ogof is thought to be through oviposition by females in the vicinity of their emergence sites.

     

Fine Structure of Sarcocystis cruzi Schizonts

SYNOPSIS Schizogony of Sarcocystis cruzi Hasselmann (syn. S. fusiformis Railliet) takes place in vascular endothelial cells 26 to 33 days after cattle ingest sporocysts from dogs. Kidney cortex from a heavily infected, dexamethasone-treated bovine was fixed for electron microscopy to determine the method of schizogonie development. Schizogony takes place by endopolygeny characterized by marked enlargement of the parasite nucleus, formation of nuclear lobes, presence of numerous spindles with adjacent pairs of centrioles along the nucleus, and simultaneous formation of daughter merozoites in the cytoplasm adjacent to the spindle poles. Endopolygeny in S. cruzi differs from that in other Sporozoa in that merozoite anlagen are seen in the cytoplasm before any nuclei divide. The resultant merozoites continue development and, when mature, resemble other sporozoan zoites. Upon release from the host cell into capillaries, they travel to muscle tissue to continue the life cycle by forming sarcocysts.     

Phenotypic Variation and Systemic Cancer in the FAMMM Syndrome

Familial atypical multiple mole melanoma (FAMMM) syndrome, a cancer-associated genodermatosis, is a dominantly inherited heterogeneous disorder with variable expressivity of both its cutaneous and cancer phenotypes. By using a verified historical review technique of cancer documentation (idout patient health records, pathology reports/slides, autopsy reports/slides, and death certificates) of all anatomic sites in all members of a modified nuclear pedigree (first-degree relatives plus maternal and paternal grandparents, aunts, and uncles) over several generations, we showed that the FAMMM syndrome is similar to the majority of autosomal dominant inherited cancer-associated genodermatoses and has excessive risk for cancer of multiple anatomic sites. With respect to the FAMMM syndrome, these cancers involved the breast, respiratory tract, gastrointestinal system, the eye (intraocular melanoma), and the lymphatic system. These FAMMM pedigrees showed some of the following distinctive characteristics of hereditary cancer: 1) integral patterns of cancer within and between pedigrees; 2) early age of onset of cancer; 3) prolonged survival of some pedigree members with cancer; and 4) an excess of multiple primary melanomas and cancers of variable anatomic sites. The presence of these features indicates that these cancers of variable anatomic sites may be etiologically associated with the FAMMM syndrome. Heterogeneity should be investigated in FAMMM pedigrees with attention to consistent differences in size and distribution of atypical lesions, age at cancer onset, and pattern of tumor occurrences. The occurrence of FAMMM pedigrees in the general population or among pedigrees of probands with atypical nevi is not known. The occurrence of systemic cancers in these FAMMM pedigrees requires the development of cancer surveillance programs that are specifically modified to the particular cancer pattern of each pedigree.