Relationships between Motor Cell Ultrastructure and Leaf Movements in Samanea saman

We examined the fine structure of motor cells in the secondary pulvinus of Samanea saman (Jacq.) Merrill, to aid in analyzing the cellular basis for K⁺ and Cl^? driven, turgor regulated circadian leaflet movements. Pulvini that were (a) open (horizontal) in the light, (b) closed (vertical) in the dark, or (c) at an intermediate angle after 96-h incubation in H₂O in darkness, were cut into cross sections, sub-divided into quadrants, and prepared for electron microscopy by standard methods. The walls of many cells are ridged, appearing scalloped in cross section, the plasmalemma following the wall contours. Plasmodesmata localized in pit fields are most numerous in the inner cortex of the extensor (abaxial), and least numerous in the outer cortex of the flexor (adaxial) (3.9 and 0.7, respectively, per μm² wall area). Vacuole size, number of vacuoles per cell, and the condition of the electron dense precipitate within the vacuole also vary with cell location, multivacuolation being most pronounced in the outer cortex of the extensor. Chloroplasts are dimorphic: those in cells close to the vascular tissue are very large, circular in cross section, and contain huge starch deposits at all times, while those in the remainder of the cortex are smaller, usually oblong, and contain large starch deposits at the beginning of the dark period, but are devoid of starch at the beginning of the light period. However, both types of chloroplasts in excised pulvini incubated in H²O in darkness for 96 h still contain starch deposits, indicating that (1) light may promote starch degradation, or (2) starch degradation and resynthesis may be rhythmic.     

Cofactor Binding and Oxygen Equilibria in Haemoglobin

THE oxygen affinity of haemoglobin is profoundly affected by the presence of low concentrations of organic phosphates, in particular 2,3-diphosphoglycerate (DPG)^1–5. This phenomenon, which has now been widely recognized as a physiologically vital control mechanism^6–10, can be explained qualitatively by our observations² that deoxyhaemoglobin has a single strong binding site for the cofactor, which in consequence stabilizes it in relation to the oxygenated state. The binding site is associated with the β chains¹¹ and it has been identified as the cavity at the conjunction of the N-termini of these chains^5,12–18, lying therefore on the dyad axis of the tetramer.     

The regeneration ecology of Kunzea ericoides (A. Rich.) J. Thompson at Coranderrk Reserve,Healesville

The spatial structure, age structure and population dynamics of the shrub Kunzea ericoides (A. Rich.) J. Thompson were investigated at Coranderrk Reserve, near Healesville, Victoria, Australia. The shrub is known to be invasive in many areas and, although indigenous to the reserve, has greatly increased its population size and distribution within the reserve in the past 30 years. Dendrochronology showed a constant relationship between age and stem diameter for K. ericoides in the reserve. The spatial structure of the variable stem diameter was investigated by the use of spatial correlograms and results suggested that K. ericoides is spreading via the formation of discrete clumps and gap-phase regeneration. The two main populations in the reserve recruited continuously in time but patchily in space. A simple statistical model for size–frequency data showed that K. ericoides is expanding faster in some areas of the reserve than others. The trend of expansion of K. ericoides may be irreversible. Intensive management of Coranderrk Reserve will be required if K. ericoides is to be controlled and the conservation value of the reserve maintained.     

Thermal requirements for seed germination in Miscanthus compared with Switchgrass (Panicum virgatum), Reed canary grass (Phalaris arundinaceae), Maize (Zea mays) and perennial ryegrass (Lolium perenne)

The high establishment costs of Miscanthus by clonal propagation are a barrier to widespread deployment. Direct sowing is the cheapest method, but limited field trials have given generally poor results. Miscanthus, a perennial grass with C₄ photosynthesis has tropical origins, but is found growing both at high latitudes (>40°) and altitudes (>1000 m) in Asia. In this paper, we investigate if significant variation in the thermal requirements for germination exist in 10 Miscanthus sinensis half‐sib families and compare these with Panicum virgatum (Switchgrass – Trailblazer), Phalaris arundinaceae (Reed canary grass – P10) and Lolium perenne (perennial ryegrass cv AberDart) and maize (Zea mays cv Aviso). The comparisons were made on a thermal gradient bar with a controlled temperature oscillating ± 5 °C on a 12 h cycle and germination was monitored daily for 35 days at mean temperatures ranging from 5.3 to 26.5 °C. Base temperatures were calculated below which germination of at least 50% of viable seeds ceased. Base temperatures were lowest for L. perenne and Zea mays at 3.4 and 4.5 °C respectively; for different Miscanthus half‐sib families base temperatures ranged between 9.7 and 11.6 °C and these were higher than maize and switchgrass which share C₄ photosynthesis with Miscanthus. Parameters derived from germination and temperature were used to predict germination patterns in Europe based on historical climate data. We predict that seed establishment of Miscanthus in spring time is unlikely to be viable in Northern Europe under present climatic conditions without crop management practices aimed at raising soil temperature, and that useful variation in thermal requirement for germination in Miscanthus is available which should facilitate seed germination in other regions.     

Biotic and abiotic constraints to a plant invasion in vegetation communities of Tierra del Fuego

The biotic resistance theory relates invader success to species richness, and predicts that, as species richness increases, invasibility decreases. The relationship between invader success and richness, however, seems to be positive at large scales of analysis, determined by abiotic constraints, and it is to be expected that it is negative at small scales, because of biotic interactions. Moreover, the negative relationship at small scales would be stronger within species of the same functional group, because of having similar resource exploitation mechanisms. We studied the relationship between the cover of a worldwide invader of grasslands, Hieracium pilosella L., and species richness, species diversity and the cover of different growth forms at two different levels of analysis in 128 sites during the initial invasion process in the Fuegian steppe, Southern Patagonia, Argentina. At regional level, the invader was positively correlated to total (r = 0.28, P = 0.003), exotic (r = 0.273, P = 0.004), and native species richness (r = 0.210, P = 0.026), and to species diversity (r = 0.193, P = 0.041). At community level, we found only a weak negative correlation between H. pilosella and total richness (r = ?0.426, P = 0.079) and diversity (r = ?0.658, P = 0.063). The relationship between the invader and other species of the same growth form was positive both at regional (r = 0.484, P < 0.001) and community (r = 0.593, P = 0.012) levels. Consequently, in the period of establishment and initial expansion of this exotic species, our results support the idea that invader success is related to abiotic factors at large scales of analysis. Also, we observed a possible sign of biotic constraint at community level, although this was not related to the abundance of species of the same growth form.     

Comparison of urinary creatine with other biomarkers for detection of cadmium induced testicular damage

In this study, biomarkers of testicular damage were compared. In particular, urinary creatine was evaluated as a non-invasive marker of damage. Male rats were exposed to various doses of cadmium chloride, an established testicular toxicant. Pathological damage, testes weights, urinary creatine and creatinine, serum LDH-C4 and serum testosterone were determined. Cadmium chloride caused dose-dependent damage to the testes undetectable at the lowest dose (0.75 mg kg-1) but apparent at a dose of 1.125 mg kg-1. Urinary creatine was significantly raised after doses of 1.125 mg kg-1 and above 24-48 hr after dosing, and at the highest dose within 24 hr after dosing. Testes weight and serum testosterone were significantly decreased, and LDH-C4 significantly increased, at the highest dose (3.0 mg kg-l). Therefore urinary creatine was the most sensitive marker of acute cadmium-induced testicular damage and dysfunction.     

Characterization of Mouse Pmel 17 Gene and Silver Locus

Pmel 17 cDNA clones, isolated from wild-type and si/si murine melanocytes, were sequenced and compared. A single nucleotide (A) insertion was found in the putative cytoplasmic tail of the si/si Pmel 17 cDNA clone. This insertion is predicted to alter the last 24 amino acids at the C-terminus and to extend the Pmel 17 protein by 12 residues. The mutation was confirmed by the sequence of the PCR-amplified genomic region including the mutation site. Silver Pmel 17 was not recognized by antibodies directed toward the C-terminal amino acids of wild-type Pmel 17, indicating a defect in this region. These results indicate that silver Pmel 17 protein has a major defect at the carboxyl terminus.