Growth and maturation of the 'autumn-fruiting type' of Sargassum horneri (Fucales, Phaeophyta) and comparisons with the 'spring-fruiting type'

The growth and maturation period of the autumn-fruiting population ot Sargassum horneri C. Agardh (Phaeophyta) was investigated in Hiroshima Bay, Seto Inland Sea. Surveyed traits were compared to those of the spring-fruiting type and ecological features of this species were discussed. The annual lifetime of the autumn-fruiting population could be divided into four phases according to the daily increase in thalius length:phase I from December to May (increase in length < 0.1 mm/ day), phase II from May to September (= 0.3–1.0 mm/ day), phase Ml (from September to December > 10 mm/day) and phase IV which was the senescence phase from December to March. Receptacle formation‘as observed in November and gamete release from November to February. Conversely, the spring-fruiting type germinated in April and exhibited swifter growth in its early stage of development than the autumn-fruiting type. Rapid increase in thalius iength in autumn was common in both fruiting types, although the spring-fruiting type continued to grow during winter. Receptacle formation of the spring-fruiting type started in February but gamete release was not observed until April and May. The difference in life-history patterns of both types of S. horneri was in the overwintering period. The autumn-fruiting type spent that season as germi-ings or as young plants exhibiting slow-paced growth, while the spring-fruiting type overvwintered as adult thal-li preparing for gamete release in spring.     

Axopodial contraction in the heliozoon Raphidiophrys contractilis requires extracellular Ca2+

Axopodial contraction of the centrohelid heliozoon Raphidiophrys contractilis was induced by mechanical or electrical stimulation. For inducing contraction, extracellular Ca(2+) was required. The threshold level of extracellular Ca(2+) was between 10(-6)-10(-7) M. The speed of axopodial contraction was faster than 3.0 mm/sec. Re-elongation of axopodia started just after contraction, and its initial velocity was approximately 0.30 microm/sec. Electron microscopic observations were carried out using an improved fixative that contained 1 mg/ml ruthenium red and 15 microM Taxol. This fixative prevented artificial retraction of axopodia and resulted in better fixation. A bundle of hexagonally-arranged microtubules was observed in each axopodium, but no other filamentous structures were detected, suggesting that the contractile machinery of axopodia in R. contractilis may be different from that in actinophryid heliozoons in which Ca(2+)-dependent contractile filaments are employed for contraction.     

Nicotiana suaveolens accessions with different ploidy levels exhibit different reproductive isolation mechanisms in interspecific crosses with Nicotiana tabacum

Journal of Plant Research - Reproductive isolation, including prezygotic and postzygotic barriers, is a mechanism that separates species. Many species in the Nicotiana section Suaveolentes exhibit...     

Importance of physical plant properties on methane transport through several rice cultivars

The transport rate of methane from a nutrient solution to the atmosphere via rice plants was controlled both by the methane concentration in the nutrient solution and by plant physiology. Measurements on 11 rice cultivars indicated that the conductance of the rice plant for methane increased as the plants developed. The conductance varied from 0.3±0.2 to 1.2±0.7 μmol min^-1 mM^-1 plant^-1 during the tillering stage, and from 0.6±0.3 to 2.5±0. 2 μmol min^-1 mM^-1 plant^-1 during the reproduction stage. Based on measurements of all plants, the conductance positively correlated with parameters of plant size. Conductance correlated best with stem inter-cellar volume at the tillering stage, and with root volume at the reproduction stage. For both stages taken together, the correlation between conductance and root volume was the most significant. The conductance could be approximated by a multiple linear regression using root volume and the length of root bundle. Higher conductance was found to generally associate with the plants with larger root volume, heavier root fresh weight. This revised version was published online in June 2006 with corrections to the Cover Date.     

Behavioural changes induced by the conjugation-inducing pheromones,gamone 1 and 2, in the ciliate Blepharisma japonicum

Preconjugant interactions between complementary mating-type cells in ciliates occur before sexual reproduction. The interactions include retardation of swimming behaviour, courtship dancing, chemoattraction, nuclear activation, cell division, or cell agglutination, depending on ciliate species. In Blepharisma japonicum, chemoattraction of mating-type I by mating-type II has been reported previously. It has been shown that chemoattraction here is caused by a conjugation-inducing substance called gamone 2 secreted by mating-type II cells. In this study, we show that mating-type II cells accumulate near the site where gamone 1 secreted by mating-type I cells is present at a high concentration. We also show that the behaviour of individual cells changes when exposed to the complementary mating-type gamone; cells begin to rotate and swim slowly, thus shortening their minimum path length (final displacement of a cell from its origin). These results suggest that gamones 1 and 2 induce behavioural changes in type II and I cells, respectively, and that gamone-stimulated cells may accumulate at the site with the highest activity of the complementary gamone, after repetition of swimming changes in the gradient of gamone concentration. This reciprocal induction of the changes in behaviour may increase the probability of sexual encounters for conjugation.     

Ca2+-dependent in vitro contractility of a precipitate isolated from an extract of the heliozoon Actinophrys sol

Contraction of axopodia in actinophrid heliozoons (protozoa) is induced by a unique contractile structure, the "contractile tubules structure (CTS)". We have previously shown that a cell homogenate of the heliozoon Actinophrys sol yields a precipitate on addition of Ca2+ that is mainly composed of filamentous structures morphologically identical to the CTS. In this study, to further characterize the nature of the CTS in vitro, biochemical and physiological properties of the precipitate were examined. SDS-PAGE analysis showed that the Ca2+-induced precipitate was composed of many proteins, and that no proteins in the precipitate showed any detectable changes in electrophoretic mobility on addition of Ca2+. Addition of extraneous proteins such as bovine serum albumin to the cell homogenate resulted in cosedimentation of the proteins with the Ca2+-induced precipitate, suggesting that the CTS has a high affinity for other proteins that are not related to precipitate formation. Appearance and disappearance of the precipitate were repeatedly induced by alternating addition of Ca2+ and EGTA, and its protein composition remained unchanged even after repeated cycles. When adhered to a glass surface, the precipitate showed Ca2+-dependent contractility with a threshold of 10-100 nM, and this contractility was not inhibited by colchicine or cytochalasin B. The precipitate repeatedly contracted and relaxed with successive addition and removal of Ca2+, indicating that the contraction was controlled by Ca2+ alone with no need for any other energy supply. From our characterization of the precipitate, we concluded that its Ca2+-dependent formation and contraction are associated with the unique contractile organelle, the "contractile tubules structure".     

Human papilloma virus type 16 infection and the early onset of cervical cancer

Human papilloma viruses (HPV), particularly type 16, have been associated with cervical cancer. It has been noted that the average onset of cervical cancer is occurring in younger women coupled with a higher prevalence of cervical HPV infection. However, the correlation between HPV 16 infection and the early onset of cervical cancer is still unclear. We hypothesize that HPV infection is an indicator of early onset of cervical cancer. To test this hypothesis, cervical smears from 197 women were evaluated by the polymerase chain reaction for HPV 16. These data revealed that the HPV 16-positive women were significantly younger than the HPV 16-negative women. Moreover, the average age of HPV 16-positive women with CIN 3 or invasive cancer was significantly younger compared with the other groups. These data clearly suggest that HPV 16 infection is a significant risk factor for the progression for cervical cancer in a young population of women.