Phylogenetic evidence for a major reversal of life-history evolution in plethodontid salamanders

The transition from aquatic to terrestrial eggs is a key evolutionary change that has allowed vertebrates to successfully colonize and exploit the land. Although most amphibians retain the primitive biphasic life cycle (eggs deposited in water that hatch into free-living aquatic larvae), direct development of terrestrial eggs has evolved repeatedly and may have been critical to the evolutionary success of several amphibian groups. We provide the first conclusive evidence for evolutionary reversal of direct development in vertebrates. The family Plethodontidae (lungless salamanders) contains the majority of salamander species, including major radiations of direct developers. We reconstruct the higher level phylogenetic relationships of plethodontid salamanders using molecular and morphological data and use this phylogeny to examine the evolution of direct development. We show that the predominantly biphasic desmognathines, previously considered the sister group of other plethodontids, are nested inside a group of direct-developing species (Plethodontini) and have re-evolved the aquatic larval stage. Rather than being an evolutionary dead end, the reversal from direct developing to biphasic life history may have helped communities in eastern North America to achieve the highest local diversity of salamander species in the world.     

Effects of light on direct and indirect defences against herbivores of young plants of Mallotus japonicus demonstrate a trade-off between two indirect defence traits

Background and Aims

Although most studies on plant defence strategies have focused on a particular defence trait, some plant species develop multiple defence traits. To clarify the effects of light on the development of multiple defence traits, the production of direct and indirect defence traits of young plants of Mallotus japonicus were examined experimentally under different light conditions.

Methods

The young plants were cultivated under three light conditions in the experimental field for 3 months from May to July. Numbers of ants and pearl bodies on leaves in July were examined. After cultivation, the plants were collected and the developments of trichomes and pellucid dots, and extrafloral nectaries (EFNs) on the leaves were examined. On plants without nectar-collecting insects, the size of EFNs and the volume of extrafloral nectar secreted from the EFNs were examined.

Key results

Densities of trichomes and pellucid dots did not differ significantly among the plants under the different light conditions, suggesting that the chemical and physical defences function under both high and low light availability. The number of EFNs on the leaves did not differ significantly among the plants under the different light conditions, but there appeared to be a trade-off between the size of EFNs and the number of pearl bodies; the largest EFNs and the smallest number of pearl bodies were found under high light availability. EFN size was significantly correlated with the volume of extrafloral nectar secreted for 24 h. The number of ants on the plants was smaller under low light availability than under high and moderate light availability.

Conclusions

These results suggest that direct defence traits function regardless of light conditions, but light conditions affected the development of indirect defence traits.     

Sheep grazing vs. cutting: regeneration and soil nutrient exploitation of the grassland weed Rumex obtusifolius

Broad-leaved dock (Rumex obtusifolius L., Polygonaceae) is an agronomically important perennial weed causing decreases in pasture yields and fodder quality. Non-chemical control measures for dock are often limited to frequent pulling and cutting, additionally it is usually avoided by grazing animals. Here, the regeneration of R. obtusifolius in a Rumex-infested grassland grazed by a sheep breed that explicitly feeds on dock (Ovis aries L. cv. East Prussian Skudden) was compared to cutting. Therefore, regeneration of 90 R. obtusifolius plants of three different size classes was monitored in three plots during three grazing and cutting cycles. Plant height and number of fruit-stands of regrown R. obtusifolius was significantly lower, number of leaves significantly higher after grazing than after cutting, while plant diameter was unaffected. Initially medium and large-sized plants (>40 cm diameter) were significantly more sensitive to grazing or cutting than initially smaller sized plants. Soil nitrate and ammonium concentrations in the vicinity of R. obtusifolius correlated with some regrowth parameters but were not affected by grazing or cutting. Sheep-grazed grassland communities comprised fewer legumes (p = 0.002), more grasses (p = 0.010) and fewer sward gaps (p = 0.025) than cut grassland. At the end of the experiment, abundance of R. obtusifolius in sheep grazed plots was lower than in cut plots (p = 0.089) suggesting that regrowth potential of this weed was depleted by continuous grazing and higher sward density. In conclusion, these data suggest that sheep could be considered in grassland management schemes to both directly and indirectly control Rumex infestations.     

Histological characterization of in vitro adventitious organogenesis in Citrus sinensis

The adventitious bud development was induced in epicotyl segments of Valencia sweet orange (Citrus sinensis L. Osbeck). Seeds were cultured in vitro for three weeks in the dark, followed by one week at a 16-h photoperiod. Epicotyl segments were cultured horizontally for the induction of organogenesis in Murashige and Tucker (1969, MT) culture medium supplemented with 1.0 mg dm⁻³ benzylaminopurine. Samples were observed by light and scanning electron microscopy from day zero to day 25, when buds were well grown. It was shown that the adventitious buds originated directly from the cambial region on the cut ends of the explants.     

Efficient and repetitive production of leaf-derived somatic embryos of Oncidium

Oncidium cultivars gave different embryogenic responses of leaf explants when affected by auxins (2,4-D, IAA, IBA and NAA), cytokinins (2iP, BA, kinetin, TDZ and zeatin), sucrose, NaH₂PO₄, casein hydrolysate, peptone, and glutamine. The best embryogenic responses of cv. Sweet Sugar were at 20 g dm⁻³ sucrose, 85 mg dm⁻³ NaH₂PO₄ and 3 mg dm⁻³ kinetin, respectively. The development of somatic embryos on leaf explants of cv. Sweet Sugar was delayed for about 10 – 20 d in comparison with cv. Gower Ramsey. On growth regulator-free medium, about 40 % of leaf derived embryos of cv. Gower Ramsey were fused together in their basal parts and so called multiple-state embryos. However, under the same condition, the embryos of cv. Sweet Sugar were all in multiple-state form.     

Caspase-8 acts as a key upstream executor of mitochondria during justicidin A-induced apoptosis in human hepatoma cells

Justicia procumbens is a traditional Taiwanese herbal remedy used to treat fever, pain, and cancer. Justicidin A, isolated from Justicia procumbens, has been reported to suppress in vitro growth of several tumor cell lines as well as hepatoma cells. In this study, justicidin A activated caspase-8 to increase tBid, disrupted mitochondrial membrane potential (Delta psi(m)), and caused the release of cytochrome c and Smac/DIABLO in Hep 3B and Hep G2 cells. Justicidin A also reduced Bcl-x(L) and increased Bax and Bak in mitochondria. Caspase-8 inhibitor (Z-IETD) attenuated the justicidin A-induced disruption of Delta psi(m). Growth of Hep 3B implanted in NOD-SCID mice was suppressed significantly by oral justicidin A (20 mg/kg/day). These results indicate that justicidin A-induced apoptosis in these cells proceeds via caspase-8 and is followed by mitochondrial disruption.     

Direct shoot and cormlet regeneration from leaf explants of ‘Silk’ banana (AAB)

Summary Direct shoot and cormlet regeneration from leaf explants were obtained in triploid dessert banana cultivar Nanjanagud Rasabale (NR) that is classified under the group ‘Silk’ and has the genotype AAB. The response for both cormlet and direct shool formation was observed only in leaf explants obtained from shoots cultured in liquid medium but not in similar explants obtained from shoots grown on gelled medium. Shoot initiation occurred after a sequential culture of leaf (sheath) explants on modified Murashige and Skoog (MS) medium supplemented with different growth regulators. In the sequence, the leaf explants were cultured first on medium with a high level (22.4 μM) of benzyladenine (BA), second on indolc-3-butyric acid (IBA) supplemented medium, and third on reduced BA medium under incubation in the dark. The highest adventitious shoot regeneration in 24% of the explants, with the number of shoots ranging from 2 to 3 per explant, occurred in the explants incubated at the first step in medium with 22.4 and 0.198 μM IBA. Further growth and complete shoot formation occurred under incubation in a 16-h photoperiod. While keeping the culture conditions constant and replacing BA with picloram (0.83–20.71 μM) in the initial step, adventious origin of cormlets occurred in 12% of the explants. However, when rhizome explants (also obtained from shoots grown in liquid medium) were cultured with various growth regulators in the first step, medium containing 2,4,5-trichlorophenoxyacctic acid (7.82 μM) produced friable callus that re-differentiated into roots only. Physical forms of the medium, ie.e. agar-gelled or liquid, imparted specific effects on the extent of multiplication of leaf-regenerated shoots with no differences in morphology and growth patterns when compared to those of meristem-derived plants.