Lead accumulation in photosynthetic Euglena gracilis depends on polyphosphates and calcium.

Worldwide increasing levels of lead in water systems require the search for efficient ecologically friendly strategies to remove it. Hence, lead accumulation by the free-living algae-like Euglena gracilis and its effects on cellular growth, respiration, photosynthesis, chlorophyll, calcium, and levels of thiol- and phosphate-molecules were analyzed. Photosynthetic cells were able to accumulate 4627 mg lead/kgDW after 5 days of culture with 200 µM Pb2+. Nevertheless, exposure to 50, 100 and 200 µM Pb2+ for up to 8 days did not modify growth, viability, chlorophyll content and oxygen consumption/production. Enhanced biosynthesis of thiol molecules and polyphosphates, i.e. the two canonical metal ion chelation mechanisms in E. gracilis, was not induced under such conditions. However, in cells cultured in the absence of phosphate, lead accumulation and polyphosphate content markedly decreased, while culturing in the absence of sulfate did not modify the accumulation of this metal. In turn, the total amount of intracellular calcium slightly increased as the amount of intracellular lead increased, whereas under Ca2+ deficiency lead accumulation doubled. Therefore, the results indicated that E. gracilis is highly resistant to lead through mechanisms mediated by polyphosphates and Ca2+ and can in fact be classified as a lead hyperaccumulator microorganism.

Nickel accumulation by the green algae-like Euglena gracilis.

Nickel accumulation and nickel effects on cellular growth, respiration, photosynthesis, ascorbate peroxidase (APX) activity, and levels of thiols, histidine and phosphate-molecules were determined in Euglena gracilis. Cells incubated with 0.5-1mM NiCl2 showed impairment of O2 consumption, photosynthesis, Chl a+b content and APX activity whereas cellular integrity and viability were unaltered. Nickel accumulation was depressed by Mg2+ and Cu2+, while Ca2+, Co2+, Mn2+ and Zn2+ were innocuous. The growth half-inhibitory concentrations for Ni2+ in the culture medium supplemented with 2 or 0.2mM Mg2+ were 0.43 or 0.03mM Ni2+, respectively. Maximal nickel accumulation (1362mg nickel/Kg DW) was achieved in cells exposed to 1mM Ni2+ for 24h in the absence of Mg2+ and Cu2+; accumulated nickel was partially released after 72h. GSH polymers content increased or remained unchanged in cells exposed to 0.05-1mM Ni2+; however, GSH, cysteine, γ-glutamylcysteine, and phosphate-molecules all decreased after 72h. Histidine content increased in cells stressed with 0.05 and 0.5mM Ni2+ for 24h but not at longer times. It was concluded that E. gracilis can accumulate high nickel levels depending on the external Mg2+ and Cu2+ concentrations, in a process in which thiols, histidine and phosphate-molecules have a moderate contribution.

Chromium uptake, retention and reduction in photosynthetic Euglena gracilis.

Photosynthetic Euglena gracilis grown with different K(2)CrO(4) concentrations was analyzed for its ability to take up, retain and reduce Cr(VI). For comparison, cells were also exposed to CrCl(3). Cellular Cr(VI) uptake at pH 7.2 showed a hyperbolic saturation pattern with K (m) of 1.1 mM, V (m) of 16 nmol (h x 10(7) cells)(-1), and K (i sulfate) of 0.4 mM. Kinetic parameters for sulfate uptake were similar, K (m) = 0.83 mM, V (m) = 15.9 nmol (h x 10(7)cells)(-1) and K (i chromate) = 0.3 mM. The capacity to accumulate chromium depended on the ionic species, external concentration and pH of the incubation medium. Cr(VI) or Cr(III) accumulation was negligible in the acidic (pH 3.5) culture medium, in which Cr(VI) was abiotically reduced to Cr(III). At pH 7.2 Cr(VI) was fully stable and high accumulation (>170 nmol/1 x 10(7) cells at 1 mM K(2)CrO(4)) was achieved; surprisingly, Cr(III) accumulation was also significant (>35 nmol/1 x 10(7) cells at 1 mM CrCl(3)). Cr(VI) was reduced by cells at pH 7.2, suggesting the presence of an external reductive activity. Cr(VI) induced an increased cysteine and glutathione content, but not in phytochelatins suggesting that chromium accumulation was mediated by monothiol compounds.

Ectodermal ablation of the third branchial arch in chick embryos and the morphogenesis of the parathyroid III gland.

The parathyroid glands have been classically considered to be derivatives of the third and fourth pharyngeal pouches in most species, including humans. Furthermore, the presence of neural crest-derived cells in the parathyroid glands connective tissue has been apparently established. However, our previous studies have provided a new hypothesis on the origin of these glands in human and chick embryos. To determine the origin of the parathyroid III (P3) gland, ectoderm of the third branchial arch was cauterized in chick embryos at Hamburger and Hamilton's stage 19 (embryonic day 3). Cauterization of the ventral half of the ectoderm was followed by the non-formation, on the same side, of the P3 gland. When the dorsal half of the ectoderm was cauterized, both the right and left P3 glands formed. Our observations suggest that the ectoderm of the ventral half of the third branchial arch is necessary for the organization of the P3 gland.

Development of the human wrist joint ligaments.

BACKGROUND: Many studies have been published on the development of the human wrist joint, but scant attention has been given to the development of the wrist joint ligaments. Moreover, traditional description of wrist anatomy usually depict only the superficial capsular fibers of the wrist joint. The only ligamentous structure to receive much attention is the articular disc of the wrist joint, which has been described as a fibrocartilaginous structure extending from the medial edge of the lower end of the radius to the ulnar styloid process. METHODS: In the present report, we synthesize our observations in the wrist joint ligaments in 35 serially sectioned human embryonic and fetal hands (16 embryos and 19 fetuses). RESULTS: The interosseous intercarpal ligaments are organized from the mesenchyme, which, until O'Rahilly's stage 23, fills the intercarpal spaces. These ligaments are not individually distinguishable until the 9th week of development. The collateral ligaments begin to form in O'Rahillys's stage 22 and are completely formed by the end of week 10. The palmar radiocarpal and ulnocarpal ligaments (beginning with the palmar radiocarpal ligament) begin to form in O'Rahilly's stage 23 and are fully developed by the end of week 10. At this time, development of the dorsal radiocarpal ligament begins; this process is completed by the end of week 13. The articular disc which is initially formed of a single element, first appears in O'Rahilly's stage 23 and its organization is completed at week 10 of development. CONCLUSIONS: We establish the morphogenetic time-table of the wrist joint ligaments. Our descriptive findings may help explain carpal motion and the origin of wrist injuries.

Grafts of the third branchial arch in chick embryos.

The parathyroid glands have been classically considered derivatives of the third and fourth pharyngeal pouches in most species, including humans. The presence of neural crest-derived cells in parathyroid glands connective tissue has apparently been established. However, our previous studies have provided a new hypothesis on the origin of these glands in human and chick embryos. To determine the true origin of the third parathyroid (parathyroid III) gland in the chick embryo, pieces of the third branchial arch from donor chick embryos at Hamburger and Hamilton's stage 19 (embryonic day 3) were grafted to host chick embryos at the same stage of development. Starting from Hamburger and Hamilton's stage 27 (embryonic day 5), a structure identified as the parathyroid III appeared in the ectodermal (epipharyngeal) placode of the third branchial arch graft, from which it subsequently became separated at Hamburger and Hamilton's stage 28 (embryonic day 5.5) and continued to develop and mature. Our findings suggest the conclusion that the parathyroid III gland begins to develop from the epipharyngeal placode, so that this gland, from our point of view, could be considered ectodermal in nature.

Development of the human submandibular salivary gland.

The development and morphogenetic timetable of the submandibular gland was studied in 37 human embryos and human fetuses. The medial paralingual groove constituted the anlage of the submandibular gland: Its anterior three-quarters gave rise to Wharton's duct, and its posterior quarter to the submandibular gland proper. The sublingual process of the submandibular gland originated from a lateral ectodermal bud of the anlage of the submandibular gland, in the posterior quarter of the medial paralingual groove.

Developmental differences in the ossification process of the human corpus and ramus mandibulae.

A correlation was sought between the organization of the dental crest and the ossification of the corpus mandibulae in 14 human embryos and 13 human fetuses. The different types of ossification between the corpus and the ramus mandibulae suggest that the cartilago mandibularis (meckeliensis) guides the formation of the mandibula, while the dental crest acts as a coorganizer. In the area of the foramen mentale, the lamina dentalis begins to invaginate (to give rise to the dental crest), and at this level intramembranous ossification of the corpus mandibulae commences. These findings, together with the presence of the cartilago mandibularis before the appearance of the dental crest, and the fact that the former is seen along the entire length of the mandibula (from the symphysis mandibulae to the capsula otica), support the hypothesis that the dental crest, rather than the cartilago mandibularis, acts as the coorganizer in the corpus mandibulae.

Relationships between the parotid gland and the facial nerve during human development.

A correlation was sought between the organization of the parotid gland and the formation of the large vessels and nerves that passed through the glands of 12 human embryos and 12 human fetuses. There was no evidence that the gland became a bilobate structure as a result of the course of the facial nerve, whose interglandular branches were surrounded during development by the multidirectional ramifications of the expanding parotid anlage.

Histogenesis of the spleen in the human embryo in O'Rahilly's stages 17 to 23.

A histological study of the spleen in 30 human embryos in O'Rahilly's stages 17-23 revealed that the splenic anlage is composed of mesenchymal elements. Furthermore, the spleen is formed by a cytoreticulum containing a number of cells similar in appearance to lymphoid elements. No evidence of a celomocapsular separation is seen in this period.

Origin of the ultimobranchial body and its colonizing cells in human embryos.

The early development of the ultimobranchial body and its colonizing cells was studied in human embryos (O'Rahilly's stages 14 and 15). In our studies we have obtained evidence that permits us to propose a new hypothesis on the origin of both the ultimobranchial body and its colonizing cells. Based on our interpretation of the morphogenetic features in human development, we think that the ultimobranchial body derives from the fifth endodermal pharyngeal pouch, which is colonized, from O'Rahilly's stage 14 on, by cellular material of ectodermal placodial nature that originates in the most caudal portion of the epicardiac branchial placode.

Morphogenesis of the ultimobranchial body and its colonizing cells in the chick embryo.

The development of the ultimobranchial body and its colonizing cells was studied in chick embryos in Hamburger-Hamilton's stages 21 to 46. The most significant observations included the following: 1.-The ultimobranchial body is a separate morphological entity with particular characteristics distinguishing it from the fourth pharyngeal pouch in all developmental stages. 2.-The fifth pharyngeobranchial ducts disappear in Hamburger-Hamilton's stage 27. 3.-From Hamburger-Hamilton's stage 27 on, the left ultimobranchial body is in contact with the caudal end of the left parathyroid IV primordium. 4.-The group made up of the ultimobranchial body and its colonizing cells at no time fuses with the thyroid gland.