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G Guignard

Publications and source records attributed to G Guignard.

8 recordsLinked to original sources
PubMed2004

Ultrastructure of early jurassic fossil plant cuticles: Pachypteris gradinarui Popa.

Exceptional preservation of extinct Pachypteris extra-epidermal cuticle enabled the first detailed statistical measurements of its ultrastructure using transmission electron microscopy. Pachypteris is a leaf genus of the Mesozoic belonging to seed fern foliage of the order Corystospermales. The species studied in this paper is Pachypteris gradinarui Popa [Rev. Palaeobot. Palynol. 111 (2000) 31], based on fossils which are Early Jurassic in age (Hettangian-Sinemurian, approximately 205-190 million years old). Both the upper and the lower cuticles were thoroughly examined, including the detail of the stomatal complexes and epidermal cells. The data obtained from our TEM analysis, together with the confidence intervals, were very useful to give precise description of the cuticles as they distinguished between upper and lower epidermal and stomatal cell types. Moreover a combination of characters was used to develop the first dichotomous key based on ultrastructural characters, i.e. not only the total thickness of the cuticle but also details and proportions of A cuticle proper and B cuticular layer. Comparisons with ultrastructures known from other Pachypteris species show that the influence of space and time, diagenetic processes, and/or processes related to technical procedures, seem to be minimal within this genus. Detailed studies of this type may be very useful for further comparisons among other species and at higher taxonomical ranks.

Fossils↗
PubMed2003

Coffee diterpenes prevent benzo[a]pyrene genotoxicity in rat and human culture systems.

The coffee-specific diterpenes cafestol and kahweol (C+K) have been identified as two important chemoprotective agents in coffee. In the present study, the potential preventive effects of C+K against the genotoxicity of B[a]P were investigated in rat primary hepatocytes and in human bronchial Beas-2B cells. Several independent mechanisms were identified and their respective contribution to the overall protective effects was determined. A marked dose-dependent inhibition by C+K of B[a]P DNA-binding was found in cells of both origins. However, data showed that the significant induction by C+K of the detoxifying enzyme GST-Yp subunit is the key mechanism of protection against B[a]P DNA-binding in rat liver. In contrast, the phase I-mediated mechanism where C+K produce an inhibition of CYP 1A1 induction by B[a]P is of key significance for the C+K protection in human Beas-2B cells. Moreover, this effect suggests a novel mechanism of chemoprotection by the coffee diterpenes cafestol and kahweol.

Animals↗
PubMed2001

Sun and shade leaves? Cuticle ultrastructure of Jurassic Komlopteris nordenskioeldii (Nathorst) Barbacka.

An ultrastructural transmission electron microscope (TEM) study of fossil leaf cuticles from the Jurassic pteridosperm Komlopteris nordenskioeldii (Nathorst) Barbacka from the Mecsek Mountains (South Hungary) was conducted. Remnants of cuticles of leaves originating from so-called "sun and shade" environments were sectioned with a diamond knife, transversally as well as longitudinally. Although the present study showed a simple type of cuticle in this pteridosperm, differences were observed in the occurrence of its components, such as electron lucent amorphous material and various densities of granules, which give rise to different zones. The included fibrilous elements appeared to be made of aggregated and aligned granules, equivalent in size and electron density to nearby non-fibrilous granular regions. The combinations of these ultrastructural features allow distinctions between four types of cuticle: sun upper, sun lower, shade upper and shade lower. Considering the distinction made earlier in two types of cuticle and supposed to be related to sun and shade on the basis of macroscopical and microscopical features, four types only on the basis of differences in thickness, the present study reinforces the distinctions with ultrastructural microcharacteristics. As this study shows the variations in ultrastructure of cuticle among the four types, the differences observed may reveal the great sensitivity of some plants to environment. At the same time, it points out the importance, in ultrastructural studies of cuticles, of studying a number of samples for one taxon.

Journal Article↗
PubMed1999

Morphological and Ultrastructural Studies on in situ Spores of Oligocarpia (Gleicheniaceae) from the Lower Permian of Xinjiang, China.

Though the fossil genus Oligocarpia is generally regarded to be of gleicheniaceous affinity, nothing is currently known about its spore ultrastructure. In this article, the micromorphology and ultrastructure of in situ spores of gleicheniaceous affinity are investigated for the first time with scanning electron microscopy and transmission electron microscopy from a compression specimen of Oligocarpia kepingensis Wang and Wu collected from the Lower Permian of Xinjiang, northwest China. Spores of O. kepingensis closely resemble the dispersed taxon Leiotriletes (Naumova) Potonié et Kremp. At the ultrastructural level, the exospore consists of three-layered subdivisions, including a degraded and weakly preserved thin inner layer, a complex and elaborate middle layer, and homogeneous outer layer. Comparisons are made between Oligocarpia spores and those of other related fossils, as well as extant taxa based on morphological and ultrastructural evidence. These data indicate that, despite clear differences in leaf morphology, O. kepingensis has a close relationship to the family Gleicheniaceae.

Journal Article↗
PubMedDate not supplied

[Acute hydronephrosis in children].

Out of 350 cases of hydronephrosis due to malformation of the ureteropelvic junction, seventeen were acute. Two of these cases, localized in a single kidney, induced anuria in one case, and rupture of the kidney in the other (a baby aged 17 days). The fifteen other cases were revealed by an extremely painful symptomatology, which might have led to severe diagnostic errors. The diagnosis relies on IVU during the period of pain, visualizing a kidney which is barely functioning, if at all. An aberrant vessel was found on the lower pole in 75 per cent of cases, but this, like infection, is only an aggravating factor, though infection may necessitate temporary diversion by cutaneous nephrostomy. All fifteen patients were treated by ureteropelvic resection, and the results were always better than for chronic hydronephrosis because the calicopelvic dilatation is reversible in acute hydronephrosis, and the renal parenchyma still function correctly.

Acute Disease↗