Seasonal variation in hydrochloric acid, malic acid, and calciumions secreted by the trichomes of chickpea (Cicer arietinum)

A novel experimental set-up and method of recording of electrical potential differences in plants have been developed which enable continuous, 8-channel monitoring of electrical activity over extended periods of time using inserted, extracellular electrodes. The investigations were carried out on 21- to 23-day-old Helianthus annuus plants, and spontaneously-generated action potentials were recorded during monitoring sessions lasting for 3 days and nights. Characteristics of these spontaneous action potentials were elaborated, adopting as parameters their typical form, amplitude, duration, velocity, direction, and distance of propagation and frequency of occurrence in morphologically different parts of the plant, Variability, similarities, and interdependence of the above parameters in individual plants and in a group of 15 plants were determined. A hypothesis concerning propagation of action potentials in plants along specific impulse-propagating 'columns' is discussed. The frequency of generated impulses is highest at night and lowest in the day and also displays an apparent 24-h rhythm. Presumably this mechanism is under both endogenous and exogenous control and may be partly dependent on a biological clock.     

Hereditary desmoid disease in a family with a germline Alu I repeat mutation of the APC gene

Two families with autosomal dominantly inherited desmoid tumors have recently been shown to have germline mutations at the 3' end of the APC gene. We subsequently identified an Amish family with autosomal dominantly inherited desmoid tumors. Genetic analysis performed on one family member, a 47-year-old man with multiple desmoid tumors and no colon polyps, revealed a protein truncating mutation in the middle of the APC gene. The truncating mutation is the result of a 337-bp insertion of an Alu I sequence into codon 1526 of the APC gene. The presence of a poly(A) tail at the 3' end of the insertion suggests that the Alu I sequence was inserted by a retrotranspositional event. Germline insertions of Alu I sequences have occasionally been reported to cause other genetic diseases including type I neurofibromatosis, hereditary site-specific breast cancer (BRCA2), and hemophilia B. However, this is the first report of a germline mutation of the APC gene resulting from an Alu I insertion.     

The interplay among chromatin dynamics, cell cycle checkpoints and repair mechanisms modulates the cellular response to DNA damage

Cells are continuously under the assault of endogenous and exogenous genotoxic stress that challenges the integrity of DNA. To cope with such a formidable task cells have evolved surveillance mechanisms, known as checkpoints, and a variety of DNA repair systems responding to different types of DNA lesions. These lesions occur in the context of the chromatin structure and, as expected for all DNA transactions, the cellular response to DNA damage is going to be influenced by the chromatin enviroment. In this review, we will discuss recent studies implicating chromatin remodelling factors and histone modifications in the response to DNA double-strand breaks (DSBs) and in checkpoint activation in response to UV lesions.     

Intraspecific trait variability and genetic diversity in the adaptive strategies of serpentine and non-serpentine populations of Silene paradoxa L.

Plant and Soil - We investigated whether individuals of Silene paradoxa L., grown in serpentine and non-serpentine soils, displayed variation in functional traits and adaptive strategies...     

DNA sequence polymorphism and divergence at the erect wing and suppressor of sable loci of Drosophila melanogaster and D. simulans

Several evolutionary models of linked selection (e.g., genetic hitchhiking, background selection, and random environment) predict a reduction in polymorphism relative to divergence in genomic regions where the rate of crossing over per physical distance is restricted. We tested this prediction near the telomere of the Drosophila melanogaster and D. simulans X chromosome at two loci, erect wing (ewg) and suppressor of sable [su(s)]. Consistent with this prediction, polymorphism is reduced at both loci, while divergence is normal. The reduction is greater at ewg, the more distal of the two regions. Two models can be discriminated by comparing the observed site frequency spectra with those predicted by the models. The hitchhiking model predicts a skew toward rare variants in a sample, while the spectra under the background-selection model are similar to those of the neutral model of molecular evolution. Statistical tests of the fit to the predictions of these models require many sampled alleles and segregating sites. Thus we used SSCP and stratified DNA sequencing to cover a large number of randomly sampled alleles (approximately 50) from each of three populations. The result is a clear trend toward negative values of Tajima's D, indicating an excess of rare variants at ewg, the more distal of the two loci. One fixed difference among the populations and high FST values indicate strong population subdivision among the three populations at ewg. These results indicate genetic hitchhiking at ewg, in particular, geographically localized hitchhiking events within Africa. The reduction of polymorphism at su(s) combined with the excess of high-frequency variants in D. simulans is inconsistent with the hitchhiking and background-selection models.     

Atropisomeric quinazolin-4-one derivatives are potent noncompetitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists

Piriqualone (1) was found to be an antagonist of AMPA receptors. Structure activity optimization was conducted on each of the three rings in 1 to afford a series of potent and selective antagonists. The sterically crowded environment surrounding the N-3 aryl group provided sufficient thermal stability for atropisomers to be isolated. Separation of these atropisomers resulted in the identification of (+)-38 (CP-465,022), a compound that binds to the AMPA receptor with high affinity (IC50 = 36 nM) and displays potent anticonvulsant activity.     

DNA decay and limited Rad53 activation after liquid holding of UV-treated nucleotide excision repair deficient S. cerevisiae cells

The DNA damage checkpoint is a surveillance mechanism activated by DNA lesions and devoted to the maintenance of genome stability. It is considered as a signal transduction cascade, involving a sensing step, the activation of a set of protein kinases and the transmission and amplification of the damage signal through several phosphorylation events. In budding yeast many players of this pathway have been identified. Recent work showed that G1 and G2 checkpoint activation in response to UV irradiation requires prior recognition and processing of UV lesions by nucleotide excision repair (NER) factors that likely recruit checkpoint proteins near the damage. However, another report suggested that NER was not required for checkpoint function. Since the functional relationship between repair mechanisms and checkpoint activation is a very important issue in the field, we analyzed, under different experimental conditions, whether lesion processing by NER is required for checkpoint activation. We found that DNA damage checkpoint can be triggered in an NER-independent manner only if cells are subjected to liquid holding after UV treatment. This incubation causes a time-dependent breakage of DNA strands in NER-deficient cells and leads to partial activation of the checkpoint kinase. The analysis of the genetic requirements for this alternative activation pathway suggest that it requires Mec1 and the Rad17 complex and that the observed DNA breaks are likely to be due to spontaneous decay of damaged DNA.     

The nuclear reticulum in placental cells ofLilium regale is a part of the endomembrane system

Summary Placental cells line the ovarian transmitting tract inLilium regale and produce exudates for secretion. Sections through the highly lobed nuclei of these cells reveal the presence of membrane profiles which form vesicles with varying dimensions in cross section. Computer reconstruction of the nucleus reveals that the vesicle profiles form a complex reticulum of tubular cisternae, which spans the whole nucleus, enclosing a maze of continuous lumen space. Connections between the vesicles and the inner nuclear envelope are visible at various points along the nuclear envelope. This complex network of tubules which constitutes the reticulum arises from the inner nuclear membrane. The nuclear reticulum dramatically increases the inner-envelope surface area, comprising 82% of the total membrane perimeter of inner nuclear envelope and nuclear reticulum. The inner nuclear envelope invaginates into the nucleus forming the nuclear reticulum and the outer nuclear envelope evaginates into the endoplasmic reticulum (ER), indicating that there is a continuity between the lumens of the nuclear reticulum and the ER. The nuclear reticulum is labelled with zinc iodide-osmium tetroxide, a staining pattern identical to that seen in the ER. Positive reaction to the zinc iodide-osmium tetroxide indicates that the nuclear reticulum is a site for Ca²⁺ deposition. The nuclear reticulum forms an extension of the endomembrane system which reaches deep into the nucleoplasm. The lumenal continuity of this system means that there is a channel for communication from the cytoplasm into the nucleoplasm, and that this channel sequesters calcium.Abbreviations ER endoplasmic reticulum - TEM transmission electron microscope - ZIO zinc iodide-osmium tetroxide