Circadian clock adjustment to plant iron status depends on chloroplast and phytochrome function

Plant chloroplasts are not only the main cellular location for storage of elemental iron (Fe), but also the main site for Fe, which is incorporated into chlorophyll, haem and the photosynthetic machinery. How plants measure internal Fe levels is unknown. We describe here a new Fe‐dependent response, a change in the period of the circadian clock. In Arabidopsis, the period lengthens when Fe becomes limiting, and gradually shortens as external Fe levels increase. Etiolated seedlings or light‐grown plants treated with plastid translation inhibitors do not respond to changes in Fe supply, pointing to developed chloroplasts as central hubs for circadian Fe sensing. Phytochrome‐deficient mutants maintain a short period even under Fe deficiency, stressing the role of early light signalling in coupling the clock to Fe responses. Further mutant and pharmacological analyses suggest that known players in plastid‐to‐nucleus signalling do not directly participate in Fe sensing. We propose that the sensor governing circadian Fe responses defines a new retrograde pathway that involves a plastid‐encoded protein that depends on phytochromes and the functional state of chloroplasts.     

Effect of maximal respiratory manoeuvres on bronchial sensitivity of asthmatic patients as compared to normal people.

Cumulative dose-response curves to carbachol given by aerosol were established using plethysmographic measurements of specific airways resistance (SRaw) in 10 patients with asthma and five healthy subjects. Two experiments were performed--a control test and one in which maximal respiratory manoeuvres (MRM) (two maximal inspirations and two maximal expirations) were made before each carbachol inhalation. MRM did not modify the dose-response curves in the normal subjects. In the patients these manoeuvres enhanced the bronchoconstrictor effect of carbachol: curves were shifted to the left and the mean dose of carbachol producing a twofold increase in initial SRaw was decreased from 0.373 mg to 0.189 mg (P less than 0.001). Bronchial provocation tests using methods which require MRM--for example, forced expiratory volume at one second--could overestimate the bronchial sensitivity of patients with asthma.     

First descriptions of Coelometopini pupae (Coleoptera: Tenebrionidae) from Australia,Southeast Asia and the Pacific region,with comments on phylogenetic relationships and antipredator adaptations

Abstract. The pupal stage of ten Coelometopini species occurring in Australia, New Guinea, Southeast Asia and the Pacific region are described and a key for their identification is provided. The species are Chrysopeplus expolitus Broun, Derosphaerus hirtipes Kaszab, Hypaulax crenata (Boisduval), Leprocaulus borneensis Kaszab, Metisopus purpureipennis Bates, Promethis carteri Kaszab, P. nigra (Blessig), P. quadraticollis (Gebien), P. quadricollis Pascoe and P. sulcigera (Boisduval). The gin trap structures of D. hirtipes and P. quadraticollis are described in detail using scanning electron micrographs. A summary of antipredator structures of all known Coelometopini pupae is given. The phylogenetic value of pupal characters is assessed at intra‐ and intergeneric levels within the tribe.     

Tn1545: a conjugative shuttle transposon

Summary Tn1545, from Streptococcus pneumoniae BM4200, confers resistance to kanamycin (aphA-3), erythromycin (ermAM) and tetracycline (tetM). The 25.3 kb element is self-transferable to various Gram-positive bacterial genera where it transposes. Tn1545 was cloned in its entirety in the recombination deficient Escherichia coli HB101 where it was unstable. The three resistance genes aphA-3, ermAM and tetM were expressed but were not transferable to other E. coli cells. Tn1545 transposed from the hybrid plasmid to multiple sites of the chromosome of its new host. The element re-transposed, at a frequency of 5×10^-9, from the chromosome to various sites of a conjugative plasmid where it could be lost by apparently clean excision. The element transformed and transposed to the chromosome of Bacillus subtilis. The properties of the conjugative shuttle transposon Tn1545 may account for the recent emergence of genes from Gram-positive bacteria in Gramnegative organisms.     

Evidence for a dual mechanism of chick embryo fibroblast adhesion on fibronectin and laminin substrata

Eight-day-old chick embryo fibroblasts were shown to adhere specifically to fibronectin and laminin substrata. Moreover, the Scatchard analysis reveals 540,000 binding sites per cell for the fibronectin with a dissociation constant (Kd) of 1.35 microM and 5,500 binding sites per cell for laminin with a Kd of 1.5 nM. Furthermore, cell-fibronectin interactions are mediated by plasma membrane proteins of high molecular weight (HMW) (150K and 125K) insensitive to trypsin treatment and low molecular weight (LMW) proteins (95K, 80K, 65K and 45K) sensitive to trypsin treatment. Adhesion of 8-day-old chick embryo fibroblasts on laminin is mediated by plasma membrane proteins highly sensitive to trypsin treatment. Regarding the paucity of laminin-binding sites, the identification of laminin receptor could not be achieved. Nevertheless, this study provides quantitative and qualitative evidences for different mechanisms of 8-day-old chick embryo fibroblasts on laminin and fibronectin.     

Phospholipase A2 activity of rat stomach

Phospholipase A activity in rat stomach wall and in gastric content was studied using [1-14C]dioleoylphosphatidylcholine as substrate. The optimum activity of the stomach wall was found to take place at pH 7.0. During optimal phospholipase action about 40% of the [1-14C]oleic acid released was due to an active intracellular lysophospholipase. The gastric phospholipase required 5 mM Ca2+ for full activity and is inhibited by EDTA. It specifically hydrolyzed the sn-2 position of the phospholipid molecule. The enzyme was heat labile and inactivated by acidification at pH 3.0. The gastric content enzyme had a lower specific activity and an optimum pH of 8.0. It was heat stable and was not inactivated by acidification. These results indicate that gastric content phospholipase A is of pancreatic origin, via a duodenal reflux. By ligating the stomach we were able to further confirm that the gastric wall phospholipase was different from that of the gastric content. It originated from the stomach mucosa. Subcellular fractionation suggests that the gastric phospholipase A2 is essentially bound to the plasma membrane. About 6% of the activity was found to be soluble. Biopsies of human gastric mucosa displayed a phospholipase A activity which had similar properties to that of rat gastric enzyme. The physiological function of this enzyme is discussed in terms of prostaglandin synthesis via the release of arachidonic acid.