Acclimation of liverwort Marchantia polymorpha to physiological drought reveals important roles of antioxidant enzymes, proline and abscisic acid in land plant adaptation to osmotic stress.

Liverwort Marchantia polymorpha is considered as the key species for addressing a myriad of questions in plant biology. Exploration of drought tolerance mechanism(s) in this group of land plants offers a platform to identify the early adaptive mechanisms involved in drought tolerance. The current study aimed at elucidating the drought acclimation mechanisms in liverwort's model M. polymorpha. The gemmae, asexual reproductive units of M. polymorpha, were exposed to sucrose (0.2 M), mannitol (0.5 M) and polyethylene glycol (PEG, 10%) for inducing physiological drought to investigate their effects at morphological, physiological and biochemical levels. Our results showed that drought exposure led to extreme growth inhibition, disruption of membrane stability and reduction in photosynthetic pigment contents in M. polymorpha. The increased accumulation of hydrogen peroxide and malondialdehyde, and the rate of electrolyte leakage in the gemmalings of M. polymorpha indicated an evidence of drought-caused oxidative stress. The gemmalings showed significant induction of the activities of key antioxidant enzymes, including superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase and glutathione S-transferase, and total antioxidant activity in response to increased oxidative stress under drought. Importantly, to counteract the drought effects, the gemmalings also accumulated a significant amount of proline, which coincided with the evolutionary presence of proline biosynthesis gene Δ1-pyrroline-5-carboxylate synthase 1 (P5CS1) in land plants. Furthermore, the application of exogenous abscisic acid (ABA) reduced drought-induced tissue damage and improved the activities of antioxidant enzymes and accumulation of proline, implying an archetypal role of this phytohormone in M. polymorpha for drought tolerance. We conclude that physiological drought tolerance mechanisms governed by the cellular antioxidants, proline and ABA were adopted in liverwort M. polymorpha, and that these findings have important implications in aiding our understanding of osmotic stress acclimation processes in land plants.

Nectar-dwelling microbes of common tansy are attractive to its mosquito pollinator, Culex pipiens L.

BACKGROUND: There is widespread interkingdom signalling between insects and microbes. For example, microbes found in floral nectar may modify its nutritional composition and produce odorants that alter the floral odor bouquet which may attract insect pollinators. Mosquitoes consume nectar and can pollinate flowers. We identified microbes isolated from nectar of common tansy, Tanacetum vulgare, elucidated the microbial odorants, and tested their ability to attract the common house mosquito, Culex pipiens. RESULTS: We collected 19 microbial isolates from T. vulgare nectar, representing at least 12 different taxa which we identified with 16S or 26S rDNA sequencing as well as by biochemical and physiological tests. Three microorganisms (Lachancea thermotolerans, Micrococcus lactis, Micrococcus luteus) were grown on culture medium and tested in bioassays. Only the yeast L. thermotolerans grown on nectar, malt extract agar, or in synthetic nectar broth significantly attracted Cx. pipiens females. The odorant profile produced by L. thermotolerans varied with the nutritional composition of the culture medium. All three microbes grown separately, but presented concurrently, attracted fewer Cx. pipiens females than L. thermotolerans by itself. CONCLUSIONS: Floral nectar of T. vulgare contains various microbes whose odorants contribute to the odor profile of inflorescences. In addition, L. thermotolerans produced odorants that attract Cx. pipiens females. As the odor profile of L. thermotolerans varied with the composition of the culture medium, we hypothesize that microbe odorants inform nectar-foraging mosquitoes about the availability of certain macro-nutrients which, in turn, affect foraging decisions by mosquitoes.

Asymptomatic fatal post-lobectomy hemopericardium.

We report a case of an asymptomatic post-lobectomy hemopericardium in a female who died suddenly at day two post surgery. Autopsy revealed no pathologic findings, but 250 ml of blood and clots in the pericardium and a non-significant injury to the epicardial fat overlying the circumflex artery territory.

Asian earthquake: report from the first volunteer British hospital team in Pakistan.

At 8:52 am on 8 October 2005 a massive earthquake wracked northern Pakistan and Kashmir. Various teams were sent to Islamabad and the disaster region from the UK. We discuss the types of injury patterns seen and recommend that a central register of volunteers should be created to deal with similar situations in the future.