Unraveling metabolic mechanisms behind chloroplast desiccation tolerance: Chlorophyllous fern spore as a new promising unicellular model.

Fern spores are unicellular structures produced by the sporophyte generation that give rise to the haploid gametophyte. When released from the sporangium, spores are desiccation tolerant (DT) in the royal fern (Osmunda regalis) and contain fully developed chloroplasts. As a consequence, this type of spores is called chlorophyllous spores (CS). Upon transfer to germination conditions, CS initiate a process of imbibition that suppresses DT in 72 h, before the germination starts. In parallel to such change in DT, thylakoids undergo a profound remodelling in composition and function. Firstly, sustained quenching of chlorophyll fluorescence is relaxed, giving rise to photochemically active CS, while lipid composition shifts from that of a resting structure to a metabolically active cell. Basically trigalactolipids decreased in favour of monogalactolipids, with a parallel desaturation of fatty acids. Storage lipids such as triacylglycerol were quickly depleted. These results highlight the importance of the structure of thylakoids lipid as a key to protect membrane integrity during desiccation, together with the saturation of fatty acids and the constitutive chlorophyll quenching to prevent oxidative damage. The CS used here, in which the same cell shifts from DT to sensitive strategy in 72 h, reveal their potential as unicellular models for future studies on DT.

The organic air pollutant cumene hydroperoxide interferes with NO antioxidant role in rehydrating lichen.

Organic pollutants effects on lichens have not been addressed. Rehydration is critical for lichens, a burst of free radicals involving NO occurs. Repeated dehydrations with organic pollutants could increase oxidative damage. Our aim is to learn the effects of cumene hydroperoxide (CP) during lichen rehydration using Ramalina farinacea (L.) Ach., its photobiont Trebouxia spp. and Asterochloris erici. Confocal imaging shows intracellular ROS and NO production within myco and phycobionts, being the chloroplast the main source of free radicals. CP increases ROS, NO and lipid peroxidation and reduces chlorophyll autofluorescence, although photosynthesis remains unaffected. Concomitant NO inhibition provokes a generalized increase of ROS and a decrease in photosynthesis. Our results suggest that CP induces a compensatory hormetic response in Ramalina farinacea that could reduce the lichen's antioxidant resources after repeated desiccation-rehydration cycles. NO is important in the protection from CP.

Suitability of chloroplast LSU rDNA and its diverse group I introns for species recognition and phylogenetic analyses of lichen-forming Trebouxia algae.

To date, species identification of lichen photobionts has been performed principally on the basis of microscopic examinations and molecular data from nuclear-encoded genes. In plants, the chloroplast genome has been more readily exploited than the nuclear genome for systematic investigations. At the present time, very little information is available about the chloroplast genome of lichen-forming algae. For this reason, we have sequenced a portion of the gene encoding for the chloroplast large sub-unit rRNA (LSU rDNA) as a new molecular marker. Sequencing of the chloroplast LSU rDNAs revealed the existence of an unusual diversity of group I introns (a total of 31) within 15 analyzed Trebouxia species. The number, sequence and insertion site of these introns were very different among species, contributing to their recognition. A relatively large intron-free portion of the chloroplast LSU rDNA and part of the nuclear ribosomal cistron (18S-5.8S-26S) between the nuclear internal transcribed spacers (nrITS) were subjected to phylogenetic analyses. The obtained results indicate that data combination from both nuclear and chloroplast sequences can improve phylogenetic accuracy. Herein, we propose the suitability of both intronic and exonic sequences of the chloroplast LSU rDNA for species recognition, and an exonic sequence spanning from position 879 to 1837 in the Escherichia coli 23S rDNA for phylogenetic analyses of Trebouxia phycobionts.

[Pancreatic disease in patients with HIV treated with didanosine (DDI)]. / Afectación pancreática en pacientes VIH tratados con didanosina (DDI).

Pancreatic involvement has been studied in 70 HIV infected patients, in diverse stages, that were treated with didanosine (ddI), both as monotherapy or associated to zidovudine; 38% of patients presented adverse reaction that obliged to withdraw the medication: pancreatitis (4%), hyperamylasemia (21%) and abdominal pain and/or diarrhea (12%). The possible causes in presentation of adverse effects were evaluated: route of infection, stage of HIV infection, use of pentamidine or trimethoprim-sulfamethoxazole for preventing Pneumocystis carinii pneumonia, administration of ddI in monotherapy or in combined form with zidovudine, time of treatment and level of CD4 lymphocytes. The outcome of adverse effects is related significantly only with the most advanced stage of HIV infection.