Photoprotection, photosynthesis and growth of tropical tree seedlings under near-ambient and strongly reduced solar ultraviolet-B radiation

Seedlings of two late-successional tropical rainforest tree species, Tetragastris panamensis (Engler) O. Kuntze and Calophyllum longifolium (Willd.), were field grown for 3-4 months at an open site near Panama City (9 degrees N), Panama, under plastic films that either transmitted or excluded most solar UV-B radiation. Experiments were designed to test whether leaves developing under bright sunlight with strongly reduced UV-B are capable of acclimating to near-ambient UV-B conditions. Leaves of T. panamensis that developed under near-ambient UV-B contained higher amounts of UV-absorbing substances than leaves of seedlings grown under reduced UV-B. Photosynthetic pigment composition, content of alpha-tocopherol, CO(2) assimilation, potential photosystem II (PSII) efficiency (evaluated by F(v)/F(m) ratios) and growth of T. panamensis and C. longifolium did not differ between seedlings developed under near-ambient and reduced solar UV-B. When seedlings were transferred from the reduced UV-B treatment to the near-ambient UV-B treatment, a pronounced inhibition of photosynthetic capacity was observed initially in both species. UV-B-mediated inhibition of photosynthetic capacity nearly fully recovered within 1 week of the transfer in C. longifolium, whereas in T. panamensis an about 35% reduced capacity of CO(2) uptake was maintained. A marked increase in UV-absorbing substances was observed in foliage of transferred T. panamensis seedlings. Both species exhibited enhanced mid-day photoinhibition of PSII immediately after being transferred from the reduced UV-B to the near-ambient UV-B treatment. This effect was fully reversible within 1d in T. panamensis and within a few days in C. longifolium. The data show that leaves of these tropical tree seedlings, when developing in full-spectrum sunlight, are effectively protected against high solar UV-B radiation. In contrast, leaves developing under conditions of low UV-B lacked sufficient UV protection. They experienced a decline in photosynthetic competence when suddenly exposed to near-ambient UV-B levels, but exhibited pronounced acclimative responses.     

Limitation of nocturnal import of ATP into Arabidopsis chloroplasts leads to photooxidative damage

When grown in short day conditions and at low light, leaves of Arabidopsis plants with mutations in the genes encoding two plastidial ATP/ADP transporters (so-called null mutants) spontaneously develop necrotic lesions. Under these conditions, the mutants also display light-induced accumulation of H(2)O(2) and constitutive expression of genes for copper/zinc superoxide dismutase 2 and ascorbate peroxidase 1. In the light phase, null mutants accumulate high levels of phototoxic protoporphyrin IX but have only slightly reduced levels of Mg protoporphyrin IX. The physiological changes are associated with reduced magnesium-chelatase activity. Since the expression of genes encoding any of the three subunits of magnesium-chelatase is similar in wild type and null mutants, decreased enzyme activity is probably due to post-translational modification which might be due to limited availability of ATP in plastids during the night. Surprisingly, the formation of necrotic lesions was absent when null mutants were grown either in long days and low light intensity or in short days and high light intensity. We ascribe the lack of lesion phenotype to increased nocturnal ATP supply due to glycolytic degradation of starch which may lead to additional substrate-level phosphorylation in the stroma. Thus, nocturnal import of ATP into chloroplasts represents a crucial, previously unknown process that is required for controlled chlorophyll biosynthesis and for preventing photooxidative damage.     

Comparison of sister species identifies factors underpinning plastid compatibility in green sea slugs

The only animal cells known that can maintain functional plastids (kleptoplasts) in their cytosol occur in the digestive gland epithelia of sacoglossan slugs. Only a few species of the many hundred known can profit from kleptoplasty during starvation long-term, but why is not understood. The two sister taxa Elysia cornigera and Elysia timida sequester plastids from the same algal species, but with a very different outcome: while E. cornigera usually dies within the first two weeks when deprived of food, E. timida can survive for many months to come. Here we compare the responses of the two slugs to starvation, blocked photosynthesis and light stress. The two species respond differently, but in both starvation is the main denominator that alters global gene expression profiles. The kleptoplasts'' ability to fix CO₂ decreases at a similar rate in both slugs during starvation, but only E. cornigera individuals die in the presence of functional kleptoplasts, concomitant with the accumulation of reactive oxygen species (ROS) in the digestive tract. We show that profiting from the acquisition of robust plastids, and key to E. timida''s longer survival, is determined by an increased starvation tolerance that keeps ROS levels at bay.     

Xanthophyll cycle and energy-dependent fluorescence quenching in leaves from pea plants grown under intermittent light

The possible role of zeaxanthin formation and antenna proteins in energy-dependent chlorophyll fluorescence quenching (qE) has been investigated. Intermittent-light-grown pea (Pisum sativum L.) plants that lack most of the chlorophyll a/b antenna proteins exhibited a significantly reduced qE upon illumination with respect to control plants. On the other hand, the violaxanthin content related to the number of reaction centers and to xanthophyll cycle activity, i.e. the conversion of violaxanthin into zeaxanthin, was found to be increased in the antenna-protein-depleted plants. Western blot analyses indicated that, with the exception of CP 26, the content of all chlorophyll a/b-binding proteins in these plants is reduced to less than 10% of control values. The results indicate that chlorophyll a/b-binding antenna proteins are involved in the energy-dependent fluorescence quenching but that only a part of qE can be attributed to quenching by chlorophyll a/b-binding proteins. It seems very unlikely that xanthophylls are exclusively responsible for the qE mechanism.Abbreviations CAB chlorophyll a/b-binding - Chl chlorophyll - F_V variable fluorescence - IML intermittent light - LHC light harvesting complex - PFD photon flux density - qP photochemical quenching of chlorophyll fluoresence - qN non-photochemical quenching - qE energy-dependent quenching - qI photoinhibitory quenching - qT quenching by state transition     

水稻涝害生理及其与水稻生产的关系

概述了水稻涝害生理、影响水稻涝害的因素以及涝害与水稻生产的关系,提出了减轻涝害的途径与灾后的补救措施。     

Crossover Localisation Is Regulated by the Neddylation Posttranslational Regulatory Pathway

Crossovers (COs) are at the origin of genetic variability, occurring across successive generations, and they are also essential for the correct segregation of chromosomes during meiosis. Their number and position are precisely controlled, however the mechanisms underlying these controls are poorly understood. Neddylation/rubylation is a regulatory pathway of posttranslational protein modification that is required for numerous cellular processes in eukaryotes, but has not yet been linked to homologous recombination. In a screen for meiotic recombination-defective mutants, we identified several axr1 alleles, disrupting the gene encoding the E1 enzyme of the neddylation complex in Arabidopsis. Using genetic and cytological approaches we found that axr1 mutants are characterised by a shortage in bivalent formation correlated with strong synapsis defects. We determined that the bivalent shortage in axr1 is not due to a general decrease in CO formation but rather due to a mislocalisation of class I COs. In axr1, as in wild type, COs are still under the control of the ZMM group of proteins. However, in contrast to wild type, they tend to cluster together and no longer follow the obligatory CO rule. Lastly, we showed that this deregulation of CO localisation is likely to be mediated by the activity of a cullin 4 RING ligase, known to be involved in DNA damage sensing during somatic DNA repair and mouse spermatogenesis. In conclusion, we provide evidence that the neddylation/rubylation pathway of protein modification is a key regulator of meiotic recombination. We propose that rather than regulating the number of recombination events, this pathway regulates their localisation, through the activation of cullin 4 RING ligase complexes. Possible targets for these ligases are discussed.     

Wachstumsprozesse bei Umbilicaria cylindrica

Cilien und Rhizinomorphe entstehen bei Umbilicaria cylindrica aus dem Rindengewebe, wobei ein Zusammenhang mit dem Wachstum der Pruina besteht. Ein ontogenetischer Unterschied zwischen Cilien und Rhizinomorphen besteht nicht. Junge Thallusloben entwickeln sich laminai auf alten Thalli. Hierbei kann der Mutterthallus auf zwei verschiedene Weisen aufgebrochen werden. Anhangsorgane entwickeln sich bevorzugt an Orten starken Thalluswachstums, zu denen neben jungen Loben manchmal auch Fruchtkörperanlagen gehören.     

Assessment of myocardial abnormalities in rheumatoid arthritis using a comprehensive cardiac magnetic resonance approach: a pilot study

Introduction  

Rheumatoid arthritis (RA) is a multi-organ inflammatory disorder associated with high cardiovascular morbidity and mortality. We sought to assess cardiac involvement using a comprehensive cardiac magnetic resonance imaging (cMRI) approach and to determine its association with disease characteristics in RA patients without symptomatic cardiac disease.     

Caffeic Acid Phenylethyl Ester and MG-132 Have Apoptotic and Antiproliferative Effects on Leukemic Cells But Not on Normal Mononuclear Cells

Chemotherapy aims to limit proliferation and induce apoptotic cell death in tumor cells. Owing to blockade of signaling pathways involved in cell survival and proliferation, nuclear factor κB (NF-κB) inhibitors can induce apoptosis in a number of hematological malignancies. The efficacy of conventional chemotherapeutic drugs, such as vincristine (VCR) and doxorubicine (DOX), may be enhanced with combined therapy based on NF-κB modulation. In this study, we evaluated the effect of caffeic acid phenylethyl ester (CAPE) and MG-132, two nonspecific NF-κB inhibitors, and conventional chemotherapeutics drugs DOX and VCR on cell proliferation and apoptosis induction on a lymphoblastoid B-cell line, PL104, established and characterized in our laboratory. CAPE and MG-132 treatment showed a strong antiproliferative effect accompanied by clear cell cycle deregulation and apoptosis induction. Doxorubicine and VCR showed antiproliferative effects similar to those of CAPE and MG-132, although the latter drugs showed an apoptotic rate two-fold higher than DOX and VCR. None of the four compounds showed cytotoxic effect on peripheral mononuclear cells from healthy volunteers. CAPE- and MG-132-treated bone marrow cells from patients with myeloid and lymphoid leukemias showed 69% (P < .001) and 25% decrease (P < .01) in cell proliferation and 42% and 34% (P < .01) apoptosis induction, respectively. Overall, our results indicate that CAPE and MG-132 had a strong and selective apoptotic effect on tumor cells that may be useful in future treatment of hematological neoplasias.