Phosphorus supply drives rapid turnover of membrane phospholipids in the diatom Thalassiosira pseudonana

In low-phosphorus (P) marine systems, phytoplankton replace membrane phospholipids with non-phosphorus lipids, but it is not known how rapidly this substitution occurs. Here, when cells of the model diatom Thalassiosira pseudonana were transferred from P-replete medium to P-free medium, the phospholipid content of the cells rapidly declined within 48 h from 45±0.9 to 21±4.5% of the total membrane lipids; the difference was made up by non-phosphorus lipids. Conversely, when P-limited T. pseudonana were resupplied with P, cells reduced the percentage of their total membrane lipids contributed by a non-phosphorus lipid from 43±1.5 to 7.3±0.9% within 24 h, whereas the contribution by phospholipids rose from 2.2±0.1 to 44±3%. This dynamic phospholipid reservoir contained sufficient P to synthesize multiple haploid genomes, suggesting that phospholipid turnover could be an important P source for cells. Field observations of phytoplankton lipid content may thus reflect short-term changes in P supply and cellular physiology, rather than simply long-term adjustment to the environment.     

Expression of AtSAP5 in cotton up-regulates putative stress-responsive genes and improves the tolerance to rapidly developing water deficit and moderate heat stress

The regulation of gene expression is a key factor in plant acclimation to stress, and it is thought that manipulation of the expression of critical stress-responsive genes should ultimately provide increased protection against abiotic stress. The aim of this study was to test the hypothesis that the ectopic expression of the AtSAP5 (AT3G12630) gene in transgenic cotton (Gossypium hirsutum, cv. Coker 312) will improve tolerance to drought and heat stress by up-regulating the expression of endogenous stress-responsive genes. The SAP5 gene is a member of the stress-associated family of genes that encode proteins containing A20/AN1 zinc finger domains. Under non-stressful conditions, cotton plants that expressed the AtSAP5 gene showed elevated expression of at least four genes normally induced during water deficit or heat stress. The rate of net CO(2) assimilation A for three of four transgenic lines tested was less sensitive to rapidly developing water deficit over 4d than untransformed wild-type plants, but the recovery of A following drought was not significantly affected. The enhanced protection of photosynthesis during drought was determined to be primarily at the biochemical level, since the extent of stomatal closure was not significantly different for all genotypes. Expression of AtSAP5 resulted in the complete protection of photosystem (PS) II complexes from photodamage at mid-day after 4d of drought, whereas wild-type plants experienced a 20% decline in active photosystem II (PSII) complexes. In addition, enhanced protection of seedling growth and leaf viability was associated with the expression of AtSAP5. Since A for the transgenic plants was significantly more heat tolerant than A for wild-type plants, we conclude that ectopic expression of SAP genes is a potentially viable approach to improving carbon gain and productivity for cotton grown in semi-arid regions with severe drought and heat stress.     

Protecting cotton photosynthesis during moderate chilling at high light intensity by increasing chloroplastic antioxidant enzyme activity.

This study examined the effect of increasing chloroplastic superoxide dismutase (SOD), ascorbate peroxidase (APX), or glutathione reductase (GR) activity via plant transformation of cotton on the initial recovery of photosynthesis following exposures to 10 degrees C and high photon flux density (PFD). Growing wild-type or non-expressing segregate plants (controls) and transformants at two PFDs (600 micromol m(-2) s(-1) and full sun) resulted in a range of total antioxidant enzyme activities. Total SOD activities above that for control leaves grown in full sun did not substantially improve the recoveries of CO(2)-saturated photosynthesis, especially for stress treatments lasting more than 1 h, while elevated APX or GR activity did improve recoveries after 1-3 h of the chilling treatment. No synergistic effects were noted when the activities of more than one antioxidant enzyme were elevated in transgenic hybrids. Although these results suggest that the protection of photosynthesis can be realized by reducing either superoxide or H(2)O(2) levels, thereby reducing the possibility of hydroxyl radical formation, the situation is complicated, since elevated APX or GR activity can improve recoveries even when additional SOD activity has no effect. In conclusion, to enhance the protection of photosynthesis using stroma-targeted antioxidant enzymes, enhancing metabolism associated with H(2)O(2) is more effective than enhancing the capacity for superoxide scavenging. Although small, the improvement in the protection of photosynthetic capacity may be sufficient to improve cotton yield in temperate regions with large diurnal temperature fluctuations.     

Post-translational processing of bovine chondromodulin-I

Chondromodulin-I (ChM-I) is a small glycoprotein that is abundant in fetal cartilage. Mature chondromodulin-I is processed from a larger precursor form, presumably at a proteolytic site RERR-ELVR. The precursor, mature chondromodulin-I and two processed products, the remnant left after removal of mature chondromodulin-I and a smaller, unglycosylated form, were identified using antipeptide antisera. The products of chondromodulin-I precursor processing were seen in cultured chondrocytes, a stable long-term culture chondrosarcoma cell line, as well as Chinese hamster ovary (CHO) cells transfected with an expression plasmid that contained cDNA coding for the chondromodulin-I precursor. Pulse-chase analysis allowed a processing pathway to be analyzed for chondromodulin-I. To further dissect the processing events, three constructs that express recombinant wild-type or mutant chondromodulin-I were transfected into CHO cells. We showed that chondromodulin-I is cleaved intracellularly at the predicted cleavage site, and that the mature glycopeptide is rapidly secreted immediately after processing. The chondromodulin-1 precursor has a short half-life and is not readily apparent in tissue samples, suggesting that chondromodulin is not a member of the juxtacrine family of growth factors, despite some similarities. The smaller unglycosylated form of chondromodulin-I was only observed in cartilage and not in short-term cultures or transfected cells, suggesting an extracellular processing event. No processing occurred when the precursor cleavage site was mutated to RERQ-SLVR or when precursor chondromodulin-I was expressed in the furin-deficient CHO cell line, suggesting the involvement of furin in processing.     

Transgenic overproduction of glutathione reductase does not protect cotton, Gossypium hirsutum (Malvaceae), from photoinhibition during growth under chilling conditions

In some studies, tissues from plants that have been genetically transformed to overproduce antioxidant enzymes sustain less damage when abruptly exposed to short-term chilling in the laboratory. However, few studies have examined the performance of transgenic plants during longer-term growth under chilling conditions. We compared growth of transgenic cotton that overproduces glutathione reductase (GR+; ～40-fold overproduction) to growth of the wild type in a controlled environment chamber as leaf temperature was lowered from 28° to 14°C over 9 d and for a subsequent 9-d period at 14°C. In wild-type and GR+ cotton, chilling temperatures resulted in decreased dark-adapted F(v)/F(m) (the ratio of variable to maximal fluorescence; a measure of maximum photosystem II quantum yield) and mid-light period photosystem II quantum yield, coupled with increased 1 - q(P) (a nonlinear estimate of the reduction state of the primary quinone acceptor of photosystem II). The capacity for photosynthetic oxygen evolution decreased during the first portion of the chilling exposure, but recovered slightly during the second half. At no point during the chilling exposure did the performance of GR+ plants differ significantly from that of wild-type plants in any of the above parameters. The absence of an effect of GR overproduction under longer-term chilling may be explained, in part, by the fact that wild-type cotton acclimated to chilling by upregulating native GR activity.     

Microarray genomotyping of key experimental strains of Neisseria gonorrhoeae reveals gene complement diversity and five new neisserial genes associated with Minimal Mobile Elements.

Background  

There are four widely used experimental strains of N. gonorrhoeae, one of which has been sequenced and used as the basis for the construction of a multi-strain, mutli-species pan-neisserial microarray. Although the N. gonorrhoeae population structure is thought to be less diverse than N. meningitidis, there are some recognized gene-complement differences between strains, including the 59 genes of the Gonococcal Genetic Island. In this study we have investigated the three experimental strains that have not been sequenced to determine the extent and nature of their similarities and differences.     

A Chlorophyll Fluorescence Analysis of the Allocation of Radiant Energy Absorbed in Photosystem 2 Antennae of Cotton Leaves During Exposure to Chilling

When dark-acclimated cotton (Gossypium hirsutum L. cv. Coker 312) leaves, pre-treated with lincomycin to inhibit chloroplast protein repair processes, were exposed to 10 °C and a PPFD of 500 mol m^-2 s^-1, the proportion of excitation energy entering photochemistry (P) increased, but only to 5 % of the total energy absorbed at steady state levels of P, which were reached at 40 min of irradiation. Thermal dissipation (D) of absorbed energy increased throughout the 360 min irradiation period and accounted for the greatest portion of absorbed energy at 10 °C. When D was partitioned into constitutive (D_CON), regulated (D_REG), and photoinhibitory (D_PI) components, it was primarily composed of D_REG, the readily reversible portion of D. However, the induction of D was slow at 10 °C. Sixty minutes were required for D to reach 70 % of the energy absorbed. Considerable absorption of energy in excess of that utilized in photochemistry or dissipated thermally (designated as E) occurred, especially during induction of P and D. Over the irradiation period, the time-dependent averaged E exhibited an inverse, linear relationship with the ratio of variable (F_v) to maximum (F_m) fluorescence (PS2 efficiency) and a linear relationship with D_PI. We propose that time-dependent averaged E may be useful for estimating the potential for damage to PS2 under stressful environmental conditions.     

Role of CD8+ T cells in endogenous interleukin-10 secretion associated with visceral leishmaniasis

This study examined the role and source of endogenous interleukin-10 (IL) secretion in visceral leishmaniasis (VL). The amounts of endogenous and Leishmania specific IL-10 and interferon-gamma (IFN) secreted by peripheral blood mononuclear cells (PBMC) from VL patients were compared. The correlation coefficient between endogenous IL-10 secretion and Leishmania specific IFN-gamma was -0. 77, suggesting a major role for endogenous IL-10 secretion in VL. The effects of CD4+ and CD8+ T cell clones, isolated from a treated VL patient, on IL-10 secretion were assayed by mixing the clones with autologous, inactivated PBMC. The CD8+ clones mediated increased levels of IL-10 secretion in the presence of PBMC alone suggesting that CD8+ T cells may mediate endogenous IL-10 secretion.     

Phloem flow and sugar transport in Ricinus communis L. is inhibited under anoxic conditions of shoot or roots

Anoxic conditions should hamper the transport of sugar in the phloem, as this is an active process. The canopy is a carbohydrate source and the roots are carbohydrate sinks. By fumigating the shoot with N₂ or flooding the rhizosphere, anoxic conditions in the source or sink, respectively, were induced. Volume flow, velocity, conducting area and stationary water of the phloem were assessed by non‐invasive magnetic resonance imaging (MRI) flowmetry. Carbohydrates and δ¹³C in leaves, roots and phloem saps were determined. Following flooding, volume flow and conducting area of the phloem declined and sugar concentrations in leaves and in phloem saps slightly increased. Oligosaccharides appeared in phloem saps and after 3 d, carbon transport was reduced to 77%. Additionally, the xylem flow declined and showed finally no daily rhythm. Anoxia of the shoot resulted within minutes in a reduction of volume flow, conductive area and sucrose in the phloem sap decreased. Sugar transport dropped to below 40% by the end of the N₂ treatment. However, volume flow and phloem sap sugar tended to recover during the N₂ treatment. Both anoxia treatments hampered sugar transport. The flow velocity remained about constant, although phloem sap sugar concentration changed during treatments. Apparently, stored starch was remobilized under anoxia.