抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

http://paymanhassibi.persiangig.com/document/mittler%20oxidative.pdf

Oxidative stress, antioxidants and stress tolerance

Theory is developed to explain the carbon isotopic composition of plants. It is shown how diffusion of gaseous CO2 can significantly affect carbon isotopic discrimination. The effects on discrimination by diffusion and carboxylation are integrated, yielding a simple relationship between discrimination and the ratio of the intercellular and atmospheric partial pressures of CO2. The effects of dark respiration and photorespiration are also considered, and it is suggested that they have relatively little effect on discrimination other than via their effects on intercellular p(CO2). It is also suggested that various environmental factors such as light, temperature, salinity and drought will also have effects via changes in intercellular p(CO2). A simple method is suggested for assessing water use efficiencies in the field.

On the Relationship Between Carbon Isotope Discrimination and the Intercellular Carbon Dioxide Concentration in Leaves

In the last decade, our understanding of the processes underlying plant response to drought, at the molecular and whole-plant levels, has rapidly progressed. Here, we review that progress. We draw attention to the perception and signalling processes (chemical and hydraulic) of water deficits. Knowledge of these processes is essential for a holistic understanding of plant resistance to stress, which is needed to improve crop management and breeding techniques. Hundreds of genes that are induced under drought have been identified. A range of tools, from gene expression patterns to the use of transgenic plants, is being used to study the specific function of these genes and their role in plant acclimation or adaptation to water deficit. However, because plant responses to stress are complex, the functions of many of the genes are still unknown. Many of the traits that explain plant adaptation to drought - such as phenology, root size and depth, hydraulic conductivity and the storage of reserves - are those associated with plant development and structure, and are constitutive rather than stress induced. But a large part of plant resistance to drought is the ability to get rid of excess radiation, a concomitant stress under natural conditions. The nature of the mechanisms responsible for leaf photoprotection, especially those related to thermal dissipation, and oxidative stress are being actively researched. The new tools that operate at molecular, plant and ecosystem levels are revolutionising our understanding of plant response to drought, and our ability to monitor it. Techniques such as genome-wide tools, proteomics, stable isotopes and thermal or fluorescence imaging may allow the genotype-phenotype gap to be bridged, which is essential for faster progress in stress biology research.

Understanding plant responses to drought — from genes to the whole plant

Abiotic stress, the field environment and stress combination

Mechanisms of inorganic carbon utilization (i.e., carbon-concentrating mechanisms) in seaweeds involve uptake of HCO 3 - and carbonic anhydrase-mediated production of CO 2 . These mechanisms are needed to cope with the low concentrations of CO 2 dissolved in seawater and the low affinities of Rubisco for CO 2 in the macroalgal chloroplasts. The current study shows, for the first time, direct evidence that while Ulva rigida photosynthesizes there is continuous production of CO 2 , apparently generated from an acidification process in its boundary layer. Release of CO 2 during light periods was measured using a membrane inlet mass spectrometer, while acidification at the boundary layer was detected in pH-drift experiments. Under repetitive light (4, 70, 300 μmol photons m -2 s -1 ) and dark cycles, O 2 production rates exceeded by 10-fold that of CO 2 production under illumination. Photosynthetic release of O 2 was largely dependent on the experimental range of light intensities, while CO 2 evolution under illumination was significantly reduced at 24 °C as compare to 15 °C. Rapid acidification occuring within the unstirred layer and the consequent CO 2 release may account for an additional mechanism of inorganic carbon utilization strategies in Ulva rigida , which previously had been reported to posses an efficient carbonic anhydrase modulated carbon concentrating mechanism.

Acidification and CO 2 production in the boundary layer during photosynthesis in Ulva rigida (Chlorophyta) C. Agardh

Summary

The reasons for the apparent dominance of the toxic cyanobacterium Microcystis sp., reflected by its massive blooms in many fresh water bodies, are poorly understood. We show that in addition to a large array of secondary metabolites, some of which are toxic to eukaryotes, Microcystis sp. secretes large amounts of fibrous exopolysaccharides that form extremely long fibres several millimetres in length. This phenomenon was detected in field and laboratory cultures of various Microcystis strains. In addition, we have identified and characterized three of the proteins associated with the fibres and the genes encoding them in Microcystis sp. PCC 7806 but were unable to completely delete them from its genome. Phylogenetic analysis of the most abundant one, designated IPF-469, showed its presence only in cyanobacteria. Its closest relatives were detected in Synechocystis sp. PCC 6803 and in Cyanothece sp. strains; in the latter the genomic organization of the IPF-469 was highly conserved. IPF-469 and the other two proteins identified here, a haloperoxidase and a haemolysin-type calcium-binding protein, may be part of the fibres secretion pathway. The biological role of the fibres in Microcystis sp. is discussed.

Casting a net: fibres produced by Microcystis sp. in field and laboratory populations.

Ratio of CO2 Uptake to O2 Evolution during Photosynthesis in Higher Plants

The green alga Chlorella ohadii was isolated from a desert biological soil crust, one of the harshest environments on Earth. When grown under optimal laboratory settings it shows the fastest growth rate ever reported for a photosynthetic eukaryote and a complete resistance to photodamage even under unnaturally high light intensities. Here we examined the energy distribution along the photosynthetic pathway under four light and carbon regimes. This was performed using various methodologies such as membrane inlet mass spectrometer with stable O2 isotopes, variable fluorescence, electrochromic shift and fluorescence assessment of NADPH level, as well as the use of specific inhibitors. We show that the preceding illumination and CO2 level during growth strongly affect the energy dissipation strategies employed by the cell. For example, plastid terminal oxidase (PTOX) plays an important role in energy dissipation, particularly in high light- and low-CO2-grown cells. Of particular note is the reliance on PSII cyclic electron flow as an effective and flexible dissipation mechanism in all conditions tested. The energy management observed here may be unique to C. ohadii, as it is the only known organism to cope with such conditions. However, the strategies demonstrated may provide an insight into the processes necessary for photosynthesis under high-light conditions.

Juggling Lightning: How Chlorella ohadii handles extreme energy inputs without damage.

A low flow of air is passed through a temperature-controlled plant chamber in order to obtain relatively large (~300-500 pi l-1) differences in [O2] between influx and efflux streams. These differences are measured with a stabilized O2 electrode system incorporating elements of gas conditioning electronic zero suppression and signal amplification. Changes in [O2] of 400 pi l-1 can be detected at full scale recorder deflection against a background concentration of 21% O2. The concentrations of CO2 and H2O within the chamber are held constant by con trolled-flow C02-scrubbing and dehumidifying loops. Carbon dioxide, H2O, and O2 fluxes are measured and leaf diffusion resistance and internal [CO 2] are calculated in essentially 'real time'.

Aaron Kaplan

Papers

Acidification and CO 2 production in the boundary layer during photosynthesis in Ulva rigida (Chlorophyta) C. Agardh

Casting a net: fibres produced by Microcystis sp. in field and laboratory populations.

Ratio of CO2 Uptake to O2 Evolution during Photosynthesis in Higher Plants

Juggling Lightning: How Chlorella ohadii handles extreme energy inputs without damage.

Simultaneous Measurement of Oxygen, Carbon Dioxide, and Water Vapour Exchange in Intact Plants