Photooxidative Death in Blue-Green Algae

When incubated in the light under 100% oxygen, wild-type blue-green algae (Anacystis nidulans, Synechococcus cedrorum) die out rapidly at temperatures of 4 to 15 C, and at 35 C (or at 26 C in the case of S. cedrorum) in the absence of CO(2). Photosynthesis is impaired in these cells long before they die. Blocking of photosystem II at high temperatures in the presence of CO(2) sensitizes the algae to photooxidative death. Photooxidative death and bleaching of photosynthetic pigments are separable phenomena. Photooxidative conditions were demonstrated in Israeli fish ponds using A. nidulans as the test organism during dense summer blooms, when dissolved CO(2) is low, and in winter, when water temperatures generally drop below 15 C. This finding suggests that photooxidative death may be responsible for the sudden decomposition of blue-green blooms in summer, and may be a factor in the absence of blue-green blooms in winter.     

Protein turnover and cell-cycle initiation in yeast

The effects of short pulses of cycloheximide on the traversal of the G1 phase of the cell cycle of the yeast Saccharomyces cerevisiae were examined. Cells were released from a block at the regulatory stage of G1, termed ‘start’, and pulsed with cycloheximide. Delays in budding which were considerably longer than the length of the pulse were observed. During the delay the cells remained blocked at ‘start’. No delay in budding was observed after cycloheximide pulses, when cells were released from a cdc 24 block which arrests the budding process but not ‘start’. Overall protein synthesis did not show an additional delay after the pulse. The extra lag following cycloheximide pulses appears to reflect a unique feature of ‘start’. It may be accounted for by a requirement at ‘start’ for a labile protein with a half-life time of about 6 min.     

The role of pre-symbiotic auxin signaling in ectendomycorrhiza formation between the desert truffle <Emphasis Type="Italic">Terfezia boudieri</Emphasis> and <Emphasis Type="Italic">Helianthemum sessiliflorum</Emphasis>

The ectendomycorrhizal fungus Terfezia boudieri is known to secrete auxin. While some of the effects of fungal auxin on the plant root system have been described, a comprehensive understanding is still lacking. A dual culture system to study pre mycorrhizal signal exchange revealed previously unrecognized root–fungus interaction mediated by the fungal auxin. The secreted fungal auxin induced negative taproot gravitropism, attenuated taproot growth rate, and inhibited initial host development. Auxin also induced expression of Arabidopsis carriers AUX1 and PIN1, both of which are involved in the gravitropic response. Exogenous application of auxin led to a root phenotype, which fully mimicked that induced by ectomycorrhizal fungi. Co-cultivation of Arabidopsis auxin receptor mutants tir1-1, tir1-1 afb2-3, tir1-1 afb1-3 afb2-3, and tir1-1 afb2-3 afb3-4 with Terfezia confirmed that auxin induces the observed root phenotype. The finding that auxin both induces taproot deviation from the gravity axis and coordinates growth rate is new. We propose a model in which the fungal auxin induces horizontal root development, as well as the coordination of growth rates between partners, along with the known auxin effect on lateral root induction that increases the availability of accessible sites for colonization at the soil plane of fungal spore abundance. Thus, the newly observed responses described here of the root to Terfezia contribute to a successful encounter between symbionts.     

A synergistic effect of albumin and fibrinogen on immunoglobulin-induced red blood cell aggregation

Therapeutic administration of immunoglobulins (Ig) has the potential to precipitate thrombotic events. This phenomenon may be explained by red blood cell (RBC) aggregation, which can be potentiated by Ig. The contribution of plasma albumin and fibrinogen to Ig-induced RBC aggregation is unclear. We examined RBC aggregation in three settings: 1) patients receiving therapeutic infusions of Ig; 2) patients receiving plasma supplemented in vitro with Ig; and 3) patients receiving RBC suspensions in standard buffer with varying concentrations of albumin, Ig, and fibrinogen. Ig infusion augmented aggregation of RBCs from patients with normal or high plasma levels of albumin but decreased aggregation in those with lower plasma albumin concentrations. In vitro, RBC aggregation was significantly increased only when all three components, fibrinogen, albumin, and Ig, were present at or above normal concentrations in the suspension but was unaffected when any one of the components was absent from the suspension. Our results suggest a three-way interaction among fibrinogen, Ig, and albumin that synergistically induces RBC aggregation in plasma. Understanding these interactions may help predict clinically important phenomena related to RBC aggregation, such as thrombotic complications of Ig infusion.     

Facultative anoxygenic photosynthesis in the cyanobacterium Oscillatoria limnetica.

An isolate from H2S-rich layers of the Solar Lake, the cyanobacterium Oscillatoria limnetica, exhibits both oxygenic and anoxygenic photosynthesis. It can use Na2S as an electron donor for CO2 photoassimilation (photosystem I supplies the energy) in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea or 700-nm light. A stoichiometric ratio of approximately 2 is observed between the Na2S consumed and the photoassimilated CO2. The anoxygenic phototrophic capability of this cyanobacterium explains its growth in nature in high sulfide concentrations and indicates a selective advantage.     

Isolation of Host-Dependent and Nonparasitic Mutants of the Facultative Parasitic Bdellovibrio UKi2

Obligate host-dependent and nonparasitic mutants were isolated from a facultative parasitic Bdellovibrio strain. Thus it is possible to separate host-dependency from the ability to parasitize in bdellovibrios.