Ferredoxin-Dependent and Antimycin A-Sensitive Reduction of Cytochrome b-559 by Far-Red Light in Maize Thylakoids; Participation of a Menadiol-Reducible Cytochrome b-559 in Cyclic Electron Flow

Thylakoids from mesophyll cells of maize showed a high rateof the ferredoxin (Fd)-dependent and antimycin A (AntiA)-sensitivecyclic electron flow as determined by the quenching of 9-aminoacridinefluorescence which indicates the formation of     

Suppression of Quantum Yield of Photosystem II by Hyperosmotic Stress in Chlamydomonas reinhardtii

Addition of ethylene glycol (EG) or NaCl to cells of Chlamydomonasreinhardtii induced transient non-photochemical quenching ofChl fluorescence correlated with the inhibition of photosyntheticoxygen evolution. The induction of the quenching and subsequentrecovery proceeded not only in the light but also in the dark.The quenching was almost unaffected by the protonophore nigericin,suggesting the involvement of a type of non-photochemical quenchingattributable to a state 2 transition. Higher concentrationsof EG or NaCl caused a delay of the recovery of the maximumfluorescence yield (Fm'). Dark reduction rate of P700⁺ afterthe application of a flash light in the presence of DCMU wasenhanced by the hyperosmotic shock, suggesting a stimulatedreduction of the intersystem electron carriers. It is proposedthat the osmotic stress stimulates electron donation from stromalcomponents via the NAD(P)H dehydrogenase, which results in thereduction of the intersystem chain and triggering of a state2 transition leading to stimulated cyclic PSI activity. (Received May 16, 1995; Accepted July 26, 1995)     

Induction of diapausing amictic eggs in Synchaeta pectinata

Amictic females of a clone of S. pectinata from Star Lake (Norwich, Vermont) may produce diapausing as well as non-diapausing (subitaneous) eggs. The proportion of diapausing eggs produced in cultures was unaffected by temperature (12 vs 19 °C) or rotifer population density (minima of 0.33 vs 3 ind. ml^–1) at 19 °C. However, at 19 °C this proportion was higher in cultures maintained at a low food level suppressing reproduction (5 × 10³ cells ml^–1 Cryptomonas erosa) than in those maintained at a high food level (2 × 10⁴ cells ml^–1); the treatment effect was marginally significant (p=0.067). Consistent with the effect of low food availability, a period of starvation was very effective in inducing the development of diapausing eggs. None of 19 females cultured individually from hatching at 19 °C on C. erosa (2 × 10⁴ cells ml^–1) in 1-ml volumes produced any diapausing eggs in 4 days (0 out of 349 eggs), while 13 out of 16 females subjected to a 15-hour starvation period 6 hours after birth produced one or more diapausing eggs during that time (34% of the 158 eggs produced by the 16 females were diapausing). Diapausing eggs produced and left at 19 °C hatched after 4 to 13 days. Those produced in cultures with a low food level took significantly longer to hatch (9.7 days) than those produced in cultures with a high food level (8.1 days) (p=0.022). In natural communities, S. pectinata should be able to respond directly and rapidly to poor food conditions by producing eggs that undergo an obligatory dormant period before resuming development.     

Role for a Glycan Phosphoinositol Anchor in Fcγ Receptor Synergy

While many cell types express receptors for the Fc domain of IgG (FcγR), only primate polymorphonuclear neutrophils (PMN) express an FcγR linked to the membrane via a glycan phosphoinositol (GPI) anchor. Previous studies have demonstrated that this GPI-linked FcγR (FcγRIIIB) cooperates with the transmembrane FcγR (FcγRIIA) to mediate many of the functional effects of immune complex binding. To determine the role of the GPI anchor in Fcγ receptor synergy, we have developed a model system in Jurkat T cells, which lack endogenously expressed Fcγ receptors. Jurkat T cells were stably transfected with cDNA encoding FcγRIIA and/or FcγRIIIB. Cocrosslinking the two receptors produced a synergistic rise in intracytoplasmic calcium ([Ca²⁺]_i) to levels not reached by stimulation of either FcγRIIA or FcγRIIIB alone. Synergy was achieved by prolonged entry of extracellular Ca²⁺. Cocrosslinking FcγRIIA with CD59 or CD48, two other GPI-linked proteins on Jurkat T cells also led to a synergistic [Ca²⁺]_i rise, as did crosslinking CD59 with FcγRIIA on PMN, suggesting that interactions between the extracellular domains of the two Fcγ receptors are not required for synergy. Replacement of the GPI anchor of FcγRIIIB with a transmembrane anchor abolished synergy. In addition, tyrosine to phenylalanine substitutions in the immunoreceptor tyrosine-based activation motif (ITAM) of the FcγRIIA cytoplasmic tail abolished synergy. While the ITAM of FcγRIIA was required for the increase in [Ca²⁺]_i, tyrosine phosphorylation of crosslinked FcγRIIA was diminished when cocrosslinked with FcγRIIIB. These data demonstrate that FcγRIIA association with GPI-linked proteins facilitates FcγR signal transduction and suggest that this may be a physiologically significant role for the unusual GPI-anchored FcγR of human PMN.     

Cuticular permeability of the three tree species Prunus Iaurocerasus L., Ginkgo biloba L. and Juglans regia L.: comparative investigation of the transport properties of intact leaves, isolated cuticles and reconstituted cuticular waxes

Cuticular transport properties of intact leaves, isolated cuticularmembranes and reconstituted cuticular waxes of the three treespecies Prunus laurocerasus L., Ginkgo biloba L. and Juglansregia L. were measured using six different ¹⁴C-labelled compounds,benzoic acid, salicylic acid, 2,4-dichlorophenoxy acid, metribuzin,4-nitrophenol, and atrazine. For the same compound and the samespecies, the permeance of the intact leaf and the isolated cuticlewas equal. This provides strong evidence demonstrating thattransport properties of cuticles are not altered during isolation.Additionally, diffusion coefficients of the ¹⁴C-labelled compoundsin isolated and subsequently reconstituted cuticular wax ofthe three tree species were measured. Permeances of intact leavesand isolated cuticles could be predicted from diffusion coefficients,wax/water partition coefficients and the thickness of the transport-limitingwax layer with a mean deviation of about 1.7. This providesevidence that transport properties of recrystallized cuticularwaxes do indeed reflect barrier properties of isolated cuticularmembranes and intact leaves with in situ waxes. Thus, it canbe concluded that the investigation of cuticular permeabilityusing the three independent experimental systems of differentcomplexity give comparable results. Finally, it was observedthat permeances and diffusion coefficients measured with P.laurocerasus were always significantly lower than those measuredwith G. biloba and J. regia. This is interpreted as an ecologicaladaptation of the respective species. The evergreen speciesP. laurocerasus must be more adapted to environmental stresssuch as drought and frost injury compared to the two deciduousspecies G. biloba and J. regia. Key words: Cuticular permeability, diffusion coefficient, leaf surface, permeance, plant cuticle, transport     

Tm studies of a tertiary structure from the human hepatitis delta agent which functions in vitro as a ribozyme control element.

Viroids and other circular subviral RNA pathogens, such as the hepatitis delta agent, use a rolling circle replication cycle requiring an intact circular RNA. However, many infectious RNAs have the potential to form self-cleavage structures, whose formation must be controlled in order to preserve the circular replication template. The native structure of delta RNA contains a highly conserved element of local tertiary structure which is composed of sequences partially overlapping those needed to form the self-cleavage motif. A bimolecular complex containing the tertiary structure can be made. We show that when it is part of this bimolecular complex the potential cleavage site is protected and is not cleaved by the delta ribozyme, demonstrating that the element of local tertiary structure can function as a ribozyme control element in vitro. Physical studies of the complex containing this element were carried out. The complex binds magnesium ions and is not readily dissociated by EDTA under the conditions tested; > 50% of the complexes remain following incubation in 1 mM EDTA at 60 degrees C for 81 min. The thermal stability of the complex is reduced in the presence of sodium ions. A DNA complex and a perfect RNA duplex studied in parallel showed a similar effect, but of lesser magnitude. The RNA complex melts at temperatures approximately 10 degrees C lower in buffers containing 0.5 mM MgCl2 and 100 mM NaCl than in buffers containing 0.5 mM MgCl2 with no NaCl (78.1 compared with 87.7 degrees C). The element of local tertiary structure in delta genomic RNA appears to be a molecular clamp whose stability is highly sensitive to ion concentration in the physiological range.     

Androgen and FSH synergistically stimulate lipoprotein degradation and utilization by ovary granulosa cells

Androgen can directly modulate the induction of steroidogenic enzymes by FSH (follicle stimulating hormone) in ovary granulosa cells. In studies of its mechanism of action, we examined the androgen effect on granulosa cell interaction with lipoproteins, the physiologic source of cholesterol. After granulosa cells were cultured for 48 hours with and without androgen and/or FSH, the cells were incubated for 24 hours with ¹²⁵I-lipoproteins [human high density lipoprotein (HDL), rat HDL, or human low density lipoprotein (LDL)]. The media were then analyzed for lipoprotein protein coat degradation products (mainly ¹²⁵I-monoiodotyrosine) and progestin [mainly 20α-dihydroprogesterone (20α-DHP)]. In the absence of FSH and androgen, 2 × 10⁵ granulosa cells degraded basal levels of all three lipoproteins, but produced no measurable 20α-DHP. The addition of 10^?7 M androstenedione (A), testosterone (T), or 5α-dihydrotestosterone (DHT) had no effect on lipoprotein protein degradation or 20α-DHP production. FSH alone stimulated lipoprotein protein degradation by 50 to 300% while the addition of androgen synergistically augmented the FSH-stimulated 20α-DHP production as well as protein coat degradation of all three lipoproteins. DHT and T were both effective, indicating that androgens themselves, and not estrogen products, were responsible for the effect on lipoprotein protein degradation and 20α-DHP production. The addition of a 10-fold excess cyproterone acetate (an anti-androgen) inhibited the effect of T, suggesting that the action of T was mediated by the granulosa cell androgen receptor. Androgen and FSH also synergistically stimulated the production of ³H-progestin when the granulosa cells were incubated with either ³H-cholesterol ester core labeled human HDL or similarly labeled human LDL. This report demonstrates that androgen, in combination with FSH, augments the steroidogenic pathway of the granulosa cell from the degradation of lipoprotein and utilization of the cholesterol ester core, to the production of progestin product.     

Use of the esophageal balloon in the diagnosis of carcinomas of the head, neck and upper gastrointestinal tract

A study was undertaken to demonstrate the safety, efficacy and value of esophageal balloon cytology in the diagnosis of esophageal lesions and as a tool in screening a high-risk patient population. The sampling was performed 110 times on 96 patients, 11 with known obstructive carcinoma of the esophagus and 85 thought to be at risk for esophageal cancer: 74 with treated or untreated cancer of the head and neck area and 11 with dysphagia or other findings requiring clarification. The method was well tolerated by the patients, and the cytologic smears were of excellent quality. Malignant or suspicious cells were found in smears from 7 to 11 patients with documented esophageal cancer and in 7 of 85 patients believed to be at risk. In the latter group there were three unsuspected recurrent cancers of the oropharyngeal region and one unsuspected carcinoma in situ of the esophagus. There were no false-suspicious or false-positive results. This noninvasive technique of esophageal cytology obviously deserves additional trials as an adjunct in the diagnosis of carcinoma of the head and neck and upper gastrointestinal tract, especially in high-risk patients.     

Demonstration of the correlation of the degree of synthesis and 4-aminobutyric acid levels in the central nervous system; effect of repeated convulsive seizures

GABA turnover rates have been determined in 15 brain areas in five inbred strains of Mice or sublines (DBA/2J, C57/6J, Swiss Rb1, Swiss Rb2, Swiss Rb3). GABA turnover rates and levels are correlated (2 P less than 0.05). After repeated seizures (twice a day for 15 days), induced by an acoustic stimulus in Swiss Rb1 Mice selected for audiogenic seizures, this correlation is no longer observed.