From seed to seed: the role of photoreceptors in Arabidopsis development

As sessile organisms, plants have evolved a multitude of developmental responses to cope with the ever-changing environmental conditions that challenge the plant throughout its life cycle. Of the many environmental cues that regulate plant development, light is probably the most important. From determining the developmental pattern of the emerging seedling, to influencing the organization of organelles to best maximize energy available for photosynthesis, light has dramatic effects on development during all stages of plant life. In plants, three classes of photoreceptors that mediate light perception have been characterized at the molecular level. The phytochromes recognize light in the red portion of the spectrum, while cryptochromes and phototropins perceive blue and UVA light. In this review, we discuss the different aspects of development that are regulated by these photoreceptors in the model plant species Arabidopsis thaliana and how the phytochromes, cryptochromes, and phototropins bring about changes in development seen in the growing plant.     

CD4+-dependent immunity to Onchocerca volvulus third-stage larvae in humans and the mouse vaccination model: common ground and distinctions

Onchocerciasis is a major filarial disease and is the second most common cause of infectious blindness in the world. Disease development after infection with Onchocerca volvulus varies widely and is determined by the host's immune response to the parasite. Vector control and administration of ivermectin has reduced infection and disease rates significantly. However, limitations of these programmes, including ivermectin's selective activity on microfilariae, the need for 10-15 years of annual treatments, logistical obstacles and the potential emergence of drug-resistant strains demand alternative strategies. A vaccine that targets O. volvulus infective third-stage larvae (L3) could provide an additional tool to guarantee successful elimination of infection with O. volvulus. An essential step in the development of immunoprophylactic procedures and reagents is the identification of host immune responses toward antigens of O. volvulus L3 and L3 developing to the fourth-stage larvae that are associated with protection against these stages of the parasite. This review summarises the recent advancements in understanding the immune mechanisms in particular the CD4(+) responses to L3 stages in humans and in the mouse vaccination model. Comparison between the two uncovered common immunological elements in naturally exposed humans and mice vaccinated with radiation attenuated L3 or recombinant O. volvulus antigens, as well as significant differences. These studies promisingly suggest that the O. volvulus mouse model is a very useful adjunct to the studying of natural infection in humans and could provide us with the tools to identify the target molecules and the effector immune correlates of protection in humans responsible for attrition of L3 stages. Since some of these antigens may exist in other nematodes, any insight gained into the mechanisms of vaccine-induced anti-O. volvulus L3 protective immunity in both humans and mice could be applicable to the development of vaccines against other nematode infections.     

RF nonlinear interactions in living cells-I: nonequilibrium thermodynamic theory

Some biological experiments report effects that depend on low frequency modulation of a radiofrequency (RF) carrier. Such effects require nonlinear responses in biological preparations, which we show could be observed with great generality by the unique frequency signatures that would appear in the scattered RF energy. Following Illinger [Illinger (1982): Bioelectromagnetics 3:9-16], we considered a two part physical system. The greater part, dominated by the properties of water, interacts linearly with the RF field and is described by equilibrium thermodynamics. However, another, much smaller part, e.g., certain biological molecules and molecular subgroups, supports nonlinear interactions and is described by nonequilibrium thermodynamics. For example, a nonlinear interaction might result from scattering of RF photons from oscillators located in a region of strong field gradients, such as at membrane surfaces. A second nonlinear mechanism could appear if stress (elastic) waves were launched within the confines of the exposure vessel by RF heating. Amplitude modulation at angular frequency Omega of a carrier wave with angular frequency omega (omega < omega) produces two peaks in elastic stress in the cell structure during each period; that is, there is "full-wave demodulation." As a result of coherent nonlinear charge motion, modulation products could appear at frequencies omega +/- 2 omega and, in general, at omega +/- n 2 omega (n = 1, 2, em leader ) if vibrational harmonics at 2 n omega also are excited. Although in principle microwaves can alter the stability of a thermodynamic system by pumping a chemical transition, the degree of nonlinear coupling required for an observable instability is so great that its probability is effectively zero, unless field intensity is extremely high. A companion paper suggests an extremely sensitive method and the related instrumentation for detection of the spectrum scattered by living cells during exposure to amplitude modulated RF energy.     

The skeletal isotopic composition as an indicator of ecological and physiological plasticity in the coral genus<Emphasis Type="Italic"> Madracis</Emphasis>

Three species of the reef coral genus Madracis display skeletal isotopic characteristics that relate to depth, colony topography, and consequently to coral physiology. The joint interpretation of skeletal ¹³C and ¹⁸O provides information on the ecological plasticity and adaptation to depth of a coral species. Isotopic results are most easily understood in terms of kinetic effects, which reduce both ¹⁸O and ¹³C below isotopic equilibrium values, and metabolic effects, which only influence the skeletal ¹³C. Madracis mirabilis is adapted to depths shallower than 20 m, and shows the greatest range in kinetic effects and the strongest metabolic ¹³C enrichments caused by symbiont photosynthesis. Madracis formosa lives deeper than 40 m, and shows a reduced range of kinetic effects and relatively weak metabolic ¹³C enrichments. Madracis pharensis inhabits depths from 5 to >60 m, and does not attain the strength of kinetic effects of either of the other two species, apparently because it is not quite as well adapted to rapid growth at either extreme.     

Influence of light quality and photoperiod on flowering of Cyclamen persicum Mill. cv. ‘Dixie White’

The effect of light quality (spectral quality) and photoperiod (day length) were studied on flowering of Cyclamen persicum cv. Dixie White. Light generated from light emitting diodes (LED) i.e. monochromatic blue (10 or 12 h per day), monochromatic red (10 or 12 h per day), blue plus red (10 or 12 h per day) and fluorescent lights were used in these studies. It was found that blue plus red LEDs improved flower induction in cyclamen, the number flower buds and open flowers being highest in the plants grown under blue plus red LED (10 h per day). Blue and red LEDs alone reduced the flowering response. Peduncle length (flower stalk length) and blooming period of flowers were also influenced by light qualities and photoperiod treatments. Peduncle length was 23.8 cm on plants grown under red LED (12 h per day) treatment but 14 cm on plants grown under fluorescent light. Blooming period of flowers grown under fluorescent light was 20 d, whereas it was 40 d with the plants grown under red LEDs (10 h per day). The results indicate that flowering and subsequent growth of cyclamen can be controlled by manipulating light quality and lighting period.     

Functional correlates of leaf demographic response to gap release in saplings of a shade-tolerant tree,<Emphasis Type="Italic"> Elateriospermum tapos</Emphasis>

For a shade-tolerant SE Asian tropical tree, Elateriospermum tapos (Euphorbiaceae), we studied field-established saplings in gaps and the shaded understory to test the hypothesis that differences in leaf demography and leaf life span under contrasting light regimes should be functionally correlated with architecture, self-shading and nitrogen distribution within the sapling crown. Rates of leaf production and net leaf gain were greater for saplings in gaps than those in the understory. Median leaf life span was approximately 26 months in the gap saplings, while it was estimated to be greater than 38 months in the understory saplings. Consequently, gap saplings had a greater standing leaf number and experienced greater degrees of self-shading than understory saplings. Light availability at individual leaves, estimated by a combination of canopy photos and a three-dimensional architecture model, were negatively correlated with leaf age in gap saplings but not so in understory saplings. Leaf nitrogen content per unit area (N_area) was influenced more by light availability than by leaf age in the gap saplings. In contrast, in understory saplings, N_area was neither correlated with light availability nor with leaf age, and did not decrease significantly before 38 months in leaf age. We conclude that saplings of this shade-tolerant species apparently prolong their leaf life span in the shaded understory through slower rates of leaf production, lower standing number of leaves and lower degrees of self shading than in gap, and that the rate of decline of N_area with leaf age depends on architecture and self-shading regimes that respond to changes in light regimes.     

Reduced cellulose synthesis invokes lignification and defense responses in Arabidopsis thaliana

The cell wall determines the shape of plant cells and is also the primary interface for pathogen interactions. The structure of the cell wall can be modified in response to developmental and environmental cues, for example to strengthen the wall and to create barriers to pathogen ingress. The ectopic lignin 1-1 and 1-2 (eli1-1 and eli1-2) mutations lead to an aberrant deposition of lignin, a complex phenylpropanoid polymer. We show that the eli1 mutants occur in the cellulose synthase gene CESA3 in Arabidopsis thaliana and cause reduced cellulose synthesis, providing further evidence for the function of multiple CESA subunits in cellulose synthesis. We show that reduced levels of cellulose synthesis, caused by mutations in cellulose synthase genes and in genes affecting cell expansion, activate lignin synthesis and defense responses through jasmonate and ethylene and other signaling pathways. These observations suggest that mechanisms monitoring cell wall integrity can activate lignification and defense responses.     

Evidence that annexin II is not a putative membrane receptor for 1alpha,25(OH)2-vitamin D3

The seco-steroid hormone 1alpha,25(OH)(2)-vitamin D(3) (1,25-D(3)) is known to generate biological responses via both genomic and non-genomic rapid signal transduction pathways. The calcium regulated annexin II/p11 heterotetramer (AII(2)/p11(2)] was proposed by Baran and co-authors to be the membrane receptor responsible for mediating non-genomic, rapid actions of 1,25-D(3), based on ligand affinity labeling, competition, and saturation analysis experiments. Given the cytosolic presence of both the monomeric and heterotetrameric form of AII and their functional regulation by intracellular calcium concentrations, which are known to be affected by 1,25-D(3) rapid, non-genomic activities, we investigated in vitro the affinity of [(3)H]1,25-D(3) for the AII monomer and AII(2)/p11(2) in the absence and presence of calcium using saturation analysis and gel-filtration chromatography. Using two different techniques for separating bound from free ligand (perchlorate and hydroxylapatite (HAP)) over a series of 30 experiments, no evidence for specific binding of [(3)H]1,25-D(3) was obtained with or without the presence of 700 nM exogenous calcium, using either the AII monomer or AII(2)/p11(2). However saturable binding of [(3)H]1,25-D(3) to the lipid raft/caveolae enriched rat intestinal fraction was consistently observed (K(d) = 3.0 nM; B(max) = 45 fmols/mg total protein). AII was detected in lipid raft/caveolae enriched fractions from rat and mouse intestine and ROS 17/2.8 and NB4 cells by Western blot, but incubation in the presence of exogenous calcium did not ablate 1,25-D(3) binding as reported by Baran et al. Our results suggest that AII does not bind 1,25-D(3) in a physiologically relevant manner; however, recent studies linking AII(2)/p11(2) phosphorylation to vesicle fusion and its calcium regulated localization may make AII a possible down-stream substrate for 1,25-D(3) induced rapid cellular effects.