A model for the role of surfactants in the assembly of exine sculpture

The surface coatings of spores and pollen often show complex species or genus specific patterning and for which there is no obvious explanation in terms of evolutionary advantage. It has previously been suggested that these patterns are the product of a self-assembly process used by plants in spore and pollen wall development and are a consequence of the physical and chemical behaviour of the components and their interactions. Experiments have shown that comparable patterning and structure can be achieved by self-assembly of analogous components but the range of patterning obtainable was restricted. The introduction of specific surfactants into the reaction has now broadened the range of patterns that can be derived by this method and supports the view that surfactants must be important in the development of the naturally occurring patterns.     

A model for the passage of the neurohypophysial hormones and their related proteins through the rat neurohypophysis

The change in the radioactivity of vasopressin-neurophysin in the rat neurohypophysis after an intracisternal injection of [(35)S]cysteine was fitted to several mathematical models. The data fitted best a model in which there is a linear input of radioactive protein into one pool of the neurohypophysis, from which it is either released by an exponential process or transferred to a second pool from which it is released by a second exponential process with a rate constant much lower than the first. This model is compatible with the existence of a ;readily releasable' pool first postulated by Sachs et al. (1967). Data for the change in radioactivity of vasopressin also gave a good fit in this model. Calculation of the rate constants suggested that the first pool represented about 2% of the total hormone.     

Water relations of the pine exine

BACKGROUND AND AIMS: Water adhesion forces, water absorption capacity and permeability of the pine exine were investigated to consider a possible function of sporopollenin coatings in the control of water transport. METHODS: The experiments were carried out with sporopollenin capsules obtained from pine pollen consisting of an empty central capsule and two sacci. Changes in the concentration of excluded dextran molecules in the medium were analysed to quantify water absorption by purified exine fragments and the osmotic volume flow out of the intact central capsule. KEY RESULTS: The contact angle of sporopollenin to water is higher than the one to ethanol and lower than the one to n-heptane. The water-filled pore space in pine sporopollenin amounts to only 20.6 % of the matrix volume. A monosaccharide was excluded from 15 % and a trisaccharide from about 38 % of this space. Shrinkage of the central capsule induced by permeable osmotica was transient, whereas that induced by sodium polyacrylate (2100 g mol(-1)) was stable. Values obtained for the hydraulic conductance L(P) of the exine (0.39-0.48 microm s(-1) MPa(-1)) are comparable in size to those of biomembranes. Sodium sulfate solutions induced a significant osmotic flow through the exine (reflection coefficient at least 0.6). The exine around the central capsule can be ruptured by equilibration of its lumen with a concentrated electrolyte solution and subsequent transfer to water. The denatured protoplast along with the intact intine was ejected when pollen grains were subjected to this osmotic shock treatment. CONCLUSIONS: The pine exine is easily wetted with water and does not represent a significant barrier to water exchange either liquid or gaseous. Through osmotic burst, it can be separated from the intine. The effect of salts and small solute molecules on water fluxes may be functionally significant for rehydration upon pollination.     

Duroquinone reduction during passage through the pulmonary circulation

The lungs can substantially influence the redox status of redox-active plasma constituents. Our objective was to examine aspects of the kinetics and mechanisms that determine pulmonary disposition of redox-active compounds during passage through the pulmonary circulation. Experiments were carried out on rat and mouse lungs with 2,3,5,6-tetramethyl-1,4-benzoquinone [duroquinone (DQ)] as a model amphipathic quinone reductase substrate. We measured DQ and durohydroquinone (DQH2) concentrations in the lung venous effluent after injecting, or while infusing, DQ or DQH2 into the pulmonary arterial inflow. The maximum net rates of DQ reduction to DQH2 in the rat and mouse lungs were approximately 4.9 and 2.5 micromol. min(-1).g dry lung wt(-1), respectively. The net rate was apparently the result of freely permeating access of DQ and DQH2 to tissue sites of redox reactions, dominated by dicumarol-sensitive DQ reduction to DQH2 and cyanide-sensitive DQH2 reoxidation back to DQ. The dicumarol sensitivity along with immunodetectable expression of NAD(P)H-quinone oxidoreductase 1 (NQO1) in the rat lung tissue suggest cytoplasmic NQO1 as the dominant site of DQ reduction. The effect of cyanide on DQH2 oxidation suggests that the dominant site of oxidation is complex III of the mitochondrial electron transport chain. If one envisions DQ as a model compound for examining the disposition of amphipathic NQO1 substrates in the lungs, the results are consistent with a role for lung NQO1 in determining the redox status of such compounds in the circulation. For DQ, the effect is conversion of a redox-cycling, oxygen-activating quinone into a stable hydroquinone.     

Guanine for DNA synthesis. A compulsory route through ribonucleotide reductase.

Two alternative pathways for the synthesis of dGTP and its incorporation into DNA were studied: guanine (Gua)----GMP----GDP----dGDP----dGTP----DNA and dG----dGMP----dGDP----dGTP----DNA. To determine the contribution of each pathway to DNA synthesis independently of each other, [14C]Gua and [3H]dG tracer experiments were performed in a double-mutant S-49 mouse T-lymphoma cell line, dGuo-L, with purine nucleoside phosphorylase (EC 2.4.2.1)-deficiency and dGTP-feedback-resistant ribonucleotide reductase (RR, EC 1.17.4.1). In this cell line, dGTP pools can be selectively elevated by exogenous dG without affect RR and DNA synthesis. Although [3H]dG, but not [14C]Gua (up to 200 microM), readily expanded the cellular dGTP pool in a dose-dependent fashion in asynchronous cells, only a small fraction of the Gua flux into DNA was derived from [3H]dG, with the major fraction coming from [14C]Gua. H.p.l.c. analysis of G1- and partially enriched S-phase cells revealed that [3H]dGTP only accumulates in G1- but not in S-phase cells because of a rapid turnover of the dGTP pool during DNA synthesis. These results fail to provide evidence for cellular dGTP compartmentation and suggest that the pathway dG----dGMP----dGDP----dGTP alone has insufficient capacity to maintain DNA synthesis.     

Characteristics of current passage through plant tissue

Plant tissue connected in a d.c. circuit behaves as a capacitor, short-circuited through a resistor. Using a saw-tooth voltage (T = 2 ma, U_max = + 13 V), structural and physiological conditions in a plant tissue can be analyzed on the basis of changes in the current character.     

The Sda1 protein is required for passage through start

We have used affinity chromatography to identify proteins that interact with Nap1, a protein previously shown to play a role in mitosis. Our studies demonstrate that a highly conserved protein called Sda1 binds to Nap1 both in vitro and in vivo. Loss of Sda1 function causes cells to arrest uniformly as unbudded cells that do not increase significantly in size. Cells arrested by loss of Sda1 function have a 1N DNA content, fail to produce the G1 cyclin Cln2, and remain responsive to mating pheromone, indicating that they arrest in G1 before Start. Expression of CLN2 from a heterologous promoter in temperature-sensitive sda1 cells induces bud emergence and polarization of the actin cytoskeleton, but does not induce cell division, indicating that the sda1 cell cycle arrest phenotype is not due simply to a failure to produce the G1 cyclins. The Sda1 protein is absent from cells arrested in G0 and is expressed before Start when cells reenter the cell cycle, further suggesting that Sda1 functions before Start. Taken together, these findings reveal that Sda1 plays a critical role in G1 events. In addition, these findings suggest that Nap1 is likely to function during G1. Consistent with this, we have found that Nap1 is required for viability in cells lacking the redundant G1 cyclins Cln1 and Cln2. In contrast to a previous study, we have found no evidence that Sda1 is required for the assembly or function of the actin cytoskeleton. Further characterization of Sda1 is likely to provide important clues to the poorly understood mechanisms that control passage through G1.     

Transition within the exine of Nothofagus Blume

Pollen grains with bulged areas on their proximal and distal faces were observed in some species of Nothofagus Blume in the light and electron microscopes. Pollen grains sectioned meridionally are distinctly transitionary in character in the individual strata within the exine of one pollen grain. The tectum in the apocolpia is considerably thinner than in the mesocolpia, The thickness and the character of the bacular layer in the mesocolpia differ greatly from those of the apocolpia. The foot layer, thick and always present in the mesocolpia, is entirely lacking in the apocolpia. The significant difference in the structure and thickness of the bacular layer, as well as the partial absence of the foot layer in one pollen grain, influence the cohesion between the individual strata of the exine in the apocolpia. The cohesion between the tectum and underlying, globular stratum in the central part of the apocolpia is poor, which facilitates the separation of the tectum and its bulging at that area.     

Viability of dinoflagellate cysts after the passage through the copepod gut

Several dinoflagellate species form nonmotile, thick-walled resting cysts in their life cycle. Cysts can be ingested by planktonic and benthic organisms, but there is scarce information concerning their survival after the passage through the digestive apparatus of the grazers. We tested the germination capability of cysts produced by two neritic dinoflagellates, Scrippsiella trochoidea (F. Stein) A.R. Loeblich and Scrippsiella ramonii Montresor, after their ingestion by four copepod species. Experiments have been carried out with four species: Acartia clausi Giesbrecht, 1889; Centropages typicus Kröyer, 1849; Temora stylifera Dana, 1849; and Clausocalanus lividus Frost and Fleminger, 1968. Copepods were fed either with motile cells or cysts, and feeding and clearance rates were estimated for A. clausi, C. lividus and T. stylifera. Grazing rates on both dinoflagellates was much higher for vegetative cells than for cysts. Resting cysts were isolated from the faecal pellets and incubated to test their germination capability. S. trochoidea cysts eaten by C. typicus and T. stylifera showed a high germination rate, while cysts of the same species were not viable after the passage through the gut of A. clausi and C. lividus. In contrast, S. ramonii cysts were never able to germinate after being ingested by copepods. The observed variation in viability among the two cyst types and the different survival rates observed for S. trochoidea cysts might be related to differences in cyst morphology and to differences in the digestive process among the tested copepod species.     

Effects of seed passage through slugs on germination

Seed dispersal by invertebrates is mostly external (e.g. by ants). However, internal dispersal (endozoochory) seems to be uncommon due to size limitations. Slugs are generalist herbivores and increasing evidence suggests that they often disperse seeds. Nevertheless, we know very little on the consequences for plant recruitment. Here, we assess the effect of slug seed passage on germination and early seedling establishment of a set of nine common plant species with limited dispersal capabilities (unassisted or ant dispersed). Germination trials were performed under natural conditions (NW of Spain). Size was a clear limitation for seed ingestion: smaller seeds were eaten more readily, whereas only the largest slugs could swallow the largest seeds. All ingested seeds were voided undamaged. Only not-ingested seeds (the biggest) were damaged, with chewing marks in the surface and 0.8% (N = 250) were broken. In some cases, slugs ate the elaiosomes but discarded the seeds. Slug seed passage had an overall positive effect on total germination and sped it up in two species. Elaiosome removal by slugs had also a positive effect in Ulex europaeus seeds (+160%). However, slugs had no effect on early seedling survival and growth of the study species. Our results show that slugs are effective dispersers in terms of seed treatment in the digestive track. However, according to their reduced movement range (in the range of tens of metres; as shown by other studies), they can only provide rather limited dispersal as compared to vertebrate dispersers. This can be nonetheless significant for species with limited dispersal, e.g. unassisted and ant-dispersed plants, for which they act as non-standard dispersers.     

Ultrastructural characterization of exine development of the transient defective exine 1 mutant suggests the existence of a factor involved in constructing reticulate exine architecture from sporopollenin aggregates

A male-sterile mutant of Arabidopsis thaliana, in which filament elongation was defective although pollen fertility was normal, was isolated by means of T-DNA tagging. Transmission electron microscopy (TEM) analysis revealed that primexine synthesis and probacula formation, which are thought to be the initial steps of exine formation, were defective, and that globular sporopollenin aggregation was randomly deposited onto the microspore at the early uninucleate microspore stage. Sporopollenin aggregation, which failed to anchor to the microspore plasma membrane, was deposited on the locule wall and in the locule at the uninucleate microspore stage. However, visually normal exine with a basic reticulate structure was observed at the middle uninucleate microspore stage, indicating that the exine formation was restored in the mutant. Thus, the mutant was designated transient defective exine 1 (tde1). These results indicated that tde1 mutation affects the initial process of the exine formation, but does not impair any critical processes. Our results also suggest the existence of a certain factor responsible for exine patterning in A. thaliana. The TDE1 gene was found to be identical to the DE-ETIOLATED 2 gene known to be involved in brassinosteroid (BR) biosynthesis, and the tde1 probacula-defective phenotypes were recovered in the presence of BR application. These results suggest that BRs control the rate or efficiency of initial process of exine pattern formation.     

Accumulation of cyclin E is not a prerequisite for passage through the restriction point

The restriction point (R) is defined as the point in G(1) after which cells can complete a division cycle without growth factors and divides G(1) into two physiologically different intervals in cycling cells, G(1)-pm (a postmitotic interval with a constant length of 3 to 4 h) and G(1)-ps (a pre-DNA-synthetic interval with a variable length of 1 to 10 h). Cyclin E is a G(1) regulatory protein whose accumulation has been suggested to be critical for passage through R. We have studied cyclin E protein levels in individual cells of asynchronously growing cell populations, with respect to both passage through R and entry into S phase. We found that the postmitotic G(1) cells that had not yet reached R were negative for cyclin E accumulation. On the other hand, cells that had passed R were found to accumulate cyclin E at variable times (1 to 8 h) after passage through R and 2 to 5 h before entry into S. These kinetic data rule out the hypothesis that passage through R is dependent on the accumulation of cyclin E but suggest, instead, the converse, that passage through R is a prerequisite for cyclin E accumulation. Furthermore, we found that most of the cyclin E protein is downregulated within 1 to 2 h after entry into S.     

Phosphorylation-dephosphorylation of retinoblastoma protein not necessary for passage through the mammalian cell division cycle

Phosphorylation of the retinoblastoma protein (Rb) during the G1-phase of the mammalian cell division cycle is currently believed to be a controlling element regulating the passage of cells into S-phase. We find, however, that the suspension-grown cell lines U937, L1210, and MOLT-4 contain exclusively hyperphosphorylated Rb. Furthermore, when adherent NIH3T3 cells are grown at very low densities to avoid overgrowth and contact inhibition, they also contain only hyperphosphorylated Rb. NIH3T3 cells exhibit hypophosphorylation when the cells are grown at moderate to high cell densities. We propose that cultures of adherent cells such as NIH3T3, when grown to moderate cell densities, are made up of two populations of cells: (a) cells that are relatively isolated and therefore growing exponentially without contact inhibition, and (b) cells that are growth-inhibited by local cell density or contact inhibition. The common observation in adherent cell lines, that Rb is both hyper- and hypophosphorylated in the G1-phase and only hyperphosphorylated in the S- and G2-phases, is explained by the effects of cell density and contact inhibition. Thus, phosphorylation-dephosphorylation of Rb protein during the G1 phase is not a necessary process during the NIH3T3, L1210, MOLT-4, and U937 division cycles. We propose that phosphorylation-dephosphorylation of Rb is independent of the division cycle and is primarily determined by growth conditions throughout the division cycle.     

A magnetic field arising upon passage of an electrical current through the human arm]

Asymmetry of the magnetic field density along the arm perimeter under electric pulse with the usage of various electrodes was investigated. This research helped to prove the existence of special passageways in the human body (besides the nervous ones) which transmit the electric pulse. It was revealed that induction of electrodes into acupuncture points determined the distribution of power density along the arm section. In this case it depends upon the points used.     

Antioxidant properties of the pollen exine polymer matrix

The antioxidant properties of the polymer matrix of exine, the outer layer of pollen grain wall, were studied. The main component of this matrix is sporopollenin, a unique biopolymer resistant to mechanical and chemical damage. Samples of isolated exine purified from soluble compounds were studied with EPR using a stable nitroxyl radical TEMPO and a spin trap DMPO. At the same time, we analyzed changes in fluorescence of DCFH which detected ROS in the solution. It has been established that exine effectively reduced TEMPO and eliminated the hydroxyl radical. Also, fluorimetric analysis demonstrated that exine decomposed H₂O₂, and this ability significantly decreased after treatment of exine with feruloyl esterase or mild alkaline hydrolysis (1 M NaOH), i.e. after hydrolysis of hydroxycinnamic acid esters. After harsh hydrolysis (4 M NaOH, 170°C) of ether bonds, a large amount of hydroxycinnamic acids was released, and the exine almost completely lost its antioxidant capacity. The obtained results point to the ability of the extracellular polymer matrix of the exine to eliminate free radicals and H₂O₂ during crucial periods of male gametophyte development. The participation of ferulic acid and, possibly, of other hydroxycinnamic acids of sporopollenin in these processes has been demonstrated.