Isozyme analysis of intercontinental disjuncts within Styrax (Styracaceae): implications for the Madrean —Tethyan hypothesis

Various hypotheses have been put forward to explain the presence of sclerophyllous plant disjuncts between western North America and the Mediterranean region. The Madrean–Tethyan hypothesis postulates that the two regions were floristically connected in the Early to Middle Tertiary by way of a low-latitude migration route. Others deny the possibility of such a route, and instead postulate convergence to xerophytic conditions from more widespread mesophytic ancestors, or suggest long-distance dispersal scenarios. One example of a “Madrean–Tethyan link” between the two regions is composed of four species within the genus Styrax: S. officinalis subsp. officinalis from the Mediterranean region, S. officinalis subsp. redivivus and subsp. fulvescens from California, and three closely related species in Texas and northeastern Mexico (S. texanus, S. platanifolius, and S. youngiae). This group was examined with isozymes to assess whether patterns of genetic variation are consistent with those predicted by the Madrean–Tethyan hypothesis. Ten populations from California, six from the Mediterranean region, and three from Texas were sampled. Pairwise comparisons revealed mean genetic identity (I) estimates of 0.581 between Mediterranean and California populations, 0.470 between Mediterranean and Texas populations, and 0.640 between California and Texas populations. Two populations of a species thought by many to be the closest relative of S. officinalis on morphological grounds (S. jaliscanus) exhibited low I (0.299–0.321) relative to all other group comparisons. Intercontinentally disjunct populations of S. officinalis possessed an I value that warrants species status for the Californian and Mediterranean groups. Divergence time estimates between Madrean and Tethyan Styrax range from 5.0 to 13.8 Mya, too recent to be consistent with the Madrean–Tethyan hypothesis. However, alternative explanations for this disjunction are suboptimal in that they require the invocation of either long-distance dispersal, which appears unlikely in this group, or extinction. Nonetheless, the evidence presented here and in other recent studies casts substantial doubt on the Madrean–Tethyan hypothesis as a general explanation for the presence of Madrean and Tethyan taxa similar in overall appearance. More plants with Madrean–Tethyan distributions must be sampled before definitive conclusions regarding this aspect of Madrean and Tethyan vegetation can be reached.     

Formation and structure of infectious DNA of spleen necrosis virus.

The kinetics of formation and the structure of infectious DNA of spleen necrosis virus were determined. Nonintegrated infectious viral DNA first appeared 18 to 24 h after infection of dividing cells and persisted for more than 14 days. The nonintegrated infectious viral DNA was in the form of either a double-stranded linear DNA with a molecular weight of 6 X 10(6), detected in both the cytoplasm and nucleus, or a closed circular DNA of the same molecular weight, detected primarily in the nucleus. Integrated infectious viral DNA appeared soon after the nonintegrated infectious viral DNA and was the predominant form of infectious viral DNA late after infection. Integration of the spleen necrosis virus DNA into the chicken cell genome was demonstrated by three independent criteria. Nucleic acid hybridization indicated that the linear infectious viral DNA had a 5- to 10-fold higher specific infectivity than either the closed circular or integrated infectious viral DNA. Infectious viral DNA did not appear in infected stationary cells, indicating some cellular influence on the formation of infectious viral DNA.     

Selectivity of action of the lipoxygenase from rabbit reticulocytes on mitochondria and erythrocyte membranes]

Whereas the lipoxygenase from rabbit reticulocytes caused a large formation of malonyl dialdehyde (MDA) with rat liver mitochondria, erythrocyte ghosts were attacked only slightly independently of their type of preparation. The formation of MDA was not enhanced by release of spectrin-actin from the ghosts. The lipoxygenase did not give rise to hemolysis of intact erythrocytes. The formation of MDA was increased by heat treatment of the ghosts. Addition of cholesterol to a phospholipid emulsion inhibited the formation of MDA by the reticulocyte lipoxygenase. These results indicate that both lipid-protein interactions and the cholesterol content of the membranes may be involved in the preferential attack of the lipoxygenase on mitochondrial membranes.     

Binding of ribosomes to the 5' leader sequence (N = 258) of RNA 3 from alfalfa mosaic virus.

RNA 3 of alfalfa mosaic virus (AlMV) contains information for two genes: near the 5' end an active gene coding for a 35 Kd protein and, near the 3' end, a silent gene coding for viral coat protein. We have determined a sequence of 318 nucleotides which contains the potential initiation codon for the 35 Kd protein at 258 nucleotides from the 5' end. This long leader sequence can form initiation complexes containing three 80 S ribosomes. A shorter species of RNA, corresponding to a molecule of RNA 3 lacking the cap and the first 154 nucleotides (RNA 3') has been isolated. The remaining leader sequence of 104 nucleotides in RNA 3' forms a single 80 S initiation complex with wheat germ ribosomes. The location of the regions of the leader sequence of RNA 3 involved in initiation complex formation with 80 S ribosomes is reported.     

Investigations on the dynamic structures of adenine- and thymine-containing DNA.

The structures of poly(dA-dT), poly(dA-dBr5U) and of poly(dA).poly(dT) have been investigated in solution and in fibers, by Raman spectroscopy. Both the alternating poly(dA-dT), poly(dA-dBr5U) and non-alternating poly(dA).poly(dT) exhibit, in the region of sugar phosphate backbone vibrations, two bands of almost equal intensity at about 841 cm-1 and 817 cm-1. The analysis of the characteristic bands of thymine residues that are sensitive to sugar puckers gives indication of a significant displacement from the C(2')-endo conformer suggesting the adoption of alternative conformers such as O(4')-endo. In contrast, the diagnostic Raman bands for the sugar pucker of adenine residues suggest, instead, predominant adoption of C(2')-endo conformations. These Raman results are compatible with rapid dynamic changes of sugar puckers between C(2')-endo and O(4')-endo for the thymidine (and uridine) residues, whereas in adenine residues the sugar puckers fluctuate around the C(2')-endo pucker in all synthetic DNA molecules studied. Molecular dynamics simulations, performed on six different starting models using two distance-dependent dielectric functions epsilon(r) = 4 r and a sigmoidal dependence), all gave similar dynamic behavior in agreement with these Raman data and their interpretation. The mean calculated pseudorotation phases of the adenine residues are systematically higher (around C(2')-endo) than those of the thymine residues (close to O(4')-endo-C(1')-exo). Besides, the mean lifetimes of the thymine residues are 1.5 to 2.0-fold higher in the O(4')-endo than in the C(2')-endo domain, while those of the adenine residues are two to threefold higher in the C(2')-endo than in the O(4')-endo domain. In the Raman spectra of the alternating poly(dA-dBr5U), the splitting of a band into two components arising from the two contributions of ApBr5U and Br5UpA provides strong evidence for a repeating dinucleotide structure in solution. The calculated twist values averaged over the simulation runs are also systematically higher in the 5'T-A3' step (39 degrees) than in the 5'A-T3' step (33 degrees). Simultaneously, the calculated roll values are positive in the 5'T-A3' step (6 degrees) and negative in the 5'A-T3' step (-9 degrees), while the propeller twist values are about the same (-11 degrees to -16 degrees). On the other hand, in the homopolymer, the average twist value is close to 36 degrees with the roll angle close to 0 degrees and large propeller twist values (-20 degrees).     

Gastro-intestinal and neurohormonal peptides in the alimentary tract and cerebral complex ofCiona intestinalis (Ascidiaceae)

Summary Polypeptide-hormone producing cells were localized in the alimentary tract and cerebral ganglion ofCiona intestinalis using cytochemical, immunocytochemical and electron-microscopical methods.Antisera to the following peptides of vertebrate type were employed: bombesin, human prolactin (hPRL), bovine pancreatic polypeptide (PP), porcine secretin, motilin, vasoactive intestinal polypeptide (VIP),-endorphin, leu-enkephalin, met-enkephalin, neurotensin, 5-hydroxytryptamin (5-HT), cholecystokinin (CCK), human growth hormone (GH), ACTH, corticotropin-like intermediate lobe peptide (CLIP) and gastric inhibitory peptide (GIP).Immunoreactive cells were found both in the alimentary tract epithelium and in the cerebral ganglion for bombesin, PP, substance P, somatostatin, secretin and neurotensin. Additionally, in the cerebral ganglion only, there were cells immunoreactive for-endorphin, VIP, motilin and human prolactin. 5-HT positive cells, however, were restricted to the alimentary tract.No immunoreactivity was obtained either in the cerebral ganglion or in the alimentary tract with antibodies to leu-enkephalin, met-enkephalin, CCK, growth hormone, ACTH, CLIP and GIP. Prolactin-immunoreactive and pancreatic polypeptide-immunoreactive cells were argyrophilic with the Grimelius' stain and were found in neighbouring positions in the cerebral ganglion.At the ultrastructural level five differently granulated cell types were distinguished in the cerebral ganglion. Granules were present in the perikarya as well as in axons. The possible functions of the peptides as neurohormones, neuroregulators and neuromodulators are discussed.     

The occurrence of argyrophilic and argentaffin cells in the gut of Ciona intestinalis L.

Summary Argyrophilic and argentaffin cells occur in the stomach and intestinal epithelium of the sea-squirt, Ciona intestinalis L.. These cells are characterized by their basal swelling which contains the nucleus surrounded by small secretory granules and by a filamentous cell-apex which reaches the gut lumen. The cells are scattered unevenly within the epithelium. Their number decreases rapidly towards the lower part of the intestine. The localization, size of granules and their shape are features which differentiate these cells from other secretory cells in the gut epithelium such as mucous cells. These cells are thought to possess an endocrine function.The excellent technical assistance of Mrs. R. Sprang is gratefully acknowledged     

Induction of auxin biosynthetic enzymes by jasmonic acid and in clubroot diseased Chinese cabbage plants

Nitrilase (NIT) and myrosinase are important enzymes for auxin biosynthesis in Brassicaceae, which is increased during clubroot disease. Therefore, NIT and myrosinase levels during club development and possible regulation mechanisms were investigated. In addition, the occurrence of different nitrilase isoforms in Chinese cabbage has been shown. Nitrilase activity was enhanced in infected roots during later stages of club development (35–42 days after inoculation). However, no differences in nitrilase mRNA levels between infected and healthy roots were found during symptom development. Myrosinase expression was increased in clubbed roots at slightly earlier time points (28 days after inoculation) and also at later time points during infection. The activities of tryptophan oxidizing enzyme (TrpOxE), which catalyzes the first step in tryptophan-dependent auxin biosynthesis in Brassicaceae, and nitrilase were enhanced after treatment with jasmonic acid (JA) and methyl jasmonate. Similarly, the amount of myrosinase mRNA was increased by JA. During clubroot disease the endogenous concentration of JA increased in infected roots 3–5 weeks after inoculation. From our results it can be concluded that: (1) de novo indole-3-acetic acid (IAA) biosynthesis plays a role for symptom development of clubroot disease in Brassicaceae during later developmental stages; and (2) JA which increased during club development, may be involved in the up-regulation of three enzymes important for IAA synthesis.     

Comparison of proteins synthesized in vivo and in vitro by mRNA from isolated protoplasts

Studies of proteins synthesized in vitro by messenger RNA (mRNA) extracted from tobacco protoplasts showed that the changes in protein synthesis and especially the lack of certain proteins observed previously in isolated protoplasts did not result from a failure of translation.