Molecular markers shared by diverse apomictic Pennisetum species

Two molecular markers, a RAPD (randomly amplified polymorphic DNA) and a RFLP/STS (restriction fragment length polymorphism/sequence-tagged site), previously were found associated with apomictic reproductive behavior in a backcross population produced to transfer apomixis from Pennisetum squamulatum to pearl millet. The occurrence of these molecular markers in a range of 29 accessions of Pennisetum comprising 11 apomictic and 8 sexual species was investigated. Both markers were specific for apomictic species in Pennisetum. The RFLP/STS marker, UGT 197, was found to be associated with all taxa that displayed apomictic reproductive behavior except those in section Brevivalvula. Neither UGT197 nor the cloned RAPD fragment OPC-04₆₀₀ hybridized with any sexually reproducing representatives of the genus. The cloned C04₆₀₀ was associated with 3 of the 11 apomictic species, P. ciliare, P. massaicum, and P. squamulatum. UGT197 was more consistently associated with apomictic reproductive behavior than OPC04₆₀₀ or cloned C04₆₀₀, thus it could be inferred that UGT197 is more closely linked to the gene(s) for apomixis than the cloned C04₆₀₀. The successful use of these probes to survey other Pennisetum species indicates that apomixis is a trait that can be followed across species by using molecular means. This technique of surveying species within a genus will be useful in determining the relative importance of newly isolated markers and may facilitate the identification of the apomixis gene(s).     

Root movements: Towards an understanding through attempts to model the processes involved

Roots have the ability to change the direction of their forward growth. Sometimes these directional changes are rapid, as in mutations, or they are slower, as in tropisms. The gravitational force is always present and roots have an efficient graviperception mechanism which enables them to initiate gravitropic movements. In trying to model and simulate the course of gravitropic root movements with a view to analyse the component processes, the following aspects of the plant's interaction with gravity have been considered: (1) The level of organization (organism, organ, cell) at which the movement process is expressed; (2) whether the gravity stimulation event is dynamic or static (i.e. whether or not physiologically significant displacements take place with respect to the gravity vector); (3) the sub-systems involved in movement and the processes which they regulate; (4) the mathematical characterization of the relevant sub-systems. A further allied topic is the nature of nutational movements and whether they are linked with gravitropic movements in some way. In considering how they can best be modelled, two types of nutational movements are proponed: stochastic nutation and circumnutation. Most, if not all, natural movements developed in response to static gravistimulation can be viewed as gravimorphisms. This applies at the levels of cell, organ and organism. However, when a system at any one of these levels experiences dynamic gravistimulation, because of its inherent homeostatic properties, it is induced to regenerate a state similar to that previously held. Thus, gravitropism is a regenerative gravimorphic process at the level of the organ.     

Regulatory implications of translational frameshifting in cellular gene expression

The genetic code, once thought to be rigid, hag been found to be quite fiexible, permitting several different reading alternatives. One of these is translatlonal frameshifting, a process programmed in the mRNA sequence and which enables a +1 or -1 shift from the reading frame of the initiation codon. So far, the Involvement of translatlonal frameahifting in gene expression has been described mainly in viruses (particularly retroviruses), retrotransposons, and bacterial insertion elements, in this MicroReview., we present a survey of the cellular genes, mostly in Escherichia coil, which have been found to be expressed through a transiational frameshifting process, as well as a discussion of the regulatory implications of this process.     

Preliminary caged‐field trial,using the fungal pathogen Zoophthora radicans brefeld (zygomycetes: entomophthorales) against the diamondback moth Plutella xylostella L. (lepidoptera: Yponomeutidae) in the UK

Zoophthora radicans Brefeld was tested for control of Plutella xylostella L. in a caged‐field trial. No infection was seen in control cages, but between 36% and 68% of larvae in live samples, and 38% and 55% of larvae at the final harvest, were infected in inoculated cages, suggesting the biological control potential of this fungus.     

Effect of fructose-1,6-bisphosphate on glutamate uptake and glutamine synthetase activity in hypotix astrocyte cultures

Astrocytes are important in regulating the microencironment of neurons both by catabolic and synthetic pathways. The glutamine synthetase (GS) activity observed in astrocytes affects neurons by removing toxic substances, NH₃ and glutamate; and by providing an important neuronal substrate, glutamine. This glutamate cycle might play a critical role during periods of hypoxia and ischemia, when an increase in extracellular excitatory amino acids is observed. It was previously shown in our laboratory that fructose-1,6-bisphosphate (FBP) protected cortical astrocyte cultures from hypoxic insult and reduced ATP loss following a prolonged (18–30 hrs) hypoxia. In the present study we established the effects of FBP on the level of glutamate uptake and GS activity under normoxic and hypoxic conditions. Under normoxic conditions, [U-¹⁴C]glutamate uptake and glutamine production were independent of FBP treatment; whereas under hypoxic conditions, the initial increase in glutamate uptake and an overall increase in glutamine production in astrocytes were FBP-dependent. Glutamine synthetase activity was dependent on FBP added during the 22 hours of either normoxic- or hypoxic-treatment, hence significant increases in activity were observed due to FBP regardless of the oxygen/ATP levels in situ. These studies suggest that activation of GS by FBP may provide astrocytic protection against hypoxic injury.     

Direct determination of the enantiomeric purity of (R)- and (S)-2-hydroxy-4-phenylbutyric acid

The determination of enantiomeric purity of (R)- and (S)-2-hydroxy-4-phenylbutyric acid by chiral HPLC is described. Good resolution has been obtained on covalently bonded L-hydroxyproline saturated with Cu(II) ions. The method makes possible the determination of enantiomeric purity in media containing growing cells. © 1994 Wiley-Liss, Inc.     

Origin of the main class of repetitive DNA within selected Pennisetum species

In an attempt to identify relationships among genomes of the allotetraploid Pennisetum purpureum Schumach and closely related Pennisetum species with which it can be successfully hybridized, repetitive DNA sequences were examined. Digestion with KpnI revealed two highly repetitive fragments of 140 by and 160 bp. The possibility that these sequences could be used as genome markers was investigated. Average sequences were determined for the 140 by and 160 by KpnI families from P. purpureum and P. squamulatum Fresen. Average sequences (based upon four or five repeats) were determined for the P. glaucum (L.) R. Br. 140 by KpnI family and the diploid P. hohenackeri Hochst. ex Steud. 160 bp KpnI family. The average sequences of the 160 by KpnI families in P. purpureum and P. squamulatum differ by only nine bases. The 140 by KpnI families of the three related species, P. purpureum, P. squamulantum, and P. glaucum are nearly identical, and thus likely represent a recent divergence from a common progenitor or a common genome. Each repetitive sequence may contain internal duplications, which probably diverged following amplification of the original sequence. The 140 by KpnI repeat probably evolved from the 160 by KpnI repeat since the missing 18 by segment is part of the internal duplication that is otherwise conserved in the subrepeats. Tandemly arrayed repetitive sequences in plants are likely to be composed of subrepeats which have been duplicated and amplified.Florida Aqricultural Experiment Station series #R-02758     

Temperature-dependent sex determination in reptiles: Proximate mechanisms,ultimate outcomes,and practical applications

In many egg-laying reptiles, the incubation temperature of the egg determines the sex of the offspring, a process known as temperature-dependent sex determination (TSD). In TSD sex determination is an “all or none” process and intersexes are rarely formed. How is the external signal of temperature transduced into a genetic signal that determines gonadal sex and channels sexual development? Studies with the red-eared slider turtle have focused on the physiological, biochemical, and molecular cascades initiated by the temperature signal. Both male and female development are active processes—rather than the crganized/default system characteristic of vertebrates with genotypic sex determination—that require simultaneous activation and suppression of testis- and ovary-determining cascades for normal sex determination. It appears that temperature accomplishes this end by acting on genes encoaing for steroidogenic enzymes and steroid hormone receptors and modifying the endocrine microenvironment in the embryo. The temperature experienced in development also has long-term functional outcomes in addition to sex determination. Research with the leopard gecko indicates that incubation temperature as well as steroid hormones serve as organizers in shaping the adult phenotype, with temperature modulating sex hormone action in sexual differentiation. Finally, practical applications of this research have emerged for the conservation and restoration of endangered egg-laying reptiles as well as the embryonic development of reptiles as biomarkers to monitor the estrogenic effects of common environmental contaminants. © 1994 Wiley-Liss, Inc.     

Predation on primates: Ecological patterns and evolutionary consequences

It has long been thought that predation has had important ecological and evolutionary effects on primates as prey. Predation has been theorized to have been a major selective force in the evolution of hominids.¹ In modern primates, behaviors such as active defense, concealment, vigilance, flight, and alarm calls have been attributed to the selective pressures of predation, as has group living itself. It is clear that primates, like other animals, have evolved ways to minimize their risk of predation. However, the extent to which they have been able to do so, given other constraints of living such as their own need to acquire food, has not yet been resolved. Perhaps most hotly debated is whether predation has been the primary selective force favoring the evolution of group living in primates. Part of the difficulty in resolving the debate lies in a paucity of direct evidence of predation. This is regrettable yet understandable since primatologists, by definition, focus on the study of primates, not predators of primates (unless these are also primates). Systematic direct evidence of the effects of predation can best be obtained by studying predators that are as habituated to observers as are their primate prey. Until this is done, we must continue to rely on opportunistic accounts of predation and predation attempts, and on systematically obtained indirect evidence. Such data reveal several interesting patterns: (1) although smaller primates may have greater predation rates than larger primates, even the largest primates are not invulnerable to predation; (2) the use by primates of unfamiliar areas can result in higher predation rates, which might be one pressure favoring philopatry, or site fidelity; (3) arboreal primates are at greater risk of predation when they are more exposed (at forest edges and tops of canopies) than in more concealed locations; (4) predation by mammalian carnivores may often be episodic; and (5) terrestrial primates may not experience greater predation than arboreal primates.