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.     

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     

Cortical hypometabolism in injured brain: New correlations with the noradrenergic and serotonergic systems and with behavioral deficits

Changes with time after injury in behavioral deficits, as determined by the Morris swim test, and the in vivo specific binding of HEAT, a selective ₁-adrenoreceptor ligand, were compared with the time-course of development of cortical hypometabolism in rats with focal freezing lesions. In our trauma model, cortical hypometabolism was detectable in the lesioned hemisphere at 4 hr, became maximal (50% of normal) at 3 days and diminished towards normal on days 5 and 10 post-injury. Progressive impairment of acquisition of the Morris water maze task was demonstrated up to day 3 post-lesion with improvement thereafter. On day 3 the latency to reach criterion was 60% longer in lesioned animals than in corresponding sham-operated ones. An increase in the volume of distribution of HEAT, limited to cortical areas of the lesioned hemisphere, was demonstrable at 4 hr post-lesion and reached its maximum on day 3 (200% of normal) with subsequent return toward normal on days 5 and 10. Several types of drugs were shown previously to modify the cortical hypometabolism associated with cerebral injury. The present data indicate that the same drugs also modify the in vivo binding of HEAT and the behavioral deficits induced by brain lesions. Ibuprofen, a non-steroidal anti-inflammatory drug, p-chlorophenylalanine, an inhibitor of serotonin synthesis, ketanserin, a specific 5HT₂-receptor antagonist, and prazosin, an ₁-adrenergic receptor blocker all normalized the in vivo binding of HEAT in the cortical areas of the lesioned hemisphere. All groups of animals treated with these drugs also showed subtle, but statistically highly significant improvements in latency to locate the platform in the Morris water maze. Taken together these results show good correlation between behavioral deficits, changes in ₁-noradrenergic receptor binding and cortical hypometabolism in injured brain. This supports the hypothesis that post-injury cortical hypometabolism is a reflection of cortical functional depression in which both the serotonergic and noradrenergic neurotransmitter systems play a role, compatible with their inhibitory effects in the cortex and their postulated involvement in cortical information processing.Special issue dedicated to Dr. Leon S. Wolfe.     

Cold responses of high altitude populations

The literature on cold stress in permanent high altitude residents and sojourners in the Himalayas and Andes is reviewed. High altitude natives, as exemplified by Peruvian Quechua Indians, are relatively well protected from the cold by the efficient use of wool clothing. However, exposure to wet-cold and dry-cold conditions is present, both diurnally and seasonally. Basal metabolism in the native is slightly elevated over United States norms, and natives are able to maintain high levels of blood flow to the extremities during whole-body and local extremity cooling tests. There is suggestive evidence for a developmental pattern of acclimatization to cold, but definitive evidence for genetic tolerance to cold in the highland native is lacking.     

A streptomycin-resistant Escherichia coli mutant with ribosomes temperature-sensitive in the suppression of a nonsense codon.

Summary Cell free extracts from a streptomycin-resistant E. coli mutant which is also temperature-sensitive for Q phage were studied for suppression of a nonsense mutation at various temperatures. The streptomycin-resistant ribosomes of the mutant were found to be temperature-sensitive in suppression of an amber mutation in f2 phage coat protein while retaining the ability to synthesize proteins at an elevated temperature (42° C). The restriction of amber suppression at 42° C is assumed to be related to an alteration in the ribosomal protein S12 of the streptomycin-resistant mutant which also causes a change in its electrophoretic mobility.     

Studies on the ultrastructure and histochemistry of the lymph system of Gastrodiscoides hominis (Paramphistoma: Digenea).

The lymphatic system of the paramphistome, Gastrodiscoides hominis consists of numerous fluid-filled branches embedded in parenchyma and surrounded by extracellular material and is closely associated with the major organ systems of the fluke. The lymph matrix consists of a cytoplasmic syncytium within which nuclei, mitochondria and various sized granules and membranous structures occur. The granules found throughout the lymph system morphologically resemble autophagosomes and lysosomes. The lymph system provides a storage site for proteins which can be broken down to amino acids via autophagy, for subsequent mobilization and transport to tissues undergoing active protein synthesis. Many branches of the lymph system are surrounded by specialized parenchymal cells referred to as juxta-lymphatic cells. These cells are apparently associated with autophagic degradation of sequestered lymph cytoplasm, which may serve as an additional mechanism for the mobilization and transport of precursor molecules throughout the fluke via the parenchymal network.     

The Role of Chloride in Acetylcholine Metabolism

Abstract: The chloride dependence of acetylcholine (ACh) synthesis and release and of choline uptake was studied in synaptosomal preparations from rat brain. The substitution of propionate for chloride, in the presence of 35 m m -potassium, lowered the ACh content of the synaptosomes. However, in the presence of 5 m m -potassium, the ACh level in synaptosomes was reduced, but significantly less so. Propionate had no effect on choline acetyltransferase (EC 2.3.1.6) activity when measured in a standard chloride-containing medium. In the presence of propionate, the spontaneous release of ACh was unchanged, but potassium-stimulated release of ACh was markedly reduced as compared with a chloride-containing medium. The synthesis of ACh, as measured by the net increase in the amount of ACh in the synaptosomes and that released to the medium, was reduced with propionate at 5 m m -potassium and was totally inhibited when the potassium concentration was increased to 35 m m . Choline uptake studies revealed that with propionate only a low-affinity component of the choline transport system existed. Further, the V _max was markedly reduced when the potassium concentration was increased to 35 m m . The results suggest that under certain conditions choline transported by a low-affinity system might provide a substantial source of choline for ACh synthesis.     

Release of Endocannabinoids into the Cerebrospinal Fluid during the Induction of the Trigemino-Hypoglossal Reflex in Rats

The endocannabinoid system (ECS) plays an important role in pain processing and modulation. Since the specific effects of endocannabinoids within the orofacial area are largely unknown, we aimed to determine whether an increase in the endocannabinoid concentration in the cerebrospinal fluid (CSF) caused by the peripheral administration of the FAAH inhibitor URB597 and tooth pulp stimulation would affect the transmission of impulses between the sensory and motor centers localized in the vicinity of the third and fourth cerebral ventricles. The study objectives were evaluated on rats using a method that allowed the recording of the amplitude of evoked tongue jerks (ETJ) in response to noxious tooth pulp stimulation and URB597 treatment. The amplitude of ETJ was a measure of the effect of endocannabinoids on the neural structures. The concentrations of the endocannabinoids tested (AEA and 2-AG) were determined in the CSF, along with the expression of the cannabinoid receptors (CB1 and CB2) in the tissues of the mesencephalon, thalamus, and hypothalamus. We demonstrated that anandamide (AEA), but not 2-arachidonoylglycerol (2-AG), was significantly increased in the CSF after treatment with a FAAH inhibitor, while tooth pulp stimulation had no effect on the AEA and 2-AG concentrations in the CSF. We also found positive correlations between the CSF AEA concentration and cannabinoid receptor type 1 (CB1R) expression in the brain, and between 2-AG and cannabinoid receptor type 2 (CB2R), and negative correlations between the CSF concentration of AEA and brain CB2R expression, and between 2-AG and CB1R. Our study shows that endogenous AEA, which diffuses through the cerebroventricular ependyma into CSF and exerts a modulatory effect mediated by CB1Rs, alters the properties of neurons in the trigeminal sensory nuclei, interneurons, and motoneurons of the hypoglossal nerve. In addition, our findings may be consistent with the emerging concept that AEA and 2-AG have different regulatory mechanisms because they are involved differently in orofacial pain. We also suggest that FAAH inhibition may offer a therapeutic approach to the treatment of orofacial pain.     

Genome-scale patterns in the loss of heterozygosity incidence in Saccharomyces cerevisiae

Former studies have established that loss of heterozygosity can be a key driver of sequence evolution in unicellular eukaryotes and tissues of metazoans. However, little is known about whether the distribution of loss of heterozygosity events is largely random or forms discernible patterns across genomes. To initiate our experiments, we introduced selectable markers to both arms of all chromosomes of the budding yeast. Subsequent extensive assays, repeated over several genetic backgrounds and environments, provided a wealth of information on the genetic and environmental determinants of loss of heterozygosity. Three findings stand out. First, the number of loss of heterozygosity events per unit time was more than 25 times higher for growing than starving cells. Second, loss of heterozygosity was most frequent when regions of homology around a recombination site were identical, about a half-% sequence divergence was sufficient to reduce its incidence. Finally, the density of loss of heterozygosity events was highly dependent on the genome’s physical architecture. It was several-fold higher on short chromosomal arms than on long ones. Comparably large differences were seen within a single arm where regions close to a centromere were visibly less affected than regions close, though usually not strictly adjacent, to a telomere. We suggest that the observed uneven distribution of loss of heterozygosity events could have been caused not only by an uneven density of initial DNA damages. Location-depended differences in the mode of DNA repair, or its effect on fitness, were likely to operate as well.     

Time course changes to structural,mechanical and material properties of bone in rats after complete spinal cord injury

Objective:Characterise the spatiotemporal trabecular and cortical bone responses to complete spinal cord injury (SCI) in young rats.Methods:8-week-old male Wistar rats received T9-transection SCI and were euthanised 2-, 6-, 10- or 16-weeks post-surgery. Outcome measures were assessed using micro-computed tomography, mechanical testing, serum markers and Fourier-transform infrared spectroscopy.Results:The trabecular and cortical bone responses to SCI are site-specific. Metaphyseal trabecular BV/TV was 59% lower, characterised by fewer and thinner trabeculae at 2-weeks post-SCI, while epiphyseal BV/TV was 23% lower with maintained connectivity. At later-time points, metaphyseal BV/TV remained unchanged, while epiphyseal BV/TV increased. The total area of metaphyseal and mid-diaphyseal cortical bone were lower from 2-weeks and between 6- and 10-weeks post-SCI, respectively. This suggested that SCI-induced bone changes observed in the rat model were not solely attributable to bone loss, but also to suppressed bone growth. No tissue mineral density differences were observed at any time-point, suggesting that decreased whole-bone mechanical properties were primarily the result of changes to the spatial distribution of bone.Conclusion:Young SCI rat trabecular bone changes resemble those observed clinically in adult and paediatric SCI, while cortical bone changes resemble paediatric SCI only.