Polyamines and Anaerobic Elongation of Rice Coleoptile

The role of polyamines in the anaerobic elongation of rice (Oryzasativa L.) coleoptiles was studied. The reduced growth of ricecoleoptiles under anoxic conditions was accompanied by a massiveaccumulation of free putrescine. Putrescine was synthesizedfrom arginine in a reaction catalyzed by arginine decarboxylase(ADC). The anoxic titer of putrescine was closely correlatedwith elongation of coleoptiles. In experiments in which putrescineand inhibitors [-difluoromethylarginine (DFMA) and -difluoromethylornithine(DFMO)] of the synthesis of polyamines were exogenously supplied,we demonstrated an absolute requirement for putrescine, synthesizedby ADC, for anaerobic elongation of coleoptiles. The presenceof exogenous putrescine (alone or in combination with DFMA)increased the rate of anaerobic elongation of coleoptile by30–40%. (Received December 1, 1988; Accepted June 19, 1989)     

Accumulation and Interconversion of Amino Acids in Rice Roots under Anoxia

In excised rice roots, anaerobic degradation of proteins gaverise to an increase of free-amino acids. Anoxic accumulationof alanine, -aminobutyric acid and proline was the consequenceof the interconversion of glutamate, aspartate and amides. Theshift in the composition of the amino acid pool appears to becaused by changes in keto acid levels. The role of reactionsinvolved in amino acid interconversion and the physiologicalsignificance of these interconversions are considered and discussed. (Received November 25, 1988; Accepted June 9, 1988)     

Virulence genes are carried by a megaplasmid of the plant pathogen Pseudomonas solanacearum

Summary A class of avirulent mutants of the plant pathogenic bacterium Pseudomonas solanacearum, strain GMI1000, resistant to acridine orange (Acr^r), harbour a deletion of over 85 kb in their genome. This deletion affects, a1,000 kb megaplasmid which has previously been shown to be present in most of the strains of this species. In addition at least 11 out of 13 independent Tn5 insertions, leading to loss of virulence, are located on the megaplasmid. Nine of them are present in the region which is deleted from the Acr^r mutants. These results suggest that the majority of virulence genes identified so far are plasmid borne.     

Nitrogen fertilizer enhances vegetation establishment of a high-altitude machine-graded ski slope

Machine grading is frequently required to prepare the terrain when building high-altitude ski slopes in the Alps. However, this kind of disturbance alters the natural environment, destroying the vegetation and hampering its reestablishment. Thus, specific restoration plans are necessary to encourage the recovery of vegetation, which is already affected by different natural constraints in this harsh environment. One of the main critical factors affecting plant growth in high-altitude areas is the lack of available nitrogen (N) in the soil. In this context, the addition of a slow-release N fertilizer was carried out in an experimental revegetated ski slope between 2,800 and 2,900 m above sea level in the western Italian Alps. Both vegetation and soil were monitored during a 5-year period in order to test the effectiveness of N addition on the restoration process. Even if effects on soil carbon and N contents were negligible, vegetation was remarkably affected by the fertilization, since the total vegetation cover and the species richness significantly increased. Against the expectations, there was a remarkable increase in spontaneous forbs, rather than in most of the sown graminoids, which slightly varied during the experimental period. Actually, graminoids responded in different ways, mostly increasing (likewise forbs), but the slight decrease of the dominant Festuca nigrescens (Chewing's Fescue) masked their spread. This study confirms the noteworthy role of N in high-altitude alpine soils and consequently its importance to improve the restoration process of degraded ecosystems.     

In vivo release of adenosine from cat basal ganglia—studies with a push pull cannula

The release of newly synthesized [³H]adenosine has been studied in vivo in cat caudate nucleus and substantia nigra, using a push pull cannula. In the presence of [³H]adenosine as precursor, spontaneously released [³H]adenosine was easily detectable in superfusates of the push pull cannula. In the caudate nucleus, potassium and veratridine caused a marked and reversible increase in [³H]adenosine release. The effect of veratridine was completely blocked by tetrodotoxin (TTX) although TTX had no action by itself. Ouabain as well as glutamate, also markedly increased the release of [³H]adenosine.The specific 5′ nucleotidase inhibitor α,β-methylene ADP, did not alter the increase in the amount of [³H]adenosine obtained by veratridine, although it diminished the spontaneous release of [³H]adenosine by about 20%.Push pull cannulae were also implanted simultaneously into the caudate nucleus and substantia nigra. Potassium applied into the caudate nucleus increased the local release of adenosine but did not change that observed in the substantia nigra. When potassium was applied into the substantia nigra, it also increased the local release of adenosine but did not change that observed in the caudate nucleus.The results are discussed in term of the possible existence of “purinergic neurons” and of the relation between the adenosine release and central nervous activity.     

Adenosine Transport into Guinea-pig Synaptosomes

Abstract: Kinetics for transport of adenosine into guinea-pig neocortex synaptosomes were studied by incubating them with [¹⁴C]adenosine for up to 30 s. The apparent K _m value of the high-affinity transport system for adenosine was 21.1 μM and the V _max value was 257.3 pmol/min/mg protein. The transport system was inhibited by both compounds structurally related (compounds 554 and 555) and unrelated (dipyridamole) to adenosine. Because electrically stimulated synaptosomes release up to 1.5% of the adenosine derivative content per min, the physiological significance of adenosine uptake is discussed as a possible mechanism to compensate for the loss of adenine nucleotides from synaptosomes preparations.