Determining [H]Thymidine Incorporation into Bacterioplankton DNA: Improvement of the Method by DNase Treatment

Determination of [H] thymidine incorporation into bacterial DNA versus other macromolecules is usually achieved by NaOH and hot trichloroacetic acid hydrolysis. This procedure was found not to be specific enough. An alternative method founded on DNase treatment is proposed. Under the new method, the fraction of thymidine incorporated into DNA ranged from 10 to 83%.     

Free-living dinitrogen-fixing bacteria isolated from petroleum refinery oily sludge

Dinitrogen-fixing activity (acetylene reduction and N(2) fixation) was found in an oily sludge originating from a petroleum refinery. Two representative dinitrogen-fixing bacterial strains were isolated from this oily waste. Their nitrogenase activity was effective when they were cultivated on sterilized sludge or simple carbon substrates (organic acid salts, sugars). Using the classical methods, these strains could not be unambiguously related to other diazotrophic taxa. The landfarming process is widely used for oily sludge disposal; this study shows that oily sludges are more than a simple carbon input into the soil but that they must also be considered as real sources of dinitrogen-fixing and probably degradative microorganisms.     

Specific Inhibition of Lignification in Bryonia dioica: Effects on Thigmomorphogenesis

Rubbing-induced lignification in Bryonia dioica internodes is significantly impaired by N(o-hydroxyphenyl) and N(o-aminophenyl) sulfinamoyl tertiobutyl acetate, specific inhibitors of cinnamyl alcohol dehydrogenase, an enzyme which is strictly associated with lignin monomer synthesis. Along with the reduction of lignification, these inhibitors counteract the inhibition of elongation due to rubbing. These results indicate that lignification participates in the thigmomorphogenetic growth response of Bryonia dioica internodes. In a general way, the data point to the causal role of lignification in the limitation of plant growth.     

Calcium- and calmodulin-regulated breakdown of phospholipid by microsomal membranes from bean cotyledons

Evidence for the involvement of Ca²⁺ and calmodulin in the regulation of phospholipid breakdown by microsomal membranes from bean cotyledons has been obtained by following the formation of radiolabeled degradation products from [U-¹⁴C]phosphatidylcholine. Three membrane-associated enzymes were found to mediate the breakdown of [U-¹⁴C] phosphatidylcholine, viz. phospholipase D (EC 3.1.4.4), phosphatidic acid phosphatase (EC 3.1.3.4), and lipolytic acyl hydrolase. Phospholipase D and phosphatidic acid phosphatase were both stimulated by physiological levels of free Ca²⁺, whereas lipolytic acyl hydrolase proved to be insensitive to Ca²⁺. Phospholipase D was unaffected by calmodulin, but the activity of phosphatidic acid phosphatase was additionally stimulated by nanomolar levels of calmodulin in the presence of 15 micromolar free Ca²⁺. Calmidazolium, a calmodulin antagonist, inhibited phosphatidic acid phosphatase activity at IC₅₀ values ranging from 10 to 15 micromolar. Thus the Ca²⁺-induced stimulation of phosphatidic acid phosphatase appears to be mediated through calmodulin, whereas the effect of Ca²⁺ on phospholipase D is independent of calmodulin. The role of Ca²⁺ as a second messenger in the initiation of membrane lipid degradation is discussed.