Glyoxylate Cycle Enzymes in Peroxisomes Isolated from Petals of Pumpkin (Cucurbita sp.) during Senescence

The activities of the two unique enzymes of the glyoxylate cycle,isocitrate lyase (EC 4.1.3.1 [EC] ) and malate synthase (EC 4.1.3.2 [EC] ),were undetectable in petals of pumpkin (Cucurbita sp. AmakuriNankin) until the end of blooming, but they appeared duringsenescence. The activity of catalase (EC 1.11.1.6 [EC] ) increased,glycolate oxidase (EC 1.1.3.1 [EC] ) activity did not change, whilehydroxypyruvate reductase (EC 1.1.1.81 [EC] ) activity peaked at fullblooming stage and declined thereafter. After fractionationof cellular organelles on a sucrose density gradient, we detectedisocitrate lyase and malate synthase activities in peroxisomalfractions only from petals at the senescing stage. Northernblot analysis revealed that malate synthase mRNA increased duringpetal senescence. Citrate synthase (EC 4.1.3.7 [EC] ) and malate dehydrogenase(EC 1.1.1.37 [EC] ) activities were also present, while aconitase(EC 4.2.1.3 [EC] ) was not detectable in peroxisomal fractions. Moreoverthe presence of 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35 [EC] )and urate oxidase (EC 1.7.3.3 [EC] ) in the peroxisomal fractionsfrom senescing petals indicates that peroxisomes could be involvedboth in the ß-oxidation pathway and in the purinecatabolism during petal senescence. (Received May 25, 1991; Accepted September 25, 1991)     

Chemoreception in hydra: specific binding of glutathione to a membrane fraction.

Specific binding of reduced [35S]glutathione (GSH) was measured using a crude membrane fraction of Hydra vulgaris (attenuata). The specific binding shows both rapid displaceable and nondisplaceable components. Rapid displaceable binding accounted for 20% of the total specific binding. Data from saturation binding experiments indicates half maximal total specific binding occurs at 2 microM GSH which is similar to reported EC50 values from behavioral experiments. Calcium is required for displaceable binding of GSH to the putative receptor. Oxidized glutathione (GSSG), an antagonist of the GSH-activated feeding response, and S-methylglutathione (GSM), an agonist of the feeding response, inhibit the binding of radiolabeled GSH to the putative receptor. Glutamate, a putative competitive antagonist of the GSH-activated feeding response in hydra, does not inhibit the specific binding of radiolabeled GSH to the receptor and must therefore block the feeding response by a mechanism other than competitive inhibition.     

NADP+-isocitrate dehydrogenase in germinating cucumber cotyledons: Purification and characterization of a cytosolic isoenzyme

The activity of NADP⁺-dependent isocitrate dehydrogenase (ICDH, EC 1.1.1.42) was investigated during the post-germinative growth of cucumber ( Cucumis sativus L. cv. Marketmore) seedlings. Isoelectric focusing showed the presence of several isoenzymes, two of which represented 70–80% of the total NADP⁺-ICDH activity in cotyledons of seedlings grown in the dark. They had pI values between 4.8 and 5.8. The isoenzyme with higher pI was purified to homogeneity by hydrophobic interaction, affinity, hydroxylapatite and anion exchange chromatography. The purified isoenzyme is a dimeric protein, consisting of two apparently identical 43-kDa subunits. It is specific for NADP⁺, inhibited by ATP and by 2-oxoglutarate, whereas it is not inhibited by citrate, succinate, and glyoxylate. The data indicate that NADP⁺-ICDH from cucumber is structurally similar to ICDHs from other plants, but it shows some peculiar biochemical characteristics.     

Identification of Tuber magnatum Pico DNA markers by RAPD analysis

Summary Different species of truffle were studied in order to identify species-specific markers. The isolation of two Tuber magnatum Pico markers is reported. One of these could be used as a probe in dot blot hybridization, allowing the development of a rapid test able to identify Tuber magnatum species.     

Microsomal and cytosolic cytochrome P450 mediated benzo(a)pyrene hydroxylation in Pleurotus pulmonarius

Summary Microsomal and soluble fractions of Pleurotus pulmonarius exhibited a reduced carbon monoxide difference spectrum with P450 maxima at 448nm and 450–452nm respectively. Substrate induced Type I spectra were observed on addition of benzo(a)pyrene to both fractions. Benzo(a)pyrene hydroxylation was measured using the aryl hydrocarbon hydroxylase assay and was observed to be P450 dependent as indicated by carbon monoxide inhibition together with the substrate binding characteristics. The activity of the fractions were observed to give K_m of 200mM and 660mM and V_max of 1.25 nmol/min/nmol P450 and 0.57 nmol/min/nmol P450 for the microsomal and cytosolic fractions respectively.     

A disappearing oasis in the semi-arid Chaco: Deficient palm regeneration and establishment

Palm forests of Copernicia alba are a rare habitat in the semi-arid Chaco of Northwestern Argentina, are centres of high species diversity, and provide key resources for many species. Our goal was to assess the conservation status of five C. alba patches in Northwestern Argentina: Reserve; Embarcación; Palma Sola; Vinalito; and, Talar. We compared patches to identify the sites with greatest conservation needs based on four criteria: population size structure; palm density (of individuals with height >1.30 m); probability of seedlings being browsed; and, presence of potential seed dispersers. We found that three (Embarcación, Reserve, and Talar) out of five sites had palm densities greater than 200 individuals/ha and only one site (Embarcación) showed a reverse J-shaped size structure for height. Reserve and Embarcación had the greatest probability of seedlings being browsed (0.99 ± 0.01 and 0.88 ± 0.12, respectively). A total of 14 potential disperser species of mammals and birds were recorded across the five sites. Only Reserve harboured all of the potential dispersers, but at least two potential disperser species were recorded at the other sites. None of the palm patches studied had an adequate conservation status. However, Embarcación met three out of four criteria, and therefore it can be considered to have the best conservation status in the semi-arid Chaco. Palma Sola and Vinalito have the greatest conservation needs. To conserve C. alba in Northwestern Argentina, strategies are needed that ensure seedling establishment for future populations to reach an adequate density and structure.