The ecological significance of nickel hyperaccumulation: a plant chemical defense

Nickel hyperaccumulating plants have more than 1000 mg Ni kg^–1 dry weight when grown on nickel-bearing soils. We hypothesized that Ni hyperaccumulation could serve as a chemical defense against herbivores In feeding experiments with potential insect herbivores and Ni hyperaccumulating plants, only those inseets fed leaves from plants grown on non-nickel-bearing soil survived or showed a weight gain. Among chemical parameters measured, only Ni content of plants was sufficient to explain this result. When subjected to herbivory by lepidopteran larvae, plants grown on Ni-amended soil showed greater survival and yield than plants on unamended soil. Ni hyperaccumulation may be an effective plant chemical defense against herbivores because of its high lethality, apparent low cost, and broad spectrum of toxicity.     

Woody-tissue respiration for Simarouba amara and Minquartia guianensis,two tropical wet forest trees with different growth habits

We measured CO₂ efflux from stems of two tropical wet forest trees, both found in the canopy, but with very different growth habits. The species were Simarouba amara, a fast-growing species associated with gaps in old-growth forest and abundant in secondary forest, and Minquartia guianensis, a slow-growing species tolerant of low-light conditions in old-growth forest. Per unit of bole surface, CO₂ efflux averaged 1.24 mol m^–2 s^–1 for Simarouba and 0.83 mol m^–2s^–1 for Minquartia. CO₂ efflux was highly correlated with annual wood production (r ²=0.65), but only weakly correlated with stem diameter (r ²=0.22). We also partitioned the CO₂ efflux into the functional components of construction and maintenance respiration. Construction respiration was estimated from annual stem dry matter production and maintenance respiration by subtracting construction respiration from the instantaneous CO₂ flux. Estimated maintenance respiration was linearly related to sapwood volume (39.6 mol m^–3s^–1 at 24.6° C, r ²=0.58), with no difference in the rate for the two species. Maintenance respiration per unit of sapwood volume for these tropical wet forest trees was roughly twice that of temperate conifers. A model combining construction and maintenance respiration estimated CO₂ very well for these species (r ²=0.85). For our sample, maintenance respiration was 54% of the total CO₂ efflux for Simarouba and 82% for Minquartia. For our sample, sapwood volume averaged 23% of stem volume when weighted by tree size, or 40% with no size weighting. Using these fractions, and a published estimate of aboveground dry-matter production, we estimate the annual cost of woody tissue respiration for primary forest at La Selva to be 220 or 350 g C m^–2 year^–1, depending on the assumed sapwood volume. These costs are estimated to be less than 13% of the gross production for the forest.     

The evolutionary origin of the 35 kb circular DNA of Plasmodium falciparum: new evidence supports a possible rhodophyte ancestry

In common with other Apicomplexan parasites, Plasmodium falciparum carries two extrachromosomal DNAs, one of which, the 6 kb element, is undoubtedly mitochondrial. The second, generally referred to as the 35 kb circle, is of unknown provenance, but the nature and organization of its genetic content makes a mitochondrial association unlikely and the molecule has features reminiscent of plastid genomes. We now report the occurrence on the circle of an open reading frame specifying a predicted 470 amino acid protein that shares more than 50% identity with a gene currently known only on the plastome of red algae. This high degree of conservation confirms the 35 kb circle's plastid ancestry, and we speculate that it may have originated from the rhodoplast of an ancient red algal endosymbiont in the progenitor of the Apicomplexa.     

Partial Purification and Immunocytocharacterization of the Plasma Membrane ATPase of Jerusalem artichoke (Helianthus tuberosus L.) Tubers in Relation to Dormancy

Plasmalemma ATPase from Jerusalem artichoke tubers was studiedin relation to the dormancy of tubers. After partial purification,one peptide of 110 kDa appeared on SDS PAGE electrophoresisfrom dormant and non-dormant materials. ATPase specific activitywas twice higher on dormant material in the crude and solubilizedfractions, but was the same in both materials after partialpurification. Immunolabeling of this enzyme was made using aspecific antibody raised against the C terminal portion of theH⁺-ATPase from Arabidopsis thaliana. Immunolabeling was morepronounced in dormant material, in vitro and in situ. Severalworks had shown that the C terminal part of the enzyme couldbe involved in its regulation. The results presented are discussedin relation to the hypothesis according to which an internaleffector could modulated the plasmalemma ATPase activity, duringdormancy breaking. (Received October 25, 1993; Accepted September 6, 1994)     

Protein expression of a self-compatible allele from Lycopersicon peruvianum: introgression and behavior in a self-incompatible background

Lycopersicon peruvianum (wild tomato) is a gametophytic self-incompatible (SI) species. One natural population has been shown to harbor a self-compatible (SC) allele. A stylar protein associated with the self-compatibility allele has been elucidated using SDS-PAGE. The temporal and spatial expression of this protein is presented and compared with protein expression of two SI alleles. Hybrids containing the SC and SI alleles were used in a backcrossing program to introgress the SC allele into SI backgrounds in six independent lines. Controlled pollinations and SDS-PAGE were used to identify and select classes of progeny. After four backcross generations (approximately 97% recovery of the SI backgrounds) the SC allele still confers self-fertility in lines that contain this allele, providing evidence that the mutation to SC occurred at the S-locus and that the associated protein is likely responsible.     

Cellobiohydrolase A (CbhA) from the cellulolytic bacterium Cellulomonas fimi is a β-1,4-exoceilobiohydrolase analogous to Trichoderma reesei CBH II

The gene cbhA from the cellulolytic bacterium Cellulomonas fimi encodes a protein of 872 amino acids designated cellobiohydrolase A (CbhA). Mature CbhA contains 832 amino acid residues and has a predicted molecular mass of 85 349 Da. It is composed of five domains: an N-terminal catalytic domain, three repeated sequences of 95 amino acids, and a C-terminal cellulose-binding domain typical of other C. fimi glycanases. The structure and enzymatic activities of the CbhA cataiytic domain are closely related to those of CBH ll, an exocelloblohydrolase in the glycosyl hydrolase family B from the fungus Trichoderma reesel. CbhA is the first such enzyme to be characterized in bacteria. The data support the proposal that extended loops around the active site distinguish exohydrolases from endohydrolases in this enzyme family.     

Core fucosylation of high-mannose-type oligosaccharides in GlcNAc transferase I-deficient (Lec1) CHO cells

During studies on the fucosylation of endogenous proteins inparental (Pro5) and N-acetyl-D-glucosamine (GlcNAc) transferaseI-deficient (Lec1) Chinese hamster ovary (CHO) cells, we observedthat Lec1 cells incorporate     

Modification of sialic acids by 9-O-acetylation is detected in human leucocytes using the lectin property of influenza C virus

Influenza C virus spike glycoprotein HEF specifically recognizesglycoconjugates containing 9-O-acetyl-N-acetylneuraminic acid.The same protein also contains an esterase activity. Takingadvantage of these two properties, influenza C virus was usedas a very sensitive probe for the detection of traces of 9-O-acetyl-N-acetylneuraminicacid in human leucocytes. The binding of influenza C virus toleucocyte glycoproteins and gangliosides separated by sodiumdodecyl sulphate–polyacrylamide gel electrophoresis andthin-layer chromatography, respectively, was assayed using achromogenic esterase substrate. In this way, glycoproteins ofB-lymphocytes and T-lymphocytes were found to contain 9-O-acetylatedsialic acids. Of the various 9-O-acetylated gangliosides detected,one had the characteristics of 9-O-acetylated G^D3. The identificationof 9-O-acetylated sialic acids on distinct glycoproteins andglycolipids should be helpful in assigning a physiological roleto this sugar. O-acetylation gangliosides influenza C virus lymphocytes sialic acids     

Anthranilate synthase and chorismate mutase activities in transgenic tobacco plants overexpressing tryptophan decarboxylase fromCatharanthus roseus

TransgenicNicotiana tabacum L. Petit Havana SR1 F₁-plants expressing tryptophan decarboxylase cDNA (tdc) fromCatharanthus roseus (L.) G. Don under the control of the CaMV 35S promoter and terminator exhibited tryptophan decarboxylase (TDC) enzyme activity and accumulated tryptamine. The plants with the highest TDC activity contained 19 pkat per mg of protein. The influence of transgenic expression oftdc on the activities of anthranilate synthase (AS) and chorismate mutase (CM) were examined in 10 transgenic tobacco plants. The specific activities of these two chorismate-utilizing enzymes were not significantly affected by expression oftdc, despite their important functions as branch point enzymes in the shikimate pathway. The results indicate that the normal route of tryptophan biosynthesis in plants is sufficient to supply a considerable amount of this essential amino acid for the biosynthesis of secondary metabolites. Despite their increased tryptamine content, the growth and development of the transgenic tobacco plants expressingtdc appeared normal.