Temperate rainforest lichens in New Zealand: high thallus water content can severely limit photosynthetic CO2 exchange

CO₂ exchange rate in relation to thallus water content (WC, % of dry weight) was determined for 22 species of lichens, mainly members of the genera Pseudocyphellaria and Sticta, from a temperate rainforest, Urewere National Park, New Zealand. All data were obtained in the field, either using a standard technique in which the lichens were initially wetted (soaked or sprayed, then shaken) and allowed to slowly dry, or from periodic measurements on samples that were continuously exposed in their natural habitat. A wide range of WC was found, with species varying from 357 to 3360% for maximal WC in the field, and from 86 to 1300% for optimal WC for photosynthesis. Maximal WC for lichens, wetted by the standard technique, were almost always much less than the field maxima, due to the presence of water on the thalli. The relationships between CO₂ exchange rate and WC could be divided into four response types based on the presence, and degree, of depression of photosynthesis at high WC. Type A lichens showed no depression, and Type B only a little at maximal WC. Type C had a very large depression and, at the highest WC, CO₂ release could occur even in the light. Photosynthetic depression commenced soon after optimal WC was reached. Type D lichens showed a similar depression but the response curve had an inflection so that net photosynthesis was low but almost constant, and never negative, at higher WC. There was little apparent relationship between lichen genus or photobiont type and the response type. It was shown that high WC does limit photosynthetic CO₂ uptake under natural conditions. Lichens, taken directly from the field and allowed to dry under controlled conditions, had net photosynthesis rates that were initially strongly inhibited but rose to an optimum, before declining at low WC. The limiting effects of high WC were clearly shown when, under similar light conditions, severe photosynthetic depression followed a brief, midday, rain storm. Over the whole measuring period the lichens were rarely at their optimal WC for photosynthesis, being mostly too wet or, occasionally, too dry. Photosynthetic performance by the lichens exposed in the field was similar to that expected from the relationship between the photosynthetic rate and WC established by the standard procedure.     

Behavioural and morphological changes in ciliates induced by the predator Amoeba proteus

The predator Amoeba proteus induced behavioural and morphological changes in ciliates of the genus Euplotes. The frequency of avoidance behaviour in E. octocarinatus increased from 16±5% to 84±5% (SD) after 14 h of coexistence with the predator. The ciliate's width increased from 59±3 μm to 77±4 μm (SDM) within 48 h. Similar behavioural, but not morphological, change was induced in E. daidaleos, but neither morphological nor behavioural responses occurred in E. aediculatus. E. octocarinatus and E. daidaleos populations survived in the presence of A. proteus, whereas E. aediculatus populations became extinct by predation. Induced behavioural response seemed to be the reason for the low predation risk of E. octocarinatus and E. daidaleos. The results suggest that Euplotes ciliates have evolved specific defence mechanisms to various predators. Defensive changes are induced by a chemical substance released from A. proteus. This “kairomone” has a molecular weight between 5000 and 10000 Da. Proteolytic digestion of its activity indicated that the avoidance-inducing substance is a peptide. After the turbellarian Stenostomum sphagnetorum had induced a defensive morphology in E. octocarinatus or E. aediculatus, neither of these ciliates immediately avoided Amoeba proteus. Thus, Euplotes ciliates with a defensive morphology do not have behavioural defences in reaction to all predators.     

Effects of short-term salinity on leaf gas exchange of the fig (Ficus carica L.)

The influence of short-term salinity (day 1–day 2: 50 mol m^–3 NaCl, day 3–day 7: 100 mol m^–3 NaCl in the nutrient solution) on leaf gas exchange characteristics were studied in two fig clones (Ficus carica L.), whose root mass had been varied in relation to the leaf area. The stomatal conductance was diminished by NaCl in the first week of treatment. NaCl slightly reduced the calculated intercellular partial pressure of CO₂. The net photosynthetic rate of plants with many roots was stimulated by NaCl on some days of the first week of treatment, whereas the net assimilation rate of the plants with few roots remained unaltered or decreased by NaCl. Only the assimilation of the salt-treated plants of one clone for some days during the first week of treatment seemed to be influenced by stomatal conductance. Nonstomatal factors were primarily responsible for the changes in CO₂ uptake in response to salt and/or root treatment. The water use efficiency increased during several days of the first week of NaCl treatment. Decreased stomatal conductance, increased water use efficiency and stimualtion of the net CO₂ assimilation rate appear to enhance salt tolerance during the first few days of salinity. ei]H Lambers     

The dynamics of the cassava green mite Mononychellus tanajoa in a seasonally dry area in Kenya

The population dynamics of the cassava green mite Mononychellus tanajoa was studied on cassava during 35 weeks (early March to first of November 1989) in an experimental field near Lake Victoria in Western Kenya. The mite population peaked at the onset of the long dry season with 1,100 mites/leaf, declined sharply to a level of about 300 individuals/leaf, not to increase again until the next rainy season commenced. An indigenous phytoseiid predator Iphiseius degenerans was abundant during the dry spell with a maximum about 9 predators/leaf.A nonlinear regression analysis revealed that food depletion in combination with I. degenerans predation limited the population growth of the mites, whereas rain intensity had no effect. The predator exhibited no aggregative response to high densities of M. tanajoa and stayed mainly in the lower part of the canopy while the spider mites preferred the top, indicating that I. degenerans is a generalist predator without capacity to control M. tanajoa alone. However, in combination with another density dependent factor, such as food depletion, the predator may have prevented the spider mites from causing complete defoliation during the dry season.     

The effect of the cassava green mite Mononychellus tanajoa on the growth and yield of cassava Manihot esculenta in a seasonally dry area in Kenya

The effect of the cassava green mite Mononychellus tanajoa on the growth and yield of cassava Manihot esculenta was studied over a 10-month period in two field trials near Lake Victoria in Kenya. One plot was maintained free of mites by means of acaricide, while the other was artificially infested.The highest population density of M. tanajoa occurred during the dry season. A maximum leaf area index (LAI) of about 2 was reached at the onset of the dry season. The total leaf area of mite infested plants was reduced compared with uninfested plants during the dry spell. During the following rainy season infested plants recovered and attained the same leaf area as uninfested plants. A multiple regression model predicting the leaf area showed that 58% of the seasonal variation could be explained by plant age, soil water, and leaf injury.The net growth rate of infested plants was lower than that of uninfested plants. Maximum values of 21 (infested plants) and 49 (uninfested plants) g m^-2 week^-1 were attained at the onset of the second rainy season. No difference was found between uninfested and infested plants with respect to net assimilation rates per unit leaf area during the dry season. The net assimilation rates reached a maximum almost at the same time as the growth rates, but the infested plants peaked slightly earlier and at a lower level than the uninfested plants. M. tanajoa did not affect the relative allocation of dry matter into stems and storage roots, but the absolute allocation of dry matter declined with increasing mite injury. Thus, after 10 months the dry matter of infested plants was reduced by 29% and 21% for storage roots and stems, respectively, compared with the uninfested plants.     

Cloning and molecular analysis of the poly(3-hydroxybutyric acid) biosynthetic genes of Thiocystis violacea

From a genomic library of Thiocystis violaceae strain 2311 in L47, two adjacent EcoRI restriction fragments of 5361 base pairs (bp) and of 1978 bp were cloned. The 5361-bp EcoRI restriction fragment hybridized with a DNA fragment harbouring the Alcaligenes eutrophus poly(3-hydroxyalkanoate) (PHA) synthase operon (phbCAB) and restored the ability to synthesize and accumulate PHA in PHA-negative mutants derived from A. eutrophus. The nucleotide sequence analysis of both fragments revealed five open-reading frames (ORFs); at least three of them are probably relevant for PHA biosynthesis. The amino acid sequences of the putative proteins deduced from these genes indicate that they encode a -ketothiolase [phbA _Tv, relative molecular mass (M_r) 40850], which exhibited 87.3% amino acid identify with the -ketothiolase from Chromatium vinosum. The amino acid sequences of the putative proteins deduced from ORF2_Tv (M_r 41 450) and phbC _Tv (M_r 39 550), which were located upstream of and antilinear to phbA _Tv, exhibited 74.7% and 87.6% amino acid identify, respectively, with the corresponding gene products of C. vinosum. Downstream of and antilinear to phbC _Tv was located ORF5, which encodes for a protein of high relative molecular mass (M_r 76428) of unknown function. With respect to the divergent organisation of ORF2_Tv and phbC _Tv on one side and of phbA _Tv on the other side and from the homologies of the putative gene products, this region of the T. violaceae genome resembled very much the corresponding region of C. vinosum, which was identified recently. Correspondence to: A. Steinbüchel     

Methods of assessment of transfer of a gentamycin-resistance gene (aacC1) from genetically engineered microorganisms into agriculturally important soil bacteria

In order to assess the risk associated with the deliberate release of genetically engineered microorganisms (GEMs) into the agricultural environment, the transfer of plasmids between bacterial strains was investigated under laboratory conditions. Genetically modified Rhizobium leguminosarum and Agrobacterium tumefaciens strains carrying the gentamycin acetyltransferase resistance gene (aacC1) on various plasmids were investigated for their ability to transfer the aacC1 gene to their wild-type (w.t.) counterparts, as well as to Pseudomonas syringae. Conjugation experiments between the various strains, were carried out after the relevant characteristics and conditions for selective growth of each bacterial strain had been ascertained. After conjugations on filters had been completed, the putative transconjugants were grown in media containing antibiotics and assessed for the presence of aacC1 gene by: (a) DNA plasmid profile; (b) expression of AAC(3)-I enzyme activity; (c) colony hybridization using a ³²P-labelled DNA probe complementary to the aacC1 gene. The results obtained indicate that transfer of the aacC1 gene from genetically modified strains of R. leguminosarum into a plasmid-free strain of A. tumefaciens occurred via self-transmissible plasmids. Alternatively, genetically modified A. tumefaciens bearing the aacC1 gene on plasmids acquired from R. leguminosarum strains, transferred it ineffectively to a hardly detectable frequency. No transfer of the aacC1 gene from genetically modified R. leguminosarum or A. tumefaciens strains into P. syringae has been observed. These data indicate that in the absence of the RP4 element, genetically modified A. tumefaciens is not able to efficiently transfer aacC1 into w.t. R. leguminosarum and P. syringae. Correspondence to: A. S. Tsiftsoglou     

Purification and properties of poly(3-hydroxyvaleric acid) depolymerase from Pseudomonas lemoignei

During growth on poly(3-hydroxyvaleric acid), P(3HV), or valerate Pseudomonas lemoignei secretes a P(3HV) depolymerase. This P(3HV) depolymerase was purified from the culture medium of valerate-grown cells by ammonium sulphate precipitation, chromatography on DEAe-sephacel and CM-Sepharose CL 6B. The relative molecular masses of the native as well as the sodium dodecyl sulphate (SDS)-treated enzyme were 53 000 or 54 000, respectively. In contrast to the poly(3-hydroxybutyric acid), P(3HB), depolymerase of Comamonas sp. and P(3HB) depolymerases A and B of P. lemoignei, which are specific for the hydrolysis of P(3HB), the purified P(3HV) depolymerase hydrolysed P(3HB), P(3HV) and co-polymers of 3-hydroxybutyric acid and 3-hydroxyvaleric acid at similar rates. Poly(hydroxyalkanoic acids), consisting of monomers with six and more carbon atoms or substrates characteristic for lipases such as Tween 80 or triolein were not hydrolysed. Maximum activities were measured in 50mm TRIS-HCl buffer, pH 8.0, at 55° C. The apparent K _m values of the purified P(3HV) depolymerase for P(3HB) and P(3HV) were 77 and 65 g polyester/ml, respectively. As the main product of enzymatic hydrolysis of P(3HV), 3-hydroxyvalerate was identified. The depolymerase was insensitive to p-hydroxymercuribenzoate but sensitive to dithioerythritol and phenylmethylsulphonyl fluoride, indicating the absence of active reduced sulphur groups and the presence of essential disulphide bonds and serine residues. Correspondence to: D. Jendrossek     

Cloning and characterization of the Methylobacterium extorquens polyhydroxyalkanoic-acid-synthase structural gene

A cosmid gene bank of partially EcoRI-digested genomic DNA from Methylobacterium extorquens IBT no. 6 was screened for DNA fragments restoring polyhydroxyalkanoic-acid (PHA) accumulation in the PHA-negative mutant Alkaligenes eutrophus H16 PHB^–4. The M. extorquens PHA-synthase structural gene phaC _Mex was mapped on a 23-kbp EcoRI fragment by complementation studies, by hybridization experiments with heterologous DNA probes from A. eutrophus H16 encoding for phaA, phaB and phaC and by nucleic acid sequence analysis. Evidence for the presence of genes for a -ketothiolase or an acetoacetyl-coenzyme A reductase on this fragment was not obtained. The nucleotide sequence of a 3.7-kbp region was obtained. It contained the entire 1.815-kbp phaC _Mex plus approximately each 900-bp upstream and downstream of phaC _Mex. PhaC _Mex encoded a protein of 605 amino acods with a relative molecular mass (M_r) of 66742, which exhibited 38.1% amino acid identity with the A. eutrophus PHA synthase. Determination of the N-terminal amino acid sequence of an M_r 65 000 protein, which was enriched concomitantly with the purification of PHA granules in sucrose gradients, revealed a sequence that was identical with the amino acid sequence deduced from the most probable translation start codon except for a valine, which was obviously removed post-translationally. Enzyme analysis, which was done with the native gene and a phaC _Mex -lacZ fusion gene, gave no evidence for expression of phaC _Mex in Escherichia coli.     

HLA-DP/DR interaction in early onset pauciarticular juvenile chronic arthritis

We investigated the polymorphic second exon of the HLA-DPB1 and HLA-DRB1 genes, using in vitro DNA amplification by polymerase chain reaction (PCR) and oligonucleotide hybridization in 136 patients with early onset pauciarticular juvenile chronic arthritis (EOPA-JCA) and 199 healthy controls. The analysis of the HLA-DRB1 system revealed that most of the DRB1 alleles are not indifferent with respect to susceptibility to EOPA-JCA. There is a hierarchy of susceptible (DRB1*08, DR5), permissive (DRB1*01), moderately protective (DR2, DRB1*04), and protective (DRB1*07) alleles. In contrast, no hierarchy could be shown for the HLA-DPB1 system. DPB1*0201 was found to be susceptible. The relatively frequent alleles DPB1*0402 and DPB1*0401 seem to be indifferent. The associations with DPB1*0201, DR5, and DRB1*08 are independent of each other: that is to say they, are not brought about by linkage disequilibrium. The susceptible alleles DPB1*0201 and DR5 show evidence for interaction in the pathogenesis of EOPA-JCA. Interaction seems likely between DPB1*0201 and DRB1*08, DR5 and DRB1*08, or between DR6 and DRB1*08. The strongest interaction exists between DPB1*0201 and a common DQ factor associated with both DR5 and DRB1*08. Finally, we observed a hierarchy among the various marker combinations, where the risk of developing EOPA-JCA increases with the number of associated markers present in an individual.This work was supported by SFB217.The data presented here are part of the doctoral thesis of C. Paul.