Leaf area index determination in an alder forest: a comparison of three methods

Leaf area index (LAI) of a stand of adult black alder trees(Alnus glutinosa L., Gaertn.) was determined by means of threeindependent methods. (1) The seasonal course of LAI was directlyobtained by counting leaves in situ and adding up their areas,estimated from harvested subsamples of leaves. (2) The seasonalvariation of LAI in the stand was estimated using the Li-CorLAI-2000 PCA in parallel and with this instrument a VegetationArea Index (VAI, projected area of all phyto-elements) was actuallymeasured. (3) Maximum LAI was calculated from leaf litter collectionstaking into account specific leaf area within different layersof the alder crown. Direct LAI estimates (1) and calculationsfrom leaf litter (3) revealed the same figure of maximum LAI(4.8). This LAI was reached in August. The LAI-2000 PCA capturedthe seasonal variation and underestimated, by 11% on average,the LAI obtained directly. Compared with results gained withother broad-leaved tree species the LAI-2000 PCA values foralder were reliable. It is suggested that this is due to thehorizontal homogeneous structure of the main leaf layer. Thisis in the periphery of the crown, where 90% of the light interceptionoccurs. Taking the het-erogeneity into account a satisfactorycompatibility of the three methods applied to the alder standwas achieved. Key words: Alnus glutinosa, leaf area index, in situ counting, LAI-2000 PCA, litter collections     

Factors affecting transient gene expression in cultured radiata pine cotyledons following particle bombardment

Transfer and expression of the β–glucuronidase gene ( gusA ) in cultured cotyledons of radiata pine ( Pinus radiata D. Don ) were obtained by particle bombardment. Conditions for optimum transient expression were established by using plasmid pB[/12], delivered by gold particles, 1.6 μm in diameter, into 8-day-old cultured cotyledons. Helium pressure of 7.6 MPa, bombardment distance between the stopping screen and the target tissues of 6 cm, and 0.8 μg of plasmid DNA per bombardment proved to be the best parameters for transient expression; using these parameters 79% of bombarded cotyledons showed GUS activity, with 4.3 blue spots per cotyledon. This system was used for studying the expression of several gus-driven promoters the expression of the sunflower ubiquitin gene promoter was higher (99% of positive cotyledons, with 14.2 blue spots per cotyledon) than that of the CaMV 35S promoter, whereas the rice actin and the maize alcohol dehydrogenase gene promoters gave lower gusA expression, as determined histochemically. These results were confirmed by using the gus fluorometric assay. Use of the sunflower ubiquitin gene promoter resulted in gusA expression up to 20 days after bombardment, with a significant level of gus expressing loci per bombarded cotyledon, whereas with the CaMV 35S promoter gusA expression was lost 12 days after bombardment.     

Early helper T-cell dysfunction in simian immunodeficiency virus but not in human immunodeficiency virus type-2-infected macaques

Both naive and vaccinated macaques acquired a virus-specific proliferative helper T-cell reactivity in response to infection with the nonpathogenic human immunodeficiency virus type 2 (HIV-2). In contrast, macaques infected with the pathogenic simian immunodeficiency virus of the macaque strain (SIV_mac) did not develop a helper T-cell response. Furthermore, a vaccine-induced preexisting T-cell reactivity was abrogated after SIV_mac infection in vaccine failures. These differences may reflect the different pathogenicity of the two closely related viruses.     

Paracuaria hispanica n. sp. (Nematoda: Acuariidae), a stomach parasite of the pyrenean desman Galemys pyrenaicus Geoffr. (Insectivora: Talpidae), with a redefinition of the genus Paracuaria Rao, 1951

Adult and fourth-stage larvae of Paracuaria hispanica n. sp., from the stomach of the Pyrenean desman Galemys pyrenaicus Geoffroy (Insectivora: Talpidae) in northern and central Spain, are described. The new species differs from the other members of the genus Paracuaria (P. adunca and P. soricis), among other morphological details, in its smaller body and spicule sizes, the presence of a cuticular ring around the tip of the female tail, and the existence of lateral alae running longitudinally along its body from the cervical region to the tail. In view of the latter feature, the genus Paracuaria is redefined. The fourth stage larva of the new species is distinguished from that of P. adunca by its monocuspid deirids. P. hispanica occurred in 45% of the 20 host specimens examined.     

Efficiency of the tetracycline-dependent gene expression system: complete suppression and efficient induction of the rolB phenotype in transgenic plants

We have investigated the use of the tetracycline-dependent gene expression system to regenerate and propagate tobacco plants transformed with a gene whose product — when highly expressed — interferes with regeneration and/or further reproduction. Plants transformed with the Agrobacterium rhizogenes rolB gene under the control of the tetracycline-dependent expression system were phenotypically indistinguishable from wild type owing to efficient repression of the promoter. Induction of the rolB gene with tetracycline led to high-level expression of the rolB mRNA, which resulted in extremely stunted plants with necrotic and wrinkled leaves that did not develop a floral meristem. Upon cessation of tetracycline treatment healthy shoots developed even from severely affected meristems. Data on the dose response of the rolB phenotype as a function of tetracycline concentration demonstrate that the tetracycline-dependent gene expression system can be used to modulate the manifestation of a particular phenotype.     

Dynamics of the immune system response in cerebrospinal fluid and blood of SIVmac-infected rhesus monkeys

Paired sera and CSF samples were collected from SIV_mac-infected macaques. Animals infected with SIV_mac251 maintained low gag and high env-specific antibody levels in plasma. Increasing env-specific antibody titers in CSF were associated in one animal with strong intrathecal synthesis. SIV_mac239-infected monkeys revealed high antibody titers of gag and env-specificity, in one animal accompanied by weak intrathecal synthesis of virus-specific antibodies. In all animals, the CD4/CD8 ratio in CSF decreased faster compared to blood.