Global extent,development and economic impact of acid soils

Acid soils occupy approximately 30% or 3950 m ha of the world's ice free land area and occur mainly in two global belts where they have developed under udic or ustic moisture regimes. The northern belt (cold and temperate climate) is dominated by Spodosols, Alfisols, Inceptisols and Histosols and the southern tropical belt consists largely of Ultisols and Oxisols.Sixty-seven percent of the acid soils support forests and woodlands and approximately 18% are covered by savanna, prairie and steppe vegetation. Only 4.5% (179 m ha) of the acid soil area is used for arable crops. A further 33 m ha is utilized for perennial tropical crops. The value of the annual production in these areas is approximately US$ 129 billion. Value of products from forests, woodlands and permanent pastures on acid soils is difficult to evaluate.Forests of the tropics and wetlands have an invaluable role in global, regional and local ecosystem balance and a protective role for flora, fauna and water resources. While acid soils in the northern belt are increasingly protected and reafforested, the destructive exploitation of timber and abusive modern shifting cultivation have contributed to the loss of >250 million ha of tropical forest during the second half of this century leaving vast areas of anthropic savannas on heavily eroded and degraded acid soils.The authors believe that attempts to develop acid soils for agriculture and agroforestry in the tropics should concentrate on these deforested and abandoned areas of degraded acid soils. However, this will be difficult without significant initial investment and adequate technology. A three step development approach is suggested, which could help prevent or halt the annual destruction of >5 mill. ha tropical forests by untraditional shifting cultivators. It would help to protect the fragile natural ecosystems on tropical acid soils now considered to be indispensable for the future life on earth.     

Genomic structure and chromosomal location of the mouse pre-T-cell receptor alpha gene

The mouse pre-T-cell receptor alpha (pT) chain is a 33 000 M _r glycoprotein expressed on the surface of immature thymocytes as a disulfide-linked heterodimer with the T-cell receptor beta (TCR) chain, and in association with proteins of the CD3 complex. The cDNA for pT, isolated previously, encodes a type I transmembrane protein that is a member of the immunoglobulin (Ig) superfamily. Here we report the complete nucleotide sequence, the exon/intron structure, and the chromosomal location of the pTa gene. The gene spans about 8.4 kilobases (kb) and consists of four exons. Exon 1 encodes the 5 untranslated region, the leader peptide, and the first three amino acids of the mature protein. This exon is followed by a relatively long intron of 4.9 kb that contains many short interspersed repeats (SINEs) of the B1 and B2 family. The second exon encodes the extracellular Ig-like domain and exon 3 with just 45 base pairs the connecting peptide (CP), including the cysteine required for heterodimer formation. A similar exon/intron structure encoding corresponding parts of the mature polypeptide is found both in the Tcra and Tcrd constant region genes. The last exon encodes the transmembrane portion, the cytoplasmic tail, and about 540 nucleotides of 3 untranslated sequence, including a B2 repetitive element. In situ hybridization maps the pTa gene to the D/E1 region of mouse chromosome 17.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession number U27268     

Identification of two separable modules in the duck hepatitis B virus core protein.

Hepadnavirus replication requires the concerted action of the polymerase and core proteins to ensure packaging of the RNA pregenome and DNA maturation. The arginine-rich C terminus of the core protein plays an essential role in both of these steps while being dispensable for nucleocapsid formation. In an attempt to identify other functional domains of the core protein, we performed a series of trans-complementation experiments analyzing the ability of duck and human hepatitis B virus (DHBV and HBV) core protein subunits to support the replication of a core-defective DHBV genome. Plasmids expressing the N-terminal amino acids 1 to 67 or the remaining C-terminal portion, amino acids 67 to 262, of the DHBV core protein were cotransfected into LMH cells along with a replication-deficient construct coding for the DHBV pregenome and polymerase. Neither the N nor the C terminus alone yielded replication-competent core particles. However, cotransfection of plasmids that separately expressed both regions restored a normal replication pattern. Furthermore, the DHBV C terminus but not the N terminus could be replaced by the corresponding domain of the HBV core protein in this assay. Finally, coexpression of the complete HBV core protein and the N terminus from DHBV resulted in DHBV replication, while the HBV core protein alone was not functional. Taken together, these findings suggest a modular organization of the DHBV core protein in which the C terminus is functionally conserved among different hepadnaviruses.     

Uptake kinetics of iron-phytosiderophores in two maize genotypes differing in iron efficiency

Iron inefficiency in the maize ( Zea mays L.) mutant ysl is caused by a defect in the uptake system for Fe-phytosiderophores. To characterize this defect further, the uptake kinetics of Fe-phytosiderophores in ysl was compared to the Fe-efficient maize cultivar Alice. Short-term uptake of ⁵⁹Fe-labeled Fe-deoxymugineic acid (Fe-DMA) was measured over a concentration range of 0.03 to 300 μM. Iron uptake in Fe-deficient plants followed Michaelis-Menten kinetics up to about 30 μM and was linear at higher concentrations, indicating two kinetically distinct components in the uptake of Fe-phytosiderophores. The saturable component had similar K_m (∼ 10 μM) in both genotypes. In contrast. V_max was 5.5 μmol Fe-DMA g⁻¹ dry weight [30 min]⁻¹ in Alice, but only 0.6 μmol Fe-DMA g⁻¹ dry weight [30 min]⁻¹ in _ysl. Uptake experiments with double-labeled ⁵⁹Fe-[¹⁴C]DMA suggest that in both cultivars Fe-DMA was taken up by the roots as the intact chelate. The results indicate the existence of a high-affinity and a low-affinity uptake system mediating Fe-phytosiderophore transport across the root plasma membrane in maize. Apparently, the mutation responsible for Fe inefficiency in ysl affected high-affected uptake and led to a decrease in activity and/or number of Fe-phytosiderophore transporters.     

Improved correlation between soil exchangeable K and plant K contents on a tissue water basis

In acid volcanic soils, plant roots are thought to be injured by acidity (low pH) and/or solubilized aluminium (Al) ions. An attempt was made to separate the effects of low pH from those of Al on the elongation and viability of alfalfa (Medicago sativa L.) radicles in water culture. Root elongation was irreversively curtailed by 20 hours treatment at pH 4.0 without Al or 20 mmol m^-3 Al at pH 5.0. Viability of surface cells of root tips was detected as a degrading activity of fluorescein diacetate (FDA) by cellular esterases and subsequent accumulation of derived fluorescein within cells. Large numbers of the surface cells lost their viability after four hours exposure at the low pH. In contrast, surface cells maintained both FDA degrading activity and ability to accumulate fluorescein 20 h after initial exposure to the Al solution (20 mmol Al m^-3, pH 5.0). These results suggest that there are some significant differences in the mechanisms of phytotoxicity to alfalfa root between the two stress factors.     

Calcitonin gene-related peptide and its receptor in the thymus

Calcitonin gene-related peptide (CGRP), a 37-amino acid residue neuropeptide, was immunostained in rat thymus at two sites: a subpopulation of thymic epithelial cells, namely subcapsular/perivascular cells, were heavily stained besides some nerve fibers surrounding arteries and arterioles. The administration of nanomolar concentrations of rat -CGRP dose-dependently raised intracellular cyclic adenosine monophosphate (cAMP) levels in isolated rat thymocytes (half-maximum stimulation 1 nM) but not in cultured rat thymic epithelial cells. Peptides structurally related to CGRP (i.e., rat calcitonin or amylin) had no effect. CGRP(8–37), an N-terminally truncated form, acted as an antagonist. Peripheral blood lymphocytes did not respond to CGRP, suggesting that receptors are present only on a subpopulation of thymocytes but not on mature T cells. This was substantiated by visualization of CGRP receptors on single cells by use of CGRP-gold and -biotin conjugates of established biological activity: only a small proportion of isolated thymocytes was surface labeled. In situ, the CGRP conjugates labeled receptors on large thymocytes residing in the outer cortical region of rat thymus pseudolobules. Thus, immunoreactive CGRP is found in subcapsular/perivascular thymic epithelial cells and acts via specific CGRP receptors on thymocytes by raising their intracellular cAMP level. It is suggested that CGRP is a paracrine thymic mediator that might influence the differentiation, maturation, and proliferation of thymocytes.     

Mice deficient for the lysosomal proteinase cathepsin D exhibit progressive atrophy of the intestinal mucosa and profound destruction of lymphoid cells.

Mice deficient for the major lysosomal aspartic proteinase cathepsin D, generated by gene targeting, develop normally during the first 2 weeks, stop thriving in the third week and die in a state of anorexia at day 26 +/- 1. An atrophy of the ileal mucosa first observed in the third week progresses towards widespread intestinal necroses accompanied by thromboemboli. Thymus and spleen undergo massive destruction with fulminant loss of T and B cells. Lysosomal bulk proteolysis is maintained. These results suggest, that vital functions of cathepsin D are exerted by limited proteolysis of proteins regulating cell growth and/or tissue homeostasis, while its contribution to bulk proteolysis in lysosomes appears to be non-critical.     

Purification and characterization of a novel extracellular Streptomyces lividans 66 enzyme inactivating fusidic acid.

The wild-type strain Streptomyces lividans 66 is resistant against the steroid-like antibiotic fusidic acid. Comparative studies of the wild-type strain and a fusidic acid-sensitive mutant allowed the identification of an extracellular enzyme which inactivates fusidic acid. With the help of a combination of ultrafiltration and chromatographies with Phenyl-Sepharose and an anion exchanger, the enzyme was highly purified. Its apparent molecular mass is 48 kDa, its optimal activity ranges between 45 and 55 degrees C, and its optimal pH is 6.0 to 9.0. It is stimulated by neither monovalent nor divalent ions. The enzyme acts as a specific esterase which removes the acetyl group at C-16 from fusidic acid. The resulting intermediate is unstable, and spontaneous lactonization between C-21 and C-16 occurs rapidly.     

The genes of the lysosomal cysteine proteinases cathepsin B, H, L, and S map to different mouse chromosomes

The mouse genes for the lysosomal cysteine proteinases cathepsin B, H, L, and S were mapped to Chromosomes (Chrs) 14, 9, 13, and 3, respectively. Two of the DNA probes used in this study detected an additional, independently segregating locus. The cathepsin B-specific probe hybridized to a locus on Chr 2, and the cathepsin H probe to a locus on the X Chr. These loci either correspond to pseudogenes or to cathepsin B- and cathepsin H-related genes. The four cysteine proteinases mapped in this study lie within known regions of conserved synteny between mouse and human chromosomes, when compared with the corresponding positions of their human homologs. Assuming that the genes of the cysteine proteinase gene family arose from a common ancestral gene, our results suggest that these four cysteine proteinases had been dispersed over different chromosomes before separation of mouse and human in evolution. Received: 22 August 1996 / Accepted: 20 November 1996