We report here a factor (B cell growth factor) found in induced supernatants of the mouse thymoma EL4 that co-stimulates with anti-IgM antibodies in short-term cultures of purified B lymphocytes to induce polyclonal B cell proliferation but not antibody-forming cell production. The factor is not mitogenic for resting B cells and interacts with anti-IgM-activated B cells in a non-H-2-restricted manner. Absorption studies and molecular weight analysis reveal the factor is distinct from interleukin 2. This factor synergises with antigen, interleukin 2, and an interleukin 2-free, B cell growth factor-free T cell supernatant that contains T cell-replacing factor to produce erythrocyte-specific plaque-forming cells in cultures of highly purified B cells.

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Comparisons were made among Douglas-fir forest, aspen (broad leaf deciduous) forest and wheatgrass (C 3 ) grassland for ecosystem-level water-use efficiency (WUE). WUE was defined as the ratio of photosynthetic CO 2 assimilation rate and evapotranspiration (ET) rate. The ET data measured by eddy covariance were screened so that they overwhelmingly represented transpiration. The three sites used in this comparison spanned a range of vegetation (plant functional) types and environmental conditions within western Canada. When compared in the relative order Douglas-fir (located on Vancouver Island, BC), aspen (northern Saskatchewan), grassland (southern Alberta), the sites demonstrated a progressive decline in precipitation and a general increase in maximum air temperature and atmospheric saturation deficit (D max ) during the mid-summer. The average ( AE SD) WUE at the grassland site was 2.6 AE 0.7 mmol mol À1 , which was much lower than the average values observed for the two other sites (aspen: 5.4 AE 2.3, Douglasfir: 8.1 AE 2.4). The differences in WUE among sites were primarily because of variation in ET. The highest maximum ET rates were approximately 5, 3.2 and 2.7 mm day À1 for the grassland, aspen and Douglas-fir sites, respectively. There was a strong negative correlation between WUE and D max for all sites. We also made seasonal measurements of the carbon isotope ratio of ecosystem respired CO 2 (d R ) in order to test for the expected correlation between shifts in environmental conditions and changes to the ecosystemintegrated ratio of leaf intercellular to ambient CO 2 concentration (c i /c a ). There was a consistent increase in d R values in the grassland, aspen forest and Douglas-fir forest associated with a seasonal reduction in soil moisture. Comparisons were made between WUE measured using eddy covariance with that calculated based on D and d R measurements. There was excellent agreement between WUE values calculated using the two techniques. Our d R measurements indicated that c i /c a values were quite similar among the Douglas-fir, aspen and grassland sites, despite large variation in environmental conditions among sites. This implied that the shorter-lived grass species had relatively high c i /c a values for the D of their habitat. By contrast, the longer-lived Douglas-fir trees were more conservative in water-use with lower c i /c a values relative to their habitat D. This illustrates the interaction between biological and environmental characteristics influencing ecosystem-level WUE. The strong correlation we observed between the two independent measurements of WUE, indicates that the stable isotope composition of respired CO 2 is a useful ecosystem-scale tool to help study constraints to photosynthesis and acclimation of ecosystems to environmental stress.

Peroxisomes are the cellular location of many antioxidants and are themselves significant producers of reactive oxygen species. In this report we demonstrate the induction of peroxisome biogenesis genes in both plant and animal cells by the universal stress signal molecule hydrogen peroxide. Using PEX1–LUC transgenic plants, rapid local and systemic induction of PEX1–luciferase could be demonstrated in vivo in response to physiological levels of hydrogen peroxide. PEX1–luciferase was also induced in response to wounding and to infection with an avirulent pathogen. We propose a model in which various stress situations that lead to the production of hydrogen peroxide can be ameliorated by elaboration of the peroxisome compartment to assist in restoration of the cellular redox balance.

The Arabidopsis ABC transporter Comatose (CTS; AtABCD1) is required for uptake into the peroxisome of a wide range of substrates for ␤-oxidation, but it is uncertain whether CTS itself is the transporter or if the transported substrates are free acids or CoA esters. To establish a system for its biochemical analysis, CTS was expressed in Saccharomyces cerevisiae. The plant protein was correctly targeted to yeast peroxisomes, was assembled into the membrane with its nucleotide binding domains in the cytosol, and exhibited basal ATPase activity that was sensitive to aluminum fluoride and abrogated by mutation of a conserved Walker A motif lysine residue. The yeast pxa1 pxa2⌬ mutant lacks the homologous peroxisomal ABC transporter and is unable to grow on oleic acid. Consistent with its exhibiting a function in yeast akin to that in the plant, CTS rescued the oleate growth phenotype of the pxa1 pxa2⌬ mutant, and restored ␤-oxidation of fatty acids with a range of chain lengths and varying degrees of desaturation. When expressed in yeast peroxisomal membranes, the basal ATPase activity of CTS could be stimulated by fatty acyl-CoAs but not by fatty acids. The implications of these findings for the function and substrate specificity of CTS are discussed.Peroxisomes perform a range of different functions, including ␤-oxidation of fatty acids (FA) 2 and synthesis and degradation of bioactive, lipid-derived molecules. Import of substrates for peroxisomal metabolism is mediated by ATP binding cassette (ABC) transporters belonging to subclass D (1, 2). ABC transporters are composed of a minimum of four functional domains: two transmembrane domains, involved in substrate binding and translocation, and two nucleotide binding domains (NBDs) that bind and hydrolyze ATP, providing energy for transport (3, 4). The domains may be fused into a single polypeptide, but are frequently expressed as half-size transporters composed of a transmembrane domain fused to an NBD, which hetero-or homodimerize to form a functional transporter. Bakers' yeast (Saccharomyces cerevisiae) contains two ABCD genes that encode half-size ABC proteins: Pxa1p (peroxisomal ABC-transporter 1), and Pxa2p (5-7). The single pxa1⌬ and pxa2⌬ deletion mutants are unable to grow on oleate (C18:1) as the sole carbon source and exhibit reduced ␤-oxidation of this long-chain FA. It has been proposed that Pxa1p and Pxa2p operate as a heterodimer to form a functional transporter (6,8,9), which has been shown by indirect evidence to be required for the peroxisomal transport of the C18:1-CoA, a long-chain acyl-CoA ester, but not for import of C8:0-CoA (10). In contrast, medium-chain FAs enter yeast peroxisomes as free acids independently of Pxa1p/Pxa2p, and are activated by peroxisomal acyl-CoA synthetase, Faa2p, prior to ␤-oxidation (6).The human ABCD transporter subfamily comprises four half-size members: adrenoleukodystrophy protein (ALDP), ALD-related protein, the 70-kDa peroxisomal membrane protein (PMP70), and PMP70-related protein (PMP70R/PMP69) (1, 2). Although...