Amino acid transport in mouse peritoneal macrophages is mediated by several membrane carriers with different substrate specificity and sensitivity to environmental stimuli. We reported previously that transport activities of cystine and arginine in the macrophages were induced markedly by low concentrations of bacterial lipopolysaccharide (LPS). It is known that a variety of macrophage functions are affected by ambient oxygen tension. In this study, we have investigated the effects of oxygen on the induction of amino acid transport activity by LPS and found that the induction of cystine, but not arginine, transport activity was dependent on the ambient oxygen tension. When the macrophages were cultured with 2% O 2 in the presence of 1 ng/ml LPS, induction of cystine transport activity was reduced by ϳ70% compared with cells cultured under normoxic conditions. In macrophages, transport of cystine is mediated by a Na ؉ -independent anionic amino acid transporter named system x c Ϫ . System x c Ϫ is composed of two protein components, xCT and 4F2hc, and the expression of xCT was closely correlated with system x c Ϫ activity. A putative NF-B binding site was found in the 5-flanking region of the xCT gene, but the enhanced expression of xCT by LPS and oxygen was not mediated by NF-B binding. An increase in intracellular GSH in macrophages paralleled induction of xCT, but not ␥-glutamylcysteine synthetase. These results suggest the importance of system x c Ϫ in antioxidant defense in macrophages exposed to LPS and oxidative stress.

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Large areas of the tropical peat swamp forests in Central Kalimantan were drained to be converted into rice fields and then abandoned. A change in the soil water level due to drainage in the forests must have had a big impact on the ecology and ecophysiology of the trees in the drained remnant forests. The leaf traits of these trees in particular may have been directly or indirectly affected by drainage because of their high sensitivity to environmental change. To understand the influence of drainage on leaf traits, we investigated leaf morphological and physiological differences between intact and drained peat swamp forests in Palangka Raya, Indonesia, using 14 species distributed over both types of forests. We compared the leaf mass per unit area (LMA), leaf toughness, leaf area-and mass-based nitrogen content (N area and N mass), carbon/nitrogen ratio, total phenolics, condensed tannin and lignin content and carbon isotope ratio (13 C) of both types of forest trees. In the drained forest, trees had higher values in LMA, N area , and 13 C than in the intact forest, suggesting that such trees adjust themselves to dry conditions to increase photosynthetic ability with high water use efficiency compared with those in intact forests. We also found an increase in condensed tannin content in drained forest trees, which may offset the drainage-induced acceleration of leaf decomposition to some extent.

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