Ultramafic geoecology of South and Southeast Asia

Globally, ultramafic outcrops are renowned for hosting floras with high levels of endemism, including plants with specialised adaptations such as nickel or manganese hyperaccumulation. Soils derived from ultramafic regoliths are generally nutrient-deficient, have major cation imbalances, and have concomitant high concentrations of potentially phytotoxic trace elements, especially nickel. The South and Southeast Asian region has the largest surface occurrences of ultramafic regoliths in the world, but the geoecology of these outcrops is still poorly studied despite severe conservation threats. Due to the paucity of systematic plant collections in many areas and the lack of georeferenced herbarium records and databased information, it is not possible to determine the distribution of species, levels of endemism, and the species most threatened. However, site-specific studies provide insights to the ultramafic geoecology of several locations in South and Southeast Asia. The geoecology of tropical ultramafic regions differs substantially from those in temperate regions in that the vegetation at lower elevations is generally tall forest with relatively low levels of endemism. On ultramafic mountaintops, where the combined forces of edaphic and climatic factors intersect, obligate ultramafic species and hyperendemics often occur. Forest clearing, agricultural development, mining, and climate change-related stressors have contributed to rapid and unprecedented loss of ultramafic-associated habitats in the region. The geoecology of the large ultramafic outcrops of Indonesia's Sulawesi, Obi and Halmahera, and many other smaller outcrops in South and Southeast Asia, remains largely unexplored, and should be prioritised for study and conservation.

Rewiring of sIgM-Mediated Intracellular Signaling through the CD180 Toll-like Receptor

Chronic lymphocytic leukemia (CLL) development and progression are thought to be driven by unknown antigens/autoantigens through the B cell receptor (BCR) and environmental signals for survival and expansion including toll-like receptor (TLR) ligands. CD180/RP105, a membrane-associated orphan receptor of the TLR family, induces normal B cell activation and proliferation and is expressed by approximately 60% of CLL samples. Half of these respond to ligation with anti-CD180 antibody by increased activation/phosphorylation of protein kinases associated with BCR signaling. Hence CLL cells expressing both CD180 and the BCR could receive signals via both receptors. Here we investigated cross-talk between BCR and CD180-mediated signaling on CLL cell survival and apoptosis. Our data indicate that ligation of CD180 on responsive CLL cells leads to activation of either prosurvival Bruton tyrosine kinase (BTK)/phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/AKT-mediated, or proapoptotic p38 mitogen-activated protein kinase (p38MAPK)-mediated signaling pathways, while selective immunoglobulin M (sIgM) ligation predominantly engages the BTK/PI3K/AKT pathway. Furthermore, pretreatment of CLL cells with anti-CD180 redirects IgM-mediated signaling from the prosurvival BTK/PI3K/AKT toward the proapoptotic p38MAPK pathway. Thus preengaging CD180 could prevent further prosurvival signaling mediated via the BCR and, instead, induce CLL cell apoptosis, opening the door to therapeutic profiling and new strategies for the treatment of a substantial cohort of CLL patients.

Influence of land use and topography on distribution and bioaccumulation of potentially toxic metals in soil and plant leaves: A case study from Sekhukhuneland, South Africa

Potentially toxic metal (PTM) enrichment of the soil-plant system in ultramafic and mining regions is a global concern as it affects the food chain. With expanding mining industry, it is important to assess if anthropogenic factors (i.e., land use practices) have a greater influence in this regard compared to natural factors (i.e., topography). Localities in Sekhukhuneland, South Africa, were selected along an altitudinal gradient (i.e., topography: upper slope, footslope, valley and valley bottom) and a land use profile (i.e., rangelands, gardens, tailings and wastelands) to investigate the distribution of Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Sr and Zn of natural (i.e., ultramafic geology) and anthropogenic (i.e., mining) origin in surface soil and plant leaf tissue. Plant life form was considered as an additional factor to evaluate PTM accumulation in leaves. Findings revealed a wider distribution range for Cr and Ni in the surface soil. Co, Cu, Mg, Mo, Sr and Zn were accumulated (bioaccumulation factor, BAF > 1) in leaf tissue of 74% of the evaluated plants of which 83% were indigenous. Grasses, forbs, dwarf shrubs and shrubs showed the highest accumulation levels. Despite an observed trend in the distribution of PTMs in soils and plant leaves along the altitudinal gradient, no significant differences were determined among the topographic positions. Land use practices, however, differed significantly indicating anthropogenic interference as a predominant determinant of PTM enrichment of soil-plant systems. Metal tolerant dominant plants in Sekhukhuneland could be classified as metallophytes. Indigenous species, accumulators and excluders, showed prospects for phytoremediation and rehabilitation of metal contaminated sites, respectively. Concentrations of Cr and Co in food and medicinal plant leaves exceeded the international permissible limits, which highlighted the necessity to estimate human health risks for PTMs in metalliferous sites.

The edaphic factor and patterns of variation in Lasthenia californica (Asteraceae)

Transectional studies of Lasthenia californica in the Jasper Ridge Biological Preserve (Stanford University) have documented the existence of two races (A and C) based upon flavonoid chemistry, achene morphology, allozymes, and flowering time differences. The two races coexist on a serpentine outcrop and have maintained a sharply defined pattern of distribution for a period of at least 15 yr. The present study has revealed significant differences in the physical and chemical features of the soils harboring the two races. Soils at the lower ends of the transects, where race A plants grow, have higher pH, cation exchange capacity, relative water content, total ionic strength, percentage clay, and sodium and magnesium concentrations than do soils harboring race C plants at the upper ends of the transects. Soils supporting race C plants have higher calcium, potassium, and nickel concentrations and higher calcium:magnesium ratios. Plant tissue concentrations of ions were also significantly different in the two races. Race A plants accumulated sodium to concentrations three times those observed with race C plants. Plants from an additional 22 sites gave very similar results. Greenhouse studies indicated that the two races from Jasper Ridge show differential responses to ridge-top and ridge-bottom soils. Race A achenes germinated, grew to maturity, and set seed about equally in the two soils. Race C achenes germinated in both types of soils but showed significantly poorer growth and absolutely no flowering when found in the soils of race A plants. Differential responses to edaphic conditions on the ridge may contribute to the pattern of distribution observed over the years. It is suggested that race A plants are more tolerant of edaphic stress than race C plants and that physiological specialization may contribute to the present distribution of the two races throughout the species' range. It is not yet possible to state which is the more significant factor in driving this specialization, the chemistry of the soil or its physical characteristics, or whether there is interaction between the two. This is the first study to present evidence for soil/plant variation within a serpentine site. The linking of sodium levels to racial differentiation within the serpentine habitat is also a new discovery.