Evolution of trees and mycorrhizal fungi intensifies silicate mineral weathering

Forested ecosystems diversified more than 350 Ma to become major engines of continental silicate weathering, regulating the Earth''s atmospheric carbon dioxide concentration by driving calcium export into ocean carbonates. Our field experiments with mature trees demonstrate intensification of this weathering engine as tree lineages diversified in concert with their symbiotic mycorrhizal fungi. Preferential hyphal colonization of the calcium silicate-bearing rock, basalt, progressively increased with advancement from arbuscular mycorrhizal (AM) to later, independently evolved ectomycorrhizal (EM) fungi, and from gymnosperm to angiosperm hosts with both fungal groups. This led to ‘trenching’ of silicate mineral surfaces by AM and EM fungi, with EM gymnosperms and angiosperms releasing calcium from basalt at twice the rate of AM gymnosperms. Our findings indicate mycorrhiza-driven weathering may have originated hundreds of millions of years earlier than previously recognized and subsequently intensified with the evolution of trees and mycorrhizas to affect the Earth''s long-term CO₂ and climate history.     

Macrophage proteases can modify low density lipoproteins to increase their uptake by macrophages

When low density lipoprotein (LDL) was incubated with sonicated macrophages at acidic pH, its protein moiety was partially degraded by cathepsins B and D. The reisolated LDL was taken up by intact macrophages up to about 20 times as fast as control LDL. LDL proteolysis and its enhanced uptake could be inhibited almost entirely by the selective protease inhibitors leupeptin and pepstatin. If macrophages in atherosclerotic lesions were to release acidic proteases (either by exocytosis or following cell death) and these were to modify LDL, this may help to explain why so much cholesteryl ester accumulates in these cells.