Key changes in gene expression identified for different stages of C4 evolution in Alloteropsis semialata.

C4 photosynthesis is a complex trait that boosts productivity in tropical conditions. Compared with C3 species, the C4 state seems to require numerous novelties, but species comparisons can be confounded by long divergence times. Here, we exploit the photosynthetic diversity that exists within a single species, the grass Alloteropsis semialata, to detect changes in gene expression associated with different photosynthetic phenotypes. Phylogenetically informed comparative transcriptomics show that intermediates with a weak C4 cycle are separated from the C3 phenotype by increases in the expression of 58 genes (0.22% of genes expressed in the leaves), including those encoding just three core C4 enzymes: aspartate aminotransferase, phosphoenolpyruvate carboxykinase, and phosphoenolpyruvate carboxylase. The subsequent transition to full C4 physiology was accompanied by increases in another 15 genes (0.06%), including only the core C4 enzyme pyruvate orthophosphate dikinase. These changes probably created a rudimentary C4 physiology, and isolated populations subsequently improved this emerging C4 physiology, resulting in a patchwork of expression for some C4 accessory genes. Our work shows how C4 assembly in A. semialata happened in incremental steps, each requiring few alterations over the previous step. These create short bridges across adaptive landscapes that probably facilitated the recurrent origins of C4 photosynthesis through a gradual process of evolution.

Mechanism of 1,6-addition reactions of organocuprates: detailed NMR spectroscopic study of a cuprate-enyne pi complex.

A detailed NMR-spectroscopic study of the multiply 13C-labeled cuprate pi complexes 2, 2a and 2b was carried out. The 13C,13C coupling constants observed were interpreted in terms of a deformation of the cuprate-alkene complex from the expected idealized square plane. This conclusion is in agreement with NOESY and ROESY data acquired with unlabeled material.

The allyl complex di-&mgr;-chloro-bis

The title compound, di-&mgr;-chloro-bis[(2,3,4-eta)-ethyl 6, 6-dimethyl-5-oxohept-2-enoato]palladium(II), [Pd(2)Cl(2)(C(11)H(17)O(3))(2)], is a binuclear chloro-bridged palladium allyl complex that was obtained serendipitously From the reaction of 6,6-dimethyl-2-hepten-4-ynoate with Na(2)PdCl(4) in water-containing alcohol. The allyl group is substituted with an ester and a tert-butylcarboxy group. The dimeric molecules link via C-H.O contacts into a two-dimensional network parallel to the bc plane.