Stable isotopes in leaf water of terrestrial plants

Leaf water contains naturally occurring stable isotopes of oxygen and hydrogen in abundances that vary spatially and temporally. When sufficiently understood, these can be harnessed for a wide range of applications. Here, we review the current state of knowledge of stable isotope enrichment of leaf water, and its relevance for isotopic signals incorporated into plant organic matter and atmospheric gases. Models describing evaporative enrichment of leaf water have become increasingly complex over time, reflecting enhanced spatial and temporal resolution. We recommend that practitioners choose a model with a level of complexity suited to their application, and provide guidance. At the same time, there exists some lingering uncertainty about the biophysical processes relevant to patterns of isotopic enrichment in leaf water. An important goal for future research is to link observed variations in isotopic composition to specific anatomical and physiological features of leaves that reflect differences in hydraulic design. New measurement techniques are developing rapidly, enabling determinations of both transpired and leaf water δ¹⁸O and δ²H to be made more easily and at higher temporal resolution than previously possible. We expect these technological advances to spur new developments in our understanding of patterns of stable isotope fractionation in leaf water.     

Tim/Timeless,a member of the replication fork protection complex,operates with the Warsaw breakage syndrome DNA helicase DDX11 in the same fork recovery pathway

We present evidence that Tim establishes a physical and functional interaction with DDX11, a super-family 2 iron-sulfur cluster DNA helicase genetically linked to the chromosomal instability disorder Warsaw breakage syndrome. Tim stimulates DDX11 unwinding activity on forked DNA substrates up to 10-fold and on bimolecular anti-parallel G-quadruplex DNA structures and three-stranded D-loop approximately 4–5-fold. Electrophoretic mobility shift assays revealed that Tim enhances DDX11 binding to DNA, suggesting that the observed stimulation derives from an improved ability of DDX11 to interact with the nucleic acid substrate. Surface plasmon resonance measurements indicate that DDX11 directly interacts with Tim. DNA fiber track assays with HeLa cells exposed to hydroxyurea demonstrated that Tim or DDX11 depletion significantly reduced replication fork progression compared to control cells; whereas no additive effect was observed by co-depletion of both proteins. Moreover, Tim and DDX11 are epistatic in promoting efficient resumption of stalled DNA replication forks in hydroxyurea-treated cells. This is consistent with the finding that association of the two endogenous proteins in the cell extract chromatin fraction is considerably increased following hydroxyurea exposure. Overall, our studies provide evidence that Tim and DDX11 physically and functionally interact and act in concert to preserve replication fork progression in perturbed conditions.