Chromosome 4 controls potential water use efficiency ({delta}13C) in barley

By combining the approaches of whole-shoot carbon discriminationand genetic analysis, we found that chromosome 4 controls potentialwater use efficiency (     

Monte Carlo and Poisson–Boltzmann calculations of the fraction of counterions bound to DNA

The counterion density and the condensation region around DNA have been examined as functions of both ion size and added-salt concentration using Metropolis Monte Carlo (MC) and Poisson–Boltzmann (PB) methods. Two different definitions of the “bound” and “free” components of the electrolyte ion atmosphere were used to compare these approaches. First, calculation of the ion density in different spatial regions around the polyelectrolyte molecule indicates, in agreement with previous work, that the PB equation does not predict an invariance of the surface concentration of counterions as electrolyte is added to the system. Further, the PB equation underestimates the counterion concentration at the DNA surface, compared to the MC results, the difference being greatest in the grooves, where ionic concentrations are highest. If counterions within a fixed radius of the helical axis are considered to be bound, then the fraction of polyelectrolyte charge neutralized by counterions would be predicted to increase as the bulk electrolyte concentration increases. A second categorization—one in which monovalent cations in regions where the average electrostatic potential is ledd than ?kT are considered to be bound—provides an informative basis for comparison of MC and PB with each other and with counterion-condensation theory. By this criterion, PB calculations on the B from of DNA indicate that the amount of bound counterion charge per phosphate group is about .67 and is independent of salt concentration. A particularly provocative observatiob is that when this binding criterion is used, MC calculations quantitatively reproduce the bound fraction predicated by counterion-condensation theory for all-atom models of B-DNA and A-DNA as well as for charged cylindera of varying lineat charge densities. For example, for B-DNA and A-DNA, the fractions of phosphate groups neutralized by 2 Å hard sphere counterions are 0.768 and .817, respectively. For theoretical studies, the rediys enclosing the region in which the electrostatic potential is calculated studies, the radius enclosing the region in which the electrostatic potential is calculated to be less than ?kT is advocated s a more suitable binding or condensation radius that enclosing the fraction of counterions given by (1 – ξ^?1). A comparsion of radii calculated using both of these definitions is presented. © 1994 John Wiley & Sons, Inc.     

Calcium-dependent asymmetric movement of 3H-indole-3-acetic acid across gravistimulated isolated root caps of maize

There is evidence that the cap is the initial site of lateral auxin redistribution during the gravitropic response of roots. We tested this further by comparing asymmetric auxin redistribution across the tips of gravistimulated intact roots, decapped roots, isolated root caps and isolated apical sections taken from decapped roots. Gravistimulation caused asymmetric (downward) auxin movement across the tips of intact roots and isolated root caps but not across the tips of decapped roots or across isolated apical root segments. Naphthylphthalamic acid and pyrenoylbenzoic acid, inhibitors of polar auxin transport, inhibited asymmetric auxin redistribution across gravistimulated isolated root caps and across the tips of gravistimulated intact roots. For intact roots there was a positive correlation between the extent of inhibition of assymmetric auxin redistribution by polar auxin transport inhibitors and the extent of inhibition of asymmetric calcium chelating agent, ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid, also caused parallel inhibition of asymmetric auxin redistribution and gravitropic curvature and this effect was reversed by subsequent treatment with calcium. The results support the hypothesis that the cap is a site of early development of auxin asymmetry in gravistimulated roots and that calcium plays an important role in the development of lateral auxin redistribution.     

Microatoll microbialites of Lake Clifton,Western Australia: Morphological analogues ofCryptozoön proliferum Hall,the first formally-named stromatolite

Summary The Linnaean nameCryptozo?n proliferum Hall was proposed in 1883 for a previously undescribed life-form preserved in spectacular exposures of Cambrian limestones in New York State, USA. It is now recognised that these are exposures of stromatolitic microbialites, laminated organosedimentary structures formed from interaction between a benthic microbial community (BMC) and the environment. Microbialites are neither fossil organisms nor trace fossils. These complex structures are the products of dissipative, self-organising systems involving a BMC, the external environment and the accreting microbialite. Functionally analogous BMCs of different species compositions may build similar structures in similar environments in quite separate periods. The type exposures ofCryptozo?n proliferum show objects composed of complex, concentric rings, up to a metre in diameter, that have grown laterally without any restriction other than that provided by neighbouring structures. They are not the relicts of domes truncated by penecontemporaneous erosion or Pleistocene glaciation, but depositional forms in which upward growth was restricted. Analogous modern structures occur on a reef platform along the north east shore of hyposaline Lake Clifton, Western Australia. These are tabular thrombolitic microbialites that vary lakeward across the reef platform from low, compound structures to discrete, concentric structures up to 50 cm high. The Lake Clifton forms are, in turn, morphological analogues of microatolls found on coral reef platforms. Coral microatolls are coral colonies with flat, dead tops and living perimeters in which upward growth is constrained by the sea surface. In shallow water they form circular rims of laterally growing coral around a dead centre. In deeper water they form coral heads that develop flat tops on reaching sea level. It is concluded that both the tabular microbialites of Lake Clifton and the type exposures ofCryptozo?n proliferum are analogous to coral microatolls in both form and origin-structures that have been able to grow laterally, but in which upward growth is restricted by subaerial exposure. Similar microatoll microbialites have been described from other modern environments, including Great Salt Lake, Utah, USA and Stocking Island, Exuma Cays, Bahamas. Ancient examples may include some of the “tufa” deposits of the Basal Purbeck Formation in Dorset, UK, as well as the coalesced domal bioherms of the Upper Cambrian Arrinthrunga Formation of the Georgina Basin, Central Australia, and the “washbowl” structures described from the B?tsfjord Formation of the Varanger Peninsula, north Norway. Progress towards a reliable interpretation of ancient microbialites depends on an understanding of modern environments in which analogous structures are forming. This study of microatolls has demonstrated that other sessile life forms may create colonial ecomorphs that, used cautiously, can serve as analogues for understanding the factors controlling the growth and form of microbialites. The surprising lack of pre-Pleistocene examples of microatolls recorded to date has simply been due to their lack of recognition in the geological record. They occur in sequences from the Proterozoic onwards, and provide powerful environmental indicators of ancient reef platforms on which biological growth was adjusted to contemporary sea level.