Tracing carbon and oxygen isotope signals from newly assimilated sugars in the leaves to the tree-ring archive

The analysis of δ ¹³C and δ ¹⁸O in tree-ring archives offers retrospective insights into environmental conditions and ecophysiological processes. While photosynthetic carbon isotope discrimination and evaporative oxygen isotope enrichment are well understood, we lack information on how the isotope signal is altered by downstream metabolic processes.
In Pinus sylvestris , we traced the isotopic signals from their origin in the leaf water ( δ ¹⁸O) or the newly assimilated carbon ( δ ¹³C), via phloem sugars to the tree-ring, over a time-scale that ranges from hours to a growing season.
Seasonally, variable ¹³C enrichment of sugars related to phloem loading and transport did lead to uncoupling between δ ¹³C in the tree-ring, and the c _i/ c _a ratio at the leaf level. In contrast, the oxygen isotope signal was transferred from the leaf water to the tree-ring with an expected enrichment of 27‰, with time-lags of approximately 2 weeks and with a 40% exchange between organic oxygen and xylem water oxygen during cellulose synthesis.
This integrated overview of the fate of carbon and oxygen isotope signals within the model tree species P. sylvestris provides a novel physiological basis for the interpretation of δ ¹³C and δ ¹⁸O in tree-ring ecology.     

Inhibition of Spore Germination in the Cellular Slime Moulds

The phenomenon of auto-inhibition of spore germination has beendemonstrated in the slime moulds Dictyostelium purpureum, strainno. 2; Dictyostelium discoideum, strain no. 1; Dictyosteliummucoroides, strain no. 2; and Polysphondy-Iium violeceum, strainno. 6. A water-soluble substance present in spores was shownto cause this self-inhibition. The substance was isolated fromeach species studied. Evidence as presented indicates that thesame substance occurs in each species of Dictyostelium, butthat it differs from that found in Pv6. An attempt was alsomade to relate this inhibitory substance to the phenomenon of'differential inhibition' in Dp2, Dd, Dm2, and Pu6. An explanationbased on evidence for differential sensitivity to a common inhibitorof spore germination in Dictyostelium and an inhibition in otherthan the spore stage in Pu6 is presented. Apparent differentialproduction of a common inhibitor in Dictyostelium is also reported.     

A juvenile plesiosaur (Plesiosauria: Reptilia) from the Lower Lias (Hettangian: Lower Jurassic) of Lyme Regis, England: a pliosauroid-plesiosauroid intermediate?

A partial skull and skeleton of a small, juvenile plesiosaur, part of the historically important Philpot Collection from Lyme Regis, England, is described. It is assigned tentatively to EwycMdus arcuatus (Owen, 1840) and has a mosaic of features which make it difficult to place in a superfamily. The characters of the posterior elements of the skull and post-dentary bones are close to those expected in a plesiosauroid, whereas the anterior dentition and symphysis of the lower jaw are more typical of a pliosauroid. The specimen is placed in the Pliosauroidea pending a phylogenetic revision of the Lower Jurassic Plesiosauria. From a reconstruction of the dentition and jaw-closing muscles, it is thought to have been a predator on soft-bodied or lighdy armoured prey, such as belemnoids, ammonites or small fish.     

Weighted finite population sampling to maximize entropy

Attention is drawn to a method of sampling a finite populationof N units with unequal probabilities and without replacement.The method was originally proposed by Stern & Cover (1989)as a model for lotteries. The method can be characterized asmaximizing entropy given coverage probabilities _i, or equivalentlyas having the probability of a selected sample proportionalto the product of a set of ‘weights’ w_i. We showthe essential uniqueness of the w_i given the _i. We present twomethods for stepwise selection of sampling units, and correspondingschemes for removal of units that can be used in connectionwith sample rotation. Inclusion probabilities of any order canbe written explicitly in closed form. Second-order inclusionprobabilities _ij satisfy the condition O < _ij < _ij, whichguarantees Yates & Grundy‘s variance estimator tobe unbiased, definable for all samples and always nonnegativefor any sample size.     

Phycobiliprotein fluorescence of Nostoc punctiforme changes during the life cycle and chromatic adaptation: characterization by spectral confocal laser scanning microscopy and spectral unmixing

Many cyanobacteria are highly adaptable to light quality, and many species undergo a complex life cycle. In this study we show that adaptive changes in the photosynthetic apparatus of cyanobacteria are not only caused by environmental, but also by developmental factors. Spectral confocal laser scanning microscopy (CLSM) was used to analyse in vivo the fluorescence spectra of the photosynthetic pigments chlorophyll a (Chl a), allophycocyanin (APC), phycocyanin (PC) and phycoerythrin (PE) of two Nostoc punctiforme strains. Changes in pigment fluorescence emission occurred in different developmental stages. Strain 1:1-26 showed an emission maximum at 674 nm in motile hormogonia stages, whereas vegetative stages showed maxima at 658 and 575 nm. These changes were not caused by chromatic adaptation. In contrast, the second strain (1:1-26lg) showed distinct fluorescence spectra, pigment localization and clear chromatic adaptation in red light. When these properties are known, both strains can be easily distinguished by the spectral CLSM method, which also allows the localization of the pigments within single cells. To calculate the contribution of individual phycobiliproteins to the observed changes, fluorescence spectra were analysed by spectral unmixing. This allowed the mathematical estimation of fluorescence shares for the individual phycobiliproteins in different developmental stages and both before and after chromatic adaptation. It is concluded that care should be taken when characterizing cyanobacteria by differences in pigment fluorescence, because these differences are influenced not only by chromatic adaptation, but also developmental stages. Spectral CLSM offers a powerful method to study the phycobiliprotein composition in vivo.