Novel chloroplasts and unusual cellular ultrastructure in the "resurrection" plant Myrothamnus flabellifolia Welw. (Myrothamnaceae)

The vacuoles of three "resurrection" plants, Myrothamnus flabellifolia, Anastatica hierochuntica and Selaginella dregei were found to contain large quantities of osmiophilic material which may be part of the "resurrection" mechanism. Myrothamnus differed from the others by having mitochondria, and possibly plastids, which are separated from the remainder of the cytoplasm by sheaths or membranes during desiccation. Upon "resurrection" these barriers appear to be perforated and explain in part the faster rate of "resurrection" in Myrothamnus than in other "resurrection" plants. The chloroplasts of Myrothamnus are remarkable in that they possess "staircase" granum stacks of a type not previously described in any other plant tissue.     

Survival and recovery of perennial forage grasses under prolonged Mediterranean drought: I. Growth, death, water relations and solute content in herbage and stubble

Swards of Dactylis glomerata cultivars (cvs) KM2 and Lutetia and of Lolium perenne cvs Aurora and Vigor were grown under full irrigation or prolonged summer drought (80 d) in a field experiment in the South of France.
After irrigation was withheld, leaf extension rates of all cvs fell by 90% within 9–12 d, and rapid scorching of laminae followed. Tiller mortality at the end of the drought was very different in the cocksfoot cvs (4% for KM2 and 76% for Lutetia) and intermediate (41%) for both ryegrass cvs. Following re-watering, rates of herbage regrowth were closely correlated with tiller survival. Measured minerals contributed c . 0·52 MPa to osmotic potential in all treatments, whereas water-soluble carbohydrates (WSC) contributed 0·25 MPa under irrigation and 0·46 MPa during drought.
There was no systematic difference between the two species for summer survival under severe drought, but large differences between the cocksfoot cvs. The traits most strongly associated with superior survival were: (a) a deep root system and greater water uptake at depth; (b) low water and osmotic potentials in surviving laminae, i.e. better tolerance to dehydration; (c) large pool-size of WSC reserves (fructans having degree of polymerization >4) in entire tiller bases (stubble); (d) low accumulation of proline in stubble; (e) rapid nitrogen uptake after rewatering.     

Short‐term effects of CO2 and O2 on citrate metabolism in illuminated leaves

Although there is now a considerable literature on the inhibition of leaf respiration (CO₂ evolution) by light, little is known about the effect of other environmental conditions on day respiratory metabolism. In particular, CO₂ and O₂ mole fractions are assumed to cause changes in the tricarboxylic acid pathway (TCAP) but the amplitude and even the direction of such changes are still a matter of debate. Here, we took advantage of isotopic techniques, new simple equations and instant freeze sampling to follow respiratory metabolism in illuminated cocklebur leaves (Xanthium strumarium L.) under different CO₂/O₂ conditions. Gas exchange coupled to online isotopic analysis showed that CO₂ evolved by leaves in the light came from ‘old’ carbon skeletons and there was a slight decrease in ¹³C natural abundance when [CO₂] increased. This suggested the involvement of enzymatic steps fractionating more strongly against ¹³C and thus increasingly limiting for the metabolic respiratory flux as [CO₂] increased. Isotopic labelling with ¹³C₂‐2,4‐citrate lead to ¹³C‐enriched Glu and 2‐oxoglutarate (2OG), clearly demonstrating poor metabolism of citrate by the TCAP. There was a clear relationship between the ribulose‐1,5‐bisphosphate oxygenation‐to‐carboxylation ratio (v_o/v_c) and the ¹³C commitment to 2OG, demonstrating that 2OG and Glu synthesis via the TCAP is positively influenced by photorespiration.     

fastruct: model‐based clustering made faster

Bayesian model‐based clustering programs have gained increased popularity in studies of population structure since the publication of the software structure . These programs are generally acknowledged as performing well, but their running‐time may be prohibitive. fastruct is a non‐Bayesian implementation of the classical model with no‐admixture uncorrelated allele frequencies. This new program relies on the expectation–maximization principle, and produces assignment rivalling other model‐based clustering programs. In addition, it can be manyfold faster than Bayesian implementations. The software consists of a command‐line engine, which is suitable for batch analysis of data, and a graphical interface, which is convenient for exploring data.     

Trophic level modulates carabid beetle responses to habitat and landscape structure: a pan‐European study

1. Anthropogenic pressures have produced heterogeneous landscapes expected to influence diversity differently across trophic levels and spatial scales. 2. We tested how activity density and species richness of carabid trophic groups responded to local habitat and landscape structure (forest percentage cover and habitat richness) in 48 landscape parcels (1 km²) across eight European countries. 3. Local habitat affected activity density, but not species richness, of both trophic groups. Activity densities were greater in rotational cropping compared with other habitats; phytophage densities were also greater in grassland than forest habitats. 4. Controlling for country and habitat effects, we found general trophic group responses to landscape structure. Activity densities of phytophages were positively correlated, and zoophages uncorrelated, with increasing habitat richness. This differential functional group response to landscape structure was consistent across Europe, indicated by a lack of a country × habitat richness interaction. Species richness was unaffected by landscape structure. 5. Phytophage sensitivity to landscape structure may arise from relative dependency on seed from ruderal plants. This trophic adaptation, rare in Carabidae, leads to lower phytophage numbers, increasing vulnerability to demographic and stochastic processes that the greater abundance, species richness, and broader diet of the zoophage group may insure against.     

Free Amino-acids in the Endosperm of the Developing Coconut (Cocos nucifera)

The free amino-acids in the sap flowing from the incised inflorescenceof the coconut palm (Cocos nucifera) and in the liquid and solidendosperm of the coconut at various stages of development (4–12months from the time of opening of the spathe) have been studiedby paper and ion-exchange chromatography. The chief amino-acids in the sap were in decreasing order ofmagnitude: glutamic acid, aspartic acid, glutamine, serine,and asparagine. Smaller amounts of threonine, alanine, -aminobutyricacid, proline, valine, arginine, and tryptophan were found,along with traces of tyrosine, ß-alanine, lysine,histidine, leucine, isoleucine, and methionine. The chief amino-acids in the liquid endosperm of the nut until6 months of age were alanine, glutamic acid, serine, valine,and proline with smaller amounts of asparagine, aspartic acid,glycine, threonine, leucine, isoleucine, and glutamine. Thealanine, glutamic acid, proline, and -aminobutyric acid contentsof the liquid endosperm increased greatly as the solid endospermwas laid down, ultimately forming about 75 per cent. of thetotal free amino-acids. Nineteen amino-acids were detected atthe 8–10-month stage. -Aminobutyric acid appears in the liquid endosperm soon afterthe solid endosperm commences to form, and increases strikinglythereafter. It was also found in the free amino-acids of thesolid endosperm at all stages of development. This amino-acidwas not found in the acid hydrolysate of coconut globulin. The free amino-acids in the solid endosperm were found to reflectqualitatively the free amino-acid composition of the correspondingliquid endosperm. In addition, ß-alanine, -aminobutyricacid, phenylalanine, and tryptophan were present in small amounts.Alanine, serine, glutamic acid, and -aminobutyric acid, increasedwith age of the nut while the others increased up to 6 monthsand then decreased, only traces being found at maturity exceptin the case of aspartic acid, proline, and threonine. Twenty-oneamino-acids were detected in the free amino-acids of the solidendosperm. The source of the free amino-acids in the liquid endosperm andthe possible use of these amino-acids for protein synthesisin the coconut are briefly discussed.