Tansley Review No. 106

For three decades, hypotheses relating to the occurrence and function of cyclic nucleotides in higher plants have been highly controversial. Although cyclic nucleotides had been shown to have key regulatory roles in animals and bacteria, investigations with higher plants in the 1970s and early 1980s were criticized on the basis of (i) a lack of specificity of effects apparently elicited by cyclic nucleotides, (ii) the equivocal identification of putative endogenous cyclic nucleotides and (iii) ambiguity in the identification of enzymes connected with cyclic nucleotide. More recent evidence based on more rigorous identification procedures has demonstrated conclusively the presence of cyclic nucleotides, nucleotidyl cyclases and cyclic nucleotide phosphodiesterases in higher plants, and has identified plant processes subject to regulation by cyclic nucleotides. Here we review the history of the debate, the recent evidence establishing the presence of these compounds and their role; future research objectives are discussed.     

Agra, arboreal beetles of Neotropical forests: feisthameli group systematics (Carabidae)

Abstract. This paper is the sixth in a series designed to cover taxonomically all species groups of Agra , whose cumulative ranges extend from southernmost Texas to northernmost Argentina. The feisthameli, mixta, virgata and ohausi groups constitute the Feisthameli Section of the genus. The feisthameli group consists of seventeen species which have a composite range extending from Guatemala to Bolivia and southeastern Brazil.
Among this group, nine new species are described from the following type localities: chapada (BRAZIL, Chapada de GuimaráTes), phite (BOLIVIA, Provencia de Gutierrez), para (BRAZIL, Pará), rubra (BRAZIL, Para, SáTo Félix do Xingu), dation (BRAZIL, Minas Gerais, Teófilo Otoni), tuitis (PERU, San Martin, Tarapoto), memnon (BRAZIL, Espírito Santo, SáTo Mateus), lata (BOLIVIA, Santa Cruz), magdalena (COLOMBIA, Santander). A dot map illustrates the range of each taxon.
Distribution and relationships are discussed in general, but detailed cladistic analysis is deferred until taxonomy of other sections is completed. Species distributions correspond in part to pleistocene refuges suggested by other authors based on other classes of organisms; however, more species occur outside such centres than in them.     

Comparative Spiralian Oogenesis--Structural Aspects: An Overview

Considerable variety exists in ovarian structure and cellularinteraction in spiralians. During their development the eggsof Dwpatra cuprea, are associated with nurse cells; there areno follicle cells in this species. The nurse cells have prominentnuclei and connect to oocytes via cytoplasmic bridges throughwhich ribosomes, mitochondria and other inclusions pass. Morecommonly, follicle cells surround a portion of, or entire, oocytesin many species of spiralians. Usually, as in Ilyanassa, theyhave a well developed compliment of organelles. The structureand distribution of organelles within follicle cells impliesthat they are functionally active, but precisely in what mannerduring oogenesis is poorly understood. Other cell types, suchas Leydig and interstitial cells also seem to play a role inoogenesis. Within the oocyte, a host of components includingyolk, lipid, mitochondria, ribosomes, membranous cisternae,cortical granules, etc. are accumulated. Autosynthetic yolkformation is prevalent among spiralians. Surface differentiationincludes microvillar development. This may be uniform in someeggs or restricted to certain regions (e.g., the animal hemisphere)in other oocytes. Oocyte-follicle cell interactions change duringoogenesis. The topographical association of the oocyte withother ovarian cells influences subsequent animal-vegetal polarityand other ooplasmic differences. Examples of ooplasmic localizationsare discussed. Conventional EM has revealed no unusual corticalstructure in many oocytes although occasionally microtubulesand microfilaments are present.     

Structural and functional characterization of a novel, host penetration-related pectate lyase from the potato cyst nematode Globodera rostochiensis

The cell wall, a strong extraprotoplasmic layer surrounding plant cells that mainly consists of a variety of polysaccharides, constitutes a major barrier for potential parasites. Plant-parasitic nematodes are well equipped to overcome this barrier as they produce and secrete cell-wall-degrading enzymes. Expression profiling of various life stages of the potato cyst nematode Globodera rostochiensis revealed a novel pectate lyase gene ( Gr-pel2 , 759 bp). The Gr-PEL2 protein showed highest similarity to pectate lyases from the facultative plant-parasitic nematodes Bursaphelenchus mucronatus and B. xylophilus and the soil-inhabiting saprophytic Streptomyces and Frankia species (i.e. 40–42% identity and 58–60% similarity), whereas only a remote relatedness to the previously identified Gr-PEL1 was observed (i.e. 28% identity and 43% similarity). Transient expression of Gr-pel2 in leaves of Nicotiana benthamiana resulted in severe malformations of the infiltrated tissues, not relating to maceration and soft rot symptoms. Ca²⁺ is known to be essential for pectate lyase activity, and the most likely calcium-binding site was identified in the Gr-PEL2 protein by combining homology modelling of the three-dimensional structure, site-directed mutagenesis and transient expression in leaves. A highly charged cleft in Gr-PEL2, which is likely to be involved in substrate binding and which is also significantly more hydrophobic in Gr-PEL1, was shown to be essential for protein activity. Our results underline the broad spectrum of pectate lyases and cell-wall-degrading enzymes necessary for successful parasitism by cyst nematodes.     

Does the disturbance hypothesis explain the biomass increase in basin‐wide Amazon forest plot data?

Positive aboveground biomass trends have been reported from old-growth forests across the Amazon basin and hypothesized to reflect a large-scale response to exterior forcing. The result could, however, be an artefact due to a sampling bias induced by the nature of forest growth dynamics. Here, we characterize statistically the disturbance process in Amazon old-growth forests as recorded in 135 forest plots of the RAINFOR network up to 2006, and other independent research programmes, and explore the consequences of sampling artefacts using a data-based stochastic simulator. Over the observed range of annual aboveground biomass losses, standard statistical tests show that the distribution of biomass losses through mortality follow an exponential or near-identical Weibull probability distribution and not a power law as assumed by others. The simulator was parameterized using both an exponential disturbance probability distribution as well as a mixed exponential–power law distribution to account for potential large-scale blowdown events. In both cases, sampling biases turn out to be too small to explain the gains detected by the extended RAINFOR plot network. This result lends further support to the notion that currently observed biomass gains for intact forests across the Amazon are actually occurring over large scales at the current time, presumably as a response to climate change.     

Serum Binding of Calcium and the Red Cell Membrane in Cystic Fibrosis

THERE is evidence for a factor in the serum of cystic fibrosis patients which may play a role in the pathological manifestation of the genetic syndrome: serum of patients with cystic fibrosis alters the cilia movement of rabbit trachea in vitro¹ and of oyster cilia². This activity is apparently associated with the immunoglobulin fraction^3,4. Balfe et al.⁵ reported a modification of sodium flux in red cells obtained from patients with cystic fibrosis. In the course of searching for evidence of interaction of serum with red cells in cystic fibrosis, we found that there is a substantial increase in serum calcium binding in patients with cystic fibrosis. This seems to be associated with a modified membrane protein electrophoretic pattern of cystic fibrosis red cells in specified experimental conditions.