Life Sciences Commons^™

Disentangling Above‐ And Below‐Ground Competition Between Lianas And Trees In A Tropical Forest, Stefan A. Schnitzer, Mirjam E. Kuzee, Frans Bongers

Biological Sciences Faculty Research and Publications

1. Light is thought to be the most limiting resource in tropical forests, and thus above‐ground competition is commonly accepted as the mechanism that structures these communities. In many tropical forests, trees compete not only with other trees, but also with lianas, which compete aggressively for below‐ground resources and thus may limit tree growth and regeneration.
2. Using a replicated experiment, we tested the relative strengths of above‐ and below‐ground competition from lianas on tree saplings in a disturbed forest in Côte d’Ivoire with a heterogeneous canopy and relatively high light penetration. We planted seedlings of three tree species and subjected them …

Modulation Of Tyramine Signaling By Osmolality In An Insect Secretory Epithelium, Edward M. Blumenthal

Biological Sciences Faculty Research and Publications

The control of water balance in multicellular organisms depends on absorptive and secretory processes across epithelia. This study concerns the effects of osmolality on the function of the Malpighian tubules (MTs), a major component of the insect excretory system. Previous work has shown that the biogenic amine tyramine increases transepithelial chloride conductance and urine secretion in Drosophila MTs. This study demonstrates that the response of MTs to tyramine, as measured by the depolarization of the transepithelial potential (TEP), is modulated by the osmolality of the surrounding medium. An increase in osmolality caused decreased tyramine sensitivity, whereas a decrease in osmolality …

The Let-7 Microrna Family Members Mir-48, Mir-84, And Mir-241 Function Together To Regulate Developmental Timing In Caenorhabditis Elegans, Allison L. Abbott, Ezequiel Alvarez-Saavedra, Eric A. Miska, Nelson C. Lau, David P. Bartel, H. Robert Horvitz, Victor R. Ambros

Biological Sciences Faculty Research and Publications

The microRNA let-7 is a critical regulator of developmental timing events at the larval-to-adult transition in C. elegans. Recently, microRNAs with sequence similarity to let-7 have been identified. We find that doubly mutant animals lacking the let-7 family microRNA genes mir-48 and mir-84 exhibit retarded molting behavior and retarded adult gene expression in the hypodermis. Triply mutant animals lacking mir-48, mir-84, and mir-241 exhibit repetition of L2-stage events in addition to retarded adult-stage events. mir-48, mir-84, and mir-241 function together to control the L2-to-L3 transition, likely by base pairing to complementary sites in the …

Rna Turnover: Unexpected Consequences Of Being Tailed, James T. Anderson

Biological Sciences Faculty Research and Publications

In eukaryotic cells, the 3′ poly(A) tails found on mRNA influence their stability and translation. The discovery of a second nuclear poly(A) polymerase complex has fueled a series of reports defining a new and unexpected role for 3′ end poly(A) tails in the nuclear surveillance and turnover of noncoding RNAs and intergenic mRNAs of unknown function.

A Mechanistic Explanation For Global Patterns Of Liana Abundance And Distribution, Stefan A. Schnitzer

Biological Sciences Faculty Research and Publications

One of the main goals in ecology is determining the mechanisms that control the abundance and distribution of organisms. Using data from 69 tropical forests worldwide, I demonstrate that liana (woody vine) abundance is correlated negatively with mean annual precipitation and positively with seasonality, a pattern precisely the opposite of most other plant types. I propose a general mechanistic hypothesis integrating both ecological and ecophysiological approaches to explain this pattern. Specifically, the deep root and efficient vascular systems of lianas enable them to suffer less water stress during seasonal droughts while many competitors are dormant, giving lianas a competitive advantage …

Membrane Potential Oscillations In Reticulospinal And Spinobulbar Neurons During Locomotor Activity, James F. Einum, James T. Buchanan

Biological Sciences Faculty Research and Publications

Feedback from the spinal locomotor networks provides rhythmic modulation of the membrane potential of reticulospinal (RS) neurons during locomotor activity. To further understand the origins of this rhythmic activity, the timings of the oscillations in spinobulbar (SB) neurons of the spinal cord and in RS neurons of the posterior and middle rhombencephalic reticular nuclei were measured using intracellular microelectrode recordings in the isolated brain stem-spinal cord preparation of the lamprey. A diffusion barrier constructed just caudal to the obex allowed induction of locomotor activity in the spinal cord by bath application of an excitatory amino acid to the spinal bath. …

Water Uptake And Transport In Lianas And Co-Occurring Trees Of A Seasonally Dry Tropical Forest, Jose Luis Andrade, Frederick C. Meinzer, Stefan A. Schnitzer

Biological Sciences Faculty Research and Publications

Water uptake and transport were studied in eight liana species in a seasonally dry tropical forest on Barro Colorado Island, Panama. Stable hydrogen isotope composition (δD) of xylem and soil water, soil volumetric water content (θ_v), and basal sap flow were measured during the 1997 and 1998 dry seasons. Sap flow of several neighboring trees was measured to assess differences between lianas and trees in magnitudes and patterns of daily sap flow. Little seasonal change in θ_v was observed at 90–120 cm depth in both years. Mean soil water δD during the dry season was −19‰ at …

Role Of A Conserved Glutamate Residue In The Escherichia Coli Seca Atpase Mechanism, Christopher R. Zito, Edwin Antony, John F. Hunt, Donald B. Oliver, Manju M. Hingorani

Biological Sciences Faculty Research and Publications

Escherichia coli SecA uses ATP to drive the transport of proteins across cell membranes. Glutamate 210 in the “DEVD” Walker B motif of the SecA ATP-binding site has been proposed as the catalytic base for ATP hydrolysis (Hunt, J. F., Weinkauf, S., Henry, L., Fak, J. J., McNicholas, P., Oliver, D. B., and Deisenhofer, J. (2002) Science 297, 2018–2026). Consistent with this hypothesis, we find that mutation of glutamate 210 to aspartate results in a 90-fold reduction of the ATP hydrolysis rate compared with wild type SecA, 0.3 s^–1versus 27 s^–1, respectively. SecA-E210D also releases ADP …

Dimeric Novel Hsp40 Is Incorporated Into The Radial Spoke Complex During The Assembly Process In Flagella, Chun Yang, Mark M. Compton, Pinfen Yang

Biological Sciences Faculty Research and Publications

The radial spoke is a stable structural complex in the 9 + 2 axoneme for the control of flagellar motility. However, the spokes in Chlamydomonas mutant pf24 are heterogeneous and unstable, whereas several spoke proteins are reduced differentially. To elucidate the defective mechanism, we clone RSP16, a prominent spoke protein diminished in pf24 axonemes. Unexpectedly, RSP16 is a novel HSP40 member of the DnaJ superfamily that assists chaperones in various protein-folding-related processes. Importantly, RSP16 is uniquely excluded from the 12S spoke precursor complex that is packaged in the cell body and transported toward the flagellar tip to be …

Functional Analysis Of Subunit E Of The F1FO-Atp Synthase Of The Yeast Saccharomyces Cerevisiae: Importance Of The N-Terminal Membrane Anchor Region, Valerie Everard-Gigot, Cory D. Dunn, Brigid M. Dolan, Susanne Brunner, Robert E. Jensen, Rosemary A. Stuart

Biological Sciences Faculty Research and Publications

Mitochondrial F₁F_o-ATP synthase complexes do not exist as physically independent entities but rather form dimeric and possibly oligomeric complexes in the inner mitochondrial membrane. Stable dimerization of two F₁F_o-monomeric complexes involves the physical association of two membrane-embedded F_o-sectors. Previously, formation of the ATP synthase dimeric-oligomeric network was demonstrated to play a critical role in modulating the morphology of the mitochondrial inner membrane. In Saccharomyces cerevisiae, subunit e (Su e) of the F_o-sector plays a central role in supporting ATP synthase dimerization. The Su e protein is anchored …

Elimination Of Foreign Dna During Somatic Differentiation In Tetrahymena Thermophila Shows Position Effect And Is Dosage Dependent, Yifan Liu, Xiaoyuan Song, Martin A. Gorovsky, Kathleen M. Karrer

Biological Sciences Faculty Research and Publications

In the ciliate Tetrahymena thermophila, approximately 15% of the germ line micronuclear DNA sequences are eliminated during formation of the somatic macronucleus. The vast majority of the internal eliminated sequences (IESs) are repeated in the micronuclear genome, and several of them resemble transposable elements. Thus, it has been suggested that DNA elimination evolved as a means for removing invading DNAs. In the present study, bacterial neo genes introduced into the germ line micronuclei were eliminated from the somatic genome. The efficiency of elimination from two different loci increased dramatically with the copy number of the neo genes in the …

The Bipartite Structure Of The Trna M1A58 Methyltransferase From S. Cerevisiae Is Conserved In Humans, Sarah G. Ozanick, Annette M. Krecic, Joshua Andersland, James T. Anderson

Biological Sciences Faculty Research and Publications

Among all types of RNA, tRNA is unique given that it possesses the largest assortment and abundance of modified nucleosides. The methylation at N₁ of adenosine 58 is a conserved modification, occurring in bacterial, archaeal, and eukaryotic tRNAs. In the yeast Saccharomyces cerevisiae, the tRNA 1-methyladenosine 58 (m¹A58) methyltransferase (Mtase) is a two-subunit enzyme encoded by the essential genes TRM6 (GCD10) and TRM61 (GCD14). While the significance of many tRNA modifications is poorly understood, methylation of A58 is known to be critical for maintaining the stability of initiator tRNA^Met in yeast. …