Michigan Technological University

About: Michigan Technological University is a education organization based out in Houghton, Michigan, United States. It is known for research contribution in the topics: Population & Volcano. The organization has 8023 authors who have published 17422 publications receiving 481780 citations. The organization is also known as: MTU & Michigan Tech.

cDNA cloning, sequence analysis and seasonal expression of lignin-bispecific caffeic acid/5-hydroxyferulic acid O-methyltransferase of aspen.

Abstract: A cDNA clone (Ptomt 1) encoding a lignin-bispecific O-methyltransferase (OMT) was isolated by immunological screening of a lambda gt11 expression library prepared from mRNA of developing secondary xylem of aspen (Populus tremuloides). Nucleotide sequence analysis of Ptomt1 revealed an open reading frame of 1095 bp which encodes a polypeptide with a predicted molecular weight of 39,802, corresponding well with the size of the OMT polypeptide estimated by SDS-PAGE. Authenticity of Ptomt1 was demonstrated in part by detection of OMT activity and protein in extracts of Escherichia coli cultures transformed with a plasmid construct containing Ptomt1. In addition, peptides produced from a proteolytic digest of purified OMT and sequenced by automated Edman degradation matched to portions of the deduced amino acid sequence of Ptomt1. Comparison of this sequence to amino acid sequences of OMTs of diverse species identified regions of similarity which probably contribute to the binding site of S-adenosyl-L-methionine. Tissue-specific expression was demonstrated by northern analysis which showed that Ptomt1 hybridized to a 1.7 kb transcript from aspen developing secondary xylem and by tissue printing of aspen stems in which only the outer layer of xylem bound the antibody. A biphasic pattern of gene expression and enzyme activity for OMT was observed from xylem samples of aspen during the growing season which suggests linkage between gene expression for a monolignol biosynthetic enzyme and seasonal regulation of xylem differentiation in woody plants.

Differential Expression of Two Distinct Phenylalanine Ammonia-Lyase Genes in Condensed Tannin-Accumulating and Lignifying Cells of Quaking Aspen

Abstract: Lignins, along with condensed tannins (CTs) and salicylate-derived phenolic glycosides, constitute potentially large phenylpropanoid carbon sinks in tissues of quaking aspen (Populus tremuloides Michx.). Metabolic commitment to each of these sinks varies during development and adaptation, and depends on L-phenylalanine ammonia-lyase (PAL), an enzyme catalyzing the deamination of L-phenylalanine to initiate phenylpropanoid metabolism. In Populus spp., PAL is encoded by multiple genes whose expression has been associated with lignification in primary and secondary tissues. We now report cloning two differentially expressed PAL cDNAs that exhibit distinct spatial associations with CT and lignin biosynthesis in developing shoot and root tissues of aspen. PtPAL1 was expressed in certain CT-accumulating, non-lignifying cells of stems, leaves, and roots, and the pattern of PtPAL1 expression varied coordinately with that of CT accumulation along the primary to secondary growth transition in stems. PtPAL2 was expressed in heavily lignified structural cells of shoots, but was also expressed in non-lignifying cells of root tips. Evidence of a role for Pt4CL2, encoding 4-coumarate:coenzyme A ligase, in determining CT sink strength was gained from cellular co-expression analysis with PAL1 and CTs, and from experiments in which leaf wounding increased PAL1 and 4CL2 expression as well as the relative allocation of carbon to CT with respect to phenolic glycoside, the dominant phenolic sink in aspen leaves. Leaf wounding also increased PAL2 and lignin pathway gene expression, but to a smaller extent. The absence of PAL2 in most CT-accumulating cells provides in situ support for the idea that PAL isoforms function in specific metabolic milieus.

Stability and electronic properties of atomistically-engineered 2D boron sheets

Abstract: First principles calculations based on generalized-gradient approximation to density functional theory are performed to study structural and electronic properties of the 2D sheets consisting of the elemental boron. The results find that the boron sheet can be stable and can possess metallic or semiconducting character depending on its atomistic configuration. The unique features present in the electronic properties of the buckled {1212} and reconstructed {1221} sheets would lead to a significant variation on electronic and mechanical properties of the corresponding single-walled boron nanotubes.