Purdue University

About: Purdue University is a education organization based out in West Lafayette, Indiana, United States. It is known for research contribution in the topics: Population & Context (language use). The organization has 73219 authors who have published 163563 publications receiving 5775236 citations. The organization is also known as: Purdue & Purdue-West Lafayette.

A Unified Effort to Fight an Enemy of Wheat and Barley: Fusarium Head Blight.

Abstract: Wheat and barley are critical food and feed crops around the world. Wheat is grown on more land area worldwide than any other crop. In the United States, production of wheat and barley contributes to domestic food and feed use, and contributes to the export market and balance of trade. Fifteen years ago, Plant Disease published a feature article titled “Scab of wheat and barley: A re-emerging disease of devastating impact”. That article described the series of severe Fusarium head blight (FHB) epidemics that occurred in the United States and Canada, primarily from 1991 through 1996, with emphasis on the unparalleled economic and sociological impacts caused by the 1993 FHB epidemic in spring grains in the Northern Great Plains region. Earlier publications had dealt with the scope and damage caused by this disease in the United States, Canada, Europe, and China. Reviews published after 1997 further described this disease and its impact on North American grain production in the 1990s. This article r...

The Shikimate Pathway: Early Steps in the Biosynthesis of Aromatic Compounds.

Abstract: The shikimate pathway was discovered as the biosynthetic route to the aromatic amino acids phenylalanine, tyrosine, and tryptophan through the classic studies of Bernhard Davis and David Sprinson and their collaborators. This pathway has been found only in microorganisms and plants. Phenylalanine and tryptophan are essential components of animal diets, and animals synthesize tyrosine in a single step from phenylalanine. Thus, with respect to plant specificity, the shikimate pathway is a bit more widespread than nitrogen fixation or photosynthesis but less ubiquitous than, for example, nitrogen assi milat ion . Bacteria spend >90% of their total metabolic energy on protein biosynthesis. Consequently, the bacterial shikimate pathway serves almost exclusively to synthesize the aromatic amino acids (Herrmann, 1983; Pittard, 1987). In contrast, higher plants use these amino acids not only as protein building blocks but also, and in even greater quantities, as precursors for a large number of secondary metabolites, among them plant pigments, compounds to defend against insects and other herbivores (see Dixon and Paiva, 1995, this issue), UV light protectants, and, most importantly, lignin (Bentley, 1990; Singh et al., 1991; see Whetten and Sederoff, 1995, this issue). Under normal growth conditions, 20% of the carbon fixed by plants flows through the shikimate pathway (Haslam, 1993). Globally, this amounts to ~7 x 1015 kg each year, most of it used for the synthesis of the various secondary metabolites. And the variation in shikimate pathway-derived secondary metabolites is very extensive among plant species. The secondary metabolite makeup of a plant could be used for species classification. Different plants not only synthesize different aromatic secondary metabolites but also synthesize varying amounts of them at specific times and in specific subcellular compartments. One would expect that regulation of the differential biosynthesis of sometimes very complex molecular structures might involve regulation of the supply of the precursors influencing the rate-limiting step for carbon flow through the shikimate pathway. Recent data on transgenic potatoes give some indication that this is indeed the case (Jones et al., 1995). This review gives a short overview of the shikimate pathway and briefly introduces the seven enzymes that catalyze the sequential steps of the pathway. This is followed by a discussion of some enzymes of quinate metabolism, which use shikimate pathway intermediates as substrates, thus forming branches off the main trunk. I end by discussing some regulatory features of severa1 of the enzymes.

A local update strategy for iterative reconstruction from projections

Abstract: A method for Bayesian reconstruction which relies on updates of single pixel values, rather than the entire image, at each iteration is presented. The technique is similar to Gauss-Seidel (GS) iteration for the solution of differential equations on finite grids. The computational cost per iteration of the GS approach is found to be approximately equal to that of gradient methods. For continuously valued images, GS is found to have significantly better convergence at modes representing high spatial frequencies. In addition, GS is well suited to segmentation when the image is constrained to be discretely valued. It is shown that Bayesian segmentation using GS iteration produces useful estimates at much lower signal-to-noise ratios than required for continuously valued reconstruction. The convergence properties of gradient ascent and GS for reconstruction from integral projections are analyzed, and simulations of both maximum-likelihood and maximum a posteriori cases are included. >

A free calcium wave traverses the activating egg of the medaka, Oryzias latipes.

Abstract: Aequorin-injected eggs of the medaka (a fresh water fish) show an explosive rise in free calcium during fertilization, which is followed by a slow return to the resting level. Image intensification techniques now show a spreading wave of high free calcium during fertilization. The wave starts at the animal pole (where the sperm enters) and then traverses the egg as a shallow, roughly 20 degrees-wide band which vanishes at the antipode some minutes later. The peak free calcium concentration within this moving band is estimated to be about 30 microM (perhaps 100-1,000 times the resting level). Eggs activated by ionophore A23187 may show multiple initiation sites. The resulting multiple waves never spread through each other; rather, they fuse upon meeting so as to form spreading waves of compound origin. The fertilization wave is nearly independent of extracellular calcium because it is only slightly slowed (by perhaps 15%) in a medium containing 5 mM ethylene glycol-bis[beta-aminoethyl ether]N,N9-tetraacetic acid (EGTA) and no deliberately added calcium. It is also independent of the large cortical vesicles, which may be centrifugally displaced. Normally, however, it distinctly precedes the well-known wave of cortical vesicle exocytosis. We conclude that the fertilization wave in the medaka egg is propagated by calcium-stimulated calcium release, primarily from some internal sources other than the large cortical vesicles. A comparison of the characteristics of the exocytotic wave in the medaka with that in other eggs, particularly in echinoderm eggs, suggests that such a propagated calcium wave is a general feature of egg activation.