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Maricopa, AZ, United States

Callier V.,Arizona State University | Shingleton A.W.,Michigan State University | Shingleton A.W.,Lake Forest College | Brent C.S.,Arid Land Agricultural Research Center | And 3 more authors.
Journal of Experimental Biology | Year: 2013

Rearing oxygen level is known to affect final body size in a variety of insects, but the physiological mechanisms by which oxygen affects size are incompletely understood. In Manduca sexta and Drosophila melanogaster, the larval size at which metamorphosis is initiated largely determines adult size, and metamorphosis is initiated when larvae attain a critical mass. We hypothesized that oxygen effects on final size might be mediated by oxygen effects on the critical weight and the ecdysone titers, which regulate growth rate and the timing of developmental transitions. Our results showed that oxygen affected critical weight, the basal ecdysone titers and the timing of the ecdysone peak, providing clear evidence that oxygen affected growth rate and developmental rate. Hypoxic third instar larvae (10% oxygen) exhibited a reduced critical weight, slower growth rate, delayed pupariation, elevated baseline ecdysone levels and a delayed ecdysone peak that occurred at a lower larval mass. Hyperoxic larvae exhibited increased basal ecdysone levels, but no change in critical weight compared with normoxic larvae and no significant change in timing of pupariation. Previous studies have shown that nutrition is crucial for regulating growth rate andthe timing of developmental transitions. Here we show that oxygen level is one of multiple cues that together regulate adult size and the timing and dynamics of growth, developmental rate and ecdysone signaling. © 2013. Published by The Company of Biologists Ltd. Source

Henderson J.N.,Arizona State University | Kuriata A.M.,Arizona State University | Fromme R.,Arizona State University | Salvucci M.E.,Arid Land Agricultural Research Center | Wachter R.M.,Arizona State University
Journal of Biological Chemistry | Year: 2011

The rapid release of tight-binding inhibitors from dead-end ribulose-bisphosphate carboxylase/oxygenase (Rubisco) complexes requires the activity of Rubisco activase, an AAA+ATPase that utilizes chemo-mechanical energy to catalyze the reactivation of Rubisco. Activase is thought to play a central role in coordinating the rate of CO 2 fixation with the light reactions of photosynthesis. Here, we present a 1.9 Å crystal structure of the C-domain core of creosote activase. The fold consists of a canonical four-helix bundle, from which a paddle-like extension protrudes that entails a nine-turn helix lined by an irregularly structured peptide strand. The residues Lys-313 and Val-316 involved in the species-specific recognition of Rubisco are located near the tip of the paddle. An ionic bond between Lys-313 and Glu-309 appears to stabilize the glycine-rich end of the helix. Structural superpositions onto the distant homolog FtsH imply that the paddles extend away from the hexameric toroid in a fan-like fashion, such that the hydrophobic sides of each blade bearing Trp-302 are facing inward and the polar sides bearing Lys-313 and Val-316 are facing outward. Therefore, we speculate that upon binding, the activase paddles embrace the Rubisco cylinder by placing their hydrophobic patches near the partner protein. This model suggests that conformational adjustments at the remote end of the paddle may relate to selectivity in recognition, rather than specific ionic contacts involving Lys-313. Additionally, the superpositions predict that the catalytically critical Arg-293 does not interact with the bound nucleotide. Hypothetical ring-ring stacking and peptide threading models for Rubisco reactivation are briefly discussed. Source

Ruiz-Vera U.M.,University of Illinois at Urbana - Champaign | Siebers M.,University of Illinois at Urbana - Champaign | Gray S.B.,University of Illinois at Urbana - Champaign | Drag D.W.,University of Illinois at Urbana - Champaign | And 7 more authors.
Plant Physiology | Year: 2013

Extensive evidence shows that increasing carbon dioxide concentration ([CO2]) stimulates, and increasing temperature decreases, both net photosynthetic carbon assimilation (A) and biomass production for C3 plants. However the [CO2]-induced stimulation in A is projected to increase further with warmer temperature.While the influence of increasing temperature and [CO2], independent of each other, on A and biomass production have been widely investigated, the interaction between these two major global changes has not been tested on field-grown crops. Here, the interactive effect of both elevated [CO2] (approximately 585 μmol mol-1) and temperature (+3.5°C) on soybean (Glycine max) A, biomass, and yield were tested over two growing seasons in the Temperature by Free-Air CO2 Enrichment experiment at the Soybean Free Air CO2 Enrichment facility. Measurements of A, stomatal conductance, and intercellular [CO2] were collected along with meteorological, water potential, and growth data. Elevated temperatures caused lower A, which was largely attributed to declines in stomatal conductance and intercellular [CO2] and led in turn to lower yields. Increasing both [CO2] and temperature stimulated A relative to elevated [CO2] alone on only two sampling days during 2009 and on no days in 2011. In 2011, the warmer of the two years, there were no observed increases in yield in the elevated temperature plots regardless of whether [CO2] was elevated. All treatments lowered the harvest index for soybean, although the effect of elevated [CO2] in 2011 was not statistically significant. These results provide a better understanding of the physiological responses of soybean to future climate change conditions and suggest that the potential is limited for elevated [CO2] to mitigate the influence of rising temperatures on photosynthesis, growth, and yields of C3 crops. © 2013 American Society of Plant Biologists. All Rights Reserved. Source

Chakraborty M.,Arizona State University | Kuriata A.M.,Arizona State University | Nathan Henderson J.,Arizona State University | Salvucci M.E.,Arid Land Agricultural Research Center | And 2 more authors.
Biophysical Journal | Year: 2012

A methodology is presented to characterize complex protein assembly pathways by fluorescence correlation spectroscopy. We have derived the total autocorrelation function describing the behavior of mixtures of labeled and unlabeled protein under equilibrium conditions. Our modeling approach allows us to quantitatively consider the relevance of any proposed intermediate form, and Kd values can be estimated even when several oligomeric species coexist. We have tested this method on the AAA+ ATPase Rubisco activase (Rca). Rca self-association regulates the CO2 fixing activity of the enzyme Rubisco, directly affecting biomass accumulation in higher plants. However, the elucidation of its assembly pathway has remained challenging, precluding a detailed mechanistic investigation. Here, we present the first, to our knowledge, thermodynamic characterization of oligomeric states of cotton β-Rca complexed with Mg·ADP. We find that the monomer is the dominating species below 0.5 micromolar. The most plausible model supports dissociation constants of ∼4, 1, and 1 micromolar for the monomer-dimer, dimer-tetramer, and tetramer-hexamer equilibria, in line with the coexistence of four different oligomeric forms under typical assay conditions. Large aggregates become dominant above 40 micromolar, with continued assembly at even higher concentrations. We propose that under some conditions, ADP-bound Rca self-associates by forming spiral arrangements that grow along the helical axis. Other models such as the stacking of closed hexameric rings are also discussed. © 2012 Biophysical Society. Source

Han B.,China Jiliang University | Zhang Q.-H.,Sterling International | Byers J.A.,Arid Land Agricultural Research Center
Entomologia Experimentalis et Applicata | Year: 2012

The tea aphid, Toxoptera aurantii Boyer (Hemiptera: Aphididae), is a major pest of the tea plant, Camellia sinensis (L.) O. Kuntze (Theaceae). The attraction of the aphids to different colors and volatile compounds from tea shoots was investigated. Fourteen compounds were identified using gas chromatography-mass spectrometry from headspace samples of intact tea shoot volatiles (ITSV). Electrophysiological and behavioral responses of winged tea aphids to ITSV as well as to the full blend of 14 synthetic compounds, to a partial mixture of green leaf volatiles (GLV) included in the 14 compounds, and to individual synthetic compounds were studied by using electroantennography (EAG) and a Y-tube olfactometer. The various tea volatiles and blends were strongly active, with ITSV being the strongest. In the greenhouse and in tea plantations, sticky boards of six different colors strongly attracted tea aphids in flight, with 'rape-flower yellow' and 'Chinese olive-yellow-green' being the most attractive. Furthermore, these two boards in combination with ITSV attracted winged tea aphids more strongly than their corresponding colored sticky boards alone. In the greenhouse, plastic models of tea seedlings baited with (Z)-3-hexen-1-ol or the GLV mixture significantly attracted winged tea aphids in flight. This study demonstrates that green leaf volatiles from tea shoots are attractive to the tea aphid. The combination of these volatiles with the color light yellow or green, and the shape of tender tea shoots result in orientation flight and landing of winged tea aphids on host tea shoots. © 2012 The Netherlands Entomological Society Entomologia Experimentalis et Applicata © 2012 The Netherlands Entomological Society. Source

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