BackgroundThe plant circadian clock orchestrates 24-hour rhythms in internal physiological processes to coordinate these activities with daily and seasonal changes in the environment. The circadian clock has a profound impact on many aspects of plant growth and development, including biomass accumulation and flowering time. Despite recent advances in understanding the circadian system of the model plant Arabidopsis thaliana, the contribution of the circadian oscillator to important agronomic traits in Zea mays and other cereals remains poorly defined. To address this deficit, this study investigated the transcriptional landscape of the maize circadian system.ResultsSince transcriptional regulation is a fundamental aspect of circadian systems, genes exhibiting circadian expression were identified in the sequenced maize inbred B73. Of the over 13,000 transcripts examined, approximately 10 percent displayed circadian expression patterns. The majority of cycling genes had peak expression at subjective dawn and dusk, similar to other plant circadian systems. The maize circadian clock organized co-regulation of genes participating in fundamental physiological processes, including photosynthesis, carbohydrate metabolism, cell wall biogenesis, and phytohormone biosynthesis pathways.ConclusionsCircadian regulation of the maize genome was widespread and key genes in several major metabolic pathways had circadian expression waveforms. The maize circadian clock coordinated transcription to be coincident with oncoming day or night, which was consistent with the circadian oscillator acting to prepare the plant for these major recurring environmental changes. These findings highlighted the multiple processes in maize plants under circadian regulation and, as a result, provided insight into the important contribution this regulatory system makes to agronomic traits in maize and potentially other C4 plant species.

The rate of MgO carbothermal reduction was studied at temperatures 7 from 1350-1650°C and pressures from 0.1-100kPa based on product gas 8 analysis at near isothermal conditions. For all temperatures the initial 9 rate of carbothermal reduction increased inversely with pressure, and between conversions of 20-35% a transition occurred after which the reaction rate was maximum at 10kPa. Analysis of reacted pellets showed that the reaction stoichiometry, the ratio of C to MgO reacted, was less than unity and decreased with pressure indicating CO 2 generation was more prevalent at elevated pressures. SEM imaging revealed the dissolution of C and MgO contact with conversion, andisoconversional analysis points to a change inthe rate determining step between 1 and 10kPa. The given experimental observations argue the importance of mass transfer and gaseous intermediates. A kinetic model is formulated based on a macroscopic species balance with CO 2 as the reaction intermediate.

Cell-cell communication is essential for plants to integrate developmental programs with external cues that affect their growth. Recent advances in plant signaling have uncovered similar molecular mechanisms in shoot, root, and vascular meristem signaling that involve receptor-like kinases and small, secreted peptides. Here, we report that the receptor-like kinases TOAD2/RPK2 and RPK1 regulate root growth by controlling cell proliferation and affecting meristem size. Two types of developmental alterations were observed upon exogenous CLE peptide application. The first type was detected in all plants treated, and comprise increased proliferative activity of cells in the stem cell niche and a delay of progression in differentiation of daughter cells. The second type was changes specific to the genotypes that are sensitive to CLE-driven root meristem inhibition and include a large decrease in the occurrence of cell divisions in longitudinal files, correlating with shorter meristems and cessation of root growth. The root meristems of mutant plants are insensitive to the inhibitory effect of CLE17 peptide treatment, consistent with TOAD2/RPK2 function as a receptor for CLE peptides. In addition, a strong reduction in the expression of RPK1 protein upon CLE treatment, dependent on TOAD2/RPK2, suggests that these two RLKs mediate CLE signaling in a common pathway to control root growth.

The cell surface receptor kinase BRASSINOSTEROID-INSENSITIVE-1 (BRI1) is the major receptor for steroid hormones in Arabidopsis. Plants homozygous for loss-of-function mutations in BRI1 display a reduction in the size of vegetative organs, resulting in dwarfism. The recessive bri1-5 mutation produces receptors that do not accumulate to wild-type levels and are retained mainly in the endoplasmic reticulum. We have isolated a dominant suppressor of the dwarf phenotype of bri1-5 plants. We show that this suppression is caused by a second-site mutation in BRI1, bri1-5R1. The bri1-5R1 mutation partially rescues the phenotypes of bri1-5 in many tissues and enhances bri1-5 phenotypes above wild-type levels in several other tissues. We demonstrate that the phenotypes of bri1-5R1 plants are due to both increased cell expansion and increased cell division. To test the mechanism of bri1-5 suppression, we assessed whether the phenotypic suppression in bri1-5R1 was dependent on ligand availability and the integrity of the signaling pathway. Our results indicate that the suppression of the dwarf phenotypes associated with bri1-5R1 requires both BR biosynthesis and the receptor kinase BRI1-ASSOCIATED KINASE-1 (BAK1). Finally, we show that bri1-5R1 partially restores the accumulation and plasma membrane localization of BRI1. Collectively, our results point toward a model in which bri1-R1 compensates for the protein-folding abnormalities caused by bri1-5, restoring accumulation of the receptor and its delivery to the cell surface.

A novel method is presented to study magnesium metal vapor condensation/oxidation in CO and CO 2 atmosphere at reduced pressures. Mg(s) was evaporated and mixed with an equimolar amount of CO or CO 2 at 1000°C after which the gaseous mixture flowed through an air cooled tubular condenser. Measurements of the axial temperature profile, calculation of partial pressures and analysis of deposits within the condenser allowed for identification of deposition/condensation onset temperatures, supersaturation ratio and reaction mechanism. In the presence of CO 2 , rapid oxidation of Mg(g) has been observed. In the presence of CO, no Mg(g) oxidation was found above 950°C. Mg(g) oxidation observed at lower temperatures is believed to be initiated by CO disproportionation. The proposed mechanism is able to explain the increase in Mg metal yield with decreasing CO partial pressure. At a CO partial pressure <3 mbar, high Mg metal mass yields of >90w% were found. The presented method is applicable to the study of a variety of metal vapor/oxidizer combinations e.g. of interest in metal and solar fuel production.