Leaf photosynthesis in wheat (Triticum spp.) under conditions of low temperature and CO2 enrichment.

It is well known that photosynthetic health impacts the overall fitness of the mature plant. This study aims to determine photosynthetic vigour of spring wheat cultivars during field development as well as their biomass composition at maturity to determine which cultivars/varieties would be optimum for cellulosic ethanol production. Additionally, specimens were grown at non-acclimating (20˚C), cold acclimating (5˚C), non-acclimating high CO2 (20˚C/750 µmol mol-1 CO2) and cold-acclimating high CO2 (5˚C/750 µmol mol-1 CO2) to resolve photosynthetic responses to different environments. Plants were photoinhibited under high irradiance (5 fold growth irradiance) and low temperature (5˚C) while photochemical efficiency of PSII was monitored throughout using chlorophyll fluorescence imaging. Vegetative production was monitored using normalised difference vegetation index. De-epoxidation of xanthophyll photoprotective pigments were also recorded using HPLC and photochemical reflectance index. Additionally, carbon assimilation rate was recorded with infra-red gas analysis methods. It was discovered that no one wheat cultivar demonstrated any photosynthetic advantage in the field or under photoinhibitory conditions. However, photosynthetic differences were observed between wheat grown in different environments. Plants that were cold-acclimated or grown under high CO2 were more resilient to photoinhibitory stress. This was also reflected by most cold-acclimated cultivars having increased triose phosphate utilization, electron transport and zeaxanthin induction. Plants acclimated to high CO2 at room temperature also displayed increased electron transport and triose phosphate utilization but had decreased zeaxanthin induction. It is hypothesized increased excitation pressure in cold acclimated and high CO2 cultivars allowed for their increase in the development of photoinhibitory tolerance

Is ESN releasing fast enough to supply winter wheat nitrogen demand?

Non-Peer ReviewedThe purpose of this study is to investigate nitrogen release from various split rate applications of seed-placed environmentally smart nitrogen (ESN) and spring-applied dribble banded Agrotain-UAN (urea and ammonium nitrate solution) and broadcast Agrotain-urea in winter wheat. Cool spring soil conditions have the potential to limit nitrogen (N) release from ESN potentially limiting grain yield potential. Plant root simulator (PRS™) probes were used to monitor N soil supply. It was discovered that N supply did not vary significantly between the split-rate treatments. There were also no significant differences between grain yield and protein content. These results suggest that N release from ESN was not limited by cool spring temperatures and allowed plant vigour similar to traditional spring-applied methods

Natural variation in photosynthetic capacity, growth, and yield in 64 field-grown wheat genotypes

Increasing photosynthesis in wheat has been identified as an approach to enhance crop yield, with manipulation of key genes involved in electron transport and the Calvin cycle as one avenue currently being explored. However, natural variation in photosynthetic capacity is a currently unexploited genetic resource for potential crop improvement. Using gas-exchange analysis and protein analysis, the existing natural variation in photosynthetic capacity in a diverse panel of 64 elite wheat cultivars grown in the field was examined relative to growth traits, including biomass and harvest index. Significant variations in photosynthetic capacity, biomass, and yield were observed, although no consistent correlation was found between photosynthetic capacity of the flag leaf and grain yield when all cultivars were compared. The majority of the variation in photosynthesis could be explained by components related to maximum capacity and operational rates of CO2 assimilation, and to CO2 diffusion. Cluster analysis revealed that cultivars may have been bred unintentionally for desirable traits at the expense of photosynthetic capacity. These findings suggest that there is significant underutilized photosynthetic capacity among existing wheat varieties. Our observations are discussed in the context of exploiting existing natural variation in physiological processes for the improvement of photosynthesis in wheat. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology

Dosimetry tools and techniques for IMRT

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98734/1/MPH001313.pd

Dosimetric verification of radiation therapy including intensity modulated treatments, using an amorphous-silicon electronic portal imaging device

Radiation therapy is continuously increasing in complexity due to technological innovation in delivery techniques, necessitating thorough dosimetric verification. Comparing accurately predicted portal dose images to measured images obtained during patient treatment can determine if a particular treatment was delivered correctly. The goal of this thesis was to create a method to predict portal dose images that was versatile and accurate enough to use in a clinical setting. All measured images in this work were obtained with an amorphous silicon electronic portal imaging device (a-Si EPID), but the technique is applicable to any planar imager. A detailed, physics-motivated fluence model was developed to characterize fluence exiting the linear accelerator head. The model was further refined using results from Monte Carlo simulations and schematics of the linear accelerator. The fluence incident on the EPID was converted to a portal dose image through a superposition of Monte Carlo-generated, monoenergetic dose kernels specific to the a-Si EPID. Predictions of clinical IMRT fields with no patient present agreed with measured portal dose images within 3% and 3 mm. The dose kernels were applied ignoring the geometrically divergent nature of incident fluence on the EPID. A computational investigation into this parallel dose kernel assumption determined its validity under clinically relevant situations. Introducing a patient or phantom into the beam required the portal image prediction algorithm to account for patient scatter and attenuation. Primary fluence was calculated by attenuating raylines cast through the patient CT dataset, while scatter fluence was determined through the superposition of pre-calculated scatter fluence kernels. Total dose in the EPID was calculated by convolving the total predicted incident fluence with the EPID-specific dose kernels. The algorithm was tested on water slabs with square fields, agreeing with measurement within 3% and 3 mm. The method was then applied to five prostate and six head-and-neck IMRT treatment courses (~1900 clinical images). Deviations between the predicted and measured images were quantified. The portal dose image prediction model developed in this thesis work has been shown to be accurate, and it was demonstrated to be able to verify patients’ delivered radiation treatments.May 201