Antisense reductions in the PsbO protein of photosystem II leads to decreased quantum yield but similar maximal photosynthetic rates

Photosystem (PS) II is the multisubunit complex which uses light energy to split water, providing the reducing equivalents needed for photosynthesis. The complex is susceptible to damage from environmental stresses such as excess excitation energy and high temperature. This research investigated the in vivo photosynthetic consequences of impairments to PSII in Arabidopsis thaliana (ecotype Columbia) expressing an antisense construct to the PsbO proteins of PSII. Transgenic lines were obtained with between 25 and 60% of wild-type (WT) total PsbO protein content, with the PsbO1 isoform being more strongly reduced than PsbO2. These changes coincided with a decrease in functional PSII content. Low PsbO (less than 50% WT) plants grew more slowly and had lower chlorophyll content per leaf area. There was no change in content per unit area of cytochrome b6f, ATP synthase, or Rubisco, whereas PSI decreased in proportion to the reduction in chlorophyll content. The irradiance response of photosynthetic oxygen evolution showed that low PsbO plants had a reduced quantum yield, but matched the oxygen evolution rates of WT plants at saturating irradiance. It is suggested that these plants had a smaller pool of PSII centres, which are inefficiently connected to antenna pigments resulting in reduced photochemical efficiency.This work was supported by an Australian Postgraduate Award to SAD, the Australian Research Council Centre of Excellence in Plant Energy Biology (MRB), and grants from the Australian Research Council (WSC)

Multifocal objective perimetry compared with Humphrey full-threshold perimetry in patients with optic neuritis

BackgroundThe aim of the study is to compare multifocal visual evoked potential (mfVEP) objective perimetry with Humphrey full-threshold visual field (HVF) perimetry, in the assessment of patients with optic neuritis (ON).MethodsWe assessed 16 patients with clinically diagnosed ON. A comparison was made between the HVF and mfVEP, based on the global severity indices of both tests and number and topography of significant abnormalities detected. The latency data and inter-eye asymmetry findings on the mfVEP were also evaluated.ResultsFrom a total of 128 quadrants analysed in the 16 patients (100 affected, 28 unaffected eyes), HVF perimetry identified a scotoma in 39/128 (30.5%) quadrants, all of which were in affected eyes; the mfVEP detected a scotoma in 68/128 (53.1%) quadrants using amplitude and/or asymmetry data (XV2=7.2485, P=0.0071). Latency plots on the mfVEP identified a significant latency deviation cluster in 20/25 (80%) affected eyes. Abnormalities were also detected in 4/7 (57%) unaffected eyes. The global severity indices in the affected eyes showed a high correlation between the two tests (r=0.73).ConclusionsThe mfVEP detected more abnormalities in patients with ON than HVF perimetry. The use of latency recordings as well as combined amplitude and asymmetry plots is advantageous and has the potential to detect abnormalities not otherwise detected on HVF perimetry.Nima Pakrou, Robert Casson, Andrew Kaines and Dinesh Selv

Orbital compression by Ethmoidal adenocarcinoma

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Temperature response of in vivoRubisco kinetics and mesophyll conductance in Arabidopsis thaliana: Comparisons to Nicotiana tabacum

Biochemical models of photosynthesis use the temperature dependency of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) kinetics and mesophyll conductance to CO 2 (g m). However, the in vivo temperature response of Rubisco kinetics and g m has only been measured in the warm adapted Nicotiana tabacum; therefore, we determined these parameters in the cool-adapted Arabidopsis thaliana to see how species-dependent differences impact modeled rates of photosynthesis. While the individual Rubisco kinetic parameters in N. tabacum and A. thaliana were similar across temperatures, they collectively resulted in significantly different modeled rates of photosynthesis. Additionally, g m increased with temperature in N. tabacum but not in A. thaliana. Commentary: New challenges in modeling photosynthesis: temperature dependencies of Rubisco kinetics Biochemical models are used to predict and understand the response of photosynthesis to rising temperatures and CO2 partial pressures. These models require the temperature dependency of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) kinetics and mesophyll conductance to CO2 (gm). However, it is not known how the temperature response of Rubisco kinetics differs between species, and comprehensive in vivo Rubisco kinetics that include gm have only been determined in the warm-adapted Nicotiana tabacum. Here, we measured the temperature response of Rubisco kinetics and gm in N. tabacum and the cold-adapted Arabidopsis thaliana using gas exchange and 13CO2 isotopic discrimination on plants with genetically reduced levels of Rubisco. While the individual Rubisco kinetic parameters in N. tabacum and A. thaliana were similar across temperatures, they collectively resulted in significantly different modelled rates of photosynthesis. Additionally, gm increased with temperature in N. tabacum but not in A. thaliana. These findings highlight the importance of considering species-dependent differences in Rubisco kinetics and gm when modelling the temperature response of photosynthesis

Conjunctival squamous cell carcinoma with perineural invasion resulting in death

Conjunctival squamous cell carcinoma is generally a low-grade malignancy. A 42-year-old man presented with histologic evidence of extra-tumoral perineural invasion associated with an incompletely excised limbal conjunctival squamous cell carcinoma. Despite further surgery, close observation, plaque radiotherapy, and eyelid-sparing orbital exenteration followed by external beam radiotherapy, the patient developed intracranial perineural invasion with involvement of the trigeminal and facial nerves, ultimately resulting in death. Repeated magnetic resonance imaging with contrast failed to detect perineural invasion until late in the course of disease. Awareness of the possibility of perineural invasion in patients with conjunctival squamous cell carcinoma and of its aggressive nature may be life-saving. Nevertheless, even with initial aggressive tumor control, some patients will show an aggressive tumor growth with recurrences.A. Kaines, G. Davis, D. Selva, I. Leibovitch, T. Dodd, R. Malhotr

Cavernous haemangioma in the orbital apex: stereotactic-guided transcranial cryoextraction

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