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.
cold acclimation, metabolism, CO₂ enrichment, biomass, photosynthesis, photoinhibition
Master of Science (M.Sc.)