Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Prof. Dr. Norman PA Hüner

Abstract

I assessed the effects of cold acclimation and long-term elevated CO2 on photosynthetic performance and energy conversion efficiency of winter (cv Musketeer, cv Norstar) and spring (cv SR4A, cv Katepwa) rye (Secale cereale) and wheat (Triticum aestivum) as well as wild type (WT) and BnCBF17-over-expressing line (BnCBF17-OE) of Brassica napus cv Westar. Plants were grown at either 20/16°C (non-acclimated, NA) or 5/5°C (cold acclimated, CA) and at either ambient (380 µmol C mol-1) or elevated (700 µmol C mol-1) CO2.Compared to NA controls, CA winter cereals, Norstar and Musketeer, exhibited compact dwarf phenotype, increased rates of light-saturated CO2 assimilation (42%) and photosynthetic electron transport (48%) and higher levels of rbcL, cytosolic FBPase, Lhcb1, PsbA and PsaA at ambient CO2. This was associated with enhanced energy conversion efficiency into biomass (31%) and seed yield (20%) coupled to decreased excitation pressure and decreased energy dissipation through non-photochemical quenching (NPQ) for a given irradiance and a given CO2 concentration in CA versus NA winter cereals. The increased photosynthetic performance and energy conversion efficiency of CA winter cereals at ambient CO2 were maintained under long-term growth and development at elevated CO2. In contrast, CA spring cereals, SR4A and Katepwa, exhibited decreased CO2 assimilation rates (35%) and decreased energy conversion efficiency in biomass (40%) not only at ambient CO2 but also at long-term elevated CO2. BnCBF17-over-expression in Brassica napus resulted into dwarf phenotype, increased rates of light-saturated CO2 assimilation (38%) and photosynthetic electron transport (18%), an enhanced energy conversion efficiency with concomitant decreased reliance on photoprotection to dissipate absorbed energy through NPQ for a given irradiance and a given CO2. Compared to WT Brassica napus, BnCBF17-over-expression reduced sensitivity to feedback-limited photosynthesis during long-term growth of B. napus under elevated CO2. CBFs (C-repeat binding factors) are transcriptional activators that induce the expression of cold-regulated genes. We suggest that CBFs regulate not only freezing tolerance but also control the photosynthetic performance and energy conversion efficiency in biomass and grain yield through morphological, physiological and biochemical adjustments. Hence, targeting the CBF pathways in major crop species can be a novel approach to improve crop yield and productivity.

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