The regulation of whole-plant sink-source relationships during the life cycle of rice
Photosynthesis is the primary physiological process that determines the productivity of crops and ecosystems? Are you interested in understanding the processes that limit photosynthetic rates and crop productivity? Do you like to challenge yourself to learn combined experimental and modelling research? Here is a subject that you might consider to work for your thesis.
The process that drives the synthesis of sucrose and starch from sugar precursors in the photosynthetic Calvin–Benson cycle is called triose phosphate utilization (TPU). It is one of the three canonical biochemical limitations of photosynthesis in gas exchange analysis of C3 plants, which can give feedback inhibition on photosynthesis when carbon exports from the cycle cannot keep pace with carbon fixation. From CO2 response curves of conventional gas exchange and chlorophyll fluorescence measurements, TPU-limited photosynthesis rate (Ap) behave like no response to CO2, or sometimes, an inhibition under increasing CO2. Currently, in a biochemical photosynthesis model, either Rubisco carboxylation capacity (Vcmax) or electron transport rate (Jmax) is widely accepted as the main limiting factor to photosynthesis, while TPU received less attention, since an observable TPU limitation is only occasional and highly variable, depending on genotypes and growth conditions. However, inclusion of TPU limitation in models is important to understand the basic principles of photosynthetic mechanisms.
Recently, an apparent TPU limitation from leaf photosynthesis was observed in our leaf-colour variants from two backgrounds of rice genotypes. We hypothesise that these leaf-colour variant genotypes differ from their default counterparts in photosynthetic capacity and thus, in the extent of TPU limitation. We plan to conduct a greenhouse experiment on four rice genotypes under two or three nitrogen treatments to:
- identify the occurrence of the TPU limitation;
- explore the whole-plant physiological regulating mechanisms of TPU limitation, and
- quantify the effect of TPU limitation on photosynthesis.
- Measuring CO2response curves on adaxial and abaxial surfaces of leaves by Li-Cor
- Analysing collected data and modelling the rate of triose phosphate utilization
- Investigate the link between TPU limitation and the whole-plant source-sink ratio and nitrogen status