Project

Effect of photorespiration under water stress on photosynthetic capacity

The photorespiration reaction of leaves is theorized to alleviate bottlenecks along the carbon cycle of plant leaves, allowing photosynthesis rates to remain high. Maintaining photosynthesis can lead to higher biomass. We will explore the effect of photorespiration on photosynthetic capacity in rice varieties and link the responses using crop modelling to whole plant responses.

Project description

Photorespiration is a reaction that occurs when the leaf starts using oxygen (O2), as opposed to carbon dioxide (CO2), as its main source of energy. This has been thought of as a limitation, preventing the plant from assimilating carbon to make sugars. However, especially under stress, efficient photorespiratory cycle has been found to relief the accumulation of excessive light energy, while also ensuring the continuation of nitrogen assimilation and carbon export through amino acid production. Under stress such as water deficit, accumulation of energy at the photosystems under high light along with the reduction in electron transport rate and stomatal conductance can severely hamper photosynthesis.

We have rice lines from the IRRI germplasm collection with differences in leaf angle, leaf width and plant architecture that will be grown under two watering regimes to test the effect of knocking out photorespiration on leaf photosynthetic traits. A key goal will be to find associations between photosynthetic traits along canopy depth and related leaf traits such as nitrogen distribution, anatomy and light interception. Ultimately, we will see how this affects whole-plant water use and biomass accumulation, and possibly link it to yield production through modelling.

Objectives and methods

Key questions are:

Does reducing photorespiration enable plants to achieve higher photosynthesis rates under drought?
Which part of the photosynthesis process is most stimulated by reduced photorespiration, and which is not?
Does water deficit make photorespiration more or less important to the achievement of high photosynthetic rates?
How does genotypic variation in biochemical properties under different photorespiratory conditions affect whole plant biomass and water use? Can this be explored using crop modelling?
How does leaf composition and canopy position affect those dynamics, in regards to difference in intercepted light?

Key Measurements:

CO₂ and Light response curves under ambient and low Oxygen, at two canopy positions.
Absorptance and transmittance of leaves.
Leaf compositional traits.
Non-photochemical quenching using Multipseq.
Possible simulation of crop growth using models.

Expectations

Student should be willing and capable, after appropriate training, to conduct sampling and data collection by themselves inside the climate room, and able to conduct the measurements using the techniques above.

Required skills

Understanding of some leaf physiology, alongside willingness to work in labs and growth rooms collecting data. Some experience in data analysis will be desirable, but student will get more training throughout.