Doctor Julius Sagun
Candidature
Graduated PhD 2020
Thesis Title
Environmental Regulation of Energetics of C4 Photosynthesis
Research Project
Photosynthesis is a complex process which is the basic source of our food. Due to increasing world population and climate change, there is a call to improve photosynthesis to enhance food production over next 40 years for the important C4 crops such as maize, sorghum and sugarcane. One way to meet this goal is improving the conversion efficiency of solar energy into primary productivity during photosynthesis. Light energy conversion into biomass is one of the main limiting environmental factor for growth when crops are provided with adequate nutrients and water (Zhu et al., 2010).
The photosynthetic quantum yield (QY, CO2 fixation per absorbed photons) of C4 species is higher than those of C3 species at high temperature, due to the operation of a CO2 concentrating mechanism (CCM) which minimizes photorespiration. QY also varies among the three biochemical subtypes of C4 photosynthesis and the basis for this variation remains unresolved. Factors involved in this variation include differences in the CCM efficiency and activity of the light energy conversion reactions (termed energetics) in mesophyll cells (MC) and bundle-sheath cells (BSC) of the leaf.
This research will investigate the relationship between photosynthetic physiology and energetics in diverse C4 grasses belonging to different biochemical subtypes (NAD-ME, PEP-CK and NADP-ME) under varying environmental conditions (light and CO2). The project aims to identify potential limitations of QY in C4 crops as well as determine how energetics differs among subtypes. This will be achieved by using a combination of fluorescence, spectral and biochemical techniques to understand the underlying mechanisms of high light use efficiency in C4 grasses.
Publications
Ver Sagun J, Chow WS, Ghannoum O, (2022) 'Leaf pigments and photosystems stoichiometry underpin photosynthetic efficiency of related C-3, C-C-4 and C-4 grasses under shade', Physiologia Plantarum, vol.174, no.6, Article no.e13819
Sagun JV, Badger MR, Chow WS, Ghannoum O, (2021) 'Mehler reaction plays a role in C3 and C4 photosynthesis under shade and low CO2', Photosynthesis Research, doi 10.1007/s11120-021-00819-1
Ver Sagun J, Badger MR, Chow WS, Ghannoum O, (2019) 'Cyclic electron flow and light partitioning between the two photosystems in leaves of plants with different functional types', Photosynthesis Research, vol.142, no. 3, pp 321-334
Supervisors
A/Professor Oula Ghannoum, Prof Fred (Wah Soon) Chow (ANU)
