Doctor Harshini Pinto


Harshini PintoGraduated PhD September 2015.

Thesis Title

Resource use efficiency of C4 grasses with different evolutionary origins

Research Project

C4 photosynthesis has evolved to overcome the limitations of ancestral C3 photosynthetic pathway by operating a natural CO2 concentration mechanism. Following the depletion of CO2 concentration ([CO2]) in the atmosphere 30 million years ago, the efficiency of C3 pathway was reduced esspecially under high temperature and water deficit, conditions which promote photorespiration. Photorespiration is a wasteful process which results in loss of energy and carbon fixed by photosynthesis. Therefore, C4 photosynthesis is an adaptation that compensate for high rates of photorespiration and improves carbon efficiency. C4 plants are more productive and resource use efficient than the more prevalent C3 plants. About 50% of C4 species are grasses with 15 distinct origins distributed over 370 genera and 4600 species. At present, C4 grasses constitue 3% of the world's species and C4 -dominated grasslands contribute up to 20-25% global primary productivity. Further, C4 plants are divided into three biochemical subtypes named after the major C4 acid decarboxylase in the bundle sheath cells: NAD malic enzyme (NAD-ME), NADP-ME and PEP carboxykinase (PCK). These C4 subtypes are strongly related with taxa, and some taxa have multiple evolutionary origins.

The main aims of this study is to compare the physiological efficiencies of C4 grasses that belongs to different subtypes and evolutionary origins under conditions that promote high rates of photorespiration; low atmospheric [CO2], high temperature and low soil moisture conditions. In particular, I will focus on the relationship between resource (mainly water and nitrogen) use efficiency and the activities of key C4 cycle enzymes.

During my PhD project, I will conduct a set of glasshouse experiments using C4 grasses belonging to three biochemical subtypes and different evolutionary origins. Plants will be grown under glacial (200 ppm) and current ambient [CO2] (400 ppm), ambient and high temperature and drought and well watered conditions. I will measure leaf and plant water and nitrogen use efficiencies over the experimental period. I will also measure the activities of the key photosynthetic enzymes, Rubisco, PEPC, and the major C4 acid decarboxylases as well as bundle sheath leakiness using tunable diode laser.

Research Project Supervisors

Dr Oula Ghannoum, Professor David Tissue, Professor Jann Conroy, Dr Robert Sharwood


Pinto H, Powell JR, Sharwood RE, Tissue DT, Ghannoum O, (2016) 'Variations in nitrogen use efficiency reflect the biochemical subtype while variations in water use efficiency reflect the evolutionary lineage of C4 grasses at inter-glacial CO2', Plant, Cell and Environment, vol.39, no.3, pp 514-526

Pinto H, Sharwood RE, Tissue DT, Ghannoum O (2014). Photosynthesis of C3, C3-C4 and C4 grasses at glacial CO2. Journal of Experimental Botany, vol.65 , no.13 , pp 3669-3681 , Special Issue SI.

Pinto H, Tissue DT, Ghannoum O, (2011) 'Panicum milioides (C3-C4) does not have improved water or nitrogen economies relative to C3 and C4 congeners exposed to industrial-age climate change', Journal of Experimental Botany, vol.62, no.9, pp 3223-3234

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