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Tasnim Bhuiyan

Candidature

PhD Candidate

Thesis Title

Mechanisms of heat stress tolerance in the C4 crop sorghum

Project Summary

Tasnim BhuiyanGlobal climate change has accelerated the rise in average air temperatures, negatively affecting agricultural systems. Crops such as sorghum utilises the C4 photosynthetic cycle, which evolved to efficiently concentrate CO2 at the site of carboxylation and suppress photorespiration. This increases the catalytic efficiency of the central CO2-fixing enzyme Rubisco compared to C3 crops, where increases in temperature are known to increase oxygenation which leads to higher rates of photorespiration. C4 crops such as sorghum can sustain higher temperature optima for photosynthesis. However, temperature increases above the thermal optimum can restrict photosynthesis by impairing the physical integrity of electron transport or by affecting the activity of the photosynthetic enzymes, leading to increased flux through the photorespiratory cycle and decreases photosynthetic carboxylation carbon assimilation. Hence, future crop productivity will be severely impacted by climate change unless a deeper understanding of the capacity and underlying mechanisms that enable C4 cereal sorghum to survive high temperature is developed.
This broad challenge is the focus of this PhD project. In particular, short-term heat extremes are occurring more frequently as a result of global warming. These abrupt temperature increases above the optimum range can lead to heat stress, resulting in reversible or irreversible crop damage. Since photosynthesis is the underlying biological driver of yield in agriculture systems, this thesis is aims to understand the mechanisms that underpin the photosynthetic response of sorghum to temperature.
In the first set of experiments, I studied two sorghum lines with contrasting leaf width and photosynthetic response to temperature with preliminary evidence and one hybrid line as control. In experiment I, the three lines were grown under standard chamber condition. The temperature responses of photosynthesis were explored in vivo using leaf gas exchange and in vitro using assays of the major photosynthetic enzymes phosphoenolpyruvate carboxylase (PEPC), ribulose 1, 5 bisphosphate carboxylase/ oxygenase (Rubisco) and Nicotinamide adenine dinucleotide phosphate malic-enzymes (NADP-ME). In the second chapter, the physiological impact of heat stress were investigated in the selected sorghum lines. The photosynthetic heat tolerance were explored using leaf gas exchange in the three sorghum lines along with the chlorophyll fluorescence measurement to investigate the photochemical efficiency of photosystem II as well as thermal tolerance threshold (T50) and recovery. In chapter III, I am exploring the photosynthetic biochemistry and the molecular impact of heat stress in the sorghum lines. I am studying the in vitro enzymes assay (PEPC, Rubisco and NADPME); the activation of Rubisco and the gene expression of the photosynthetic enzymes PEPC, NADPME, Rubisco and its chaperone Rubisco activase in the sorghum lines to assess the photosynthetic responses of sorghum lines grown under water & heat stress. My thesis will highlight the possible sensitivity of different components of the C4 photosynthetic apparatus to heat stress with a view to crop improvement & food security under future climate condition.

Supervisors

Professor Oula Ghannoum, Dr Robert Sharwood, Lily Chen, Yazen Al-Salman