ABSTRACT

Heat stress is an increasingly important constraint on wheat production under climate change, yet progress in breeding for thermal tolerance is limited by the lack of robust, scalable phenotyping approaches and an incomplete understanding of the physiological mechanisms underpinning heat tolerance. My PhD project aims to develop and apply novel screening methodologies to improve the identification and characterisation of heat-tolerant wheat genotypes. 

As part of my project, we investigated the relationship between leaf Rubisco concentration and photosynthetic performance in wheat exposed to simulated heatwave conditions. We grew a set of high-performance wheat genotypes under controlled environments and subjected them to short-term high-temperature episodes designed to mimic field-relevant heatwaves. Gas exchange measurements were combined with biochemical quantification of Rubisco to assess photosynthetic responses before and after heat stress.

We found that the acclimation response depended largely on the stage of development at which the heatwave began. At the booting and anthesis stages, genotypes generally responded by downregulating Rubisco concentration, but the amount of downregulation was variable, and genotypes that maintained higher Rubisco concentration were consistently associated with greater net CO₂ assimilation rates under heatwave conditions, driven primarily by maintaining carboxylation capacity, and Rubisco activity. At the later grain filling stage this acclimation response was muted, likely due to protein being remobilised to grain. Carboxylation needs were instead maintained through increases to stomatal conductance. These findings indicate that maintaining Rubisco abundance may contribute to superior photosynthetic resilience during transient heat events and highlight Rubisco concentration as a potential physiological trait for improving wheat heat tolerance. They also highlight the potential vulnerabilities to heat stress at later stages of development without adequate water access. 

Our next steps are to assess whether these responses translate to field environments. By linking physiological responses to temperature across controlled and field environments, our research provides new insights into the mechanisms that confer heat tolerance in wheat and evaluates the extent to which controlled screening can predict field performance. The outcomes contribute both practical tools for improved phenotyping and a stronger physiological framework to support breeding strategies aimed at enhancing wheat resilience to rising temperatures.

BIOGRAPHY

John is a PhD student with the Atkin group at RSB. His work focuses on understanding how temperature and heat stress affects carbon metabolism and energy balance in crops. He joined the Atkin group in 2017 as a technician during his undergraduate studies at ANU. Not knowing any better, he decided to stick around for an honours project in 2020 and, like many others, promptly had half of his project trounced by COVID. Fortunately, the other half was enough to finish his project. He then managed to successfully stumble into a PhD program which has been much more enjoyable and had fewer lockdowns. Throughout his PhD he has met a bunch of cool people and travelled to several exotic locations where he spent a lot of time at identical-looking fields of wheat, running around in a half-panicked state trying to fix whatever temperamental, duct-taped gas exchange device he was using at the time.