Responses of leaf respiration to heatwaves

Abstract

<p>Mitochondrial respiration (<i>R</i>) is central to plant physiology and responds dynamically to daily short-term temperature changes. In the longer-term, changes in energy demand and membrane fluidity can decrease leaf <i>R</i> at a common temperature and increase the temperature at which leaf <i>R</i> peaks (T_max). However, leaf <i>R</i> functionality is more susceptible to short-term heatwaves. Catalysis increases with rising leaf temperature, driving faster metabolism and leaf <i>R</i> demand, despite declines in photosynthesis restricting assimilate supply and growth. Proteins denature as temperatures increase further, adding to maintenance costs. Excessive heat also inactivates respiratory enzymes, with a concomitant limitation on the capacity of the <i>R</i> system. These competing push-and-pull factors are responsible for the diminishing acceleration in leaf <i>R</i> rate as temperature rises. Under extreme heat, membranes become overly fluid, and enzymes such as the cytochrome c oxidase are impaired. Such changes can lead to over-reduction of the energy system culminating in reactive oxygen species production. This ultimately leads to the total breakdown of leaf <i>R</i>, setting the limit of leaf survival. Understanding the heat stress responses of leaf <i>R</i> is imperative, given the continued rise in frequency and intensity of heatwaves and the importance of <i>R</i> for plant fitness and survival.</p>