Heat tolerance of a tropical-subtropical rainforest tree species <i>Polyscias elegans</i> time-dependent dynamic responses of physiological thermostability and biochemistry

center dot Heat stress interrupts physiological thermostability and triggers biochemical responses that are essential for plant survival. However, there is limited knowledge on the speed plants adjust to heat in hours and days, and which adjustments are crucial.center dot Tropical-subtropical rainforest tree species (Polyscias elegans) were heated at 40 degrees C for 5 d, before returning to 25 degrees C for 13 d of recovery. Leaf heat tolerance was quantified using the temperature at which minimal chl a fluorescence sharply rose (T-crit). T-crit, metabolites, heat shock protein (HSP) abundance and membrane lipid fatty acid (FA) composition were quantified.center dot T-crit increased by 4 degrees C (48-52 degrees C) within 2 h of 40 degrees C exposure, along with rapid accumulation of metabolites and HSPs. By contrast, it took >2 d for FA composition to change. At least 2 d were required for T-crit, HSP90, HSP70 and FAs to return to prestress levels.center dot The results highlight the multi-faceted response of P. elegans to heat stress, and how this response varies over the scale of hours to days, culminating in an increased level of photosynthetic heat tolerance. These responses are important for survival of plants when confronted with heat waves amidst ongoing global climate change.