Wheat photosystem II heat tolerance responds dynamically to short and long-term warming

Abstract

Heat-induced inhibition of photosynthesis is a key factor in declining wheat performance and yield. Variation in wheat heat tolerance can be characterised using the critical temperature (T_crit) above which incipient damage to the photosynthetic machinery occurs. We investigated intraspecies variation and plasticity of wheat T_crit under elevated temperature in field and controlled environment experiments. We also assessed whether intraspecies variation in wheat T_crit mirrors patterns of global interspecies variation in heat tolerance reported for mostly wild, woody plants. In the field, wheat T_crit varied through the course of a day, peaking at noon and lowest at sunrise, and increased as plants developed from heading to anthesis and grain filling. Under controlled temperature conditions, heat stress (36°C) was associated with a rapid rise in wheat T_crit (i.e. within two hours of heat stress) that peaked after 3–4 days. These peaks in T_crit indicate a physiological limitation to photosystem II heat tolerance. Analysis of a global dataset (comprising 183 Triticum and wild wheat (Aegilops) species) generated from the current study and a systematic literature review showed that wheat leaf T_crit varied by up to 20°C (about two-thirds of reported global plant interspecies variation). However, unlike global patterns of interspecies T_crit variation which has been linked to latitude of genotype origin, intraspecific variation in wheat T_crit was unrelated to that. Yet, the observed genotypic variation and plasticity of wheat T_crit suggests that this trait could be a useful tool for high-throughput phenotyping of wheat photosynthetic heat tolerance.