Acclimation to high temperature during pollen development

Plants are exposed to an ever-changing biotic and abiotic environment and need to constantly adapt their development and physiology to maintain organismal and cellular homeostasis (also referred to as acclimation). An environmental parameter that is highly variable, over various time scales, is ambient temperature. High temperatures reached during the day can pose various problems for cellular functioning and strongly affect plant fitness in the longer term. As a consequence of global warming, hot days and heat waves are predicted to increase both in frequency and in intensity in many temperate regions in the coming decades (IPCC 2014 ). Given the almost complete dependency of humans on agricultural output for food, understanding the reaction of plants to high temperature stress is of great societal importance. While the majority of studies on this subject have focussed on the vegetative (sporophytic) stage of plant growth, the development and functioning of the male gametophyte, or pollen, are known to be among the most temperature-sensitive processes within the plant life cycle (Zinn et al. 2010 ). Importantly, heat-induced pollen defect is associated with reductions in seed and fruit set. In this review, we will specifically discuss the high temperature sensitivity and acclimation response of developing pollen and see how this compares to that of vegetative tissues. We will also speculate whether previous experience of high temperature by a plant may induce higher tolerance of pollen towards subsequent temperature increases, i.e. leads to acquired thermotolerance, either within an individual or in the offspring, and discuss ways in which pollen thermotolerance may be enhanced.