Short-term high temperature stress in plants: Stress markers and cell signaling

Heat stress, intensified by rising global temperatures, presents significant challenges to plant growth, development, and reproduction. Plants respond with specific physiological and molecular changes, traditionally categorized as short-term (acute) or long-term (chronic). However, current classifications often lack the precision needed to adequately characterize short-term heat stress (STHS), leaving its specific markers and biological implications under-defined. This review proposes a time-range-based classification for heat stress responses, emphasizing STHS as a distinct phase rather than a milder form of prolonged stress. We differentiate between main thermotolerance, acquired thermotolerance, and acclimatization as separate strategies tied to specific exposure patterns. We also examine the roles and dynamics of key molecular and biochemical markers, including reactive oxygen and nitrogen species (ROS/RNS), transcription factors, small RNAs, heat shock responses, antioxidants, phytohormones, and osmolytes, analyzing their functional interplay. Based on recent evidence, we re-evaluate the importance of ROS and antioxidant defense, highlighting the underestimated role of RNS and osmolytes in acute heat episodes. This review summarizes current concepts about STHS, emphasizing its distinct nature and providing a foundation for more accurate identification of early-stage stress markers in plants exposed to high temperatures.