The mechanism of heat priming, triggering alteration of secondary metabolite pathway fluxes and pools to enhance heat tolerance is not well understood. Achillea millefolium is an important medicinal herbal plant, rich in terpenoids and phenolics. In this study, the potential of heat priming treatment (35°C for 1 hr) to enhance tolerance of Achillea plants upon subsequent heat shock (45°C for 5 min) stress was investigated through recovery (0.5–72 hr). The priming treatment itself had minor impacts on photosynthesis, led to moderate increases in the emission of lipoxygenase (LOX) pathway volatiles and isoprene, and to major elicitation of monoterpene and benzaldehyde emissions in late stages of recovery. Upon subsequent heat shock, in primed plants, the rise in LOX and reduction in photosynthetic rate (A) was much less, stomatal conductance (g_s) was initially enhanced, terpene emissions were greater and recovery of A occurred faster, indicating enhanced heat tolerance. Additionally, primed plants accumulated higher contents of total phenolics and condensed tannins at the end of the recovery. These results collectively indicate that heat priming improved photosynthesis upon subsequent heat shock by enhancing g_s and synthesis of volatile and non-volatile secondary compounds with antioxidative characteristics, thereby maintaining the integrity of leaf membranes under stress.

中文翻译：

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热引发提高了光合作用的耐热性，增强了千叶蓍草中萜类化合物和苯类化合物的排放以及酚类物质的积累

热引发的机制，触发次级代谢物途径通量和池的改变以提高耐热性尚不清楚。千叶蓍草是一种重要的药用草本植物，富含萜类化合物和酚类物质。在这项研究中，热启动处理（35°C 持续 1 小时）的潜力增强了Achillea 的耐受性通过恢复（0.5-72 小时）研究在随后的热休克（45°C 持续 5 分钟）胁迫下的植物。引发处理本身对光合作用的影响较小，导致脂氧合酶 (LOX) 途径挥发物和异戊二烯的排放适度增加，并在恢复后期主要引发单萜和苯甲醛排放。在随后的热冲击，在涂底漆的植物，在LOX（上升和下降在光合速率甲）为要少得多，气孔导度（克_小号）最初被增强，萜烯排放量更大，并且回收甲发生得更快，表明耐热性增强。此外，在恢复结束时，浸渍过的植物积累了更高含量的总酚类物质和缩合单宁。这些结果共同表明，热启动通过提高g _s和具有抗氧化特性的挥发性和非挥发性次级化合物的合成来改善随后热激后的光合作用，从而保持叶膜在胁迫下的完整性。