Global warming is expected to increase drought severity in diverse environments, impacting plant performance. Plants acclimate to drought by mechanisms like stomatal closure and osmotic adjustment. Maternally inherited symbiotic microorganisms with capacity to regulate these mechanisms have the potential to influence intergenerational plant drought responses. We studied how a seedborne endophyte affects maternal drought effects on seed germination water requirements and specialized metabolites. Isotopic analysis of seed cellulose indicated that drought led to improved water use efficiency (WUE; higher δC) in endophyte-free mother plants, seemingly without affecting stomatal conductance (non-significant δO change). Alternatively, endophyte-symbiotic plants did not exhibit a change in WUE but apparently an increase in stomatal conductance (significant δO decrease). Regardless of the symbiosis, drought reduced seed production but not seed size. Endophyte symbiosis improved the seed concentration of mannitol and sorbitol, but this increment was higher under drought. Maternal plant responses to drought did not increase seed germination under reduced water potential but induced dormancy in seeds from endophyte-free but not endophyte-symbiotic plants. Our findings suggest that although differential accumulation of metabolites in seeds results from how endophyte-symbiotic plants perceive and respond to drought, this response may not form part of a mechanism that would enhance seed performance of progeny under drought.

中文翻译：

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种子传播的内生菌介导植物干旱反应和对种子特性的代际影响

全球变暖预计将加剧不同环境下的干旱严重程度，影响植物的生长。植物通过气孔关闭和渗透调节等机制来适应干旱。具有调节这些机制能力的母系遗传的共生微生物有可能影响代际植物干旱反应。我们研究了种子传播的内生菌如何影响母体干旱对种子发芽需水量和专门代谢物的影响。种子纤维素的同位素分析表明，干旱导致无内生菌的母本植物水分利用效率（WUE；较高的 δ13C）提高，似乎不影响气孔导度（δ13C 无显着变化）。或者，内生菌共生植物的 WUE 没有变化，但气孔导度明显增加（δ18O 显着降低）。无论共生如何，干旱都会减少种子产量，但不会减少种子大小。内生菌共生提高了种子中甘露醇和山梨醇的浓度，但在干旱条件下这种增量更高。在水势降低的情况下，母本植物对干旱的反应不会增加种子发芽，但会诱导无内生菌而非内生菌共生植物的种子休眠。我们的研究结果表明，尽管种子中代谢物积累的差异是由内生菌共生植物如何感知和响应干旱造成的，但这种响应可能不会形成增强干旱下后代种子性能的机制的一部分。