Abstract Postharvest heat treatment stimulates desiccation and browning of outer scales of onion (Allium cepa. L) bulb to dry papery skins. Inner scales resist the heat treatment, as evidenced by high moisture levels. During heating, inner scales showed increasing soluble sugar levels followed by higher osmolarity, vs. a dramatic decrease in both in the outer scales. Exogenous feeding of outer scales with sucrose, glucose or fructose solutions before heat treatment reduced water loss during heating, suggesting a role for soluble sugars in water retention and therefore, heat tolerance. Vacuolar invertase (VInv) is a key enzyme regulating the levels of sucrose, glucose and fructose in plant tissue. In onion outer scales, VInv activity increased during heating but reducing sugars decreased, possibly due to their rapid metabolism during scale senescence to form skin. Transcriptomic analysis demonstrated upregulation of genes involved in lignin biosynthesis and secondary cell-wall formation in outer scales during heat exposure, and upregulation of genes involved in energy-related pathways in inner scales. This study reveals the dual role of soluble sugars in different onion scales, as osmoprotectants or building blocks, under heat stress.

中文翻译：

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内源性糖水平与洋葱鳞茎的耐热性差异有关

摘要 收获后热处理会刺激洋葱 (Allium cepa. L) 鳞茎的外鳞发生干燥和褐变，从而使纸皮干燥。内部水垢抵抗热处理，高水分含量证明了这一点。在加热过程中，内部鳞片显示可溶性糖水平增加，随后是更高的渗透压，而外部鳞片则急剧下降。在热处理前用蔗糖、葡萄糖或果糖溶液外源性喂养外鳞可减少加热过程中的水分流失，表明可溶性糖在保水和耐热方面发挥作用。液泡转化酶（VInv）是调节植物组织中蔗糖、葡萄糖和果糖水平的关键酶。在洋葱外鳞中，加热过程中 VInv 活性增加，但还原糖减少，可能是由于它们在鳞屑衰老过程中快速代谢形成皮肤。转录组学分析表明，在热暴露期间参与木质素生物合成和次生细胞壁形成的基因上调，以及参与内部尺度能量相关途径的基因上调。这项研究揭示了可溶性糖在热应激下作为渗透保护剂或构建块在不同洋葱鳞片中的双重作用。