Osmotic stress, caused by the lack of water or by high salinity, is a common problem in plant roots. Osmotic stress can be reproducibly simulated with the application of solutions of the high-molecular-weight and impermeable polyethylene glycol. The accumulation of different reactive oxygen species, such as singlet oxygen, superoxide, and hydrogen peroxide, accompany this stress. Among them, singlet oxygen, produced as a byproduct of lipoxygenase activity, has been associated with limiting root growth. To better understand the source and effect of singlet oxygen, we followed its production at the cellular level in Arabidopsis (Arabidopsis thaliana). Osmotic stress initiated profound changes in plastid and vacuole structure. Confocal and electron microscopy showed that the plastids were a source of singlet oxygen accompanied by the appearance of multiple, small extraplastidic bodies that were also an intense source of singlet oxygen. A marker protein, CRUMPLED LEAF, indicated that these small bodies originated from the plastid outer membrane. Remarkably, LINOLEATE 9S-LIPOXYGENASE 5, (LOX5), was shown to change its distribution from uniformly cytoplasmic to a more clumped distribution together with plastids and the small bodies. In addition, oxylipin products of type 9 lipoxygenase increased, while products of type 13 lipoxygenases decreased. Inhibition of lipoxygenase by the SHAM inhibitor or in down-regulated lipoxygenase lines prevented cells from initiating the cellular responses, leading to cell death. In contrast, singlet oxygen scavenging halted terminal cell death. These findings underscore the reversible nature of osmotic stress-induced changes, emphasizing the pivotal roles of lipoxygenases and singlet oxygen in root stress physiology.

中文翻译：

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根中的渗透胁迫通过单线态氧产生驱动脂氧合酶依赖性质体重塑


由缺水或高盐度引起的渗透胁迫是植物根系的常见问题。渗透应力可以通过应用高分子量和不渗透的聚乙二醇溶液来重现地模拟。不同活性氧的积累，如单线态氧、超氧化物和过氧化氢，都伴随着这种压力。其中，作为脂氧合酶活性副产品产生的单线态氧与限制根系生长有关。为了更好地了解单线态氧的来源和影响，我们在拟南芥 （Arabidopsis thaliana） 中跟踪了它在细胞水平上的产生。渗透应激引发了质体和液泡结构的深刻变化。共聚焦和电子显微镜显示，质体是单线态氧的来源，伴随着多个小的质体外小体的出现，这些小质体外小体也是单线态氧的强来源。标记蛋白 CRUMPLED LEAF 表明这些小体起源于质体外膜。值得注意的是，亚油酸酯 9S-脂氧合酶 5 （LOX5） 被证明将其分布从均匀的细胞质分布转变为与质体和小体一起更加聚集的分布。此外，9 型脂氧合酶的氧磷脂产物增加，而 13 型脂氧合酶的产物减少。SHAM 抑制剂或下调的脂氧合酶系对脂氧合酶的抑制阻止了细胞启动细胞反应，从而导致细胞死亡。相比之下，单线态氧清除可阻止终末细胞死亡。这些发现强调了渗透胁迫诱导的变化的可逆性，强调了脂氧合酶和单线态氧在根系胁迫生理学中的关键作用。