BACKGROUND A structure called the pleurogram makes up a large part of the seed coat of some species in subfamilies Caesalpinioideae and Mimosoideae of Fabaceae, but little is known about its function. It has been hypothesized that this structure acts as a hygroscopic valve during the maturation drying of seeds. However, a new hypothesis has recently emerged that proposes a distinct function for the pleurogram. SCOPE Here, we provide an overview of the structure and function of the pleurogram, which is diverse and complex. This large structure can be dislodged, thereby creating a pathway for water entry into water-impermeable seeds. However, the pleurogram is nonfunctional as a pathway of water into the seed of some species. Thus, the evolutionary history of species with a pleurogram may be related to a loss/gain in its function. A complete model for the function of the pleurogram is proposed. CONCLUSIONS The pleurogram may act on several stages of the seed, from maturation to germination. As a hygroscopic valve, it regulates dehydration of the seed during maturation. As a pathway for water entry into the seed, the pleurogram acts as a water gap in seeds with physical dormancy, thereby regulating dormancy-break/germination. The occurrence of a pleurogram in several genera of legumes and Cucurbitaceae is confirmed. Single or multiple pleurograms can serve as (the) point(s) of water entry into seeds that do not otherwise have a hilar water gap.

中文翻译：

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胸膜，一种未充分研究的种子功能性状

背景 一种称为胸膜的结构构成了豆科亚科 Caesalpinioideae 和 Mimosoideae 中某些物种种皮的大部分，但对其功能知之甚少。已经假设这种结构在种子成熟干燥过程中充当吸湿阀。然而，最近出现了一个新假设，提出了胸膜造影的独特功能。范围 在此，我们概述了胸膜造影的结构和功能，它多种多样且复杂。这个大结构可以被移走，从而为水进入不透水的种子创造了一条通道。然而，胸膜作为水进入某些物种种子的途径是无效的。因此，具有胸膜造影的物种的进化历史可能与其功能的丧失/增加有关。提出了胸膜功能的完整模型。结论 胸膜造影可作用于种子的几个阶段，从成熟到发芽。作为吸湿阀，它在成熟过程中调节种子的脱水。作为水分进入种子的途径，胸膜在具有物理休眠状态的种子中充当水间隙，从而调节休眠破坏/萌发。证实在豆科植物和葫芦科的几个属中出现胸膜造影。单个或多个胸膜造影可以作为水进入种子的（该）点，否则这些种子不具有肺门水隙。作为水分进入种子的途径，胸膜在具有物理休眠状态的种子中充当水间隙，从而调节休眠破坏/萌发。证实在豆科植物和葫芦科的几个属中出现胸膜造影。单个或多个胸膜造影可以作为水进入种子的（该）点，否则这些种子不具有肺门水隙。作为水分进入种子的途径，胸膜在具有物理休眠状态的种子中充当水间隙，从而调节休眠破坏/萌发。证实在豆科植物和葫芦科的几个属中出现胸膜造影。单个或多个胸膜造影可以作为水进入种子的（该）点，否则这些种子不具有肺门水隙。