Pollen and seeds share a developmental sequence characterized by intense metabolic activity during reserve deposition before drying to a cryptobiotic form. Neither pollen nor seed development has been well studied in the absence of gravity, despite the importance of these structures in supporting future long‐duration manned habitation away from Earth. Using immature seeds (3–15 d postpollination) of Brassica rapa L. cv. Astroplants produced on the STS‐87 flight of the space shuttle Columbia, we compared the progress of storage reserve deposition in cotyledon cells during early stages of seed development. Brassica pollen development was studied in flowers produced on plants grown entirely in microgravity on the Mir space station and fixed while on orbit. Cytochemical localization of storage reserves showed differences in starch accumulation between spaceflight and ground control plants in interior layers of the developing seed coat as early as 9 d after pollination. At this age, the embryo is in the cotyledon elongation stage, and there are numerous starch grains in the cotyledon cells in both flight and ground control seeds. In the spaceflight seeds, starch was retained after this stage, while starch grains decreased in size in the ground control seeds. Large and well‐developed protein bodies were observed in cotyledon cells of ground control seeds at 15 d postpollination, but their development was delayed in the seeds produced during spaceflight. Like the developing cotyledonary tissues, cells of the anther wall and filaments from the spaceflight plants contained numerous large starch grains, while these were rarely seen in the ground controls. The tapetum remained swollen and persisted to a later developmental stage in the spaceflight plants than in the ground controls, even though most pollen grains appeared normal. These developmental markers indicate that Brassica seeds and pollen produced in microgravity were physiologically younger than those produced in 1 g. We hypothesize that microgravity limits mixing of the gaseous microenvironments inside the closed tissues and that the resulting gas composition surrounding the seeds and pollen retards their development.

中文翻译：

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芸苔期间储存储备沉积的动态。微重力下的花粉和种子发育

花粉和种子共享一个发育序列，其特征是在干燥成隐生形式之前的储备沉积期间强烈的代谢活动。在没有重力的情况下，花粉和种子的发育都没有得到很好的研究，尽管这些结构在支持未来远离地球的长期载人居住方面很重要。使用 Brassica rapa L. cv. 的未成熟种子（授粉后 3-15 天）。在哥伦比亚号航天飞机的 STS-87 飞行中产生的天体植物，我们比较了种子发育早期子叶细胞中储存储备沉积的进展。在和平号空间站上完全在微重力下生长并在轨道上固定的植物上产生的花朵中研究了芸苔属花粉的发育。储存储备的细胞化学定位显示，早在授粉后 9 天，航天植物和地面对照植物在发育中的种皮内层淀粉积累存在差异。在这个年龄，胚胎处于子叶伸长阶段，飞行和地面控制种子的子叶细胞中都有大量的淀粉粒。在航天种子中，淀粉在此阶段后得以保留，而地面对照种子中的淀粉粒尺寸减小。地面对照种子在授粉后 15 d 的子叶细胞中观察到大而发育良好的蛋白体，但在太空飞行过程中产生的种子中它们的发育延迟。与发育中的子叶组织一样，太空飞行植物的花药壁细胞和花丝含有大量大淀粉粒，而这些在地面控制中很少见。尽管大多数花粉粒看起来正常，但与地面对照相比，太空飞行植物的绒毡层仍然肿胀并持续到较晚的发育阶段。这些发育标记表明，在微重力条件下产生的芸苔属种子和花粉在生理上比 1 克产生的种子和花粉年轻。我们假设微重力限制了封闭组织内气体微环境的混合，并且由此产生的围绕种子和花粉的气体成分阻碍了它们的发育。这些发育标记表明，在微重力条件下产生的芸苔属种子和花粉在生理上比 1 克产生的种子和花粉年轻。我们假设微重力限制了封闭组织内气体微环境的混合，并且由此产生的围绕种子和花粉的气体成分阻碍了它们的发育。这些发育标记表明，在微重力条件下产生的芸苔属种子和花粉在生理上比 1 克产生的种子和花粉年轻。我们假设微重力限制了封闭组织内气体微环境的混合，并且由此产生的围绕种子和花粉的气体成分阻碍了它们的发育。