Plant reproduction under spaceflight conditions has been problematic in the past. In order to determine what aspect of reproductive development is affected by microgravity, we studied pollination and embryo development in Brassica rapa L. during 16 d in microgravity on the space shuttle (STS‐87). Brassica is self‐incompatible and requires mechanical transfer of pollen. Short‐duration access to microgravity during parabolic flights on the KC‐135A aircraft was used initially to confirm that equal numbers of pollen grains could be collected and transferred in the absence of gravity. Brassica was grown in the Plant Growth Facility flight hardware as follows. Three chambers each contained six plants that were 13 d old at launch. As these plants flowered, thin colored tape was used to indicate the date of hand pollination, resulting in silique populations aged 8–15 d postpollination at the end of the 16‐d mission. The remaining three chambers contained dry seeds that germinated on orbit to produce 14‐d‐old plants just beginning to flower at the time of landing. Pollen produced by these plants had comparable viability (93%) with that produced in the 2‐d‐delayed ground control. Matched‐age siliques yielded embryos of equivalent developmental stage in the spaceflight and ground control treatments. Carbohydrate and protein storage reserves in the embryos, assessed by cytochemical localization, were also comparable. In the spaceflight material, growth and development by embryos rescued from siliques 15 d after pollination lagged behind the ground controls by 12 d; however, in the subsequent generation, no differences between the two treatments were found. The results demonstrate that while no stage of reproductive development in Brassica is absolutely dependent upon gravity, lower embryo quality may result following development in microgravity.

中文翻译：

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芸苔中的授粉和胚胎发育。在微重力

过去，太空飞行条件下的植物繁殖一直存在问题。为了确定生殖发育的哪个方面受微重力影响，我们在航天飞机 (STS-87) 的微重力下研究了芸苔属植物的授粉和胚胎发育 16 天。芸苔属自不相容，需要机械转移花粉。在 KC-135A 飞机的抛物线飞行期间，短时间接触微重力最初用于确认在没有重力的情况下可以收集和转移相同数量的花粉粒。芸苔属在植物生长设施飞行硬件中如下生长。三个房间每个都包含六株植物，它们在发射时已有 13 天的历史。当这些植物开花时，薄薄的彩色胶带被用来指示人工授粉的日期，导致在 16 天任务结束时传粉后 8-15 天的长角果种群。剩下的三个房间里装有干燥的种子，这些种子在轨道上发芽，产生 14 d 龄的植物，在着陆时刚刚开始开花。这些植物产生的花粉与二维延迟地面控制产生的花粉具有相当的活力 (93%)。匹配年龄的长角果在航天和地面控制处理中产生了相同发育阶段的胚胎。通过细胞化学定位评估的胚胎中的碳水化合物和蛋白质储存储备也具有可比性。在航天材料中，授粉后15 d从长角果中拯救的胚胎的生长发育落后于地面对照12 d；然而，在后代中，没有发现两种处理之间的差异。