凤仙花成熟蒴果种子弹射机制研究
The Seeds Elastic Mechanism of Mature Capsules in Impatiens balsamina L.

凤仙花(Impatiens balsamina L.)的成熟蒴果在受到机械压力时，蒴果果皮会迅速内卷并将种子弹射出去。通过对不同发育时期的蒴果进行石蜡切片后发现：蒴果果皮主要由泡状细胞组成，成熟过程中泡状细胞(BCs)不断膨大并积累弹性势能。蒴果中泡状细胞沿横轴和纵轴不对称分布。在纵轴方向上，中部细胞比两侧细胞体积更大且疏松。在横轴方向上，外层细胞比内层细胞体积更大且疏松。泡状细胞在蒴果果皮中的不对称分布会产生由膨压引起的不对称的弯曲应力。随着蒴果的不断成熟，横轴和纵轴的弯曲应力逐渐增大。当横轴的弯曲应力超过蒴果缝线处所能承受的临界点后，蒴果释放横轴弯曲应力并触发纵轴弯曲应力的释放，蒴果果皮内卷将种子弹出。
The mature capsules of Impatiens balsamina L. will curl quickly and eject seeds under mechanical pressure. Through paraffin sectioning of capsules at different developmental stages, we found that capsule peel is mainly composed of bulliform cells (BCs), which continuous expanding the cell volume and accumulating elastic energy. BCs located asymmetric at both horizontal axis and vertical axis of capsules. On the vertical axis, BCs are larger and looser in the middle than that of BCs at both sides. On the horizontal axis, BCs are larger and looser in the out layer than that of BCs in the inner layer. The asymmetric distribution of BCs in the capsule peel will produce asymmetric bending stress caused by turgor pressure. As the capsule continues to mature, the bending stress on the horizontal axis and the vertical axis gradually increase. When the bending stress of the horizontal axis exceeds the critical point that the capsule can withstand at the suture line, the capsule releases the horizontal axis bending stress and triggers the release of the longitudinal axis bending stress, and the capsule peels inwardly to eject the seeds.