Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland.
J Exp Bot. 2022 Jan 5;73(1):94-109. doi: 10.1093/jxb/erab419.
In Arabidopsis, a dry stigma surface enables a gradual hydration of pollen grains by a controlled release of water. Occasionally the grains may be exposed to extreme precipitations that cause rapid water influx and swelling, eventually leading to pollen membrane rupture. In metazoans, calcium- and phospholipid-binding proteins, referred to as annexins, participate in the repair of plasma membrane damages. It remains unclear, however, how this process is conducted in plants. Here, we examined whether plant annexin 5 (ANN5), the most abundant member of the annexin family in pollen, is involved in the restoration of pollen membrane integrity. We analyzed the cellular dynamics of ANN5 in pollen grains undergoing hydration in favorable or stress conditions. We observed a transient association of ANN5 with the pollen membrane during in vitro hydration that did not occur in the pollen grains being hydrated on the stigma. To simulate a rainfall, we performed spraying of the pollinated stigma with deionized water that induced ANN5 accumulation at the pollen membrane. Interestingly, calcium or magnesium application affected pollen membrane properties differently, causing rupture or shrinkage of pollen membrane, respectively. Both treatments, however, induced ANN5 recruitment to the pollen membrane. Our data suggest a model in which ANN5 is involved in the maintenance of membrane integrity in pollen grains exposed to osmotic or ionic imbalances.
在拟南芥中，干燥的柱头表面通过控制水分释放使花粉粒逐渐水合。花粉粒偶尔可能会暴露在极端降水下，导致快速的水分涌入和肿胀，最终导致花粉膜破裂。在后生动物中，钙和磷脂结合蛋白，称为膜联蛋白，参与质膜损伤的修复。然而，目前尚不清楚这个过程在植物中是如何进行的。在这里，我们研究了花粉中丰度最高的膜联蛋白 5（ANN5）是否参与了花粉膜完整性的恢复。我们分析了在有利或应激条件下水合过程中花粉中 ANN5 的细胞动态。我们观察到 ANN5 与花粉膜的短暂结合，这种结合在柱头水合的花粉粒中不会发生。为了模拟降雨，我们用去离子水喷洒授粉的柱头，诱导花粉膜上 ANN5 的积累。有趣的是，钙或镁的应用对花粉膜性质的影响不同，分别导致花粉膜破裂或收缩。然而，这两种处理都诱导了 ANN5 向花粉膜的募集。我们的数据表明了一个模型，即 ANN5 参与维持暴露在渗透或离子失衡中的花粉粒的膜完整性。
