Free amino acids (FAAs) and protein-bound amino acids (PBAAs) in seeds play an important role in seed desiccation, longevity, and germination. However, the effect that water stress has on these two functional pools, especially when imposed during the crucial seed setting stage is unclear. To better understand these effects, we exposed Arabidopsis plants at the seed setting stage to a range of water limitation and water deprivation conditions and then evaluated physiological, metabolic, and proteomic parameters, with special focus on FAAs and PBAAs. We found that in response to severe water limitation, seed yield decreased, while seed weight, FAA, and PBAA content per seed increased. Nevertheless, the composition of FAAs and PBAAs remained unaltered. In response to severe water deprivation, however, both seed yield and weight were reduced. In addition, major alterations were observed in both FAA and proteome compositions, which indicated that both osmotic adjustment and proteomic reprogramming occurred in these naturally desiccation-tolerant organs. However, despite the major proteomic alteration, the PBAA composition did not change, suggesting that the proteomic reprogramming was followed by a proteomic rebalancing. Proteomic rebalancing has not been observed previously in response to stress, but its occurrence under stress strongly suggests its natural function. Together, our data show that the dry seed PBAA composition plays a key role in seed fitness and therefore is rigorously maintained even under severe water stress, while the FAA composition is more plastic and adaptable to changing environments, and that both functional pools are distinctly regulated.

中文翻译：

---

在拟南芥种子定居阶段，游离氨基酸和结合氨基酸对水分胁迫的复杂反应。

种子中的游离氨基酸（FAA）和蛋白质结合氨基酸（PBAA）在种子干燥，寿命和发芽中起重要作用。但是，尚不清楚水分胁迫对这两个功能库的影响，尤其是在关键种子结实阶段施加时。为了更好地理解这些影响，我们在种子定居阶段将拟南芥植物暴露于一定范围的水分限制和缺水条件下，然后评估了生理，代谢和蛋白质组学参数，尤其侧重于FAA和PBAA。我们发现，响应于严重的水分限制，种子产量下降，而每颗种子的种子重量，FAA和PBAA含量增加。但是，FAA和PBAA的组成保持不变。然而，由于严重缺水，种子的产量和重量都降低了。此外，在FAA和蛋白质组组成中均观察到重大变化，这表明在这些天然耐干性器官中发生了渗透调节和蛋白质组重编程。然而，尽管蛋白质组学发生了重大变化，但PBAA的组成并没有改变，这表明在蛋白质组重编程之后是蛋白质组平衡。先前尚未观察到响应压力的蛋白质组平衡，但是在压力下其发生强烈暗示了它的自然功能。总之，我们的数据表明，干种子PBAA组合物在种子适应性中起着关键作用，因此即使在严重的水分胁迫下也能得到严格维护，而FAA组合物更具可塑性并适应不断变化的环境，并且两个功能库均受到明显调节。在FAA和蛋白质组组成中均观察到重大变化，这表明在这些天然耐干性器官中发生了渗透调节和蛋白质组重编程。然而，尽管蛋白质组学发生了重大变化，但PBAA的组成并没有改变，这表明在蛋白质组重编程之后是蛋白质组平衡。先前尚未观察到响应压力的蛋白质组平衡，但是在压力下其发生强烈暗示了它的自然功能。总之，我们的数据表明，干种子PBAA组合物在种子适应性中起着关键作用，因此即使在严重的水分胁迫下也能得到严格维护，而FAA组合物更具可塑性并适应不断变化的环境，并且两个功能库均受到明显调节。在FAA和蛋白质组组成中均观察到重大变化，这表明在这些天然耐干性器官中发生了渗透调节和蛋白质组重编程。然而，尽管蛋白质组学发生了重大变化，但PBAA的组成并没有改变，这表明在蛋白质组重编程之后是蛋白质组平衡。先前尚未观察到响应压力的蛋白质组平衡，但是在压力下其发生强烈暗示了它的自然功能。总之，我们的数据表明，干种子PBAA组合物在种子适应性中起着关键作用，因此即使在严重的水分胁迫下也能得到严格维护，而FAA组合物更具可塑性并适应不断变化的环境，并且两个功能库均受到明显调节。