The Window of Desiccation Tolerance Shown by Early-Stage Germinating Seedlings Remains Open in the Resurrection Plant, Xerophyta viscosa

Resurrection plants are renowned for their vegetative desiccation tolerance (DT). While DT in vegetative tissues is rare in angiosperms, it is ubiquitous in mature orthodox seeds. During germination, seedlings gradually lose DT until they pass a point of no return, after which they can no longer survive dehydration. Here we investigate whether seedlings of the resurrection plant Xerophyta viscosa ever lose the capacity to establish DT. Seedlings from different stages of germination were dehydrated for 48 hours and assessed for their ability to recover upon rehydration. While a transient decline in the ability of X. viscosa seedlings to survive dehydration was observed, at no point during germination was the ability to re-establish DT completely lost in all seedlings. Pre-treatment of seedlings with PEG or sucrose reduced this transient decline, and improved the survival rate at all stages of germination. Additionally, we observed that the trait of poikilochlorophylly (or loss of chlorophyll) observed in adult X. viscosa leaves can be induced throughout seedling development. These results suggest that the window of DT seen in germinating orthodox seeds remains open in X. viscosa seedlings and that vegetative DT in Xerophyta species may have evolved from the ability to retain this program through to adulthood.复苏植物以其营养组织脱水耐性（desiccation tolerance, DT）著称。尽管被子植物的营养组织中脱水耐性较为罕见，但成熟的正常型种子（orthodox seeds）中该特性却普遍存在。在萌发过程中，幼苗的脱水耐性会逐渐丧失，直至越过不可逆临界点，此后便无法在脱水条件下存活。本研究旨在探究复苏植物Xerophyta viscosa的幼苗是否会丧失重建脱水耐性的能力。研究人员将处于不同萌发阶段的幼苗进行48小时脱水处理，并评估其复水后的恢复能力。尽管观测到Xerophyta viscosa幼苗的脱水存活能力出现短暂下降，但在整个萌发过程中，并未出现所有幼苗完全丧失重建脱水耐性能力的情况。采用聚乙二醇（polyethylene glycol, PEG）或蔗糖对幼苗进行预处理，可缓解这一短暂下降，并提升各萌发阶段幼苗的存活率。此外，研究人员观测到，成年Xerophyta viscosa叶片所具有的异叶绿素性（poikilochlorophylly，即叶绿素丧失特性）可在幼苗整个发育过程中被诱导产生。上述研究结果表明，正常型种子萌发过程中所具备的脱水耐性窗口期，在Xerophyta viscosa幼苗中依然存在；同时，Xerophyta属植物的营养组织脱水耐性，或许是通过保留该发育程序直至成年阶段演化而来。