Department of Biological Sciences, California State Polytechnic University Humboldt, Arcata, CA, 95521, USA.
New Phytol. 2023 Jul;239(1):388-398. doi: 10.1111/nph.18926. Epub 2023 Apr 18.
We analyze the oldest fossil occurrences of wound-response periderm to characterize the development of wound responses in early tracheophytes. The origin of periderm production by a cambium (phellogen), an innovation with key roles in protection of inner plant tissues, is poorly explored; understanding periderm development in early tracheophytes can illuminate key aspects of this process. Anatomy of wound-response tissues is characterized in serial sections in a new Early Devonian (Emsian; c. 400 Ma) euphyllophyte from Quebec (Canada) - Nebuloxyla mikmaqiana sp. nov. - and compared to previously described euphyllophyte periderm from the same fossil locality to reconstruct periderm development. Characterizing development in these oldest periderm occurrences allows us to propose a model for the development of wound-response periderm in early tracheophytes: by phellogen activity that is poorly coordinated laterally but bifacial, producing secondary tissues initially outwardly and subsequently inwardly. The earliest occurrences of wound periderm pre-date the oldest known periderm produced systemically as a regular ontogenetic stage (canonical periderm), suggesting that periderm evolved initially as a wound-response mechanism. We hypothesize that canonical periderm evolved by exaptation of this wound sealing mechanism, whose deployment was triggered by tangential tensional stresses induced in the superficial tissues by vascular cambial growth from within.
我们分析了最早的伤口反应周皮化石记录，以描述早期木质植物中伤口反应的发育。周皮由形成层（木栓形成层）产生的起源，这是一个在保护植物内部组织方面具有关键作用的创新，尚未得到充分探索；了解早期木质植物的周皮发育可以阐明这个过程的关键方面。在来自魁北克（加拿大）的一个新的早泥盆世（埃姆斯期；约 4 亿年前）真蕨类植物 Nebuloxyla mikmaqiana sp. nov. 的连续切片中对伤口反应组织解剖结构进行了特征描述，并与来自同一化石产地的先前描述的真蕨类周皮进行了比较，以重建周皮发育。对这些最早的周皮出现的特征描述使我们能够提出一个早期木质植物伤口反应周皮发育的模型：通过木栓形成层的活性，这种活性在侧面上协调得很差，但具有双面性，最初向外产生次生组织，然后向内产生。最早的伤口周皮发生时间早于最早的系统产生的作为常规个体发育阶段的周皮（典型周皮），这表明周皮最初是作为一种伤口反应机制进化而来的。我们假设，典型周皮是通过对这种伤口密封机制的适应进化而来的，其部署是由内部形成层的血管生长引起的表层组织的切向张力触发的。
