DataSheet_1_Endodermal apoplastic barriers are linked to osmotic tolerance in meso-xerophytic grass Elymus sibiricus.docx

Drought is the most serious adversity faced by agriculture and animal husbandry industries. One strategy that plants use to adapt to water deficits is modifying the root growth and architecture. Root endodermis has cell walls reinforced with apoplastic barriers formed by the Casparian strip (CS) and suberin lamellae (SL) deposits, regulates radial nutrient transport and protects the vascular cylinder from abiotic threats. Elymus sibiricus is an economically important meso-xerophytic forage grass, characterized by high nutritional quality and strong environmental adaptability. The purpose of this study was to evaluate the drought tolerance of E. sibiricus genotypes and investigate the root structural adaptation mechanism of drought-tolerant genotypes’ responding to drought. Specifically, a drought tolerant (DT) and drought sensitive (DS) genotype were screened out from 52 E. sibiricus genotypes. DT showed less apoplastic bypass flow of water and solutes than DS under control conditions, as determined with a hydraulic conductivity measurement system and an apoplastic fluorescent tracer, specifically PTS trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS). In addition, DT accumulated less Na, Mg, Mn, and Zn and more Ni, Cu, and Al than DS, regardless of osmotic stress. Further study showed more suberin deposition in DT than in DS, which could be induced by osmotic stress in both. Accordingly, the CS and SL were deposited closer to the root tip in DT than in DS. However, osmotic stress induced their deposition closer to the root tips in DS, while likely increasing the thickness of the CS and SL in DT. The stronger and earlier formation of endodermal barriers may determine the radial transport pathways of water and solutes, and contribute to balance growth and drought response in E. sibiricus. These results could help us better understand how altered endodermal apoplastic barriers in roots regulate water and mineral nutrient transport in plants that have adapted to drought environments. Moreover, the current findings will aid in improving future breeding programs to develop drought-tolerant grass or crop cultivars.

干旱是农牧业面临的最严峻逆境胁迫。植物适应水分亏缺的策略之一是调控根系生长与构型。根内皮层的细胞壁由凯氏带（Casparian strip, CS）与栓质层（suberin lamellae, SL）沉积形成的质外体屏障强化，可调控养分径向运输并保护维管柱免受非生物胁迫侵害。老芒麦（Elymus sibiricus）是一种具有重要经济价值的中旱生饲草，兼具优良营养品质与极强环境适应性。本研究旨在评价老芒麦不同基因型的耐旱性，并解析耐旱基因型响应干旱的根系结构适应机制。具体而言，本研究从52份老芒麦基因型中筛选出1份耐旱（DT）与1份干旱敏感（DS）基因型。通过导水率测定系统与质外体荧光示踪剂PTS（trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid, PTS）检测发现，对照条件下耐旱基因型的水分与溶质质外体旁路流量显著低于干旱敏感基因型。此外，无论是否施加渗透胁迫，耐旱基因型体内的Na、Mg、Mn和Zn积累量均低于干旱敏感基因型，而Ni、Cu和Al的积累量则更高。进一步研究显示，耐旱基因型的栓质层沉积量高于干旱敏感基因型，且渗透胁迫可诱导两种基因型的栓质层沉积。相应地，相较于干旱敏感基因型，耐旱基因型的凯氏带与栓质层沉积位置更靠近根尖。然而，渗透胁迫会促使干旱敏感基因型的屏障沉积位置更靠近根尖，而在耐旱基因型中则可能增厚凯氏带与栓质层。内皮层屏障形成更早且结构更牢固，或可决定水分与溶质的径向运输路径，进而助力平衡老芒麦的生长与干旱响应。本研究结果有助于更深入地理解根系内皮层质外体屏障的改变如何调控适应干旱环境植物的水分与矿质养分运输。此外，本研究发现可为未来培育耐旱饲草或作物品种的育种工作提供参考。