Endodermal apoplastic barriers are linked to osmotic tolerance in meso-xerophytic grass Elymus sibiricus

Abstract

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.

How plants sense and respond to osmotic stress

“…In vascular plants, CS seals the intracellular space between endodermal cells by forming a tight junction with the plasma membrane, preventing water and nutrient loss during the long‐distance transport through the stele (Geldner, 2013; Calvo‐Polanco et al, 2021; Song et al, 2023). It was found that osmotic stress can induce the early formation of CS in plant roots (Shen et al, 2015; Liu et al, 2022), suggesting that CS might play a positive role in plant tolerance to drought stress. Indeed, the absence of functional CS leads to the sensitivity of Arabidopsis to osmotic stress (Gao et al, 2023).…”

Genotype-specific responses to drought stress in Siberian wildrye (Elymus sibiricus): Insights from comparative physiological and transcriptomic analyses

“…Two genotypes (DT and DS) of E. sibiricus were used in this study 48 . Plant materials used to determine physiological phenotypes were grown in soil, materials for cutin, wax and transcriptome sequencing were cultured by hydroponics.…”

“…sibiricus, and revealed that the Casparian strip and suberin lamellae in the root endodermis played a pivotal role in the difference in drought resistance between the DT and DS genotypes 48 . Here, we performed a comparative analysis of the physiological,…”