Proline-Mediated Drought Tolerance in the Barley (Hordeum vulgare L.) Isogenic Line Is Associated with Lateral Root Growth at the Early Seedling Stage

Abstract

A vigorous root system in barley promotes water uptake from the soil under water-limited conditions. We investigated three spring barley genotypes with varying water stress responses using rhizoboxes at the seedling stage. The genotypes comprised two elite German cultivars, Barke and Scarlett, and a near-isogenic line, NIL 143. The isogenic line harbors the wild allele pyrroline-5-carboxylate synthase1-P5cs1. Root growth in rhizoboxes under reduced water availability conditions caused a significant reduction in total root length, rooting depth, root maximum width, and root length density. On average, root growth was reduced by more than 20% due to water stress. Differences in organ proline concentrations were observed for all genotypes, with shoots grown under water stress exhibiting at least a 30% higher concentration than the roots. Drought induced higher leaf and root proline concentrations in NIL 143 compared with any of the other genotypes. Under reduced water availability conditions, NIL 143 showed less severe symptoms of drought, higher lateral root length, rooting depth, maximum root width, root length density, and convex hull area compared with Barke and Scarlett. Within the same comparison, under water stress, NIL 143 had a higher proportion of lateral roots (+30%), which were also placed at deeper substrate horizons. NIL 143 had a less negative plant water potential and higher relative leaf water content and stomatal conductance compared with the other genotypes under water stress. Under these conditions, this genotype also maintained an enhanced net photosynthetic rate and exhibited considerable fine root growth (diameter class 0.05–0.35 mm). These results show that water stress induces increased shoot and root proline accumulation in the NIL 143 barley genotype at the seedling stage and that this effect is associated with increased lateral root growth.

Drought Stress Responses: Coping Strategy and Resistance

“…Moreover, the barley near-isogenic line NIL 143 , characterized by higher leaf and root proline content, showed less severe symptoms of drought, higher leaf water content, better stomatal conductance and net CO 2 assimilation than other genotypes. This barley line also exhibited increased lateral root growth, probably due to high proline accumulation [ 103 ]. Considerable evidence obtained previously revealed that drought-stress-induced expression of proline biosynthetic genes is regulated by TFs related to almost all plant hormones [ 67 ].…”

Natural diversity uncoversP5CS1regulation and its role in drought stress tolerance and yield sustainability in barley

“…Under field conditions, Scarlett accumulated 24% lower proline in the leaves compared to NIL-143 (Supporting Information: Figure S9). In addition, QPro.S42-1H ILs accumulated more proline in the spikes, and the spike abortion was significantly reduced under drought stress (Frimpong, Windt, et al, 2021). In the present study, the drought stress-induced reduction in yield attributing traits such as grain numbers per ear, grain weight per plant, harvest index, and thousand-grain weight, in particular, were higher in Scarlett compared with NIL-143 (Figure 7a,b and Supporting Information:…”

“…However, it has also been shown that proline accumulation in the leaf and the partitioning to other organs and turnover of proline are essential for proline‐mediated drought tolerance (Sharma et al, 2011). In a previous study, we demonstrated that the NIL‐143 accumulates higher proline in the roots than Scarlett (Frimpong, Anokye, et al, 2021), indicating the efficient partitioning of proline from the source (leaf) to the sink (root). Therefore, NIL‐143 is an excellent genetic material for exploring the mechanistic process of proline‐mediated osmoregulation, redox balance, photosynthetic adjustments, and cellular signaling during drought stress.…”

“…Previous studies have found a positive correlation between the osmotic adjustment capacity and grain yield in barley (Blum et al, 1999; González et al, 2008). NIL‐143 showed a higher transpiration rate and stomatal conductance compared to Scarlett, maintaining 10% higher RWC and less negative leaf water potential under drought stress conditions (Frimpong, Anokye, et al, 2021) than Scarlett, which indicates a better osmotic adjustment in NIL‐143.…”

Integration of Metabolomics and Transcriptomics for Investigating the Tolerance of Foxtail Millet (Setaria italica) to Atrazine Stress

“…In general, tolerant genotypes of crop plants accumulated more osmoprotectants with high concentrations than sensitive genotypes under stress. For example, a near-isogenic line of spring barley genotypes (NIL143) that contains the wild allele pyrroline-5-carboxylate synthase 1-P5cs1 was observed higher proline concentrations in leaf and root and less severe symptoms of drought compared with any other genotypes under reduced water availability conditions (Frimpong et al, 2021).…”