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

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, and , and a near-isogenic line, The isogenic line harbors the wild allele . 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 compared with any of the other genotypes. Under reduced water availability conditions, showed less severe symptoms of drought, higher lateral root length, rooting depth, maximum root width, root length density, and convex hull area compared with and . Within the same comparison, under water stress, had a higher proportion of lateral roots (+30%), which were also placed at deeper substrate horizons. 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 barley genotype at the seedling stage and that this effect is associated with increased lateral root growth.