Aquaporins and apoplastic barriers in nutrient-limited barley

Without the right minerals, water flow through plants is disrupted. Getting water to the leaves for photosynthesis is a task that starts in the roots and their acquisition of water and minerals. In a recent article published in Annals of Botany, Thomas Armand and colleagues investigated how mineral limitation affected a plant’s water transport.

The team grew barley plants (Hordeum vulgare) using hydroponics, so the roots were suspended in water. In that water, they could then control the concentration of nutrients and see how that affected water flow. They were particularly interested in how the supply of nitrogen and phosphate could change aquaporin (AQP) gene expression, aquaporins being the proteins that pass water between cells.

The scientists found that plants in a nutrient-limited solution had an increased root:shoot ratio. However, they also found a root-zone specific decrease in the activity of aquaporins, but not in gene expression. “[An] explanation for the lack of change in AQP gene expression in roots with lowered Lp is that AQP activity was regulated at the protein level, for example through phosphorylation and trafficking…, or could have been a consequence of stress-induced changes in plasma membrane lipid composition…” write the authors.

Armand and colleagues found that the changes induced by nutrient limitation were reversible. “The ability of low-N and also low-P plants to rapidly recover some root Lp when nutrient-sufficient medium was added points to a mechanism that is reversible or can be induced in the minutes-to-hour range,” write the authors.

“Modelling of root hydraulic conductance and Hg inhibition experiments, together with staining of root cross-sections, further suggests that some of the reduction in root Lp is due to increased formation of apoplastic barriers, particularly suberin lamellae.”