Osmotic Adjustment and Cell Wall Composition Allow Maize Fine Roots to Maintain Functionality and Growth During Drought

Fine roots play a critical role in the soil-root interface and are known to perform physiological and biochemical adjustments to maintain root performance. Yet the link among several important processes related to root tip growth and protection of functionality during drought remains largely elusive. Here we aimed to study the hydraulic properties along the length of maize fine root in conjunction with a thorough depiction of morphological changes, cell wall amount and monomer composition and primary metabolite dynamics in well-watered and drought stressed plants. Using a combination of hydraulic measurements and metabolomics procedures, we found that, in drought stressed plants, osmotic adjustment (i.e., accumulation of solutes) and changes in cell wall composition (i.e., decrease of total cell wall material including the important structural sugar monomers), are deeply coupled to allow the necessary turgor pressure and cell wall extensibility that leads to growth. Interestingly, our data suggest that this response is probably well focused in root tips of existing roots, at the expense of the overall development of the root system, probably in a strategy to enhance soil exploration for resources. Our results point to a key role of cell walls that could provide different degrees of capacitance in roots that needs to be further investigated in plants facing drought.