Meeting Abstract
Circumnutation is the oscillatory movement of a variety of plant organs including roots. Little is known about the function of below-ground circumnutation, particularly in root-heterogeneity interactions. Root tip traits that allow for exploration may be advantageous, as roots can encounter heterogeneities in their environment that prevent productive growth. Previously we studied hard surface exploration in circumnutating wild type (WT) and non-circumnutating mutant rice roots using a high-throughput automated imaging system. In experiments with rigid plates containing holes embedded in a clear gel-based medium, we observed that a root coiling behavior in non-circumnutating mutant rice roots prevented effective root-surface exploration. WT roots had higher success in finding holes, enabling deeper growth. To reveal the sensitivity of these exploration dynamics to substrate parameters, in this work we use the gel-based media to create an environment consisting of two gel layers with varying stiffness. This environment can model soil horizons with varying compaction. Roots were grown in either a soft gel upper layer to a stiffer gel bottom layer, or the opposite. WT roots displayed less than 50% success in growing deeper in both treatments. When the roots did not penetrate the lower substrate, they grew along the gel interface, showing similar exploratory dynamics as in the rigid plate experiments. However, when non-circumnutating mutant roots grew from a stiff to soft gel layer, they had a 90% success rate in penetrating deeper compared to below 60% percent success from soft to stiff. Our data indicates that WT circumnutating root tips are sensitive to environmental heterogeneities such as changing soil compactness, and that circumnutation facilitates an exploratory behavior when such heterogeneities are encountered.
