How does drought affect rice root anatomy?

To understand the link between rice root anatomy and drought response, this study was conducted to screen for genetic variations of root anatomical properties. Two greenhouse studies were conducted in soil-filled pots: one with six genotypes grown in flooded and drained treatments and the other with three genotypes to three treatments (well-watered control, moderate drought, and severe drought). Root systems were washed and nodal roots were hand-sectioned. Root cross-sections were taken half-way along the root axis, stained for suberin, and photographed under a compound microscope. Measurements of root anatomy included whole root and stele diameters, number of cell layers in the outer part of the root (OPR), cell size in the schlerenchyma layer, percent cortical aerenchyma, and suberization rating of the schlerenchyma layer and endodermis. Parameters were more affected by treatment than by genotype. Roots in the drained/drought treatment showed greater stile diameter and greater suberization of the endodermis in the first experiment. In the second experiment, increases in the proportion of root diameter that the stele comprised, diameter of schlerenchyma cells and suberization of the endodermis were found in drought treatments. Drought decreased the root diameter, number of cells in the OPR, width of the OPR, percent cortical aerenchyma, and schlerenchyma layer suberization. These results present interesting trends in root anatomy and suberization between drought and well-watered conditions. These trends imply that the OPR and endodermis have different roles under drought. It also suggests that endodermis and stele have a greater role than the schlerenchyma layer in maintaining water as drought occurs. Further screening is necessary to examine drought effects on anatomy of lateral roots as well as nodal roots near the root tips in order to identify genetic differences in rice root anatomical response to drought.