Utility of Root Cortical Cell Size and Number Cells Per File in Maize Under Water Limited Conditions.

Root traits which allow access to deep soil water at low metabolic cost are important for crop adaptation to drought. Anatomical traits affecting root tissue composition are important means for reducing maintenance respiration. The majority of functional studies of the root cortex focus on root cortical aerenchyma, but less is known regarding the utility of the living part of the cortex, or living cortical area (LCA). Little information exists on the extent of genetic variation for LCA components (cell size and cell file number) in maize and its potential impact on root metabolic cost. The objective of this study was to assess the genetic variation of living cortical area components, and to determine if genetic variation for LCA components in maize can substantially reduce root metabolic costs for soil exploration, thereby improving root growth and water acquisition under drought. In soil mesocosms in a greenhouse, we screened recombinant inbred lines (B73xMo17) for genetic variation in cell file and cell size. Contrasting lines were grown in soil mesocosms for 4 weeks and in rainout shelters in the field under drought and well watered conditions. Genotypes ranged from 8 to 16 cells per file and the variation of cell size was almost 3 times (3X). Genotypic differences in cells per file and cell size were correlated with root respiration. These results support the hypothesis that few cortical cells per file and large cells can substantially reduce the metabolic costs of soil exploration, suggesting that these traits could be useful in improving the drought tolerance of maize.