Chimungu, J.C.; Brown, K.M.; Lynch, J.P.


Plant Physiology, Oct. 2014

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The objective of this study was to test the hypothesis that large cortical cell size would improve drought tolerance by reducing root metabolic costs. Maize lines contrasting in root cortical cell size (CCS) measured as cross-sectional area were grown under well-watered and water-stressed conditions in greenhouse mesocosms and in the field in the USA and in Malawi. CCS varied among genotypes, ranging from 101 to 533 µm2.In mesocosms large CCS reduced respiration per unit root length by 59%.Under water stress in mesocosms, lines with large CCS had between 21% and 27% deeper rooting (D95), 50% greater stomatal conductance, 59% greater leaf CO2 assimilation, and between34% and44% greater shoot biomass than lines with small CCS. Under water stress in the field, lines with large CCS had between 32% and 41%deeper rooting (D95), 32% lighter stem water δ18O signature signifying deeper water capture, between 22%and30% greater leaf relative water content, between 51% and 100% greater shoot biomass at flowering, and between 99% and 145% greater yield than lines with small cells. Our results are consistent with the hypothesis that large CCS improves drought tolerance by reducing the metabolic cost of soil exploration, enabling deeper soil exploration, greater water acquisition, and improved growth and yield under water stress. These results coupled with the substantial genetic variation for CCS in diverse maize germplasm suggest that CCS merits attention as a potential breeding target to improve the drought tolerance of maize and possibly other cereal crops.