Heterogeneity in water availability alters cellular development and hydraulic conductivity along roots of a desert succulent

Plants of the desert succulent Agave deserti were grown in partitioned containers to determine whether heterogeneity in soil moisture leads to differences in cellular development and hydraulic conductivity along individual roots. Roots from containers with a dry distal compartment (furthest from the shoot), a wet middle compartment, and a dry proximal compartment had distal regions (including the root tips) that were more suberized and lignified in the endodermis and adjacent cell layers than were root regions from the wet middle compartment. Proximal root regions about 40 mm from the succulent shoot base were also relatively unsuberized, suggesting that both external and internal supplies of water delayed tissue maturation. Root segments from wet middle compartments and from dry proximal compartments had higher hydraulic conductivity than did the more suberized root segments from dry distal compartments. Unlike distal root segments from wet compartments, segments from dry compartments suffered no decrease in hydraulic conductivity after immersion in mercuric chloride, suggesting that aquaporin activity diminished for roots during drought. The possible closure of water channels could help limit root water loss to a drying soil. The delayed development of suberized cell layers may allow root regions to maximize water uptake From wet soil patches (such as under rocks), and the relatively immature, absorptive root region near the base of the shoot may help A. deserti capture wafer From a briefly wetted surface soil. (C) 2000 Annals of Botany Company.