A Study of the Exudation of Excised Maize Roots after Removal of the Epidermis and Outer Cortex

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Abstract
The fluid exudation rates and the ionic composition of the exudates of isolated maize roots were compared with those of similar roots from which the epidermal and outer cortical cells had been removed. The results indicate that in low ionic strength media the salt fluxes into the exudation stream are several times larger in the control than in the treated roots. As the ionic strength of the bathing medium increases to 10 mM KCl or greater, the salt fluxes become equal. A mechanism to account for this behaviour is discussed. The values of Lp, the hydraulic conductivity of the roots to radial water flow, are 0.26 × 10−6 cm sec−1 atm−1 for treated and 0.14 × 10−6 cm sec−1 atm−1 for control roots, but a statistical technicality precluded a significance test on this apparent difference. The kinetics of tritiated water exchange from external medium to the exudation fluid in both control and treated roots were not significantly different. The entry of labelled water seems to be achieved by the fluid exudation rate in both cases; thus the barrier to water movement to the exudate compartment remains intact after removal of the epidermis.