| Abstract: | A previous study comparing hydraulic conductivity of intactroots and cortical cells of cotton (Gossypium hirsutum L.) seedlingssuggested that substantial water flow may bypass cell membranesentirely, following a completely apoplastic pathway, and alsosuggested that phosphorus deficiency might increase bypass flow.We used fluorescent apoplastic tracers to quantify flow throughthe apoplastic bypass and to assess the effect of phosphorusdeficiency on bypass flow. Tracer concentration in shoot xylemsap was less than 0.25% of the concentration in the culturalsolution for five different tracers. Phosphorus deficiency reducedthis already low concentration even further, possibly by reducingthe number of newly emerged lateral roots which can providean alternative pathway for water entrance into the stele. Norelationship existed between hydraulic conductivity and bypassflow. We concluded that the apoplastic bypass constituted onlya small fraction of water movement into the stele. The contributionof the apoplastic bypass was not sufficient to explain differencesin hydraulic conductivity between intact roots and corticalcells, or between plants receiving high or low phosphorus treatments. Key words: Apoplastic bypass, phosphorus nutrition, cotton, hydraulic conductivity, lateral roots |
