Quantifying Apoplastic Flux through Red Pine Root Systems Using Trisodium, 3-hydroxy-5,8,10-pyrenetrisulfonate

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Abstract
The fluorescent compound trisodium, 3-hydroxy-5,8,10-pyrenetrisulfonate (PTS) was used to quantify the apoplastic flux through red pine root systems.sbd.that portion of the total water flux reaching the xylem without ever crossing a semipermeable membranes. Flow was induced by pressure through detopped root systems, and by transpiration through intact seedlings. Apoplastic flux was determined by multiplying total flux by the ratio of PTS concentration in the xylem exudate to PTS concentration in the bathing medium. Under aeration, apoplastic flux was < 1% of total flux. Under anerobic conditions, up to 50% of total flux was apoplastic, suggesting that anaerobic conditions change the pathway of water flow into root xylem. The change under anaerobic conditions was reversible. Detopped root systems under pressure and intact seedlings under transpiration gave similar results. In detopped root systems, the magnitude of the pressure gradient may alter the apoplastic contribution to total flux.
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