Abstract
It has been well documented that apoplastic bypass flow rate in rice is enhanced by salinity stress. However, the effects of heavy metals on the apoplastic bypass flow were not studied well. In this study, we show that cadmium activated apoplastic bypass flow rate of rice. 100 uM Cd2+-treatment reduced transpiration rate, however, water transport to the shoot examined the apoplastic flow tracer, PTS, was enhanced. Under non-stress condition apoplastic bypass flow rate was estimated as <5%, while 100 uM Cd treatment increased the rate up to 20%. Next we hypothesized that the increased rate of apoplastic bypass flow rate was caused of the damage of Casparian strip by Cd2+-treatment. The staining with berbeline hemisulfate indicated that the structure of the Casparian strip at the exodermis was partially broken. These facts suggest that cadmium enhance rice apoplastic bypass flow rate through damaging the Casparian stirp.
