Light activates H215O flow in rice:: Detailed monitoring using a positron-emitting tracer imaging system (PETIS)

Water ((H2O)-O-15) translocation from the roots to the top of rice plants (Oryza saliva L. ev. Nipponbare) was visualized over time by a positron-emitting tracer imaging system (PETIS). (H2O)-O-15 flow was activated 8 min after plants were exposed to bright light (1500 mu mol m(-2) s(-1)). When the light was subsequently removed, the flow gradually slowed and completely stopped after 12 min. In plants exposed to low light (500 pmol m(-2) s(-1)), (H2O)-O-15 flow was activated more slowly, and a higher translocation rate of (H2O)-O-15 was observed in the same low light at the end of the next dark period. NaCl (80 mM) and methylmercury (1 mM) directly suppressed absorption of (H2O)-O-15 by the roots, while methionine sulfoximine (1 mM), abscisic acid (10 muM) and carbonyl cyanide m-chlorophenylhydrazone (10 mM) were transported to the leaves and enhanced stomatal closure, reducing (H2O)-O-15 translocation.