Effect of Path or Sink Anoxia on Sugar Translocation in Roots of Maize Seedlings

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Abstract
After feeding the scutellum of young maize seedlings with a labeled analog of glucose, 2-deoxy-D-glucose, the progress of radioactivity along the root was following when either 70% of the path or the whole root were in strict anoxic conditions, and was compared with the translocation pattern of aerobic seedlings. Special care was taken to suppress the internal O2 transport and to control its occurrence. In air, the radioactive compounds accumulated from 30 min in the root tip mainly as an analog of sucrose. When the whole root was anoxic, the progress of the radioactivity was very slow and never reached the tip which did not survive > 8 h. When 70% of the path was in strict anoxia and the sink (root tip) in air, the translocation was not impaired and the radioactivity accumulated in the tips as fast as in aerobic controls. The addition of 3 mM NaF, which inhibits the fermentative energy production, did not modify these results. Long distance transport in maize sieve tubes has no special energy requirements and is controlled by source-sink relationship. The inhibition of sugar supply in anoxic root tips is attributed to an effect on unloading processes rather than on sink metabolism.