Effect of sink region anoxia on translocation rate.

Translocation rate, ATP level, and CO(2) production of a developing leaf (sink leaf) were studied in sugar beet (Beta vulgaris) plants prior to and during anaerobic treatment of the sink leaf. Within 3 to 5 minutes after onset of treatment with a N(2) atmosphere, translocation into the sink leaf decreased to near zero and then recovered to a level of about 50% of the control over the next 2 hours. A decline in CO(2) output and ATP levels coincided with the attainment of the new translocation rate. All three quantities returned to near control levels within 60 to 120 minutes after the sink leaf was returned to air. Swelling and ultrastructural changes in mitochondria coincided with the observed ATP level changes during inhibition and recovery periods. The first phase of marked inhibition of translocation did not coincide with low ATP level and appeared to be caused by decreased membrane permeability during the transition to anaerobic metabolism, possibly as a result of a temporary build up of toxic products. The correlation between ATP level and translocation rate suggests that ATP-dependent active transport in the sink leaf augments the driving force for translocation.