Real-time Analysis of Photoassimilate Translocation in Intact Eggplant Fruit using 11CO2 and a Positron-emitting Tracer Imaging System

A recently developed positron-emitting tracer imaging system (PETIS) noninvasively produces quantitative real-time images of the movement of various compounds in plants. To clarify the mechanism of the growth and development of the fruit of eggplant (Solanum melongena L.), we fed (CO2)-C-11 to a leaf and monitored the translocation of C-11-labeled photoassimilate into the fruit by PETIS. Continuous images of the translocation of [C-11]photoassimilate from the leaf to the fruit and inside the fruit were produced, with a shorter time resolution than reported previously. C-11 signal intensity in the fruit increased gradually, and its distribution was not uniform. The fruits were sliced after PETIS measurement and exposed to the imaging plates of a bio-imaging analyzer system. The resultant images showed the localization of C-11 activity inside the fruit, and indicated that translocation of photoassimilate within the fruit was not uniform. The velocity of photoassimilate translocation in the peduncle and changes in the rate of translocation of photoassimilate in the fruit were estimated by analysis of PETIS data. The velocity of photoassimilate translocation through the peduncle was estimated as 1.17 cm.min(-1). About 60 min after the start Of (CO2)-C-11 feeding, the C-11 activity of the fruit began to increase, and by 120 min it had reached about 8% of feeding (CO2)-C-11. These results indicate that it took about 60 min for the first [C-11]photoassimilates to reach the fruit. Real time observation of photoassimilate translocation within a fruit has never been reported. PETIS may be a powerful tool for revealing the mechanisms of fruit development and maturity.