Distribution of photoassimilates in the pea plant: chronology of events in non-fertilized ovaries and effects of gibberellic acid.

The short-lived isotope(11)C (t1/2=20.4 min) has been used to study assimilate distribution in intact pea plants (Pisum sativum L.). Radiolabel was measured at the leaf fed with(11)CO2 (feed-leaf), at the ovary of the flower subtended by this leaf, and in shoot apex and roots of individual plants. Considerable(11)C-radiolabel was detected in the young ovaries during the first days after anthesis. Thereafter, when the ovaries stopped growing the uptake of(11)C rapidly decreased. At this developmental stage only apex and roots were competing for the photoassimilates. Fertilization, however, restored the strong sink activity of the ovaries. The same effect could be achieved by applying gibberellic acid to non-fertilized ovaries. About 2 h after treatment the residual(11)C-radiolabel entering the ovary started to increase and, at about the same time, the ovary resumed growth. Feed-leaf photosynthesis, as well as export of(11)C-radiolabel out of the leaf, was not changed by the treatment. The(11)C experiments show the dynamic behaviour of the sinks during developmental stages from the day of anthesis until 5 d later and demonstrate that phytohormones may play an important role in regulating carbon distribution.