Time course of uptake of 14C-abscisic acid by Lemna gibba in relation to growth

The time course of growth of Lemna gibba L. in low concentrations of abscisic acid (ABA) and of uptake of ¹⁴C-labelled ABA into the plants was followed for up to 15 days. Fresh weight increase was arrested when the plants were transferred to ABA solutions. This inhibition was greatest during the first days after which a marked recovery took place. Dry matter production was only slightly affected by ABA. On a culture basis, the uptake of ABA was almost linear with time during the experimental period. The rate of uptake on a fresh weight basis was highest during the first two days but decreased rapidly from the third day. Most of the applied ¹⁴C remained in the culture solution throughout the experiments. Plants transferred to a solution without ABA retained most of their accumulated ¹⁴C. Possible explanations for the decrease in rate of ABA uptake and restoration of growth are discussed.