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Translocation of Radioactive Carbon after the Application of ¹⁴C-Alanine and ¹⁴CO₂ to Sunflower Leaves ¹

^a Department of Botany, University of Toronto, Toronto, Ontario, M5S IAI, Canada

¹⁴C-(UL)-L-Alanine was applied to the surface of mature leaves at the second node of sunflower (Helianthus annuus L. cv Commander) plants, under illumination. The alanine was absorbed during a 4-hour period, and some of it was metabolized by the absorbing tissue. After a lag period of about 15 minutes from first application, distribution of ¹⁴C through the plant proceeded in much the same pattern as when ¹⁴CO₂ is assimilated by similar leaves. Most, if not all, of the ¹⁴C exported from the absorbing regions was in sucrose. Only minute amounts appeared in alanine or other amino acids in surrounding parts of the leaf blade or in the petiole, although these were strongly labeled in the tissue absorbing ¹⁴C-alanine.

When ¹⁴CO₂ was supplied for 15 minutes to leaves of different ages, amino acids were lightly labeled in the leaf blade. Mature green leaves exported only sucrose. Yellowing leaves on 60-day-old plants exported a variety of substances including amino acids.

¹ This work was supported in part by the National Research Council of Canada.