Translocation of 14Carbon Within and Between Leaves

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Abstract
Plants of tobacco and a variegated variety of Pelargonium were used to investigate some aspects of translocation of 14Carbon within and between leaves, following assimilation of 14CO2 by one of the leaves. Bi-directional transport in leaves is considered to result from import into immature regions and exports from mature regions. In variegated leaves the chlorotic areas behave like immature areas in the sense that they continue to import translocate from outside the leaf to a greater extent than adjacent green areas. However, some transport occurs from green to chlorotic areas via the veins in the same leaf. Using masking techniques on tobacco leaves it was shown that labelled carbon failed to move across darkened mesophyll. This was taken to indicate that the mechanism resulting in translocation from leaves was located in the veins. Labelled carbon was shown to leave the veins of importing leaves along their entire length. A simplified technique for freeze-drying plant material prior to wax-embedding is described and some of the limitations of heat-drying as a preliminary to gross autoradiography of leaves are discussed.