ACQUISITION OF CARBON IN ELODEA-CANADENSIS MICHX

Mature shoots of Elodea canadensis Michx., grown in artificial pond wa ter, were exposed to (CO2)-C-14 or submersed in solution containing (H CO3-)-C-14 for 30 min under PAR. The macroautoradiographs indicated th at bicarbonate was used for photosynthesis, while gaseous (CO2)-C-14 w as not incorporated. Accordingly, gas exchange measurements showed no reduction of CO2-content in the cuvette. Microautoradiographs indicate d that C-14 was taken up by penetrating the epidermis of the stem and that of the lower side of the leaves. In the symplast, label was accum ulated in the chloroplasts of both epidermal layers and in the plastid envelope of the chloroplasts of cortex cells. In the stem no label oc curred inside the central cylinder. Among sieve tubes, only those of t he leaf traces were labeled. Thin layer chromatograms of extracts of l abeled plants were autoradiographed. The main spots were identified by co-chromatography as malic acid, glucose, asparagine, proline and hex ose phosphates, while sucrose appeared only slightly labeled. By SEM, strands of stretched cells with inflated ends were observed and named <<canal cells>>. In the light microscope, canal cells were found among cells of the lower leaf epidermis. Upon illumination with PAR they in creasingly were filled with gas, but in the dark no gas collected in t he canal cells. They probably are used for collecting and transferring photosynthetically produced oxygen. Accordingly, acquisition of carbo n and release of oxygen seem to follow different pathways in Elodea ca nadensis.