Cellular Localization of CO2 Fixation and Translocation of Metabolites

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Abstract
Leaves of maize (Zea mays L.) and sugar beet (Beta vulgaris L.) were enclosed in an illuminated chamber in air for 30 min after which time (14)CO(2) was released into the chamber. Two min after the (14)CO(2) was released, the leaves were removed from the chamber, and small sections were cut from them. The sections were put in small wire baskets and frozen in isopentane cooled by liquid nitrogen. Approximately 1.5 min elapsed from the removal of the leaf from the illuminated chamber until the tissue was frozen. The tissue was freeze-dried, embedded in paraffin and the cellular location of the isotopic activity was determined by radiography of leaf cross sections. Isotopic activity in maize leaves was localized in bundle sheath parenchyma. In contrast, the label in sugar beet leaves was generally distributed in the mesophyll cells. The bundle sheath cells in maize contain specialized chloroplasts which appear to have a unique capacity to incorporate CO(2). Translocation from leaves of maize was 3-fold as rapid as from sugar beet leaves in the same environment. Low light intensity did not alter the distribution pattern of fixed CO(2).