The pattern for primary products of CO2-fixation and the chloroplast structure of Amaranthus retrqflexus L., a species which incorporates carbon dioxide into C4 dicarboxylic acids as the primary product of photosynthesis, were compared in various chlorophyll containing tissues,i.e., foliage leaves, stems, cotyledons and pale-green callus induced from stem pith. Despite some morphological differences in these assimilatory tissues, malate and aspartate were identified as the major compounds labelled during a 10 sec fixation of 14CO2 in all tissues. Whereas, aspartate was the major component in C4-dicarboxylic acids formed in foliage leaves, malate predominated as the primary product in stems, cotyledons and the pale-green callus. The percentage of 14C-radioactivity incorporated into PGA and sugar-P esters increased and 14C-sucrose was detected in the prolonged fixation of 14CO2 in the light, not only in foliage leaves, but also in stems and cotyledons.
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Usuda et al. (1971) studied this question.