Carbon dioxide fixation by epidermal and mesophyll tissues of Tulipa and Commelina

Abstract

Rates of ¹⁴CO₂ fixation by epidermal tissue of Tulipa gesneriana (tulip) and Commelina diffusa are only slightly higher in the light than in the dark while in mesophyl tissues rates are much greater in the light. The first products of ¹⁴CO₂ fixation by epidermal tissue of Tulipa gesneriana and C. diffusa in the light and dark are malate and aspartate. In addition to these dominating dicarboxylic acids, 3-phosphoglyceric acid and sugar phosphates appear in the light, while in the dark only the amino acids, glutamate and glutamine become labelled. Mesophyll tissue of tulip and C. diffusa, however, gives typical CO₂ fixation patterns of the labelled products of C₃ plants. Furthermore, a period of dark ¹⁴CO₂ fixation followed by a light ¹²CO₂ chase carried out with epidermal tissue suggested that malate can act has the precursor of phosphorylated compounds of the Calvin cycle and consequently of starch. The data are consistent with the view that guard cells are able to exhibit Crassulacean acid metabolism.