Specific features of photorespiration in photosynthetically active organs of C3 plants

Abstract

Photorespiration of photosynthetically active organs of C3 plants (leaf, ear, stem, and leaf sheath) and C4 plants (leaf, tassel, stem, leaf sheath, ear husk) grown under greenhouse and field conditions was studied. Photorespiration was measured using a PTM-48A high-technology monitor of photosynthesis (Bioinstruments S.R.L., Moldova). It is shown that photorespiration (CO2 ejection after light turning off — apparent photorespiration) in C3 plants is characteristic only for their leaves. In other photosynthesizing organs, photorespiration was absent, like in the photosynthesizing organs of C4 plants. The absence of such after-light CO2 outburst was observed for 31 genotypes: 18 cereal species belonging to four species (Triticum aestivum L., T. durum Desf., Secale cereale L., and Triticale); 6 grain legumes belonging to 2 species (Pisum sativum L. and Glycine max L.); 7 species of wild and rarely cultivated genotypes (T. boeoticum Boiss., T. dicoccoides Koern., T. dicoccum Schuebl., T. spelta L., T. compactum Host., T. monococcum L., and T. sphaerococcum Persiv.), and 2 genotypes of C4 plants (Zea mays L. and Sorgum vulgaris L.). In all tested photosynthetically active genotypes, except of the C3 plant leaves, apparent photorespiration was absent, but rather active glycolate cycle operated. The activity of this cycle was determined from the activity of the key enzyme of this cycle — glycolate oxidase. It was supposed that C3 plants have two mechanisms of CO2 assimilation: the first one — the mechanism of C3 type localized in the leaves and the second one localized in other photosynthesizing organs, similar or with some elements of C4 mechanism of CO2 assimilation, limiting after-light CO2 ejection during the metabolism of glycolate.